Effect of build direction in Ti6Al4V alloy manufactured by EB-PBF on the corrosion performance of PEO coatings

Effect of build direction in Ti6Al4V alloy manufactured by EB-PBF on the corrosion performance of PEO coatings | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Effect of build direction in Ti6Al4V alloy manufactured by EB-PBF on the corrosion performance of PEO coatings Carlos A. Vargas, Alejandro A. Zuleta, Juan G. Castaño, Maryory A. Gómez, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7716426/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 04 Feb, 2026 Read the published version in The International Journal of Advanced Manufacturing Technology → Version 1 posted 5 You are reading this latest preprint version Abstract This study investigates the influence of build direction in Ti6Al4V substrates manufactured by Electron Beam Powder Bed Fusion (EB-PBF) on the performance of Plasma Electrolytic Oxidation (PEO) coatings. Because of the inherent anisotropy of additively manufactured alloys, arising from differences in thermal history between the build and transverse directions, surface treatments and coating behavior may vary. To explore this, coatings were produced in a silicate–phosphate (Si–P) electrolyte under different current densities and treatment times. The resulting coatings were characterized in terms of morphology, crystalline phase composition, and corrosion performance. The results show that, although build direction affects the initial voltage response during PEO treatment, its influence on coating thickness and porosity is minimal. X-ray diffraction revealed the presence of both anatase and rutile TiO₂ phases, with anatase formation favored at lower current densities. Importantly, PEO treatment eliminated the corrosion anisotropy observed in uncoated Ti6Al4V manufactured by EB-PBF, leading to uniform protective behavior regardless of build direction. Overall, these findings demonstrate the potential of PEO to enhance the functional performance of additively manufactured titanium alloys for biomedical and aerospace applications. In addition, they underscore the importance of electrolyte composition and process optimization in tailoring surface properties. Ti6Al4V alloy electron beam melting (EB-PBF) Plasma Electrolytic Oxidation (PEO) build direction microstructural anisotropy corrosion resistance Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 Figure 14 Figure 15 Figure 16 Figure 17 1. INTRODUCTION Ti6Al4V is a titanium alloy widely recognized for its exceptional balance of strength, low weight, and corrosion resistance. Because of this unique combination, it has become the material of choice for critical applications, including aerospace components (such as aircraft structures and engines), biomedical implants (due to its biocompatibility), marine equipment requiring resistance to saltwater, and high-performance automotive parts [1], [2], [3]. Due to the specific characteristics of applications using this alloy, manufacturing Ti6Al4V parts through powder bed Additive Manufacturing (AM) techniques, such as electron beam melting (EB-PBF) or laser melting (LPBF), has become increasingly important [4], [5]. Nevertheless, variations in the alloy’s cooling rate during AM along the build direction and transverse to it produce a differentiated microstructure of the material [6], [7], [8], [9]. As a result, anisotropy in the alloy’s properties may occur, as reflected in the mechanical and corrosion behavior of products made using these additive techniques [10], [11], [12], [13]. Given that materials used in aerospace and biomedical applications must meet high-performance demands, surface modifications are often applied to titanium alloy substrates [14], [15], [16]. Among the available approaches, electrochemical surface modification techniques have emerged as excellent alternatives because they are easy to implement and produce coatings that combine good mechanical properties, improved corrosion resistance, and favorable biological responses [17], [18]. However, it remains necessary to analyze whether the differences in microstructure observed in alloys produced by AM could also lead to differentiated coatings, depending on the surface being modified. This involves considering both the build and transverse directions, as well as assessing whether there is an effect on the anisotropy of properties, similar to what has been observed in unmodified substrates. Although previous studies have evaluated the effects of surface modification on additively manufactured titanium alloys—particularly on coating properties and performance—the influence of the anisotropic microstructure of the surface on the resulting coatings has not been systematically explored [19], [20], [21]. Furthermore, little research has addressed how these properties might vary depending on the build direction (longitudinal or transverse), especially in the context of critical applications such as aerospace and biomedical engineering. This gap makes it difficult to optimize coating processes and designs for achieving uniform and predictable performance. In this regard, Decha-umphai et al. [22] reported, through conventional anodizing, differential coating growth on the alpha (α) and beta (β) phases of Ti6Al4V substrates printed by LPBF. Similarly, Qing-bo Yan et al. [23] compared the surface characteristics and corrosion performance of Ti6Al4V substrates produced by LPBF and EB-PBF and modified using Plasma Electrolytic Oxidation (PEO). They observed differences in the phase composition and roughness of TiO 2 coatings, with LPBF samples exhibiting higher corrosion resistance. Despite this, neither of these studies considered the effect of the build direction of parts produced by AM. By contrast, Liu et al. [24] conducted an initial evaluation of the differences in microstructure associated with build direction. They found that the pore size, film thickness, and roughness of PEO coatings were influenced by build direction when the Ti6Al4V alloy was modified by annealing. As observed in the literature, most studies have focused on characterizing coatings or substrate properties separately, without providing a comprehensive evaluation of how microstructural differences—arising from the build direction of the printed substrate—affect coating behavior. This issue is critical for ensuring stability and reliable performance in demanding applications. Therefore, further investigation into the anisotropy of microstructures obtained in alloys processed by AM is necessary. Against this backdrop, this paper aims to evaluate the effect of build direction in Ti6Al4V alloys produced by Electron Beam Powder Bed Fusion (EB-PBF) on the properties of coatings deposited on them by PEO. For this purpose, substrates oriented along both the build and transverse directions were coated and subsequently characterized in terms of their microstructure, corrosion resistance, and crystalline phase composition. 2. MATERIALS AND METHODS 2.1 Sample preparation A Ti6Al4V substrate was fabricated using an ARCAM S12 electron beam melting system (ARCAM, Mölndal, Västra Götaland, Sweden). The build employed GE Additive’s standard Ti–6Al–4V alloy (grade 5) plasma-atomized powder (Arcam AB, Mölndal, Sweden). During production, an acceleration voltage of 60 kV was applied, with a maximum beam power of 4 kW. The process took place under vacuum conditions at a pressure of about 10 − 4 mbar, with the operational temperature ranging between 600 and 700°C. In addition, each layer of the build was consistently 50 µm thick. From the additively manufactured specimens (bar part, Fig. 1 ), substrates were sectioned into pieces measuring10 mm in diameter and 3 mm in thickness along the transverse direction, and into 10×10×3 mm pieces along the build direction, for subsequent PEO treatment. To ensure uniform surface conditions, the substrates were first ground using silicon carbide paper of varying grit sizes (400, 600, 800, 1000, 1500, and 2500). They were then polished with diamond abrasive lapping fluid to achieve a mirror-like finish. Following polishing, the samples were thoroughly cleaned with distilled water and subsequently degreased ultrasonically in acetone for 5 min. Afterwards, they were rinsed, dried with a cool air stream, and finally stored in a desiccator until further processing. 2.2 PEO coating preparation PEO treatment was carried out by immersing the substrates into an electrolyte solution under specific process conditions, as detailed in Table 1 . A total of 0.4 L of electrolyte was held in a stainless-steel cell, which was placed in a cooled water bath to keep the temperature below 30°C. The titanium substrate served as the anode, while the cell itself acted as the cathode. The process was conducted in galvanostatic mode to generate the desired anodic coatings, employing a DC power supply (Kepco BHK 500–0.4 MG). Voltage and current data were recorded using National Instruments LabVIEW 8.1 software to enable real-time monitoring of the process. Once the PEO treatment was completed, the samples were removed from the electrolyte, cleaned in an ultrasonic bath with deionized water for 15 min to prepare the surface and finally dried using cold air. Table 1 Process variables and bath composition for PEO treatment. Process conditions Factors Levels Electrolyte Si-P Time [s] 600 1000 Current density [mA/cm²] 50 100 Surface to coat L: Build direction T: Transverse to build direction Bath composition Component (g/L) Si-P Na₃PO₄·12H₂O 10.0 Na₂SiO₃·5H₂O 2.0 EDTANa₂ 3.7 NaOH 2.0 2.3 PEO coating characterization Scanning Electron Microscopy (SEM) was employed to analyze the surface characteristics and cross-sectional structure of the coated samples. These analyses were performed with a JEOL 6490LV microscope and a Thermo Fisher Scientific Apreo 2 field-emission scanning electron microscope, with the latter providing high-resolution imaging. In addition, SEM was used to study the microstructure of the samples prior to any surface modifications. For the preparation of mirror-polished surfaces, metallographic techniques were applied, including treatment with Kroll’s reagent. Subsequently, the cross-sectional morphologies of the PEO coatings were analyzed using an FEI QUANTA 3D FEG dual-beam SEM/FIB microscope. This setup enabled detailed observation of coating cross-sections to determine thickness and assess the morphology of pores throughout the layer. Furthermore, film thickness, pore size, and pore size distribution were accurately quantified from both top-view and cross-sectional SEM images, using their respective measuring scales together with the analysis tools provided by ImageJ software [25]. The phase composition of the substrates and PEO coatings was then examined by X-ray Diffraction (XRD) using an Empyrean Alpha 1 diffractometer. The analysis employed Cu–K radiation, with a step size of 0.02 ° /min and a scan range from 20° to 70° in 2θ. Finally, various phases were identified through Rietveld refinement in combination with several patterns included in the High Score Plus software. 2.4 PEO coating performance To evaluate the protective behavior of the coatings and the kinetics (rate) of the associated corrosion reactions, Open Circuit Potential (OCP), Electrochemical Impedance Spectroscopy (EIS), and potentiodynamic linear polarization methods were employed. Simulated Body Fluid (SBF) was prepared following standard protocols so as to ensure consistency in testing conditions. The corrosion cell consisted of an Ag/Cl reference electrode and a graphite counter electrode, while the coated samples served as the working electrodes. All tests were analyzed using PSTrace software (PalmSens) and an Autolab potentiostat (Metrohm). Furthermore, electrochemical tests were conducted in SBF, the composition of which is provided in Table 2 . To stabilize the OCP, all samples were immersed in SBF for 1 h prior to polarization testing. For the linear polarization test in SBF, a voltage range of -1000 to 1000 mV was applied at a scan rate of 1 mV/s. Table 2 Preparation of 1000 ml of SBF (components, quantities, and preparation sequence). Sequence Reactive Quantity 1 NaCl 8.035 g 2 NaHCO 3 0.355 g 3 KCl 0.225 g 4 K 2 HPO 4 3H 2 O 0.231 g 5 MgCl 2 6H 2 O 0.311 g 6 1M-HCl 39 mL 7 CaCl 2 0.292 g 8 Na 2 SO 4 0.072 g 9 Tris 6.118 g 10 1M-HCl 0–5 mL 3. RESULTS 3.1 Plasma electrolytic oxidation Figure 2 presents the voltage–time curves for the PEO treatment conducted on EB-PBF substrates under the conditions specified in Table 1 . As can be seen, the voltage trends for PEO durations of 600 and 1000 s were similar when tested under the same surface orientation and current density, thereby demonstrating good reproducibility of the process. However, at a higher current density (100 mA/cm²), the voltage rose compared to that at 50 mA/cm², and the final voltage was also slightly higher (Figs. 2 a and 2 b). This increase is attributed to the greater energy input, which in turn affects the morphology and phase composition of the coatings [26]. Consequently, these results indicate that each PEO treatment reaches a maximum coating thickness at different rates, depending on the growth dynamics controlled by the specific process parameters [27], [28], as will be discussed later. Figures 2 c–f illustrate the effect of build direction on the PEO treatment, indicating that higher voltages were observed along the build direction (L). Nevertheless, as the voltage stabilized, the levels became comparable for both substrates. This behavior suggests that microstructural differences associated with build direction may influence transport and energy dissipation during PEO treatment, potentially leading to variations in coating morphology between the build and transverse directions in EB-PBF substrates. Although few studies have assessed the effect of build direction on PEO-treated substrates, research has shown differential growth of PEO coatings due to microstructural variations, such as differences in grain size or the distribution of α, α’, and β phases induced by annealing heat treatments on substrate surfaces [24]. Other studies have also confirmed differential coating growth on the α and β phases of printed substrates in conventional anodizing, which represents the initial phase of the PEO process [22]. In particular, Wu et al. [29] reported that discharge events tend to initiate in β-rich regions, commonly located along grain boundaries, resulting in a more porous and rapidly growing oxide layer. By contrast, areas dominated by the α phase yield a more compact and protective oxide film [29]. Therefore, a possible explanation for the higher voltages observed in the build direction is that, in the early stages of the process, microstructural effects such as grain boundaries and a higher presence of retained β phase within the grains (Fig. 3 ) influence coating growth, since the voltage reflects the resistance of the developing layer. Once a certain coating thickness is reached (where resistance to current flow becomes similar for both already-coated substrates), the voltage difference decreases, leading to the stabilization of the process. Finally, it is noteworthy that the voltage gap between the coated substrates (build and transverse directions) became smaller at the highest current density of 100 mA/cm² compared with 50 mA/cm². This trend could be linked to faster coating growth and process stabilization at 100 mA/cm². 3.2 Morphological characterization Before analyzing the coating morphologies via SEM, the microstructure of the bare Ti6Al4V surface was examined. As shown in Fig. 3 , the SEM images depict the distribution of β and α phases both along and transverse to the build direction. Along the build direction, the grains appeared elongated, with significant propagation of α phases from the grain boundaries and a high presence of retained β phase within the grains (Figs. 3 a and 3 b). Conversely, in the transverse direction, the microstructure revealed grains with the typical equiaxed morphology as reported in the literature [7]. These grains correspond to prior β phases, with a fine distribution of α phases both inside the grains and along their boundaries (Figs. 3 c and 3 d). Overall, these observations confirm the microstructural anisotropy of Ti6Al4V substrates produced by EB-PBF. Figures 4 and 5 summarize the coating morphologies and porosity under different PEO treatment conditions. In general, higher current densities were found to increase porosity and pore size, particularly in treatments conducted for 1000 s. This effect can be explained by the greater energy input at higher voltages, as indicated by the voltage–time curves in Fig. 2 . Under such conditions, the frequency of discharges rises, leading to a more significant increase in pore sizes [26], [30], [31]. During the intermediate stage between dielectric breakdown and voltage stabilization, discharges become more intense; however, once the voltage stabilizes, their intensity decreases [32], [33], [34]. Unlike the stage prior to voltage stabilization, this phase is characterized by fewer discharges, which persist at fixed points for longer periods. This behavior may be associated with the presence of discharge channels, which generate larger pores and even volcano-like pore structures, as shown in Fig. 6 . Figure 6 highlights the formation of cracks during PEO coating deposition. This can be attributed to the higher voltages reached during the process, which increase thermal stress and ultimately promote the formation of these defects [35], [36], [37]. In addition, the Focused Ion Beam (FIB) cross-sectional images (Fig. 7 ) reveal that surface cracks can extend through the entire coating thickness, potentially reaching the titanium alloy substrate through pores or fissures present within the coating. This observation suggests that such defects may act as pathways for corrosive agents, thereby compromising the protective function of the coatings [38], [39]. Additionally, various pore types were observed: Pores located near the interface with the alloy substrate (Fig. 7 a). Large and small pores formed during intermediate stages of the process, later sealed by subsequently deposited layers during the PEO treatment (Figs. 7 b and 7 d). Interconnected pores situated in the middle of the coating thickness, connected to cracks propagating from the external layer of the coating (Figs. 7 c and 7 e). Variations in coating thickness caused by the presence of discharge channels expelling material around them (Fig. 7 f). These features are consistent with the typical microstructural characteristics of PEO coatings, where microdischarges during the process lead to the formation of pores and cracks, potentially affecting the coating’s protective properties. Finally, Fig. 8 shows that coating thickness increases with both current density and processing time, which is in line with observations reported in previous studies [40], [41]. This behavior is influenced by the irregular surface topography of the coatings, characterized by valleys and protuberances associated with pores generated by discharge channels (Figs. 7 f and 6 ). Furthermore, coatings formed in the longitudinal (L) direction of the Ti6Al4V substrate were slightly thicker than those in the transverse (T) direction. This difference is consistent with the higher voltage rise observed in the L direction during the intermediate stage of the PEO treatment—between dielectric breakdown and voltage stabilization (Figs. 2 c–f and 8 ). 3.3 Phase composition of coatings Figure 9 presents the XRD spectra of the coatings, revealing peaks corresponding to the anatase and rutile crystalline phases of TiO₂. Notably, no crystalline phases related to silica were detected, which agrees with previous studies reporting a predominance of amorphous phases even at high silicate concentrations [42]. Furthermore, it has been reported that silicon-rich electrolytes tend to inhibit the formation of anatase and rutile, whereas phosphorus-containing formulations promote their crystallization [42], [43], [44]. This observation is consistent with the present findings. Table 3 lists the Miller indices of the peaks identified in the XRD spectra of the coatings, determined using HighScore software and based on reference standards 96-900-9087 (anatase) and 96-900-9084 (rutile). The most intense peaks clearly correspond to the characteristic reflections from which the contents of the anatase and rutile phases can be quantified. Table 3 Crystallographic indices estimated from the XRD spectra of the PEO coatings. Intensity [%] d-spacing [Å] 2 Q [°] h k l Anatase/Rutile 100 3.51663 25.306 0 0 1 A 100 3.24822 27.436 1 1 0 R 45.7 2.48695 36.087 0 1 1 R 6 2.43086 36.949 0 1 3 A 19.3 2.37863 37.791 0 0 4 A 18.2 2.18716 41.243 1 1 1 R 27.9 1.89257 48.034 0 2 0 A 18 1.70011 53.884 0 1 5 A 55.5 1.68733 54.325 1 2 1 R 16.4 1.62427 56.62 2 2 0 R 13.2 1.48097 62.682 0 2 4 A 7.7 1.47897 62.777 0 0 2 R 8 1.45274 64.043 1 3 0 R 6.6 1.33823 70.285 2 2 0 A 2.8 1.25069 76.035 0 3 1 A The mass fractions of anatase (W A ) and rutile (W R ) in the PEO coatings were quantified by comparing the integrated areas of the diffraction peaks at 2θ values of 25.3° (anatase) and 27.4° (rutile), using the Spurr–Myers equations ( 1 ) and ( 2 ). $$\:{W}_{A}=\frac{1}{\left(1+0.88\text{*}\raisebox{1ex}{${A}_{A}$}\!\left/\:\!\raisebox{-1ex}{${A}_{R}$}\right.\right)}$$ 1 $$\:{W}_{R}=\frac{1}{\left(1+1.26\text{*}\raisebox{1ex}{${A}_{R}$}\!\left/\:\!\raisebox{-1ex}{${A}_{A}$}\right.\right)}$$ 2 In these equations, A A and A R represent the integrated peak areas of anatase and rutile, respectively. The calculated values are presented in Fig. 10 . As can be seen, the anatase content increased with process time and current density. This trend can be attributed to the stronger thermal effects of microdischarges, which favor crystallization from the amorphous phase. Moreover, the conversion of anatase to rutile was more pronounced under the L-600-50 and T-600-50 treatment conditions, characterized by shorter exposure times and lower current densities. In these cases, the voltage did not stabilize within the 600-second process duration (Figs. 11 a and 11 b). During the pre-stabilization phase, a high density of small, energetic microdischarges was observed, facilitating the transformation. As the process approached voltage stabilization, however, the discharges became less frequent, larger, and lower in energy, thereby reducing the efficiency of the conversion [33], [34], [36], [45]. At a current density of 100 mA/cm², voltage stabilization coincided with the simultaneous formation of anatase and rutile phases. At this stage, the increased electrical resistance of the coating acted as a thermal barrier, restricting discharge intensity. The discharges evolved into spark-type events—visually more intense but with lower effective energy dissipation—potentially slowing the anatase-to-rutile conversion rate. Figure 12 shows the voltage profiles and microdischarges of the PEO treatments with the highest anatase and rutile content (L-1000-100 and L-600-50; see Fig. 10 ). For L-1000-100, dielectric breakdown generated an initial stage of high discharge density and energy (483 s), followed by 517 s of stabilized voltage characterized by less frequent, larger, and lower-energy discharges, favoring the coexistence of both phases (Fig. 12 a). In contrast, L-600-50 did not reach voltage stabilization and instead maintained a regime of high discharge density and energy for a longer duration, which also promoted the formation of both phases, although rutile predominated (Fig. 12 b). Finally, the build direction did not have a significant effect on crystallization, suggesting the need for further analysis using complementary techniques. 3.4 Corrosion performance of coatings Figure 13 presents the Nyquist plots from EIS measurements of coatings produced under different processing conditions. Overall, the highest impedance modulus was observed for PEO treatments at 50 mA/cm² (600 − 50 and 1000-50), while the lowest value was recorded at the highest current density of 100 mA/cm² (Figs. 13 a and 13 b). This trend coincided with the Bode modulus plot at low frequencies, particularly for coatings generated in the build direction (Fig. 13 c). According to these results, PEO coatings obtained at high current density exhibit lower corrosion resistance, resulting in reduced resistance to charge transfer and corrosion-related processes such as ion diffusion through coating pores, charge transfer across the interface, and chemical reactions. The Bode plots revealed two phase angles at lower and higher frequencies (Figs. 13 e and 13 f). Notably, coatings produced under the 600 − 50 condition showed relatively high phase angles at both high and low frequency ranges, indicating superior corrosion resistance and a strong barrier effect across the entire structure. This behavior was observed consistently in both build directions (longitudinal and transverse), demonstrating that the chosen processing parameters provide robust protection regardless of substrate anisotropy. The equivalent circuit in Fig. 14 models the electrochemical behavior of PEO coatings on Ti6Al4V. In this model, R1 represents the resistance of the electrolyte; R2, the resistance of the porous layer; R5, the resistance of the dense inner layer; and R8, the charge transfer resistance—a configuration previously applied in studies of PEO coatings on titanium [23], [37], [46]. Based on this model, and using the Nyquist and Bode plots together with the polarization curves (Fig. 15 ), the corrosion parameters were determined. The results indicate an increase in corrosion current density (Icorr) with both longer processing time and higher applied current density. In some cases, higher resistance in the porous and inner layers of the coatings correlated with lower Icorr values, as observed in samples T-600-50 and L-600-50. In contrast, lower resistance in these layers was associated with higher Icorr values, as seen in samples T-1000-100 and L-1000-100. This behavior could be explained by morphological variations within the coating, including the presence of internal pores, defects at the interface with the substrate, and cracks connected to pores throughout the coating thickness. As evidenced by the FIB images (Fig. 7 ), these features may influence the corrosion rate depending on their nature and distribution. Figure 16 displays the potentiodynamic polarization curves of the coatings, along with a comparison to uncoated Ti6Al4V surfaces. In Fig. 16 a, differences in corrosion behavior between the build direction (L) and the transverse direction (T) are observed for the uncoated Ti6Al4V alloy produced by EB-PBF, in terms of both corrosion potential and current density. Specifically, the polarization curves of uncoated samples revealed a higher corrosion rate on the surfaces along the build direction (L), as evidenced by a more negative Ecorr and higher Icorr compared to the transverse direction (T). This behavior, consistent with findings in earlier studies on corrosion in additively manufactured surfaces [11], [47], is attributed to the microstructural anisotropy of the titanium alloy. In particular, the higher β-phase content along the L direction (Fig. 3 ) increases its susceptibility to corrosion. For coated samples, the corrosion potentials shifted toward more positive values, indicating a reduced tendency for corrosion compared with uncoated surfaces. Additionally, the corrosion current density decreased (Figs. 16 b and 16 c), confirming a lower corrosion rate, particularly for surfaces coated under PEO conditions at 50 mA/cm² (samples 600 − 50 and 1000-50) (Figs. 17 a and 17 b). This trend was consistent for surfaces oriented both along the build direction (L) and transverse to it (T). When comparing the corrosion performance of coatings obtained in the L and T directions, no significant differences were observed, which suggests that build direction has no effect on the formation of PEO coatings. However, the PEO coating significantly reduced the corrosion rate of the surface in the L direction, thereby eliminating the pronounced difference in corrosion performance between the two directions observed in uncoated Ti6Al4V surfaces. In other words, PEO treatment removes the corrosion anisotropy introduced by the build direction in samples produced by EBM, as shown in Fig. 17 c. 4. CONCLUSIONS The build direction of Ti6Al4V substrates produced by EB-PBF was found to exert a moderate influence on certain properties of ceramic coatings formed via the PEO technique. Although the anisotropic microstructure associated with the build direction affects some morphological characteristics of the coating, no pronounced differential growth of the anodic layer—such as that typically reported in conventional anodizing processes—was observed. The build direction of EB-PBF-manufactured substrates was found to influence the initial voltage response during PEO treatment. Higher values were observed in the L direction, primarily due to microstructural differences—particularly the greater presence of the β phase in this orientation. At later stages, however, coating growth and the associated increase in thickness progressively reduced this effect. This attenuation became even more pronounced when a current density of 100 mA/cm² was applied, which promoted faster coating growth and earlier stabilization of the process. The corrosion results demonstrate that PEO treatment effectively eliminates the anisotropic corrosion behavior of uncoated Ti6Al4V surfaces, thereby providing uniform protection regardless of build direction. Declarations Competing Interests The authors declare that they have no relevant financial or non-financial interests to disclose. Funding The authors declare that no funds, grants, or other support were received during the preparation of this manuscript. Author Contributions All authors contributed to the conception and design of the study. Data collection and analysis were carried out by Carlos A. Vargas, Alejandro A. Zuleta, and Jose A. Tamayo. Material preparation was performed by Carlos A. Botero. The first draft of the manuscript was written by Carlos A. Vargas, Maryory A. Gómez, and Juan G. Castaño. All authors provided feedback on earlier versions, and all read and approved the final version of the manuscript. ACKNOWLEDGMENTS The authors would like to thank the institutions that contributed to this research—Instituto Tecnológico Metropolitano, Universidad de Antioquia, Universidad Pontificia Bolivariana, and Mid Sweden University—for providing access to equipment and laboratory facilities within the framework of the research project entitled " Evaluación del desempeño superficial de piezas de Ti6Al4V obtenidas por manufactura aditiva para artroplastia de cadera y determinación de predictores de satisfacción ” ( “Evaluation of the surface performance of Ti6Al4V parts obtained by additive manufacturing for hip arthroplasty and identification of satisfaction predictors” ). We also extend our gratitude to ITM Translation Agency ( [email protected] ) for their support in editing the manuscript in English References N. Ariyasu, S. Matsumoto, T. Kitaura, S. Nishiyama, and Y. Yonesho, “Manufacturing Technology of Titanium Products for Aerospace Industry,” 2021. E. Marin and A. Lanzutti, “Biomedical Applications of Titanium Alloys: A Comprehensive Review,” Materials , vol. 17, no. 1, 2024, doi: 10.3390/ma17010114. A. S. Oryshchenko, I. V Gorynin, V. P. Leonov, A. S. Kudryavtsev, V. I. Mikhailov, and E. V Chudakov, “Marine titanium alloys: Present and future,” Inorganic Materials: Applied Research , vol. 6, no. 6, pp. 571–579, 2015, doi: 10.1134/S2075113315060106. A. A. Salim, H. Bakhtiar, S. K. Ghoshal, and M. S. A. Aziz, “3D-printed titanium-aluminum-vanadium alloy produced at various laser powers: evaluation of microstructures and mechanical characteristics,” The International Journal of Advanced Manufacturing Technology , vol. 132, no. 7, pp. 3671–3681, 2024, doi: 10.1007/s00170-024-13616-6. T. Zhang and C. T. Liu, “Design of titanium alloys by additive manufacturing: A critical review,” Advanced Powder Materials , vol. 1, no. 1, p. 100014, Jan. 2022, doi: 10.1016/J.APMATE.2021.11.001. W. Huang, X. Chen, X. Huang, H. Wang, and Y. Zhu, “Anisotropic Study of Ti6Al4V Alloy Formed by Selective Laser Melting,” JOM , vol. 73, no. 12, pp. 3804–3811, 2021, doi: 10.1007/s11837-021-04765-0. H. K. Rafi, N. V. Karthik, H. Gong, T. L. Starr, and B. E. Stucker, “Microstructures and mechanical properties of Ti6Al4V parts fabricated by selective laser melting and electron beam melting,” J Mater Eng Perform , vol. 22, no. 12, pp. 3872–3883, 2013, doi: 10.1007/s11665-013-0658-0. A. A. Antonysamy, J. Meyer, and P. B. Prangnell, “Effect of build geometry on the β-grain structure and texture in additive manufacture of Ti6Al4V by selective electron beam melting,” Mater Charact , vol. 84, pp. 153–168, 2013, doi: 10.1016/j.matchar.2013.07.012. N. Hrabe and T. Quinn, “Effects of processing on microstructure and mechanical properties of a titanium alloy (Ti-6Al-4V) fabricated using electron beam melting (EBM), Part 2: Energy input, orientation, and location,” Materials Science and Engineering A , vol. 573, pp. 271–277, Jun. 2013, doi: 10.1016/j.msea.2013.02.065. V. Dehnavi et al. , “Corrosion Behaviour of Electron Beam Melted Ti6Al4V: Effects of Microstructural Variation,” J Electrochem Soc , vol. 167, no. 13, p. 131505, Jan. 2020, doi: 10.1149/1945-7111/abb9d1. X. Gong et al. , “Building direction dependence of corrosion resistance property of Ti–6Al–4V alloy fabricated by electron beam melting,” Corros Sci , vol. 127, pp. 101–109, 2017, doi: 10.1016/j.corsci.2017.08.008. Y. Kok et al. , “Anisotropy and heterogeneity of microstructure and mechanical properties in metal additive manufacturing: A critical review,” Mater Des , vol. 139, pp. 565–586, Feb. 2018, doi: 10.1016/J.MATDES.2017.11.021. H. M. Hamza, K. M. Deen, A. Khaliq, E. Asselin, and W. Haider, “Microstructural, corrosion and mechanical properties of additively manufactured alloys: a review,” Critical Reviews in Solid State and Materials Sciences , vol. 47, no. 1, pp. 46–98, 2022, doi: 10.1080/10408436.2021.1886044. P. Pesode and S. Barve, “Surface modification of titanium and titanium alloy by plasma electrolytic oxidation process for biomedical applications : A review,” Mater Today Proc , vol. 46, pp. 594–602, 2021, doi: 10.1016/j.matpr.2020.11.294. J. Alipal et al. , “An updated review on surface functionalisation of titanium and its alloys for implants applications,” Mater Today Proc , vol. 42, pp. 270–282, 2021, doi: 10.1016/j.matpr.2021.01.499. M. Aliofkhazraei et al. , “Review of plasma electrolytic oxidation of titanium substrates : Mechanism , properties , applications and limitations,” Applied Surface Science Advances , vol. 5, no. January, p. 100121, 2021, doi: 10.1016/j.apsadv.2021.100121. E. K. Baldin et al. , “Copper incorporation by low-energy ion implantation in PEO-coated additively manufactured Ti6Al4V ELI: Surface microstructure, cytotoxicity and antibacterial behavior,” J Alloys Compd , vol. 940, 2023, doi: 10.1016/j.jallcom.2023.168735. D. Madhuri et al. , “Development and Characterization of High Emittance and Low-Thickness Plasma Electrolytic Oxidation Coating on Ti6Al4V for Spacecraft Application,” J Mater Eng Perform , vol. 30, pp. 4072–4082, 2021. Z. Mukhtar, A. Dey, and N. Kundan, “Optimized surface engineering of Ti-6Al-4V: Comprehensive coating evaluation for biomedical applications,” Surfaces and Interfaces , vol. 56, no. December 2024, p. 105735, 2025, doi: 10.1016/j.surfin.2024.105735. S. Demirci and M. M. Tünçay, “Surface engineering of additively manufactured Ti-6Al-4V alloys: A comparative study on micro/nanoscale topographies for biomedical applications,” Mater Today Commun , vol. 42, p. 111010, Jan. 2025, doi: 10.1016/j.mtcomm.2024.111010. A. Kumar and G. Singh, “Surface modification of Ti6Al4V alloy via advanced coatings: Mechanical, tribological, corrosion, wetting, and biocompatibility studies,” J Alloys Compd , vol. 989, no. April, p. 174418, 2024, doi: 10.1016/j.jallcom.2024.174418. D. Decha-umphai et al. , “Effects of post-processing on microstructure and adhesion strength of TiO2 nanotubes on 3D-printed Ti-6Al-4V alloy,” Surf Coat Technol , vol. 421, no. June, p. 127431, 2021, doi: 10.1016/j.surfcoat.2021.127431. Q. Yan et al. , “A comparative study of surface characterization and corrosion behavior of micro-arc oxidation treated Ti–6Al–4V alloy prepared by SEBM and SLM,” Journal of Iron and Steel Research International , Jul. 2022, doi: 10.1007/s42243-022-00800-9. Y. C. Liu, T. W. Xu, S. S. Zhang, B. J. Lv, and H. B. Ji, “Effect of annealing and build direction on microarc oxidation coatings and its apatite induction ability of Ti6Al4VE alloy manufactured by selective laser melting,” J Mater Res , 2022, doi: 10.1557/s43578-022-00830-9. C. A. Schneider, W. S. Rasband, and K. W. Eliceiri, “NIH Image to ImageJ: 25 years of image analysis,” Nat Methods , vol. 9, no. 7, pp. 671–675, 2012, doi: 10.1038/nmeth.2089. Y. Yangi and H. Wu, “Effects of Current Density on Microstructure of Titania Coatings by Micro-arc Oxidation,” J Mater Sci Technol , vol. 28, no. 4, pp. 321–324, Apr. 2012, doi: 10.1016/S1005-0302(12)60062-0. G. Mortazavi, J. Jiang, and E. I. Meletis, “Investigation of the plasma electrolytic oxidation mechanism of titanium,” Appl Surf Sci , vol. 488, pp. 370–382, Sep. 2019, doi: 10.1016/J.APSUSC.2019.05.250. S. Aliasghari, P. Skeleton, and G. E. Thompson, “Plasma electrolytic oxidation of titanium in a phosphate/silicate electrolyte and tribological performance of the coatings,” Appl Surf Sci , vol. 316, no. 1, pp. 463–476, Oct. 2014, doi: 10.1016/J.APSUSC.2014.08.037. T. Wu et al. , “Role of polymorph microstructure of Ti6Al4V alloy on PEO coating formation in phosphate electrolyte,” Surf Coat Technol , vol. 428, no. November, p. 127890, 2021, doi: 10.1016/j.surfcoat.2021.127890. I. Han, J. H. Choi, B. H. Zhao, H. K. Baik, and I. S. Lee, “Changes in anodized titanium surface morphology by virtue of different unipolar DC pulse waveform,” Surf Coat Technol , vol. 201, no. 9–11, pp. 5533–5536, Feb. 2007, doi: 10.1016/J.SURFCOAT.2006.07.102. Z. G. Karaji et al. , “Effects of plasma electrolytic oxidation process on the mechanical properties of additively manufactured porous biomaterials,” Materials Science and Engineering: C , vol. 76, pp. 406–416, Jul. 2017, doi: 10.1016/J.MSEC.2017.03.079. G. Li et al. , “Review of micro-arc oxidation of titanium alloys: Mechanism, properties and applications,” J Alloys Compd , vol. 948, p. 169773, 2023, doi: 10.1016/j.jallcom.2023.169773. M. Petkovic, S. Stojadinovic, R. Vasilic, I. Belca, B. Kasalica, and L. Zekovic, “Plasma electrolytic oxidation of tantalum,” Serbian Journal of Electrical Engineering , vol. 9, no. 1, pp. 81–94, 2012, doi: 10.2298/sjee1201081p. F. Jaspard-Mécuson et al. , “Tailored aluminium oxide layers by bipolar current adjustment in the Plasma Electrolytic Oxidation (PEO) process,” Surf Coat Technol , vol. 201, no. 21 SPEC. ISS., pp. 8677–8682, 2007, doi: 10.1016/j.surfcoat.2006.09.005. W. Yao et al. , “Micro‐arc oxidation of magnesium alloys: A review,” J Mater Sci Technol , vol. 118, pp. 158–180, Aug. 2022, doi: 10.1016/J.JMST.2021.11.053. Y. liang Cheng, X. Q. Wu, Z. gang Xue, E. Matykina, P. Skeldon, and G. E. Thompson, “Microstructure, corrosion and wear performance of plasma electrolytic oxidation coatings formed on Ti–6Al–4V alloy in silicate-hexametaphosphate electrolyte,” Surf Coat Technol , vol. 217, pp. 129–139, Feb. 2013, doi: 10.1016/J.SURFCOAT.2012.12.003. X. Zhang, Y. Wu, Y. Lv, Y. Yu, and Z. Dong, “Formation mechanism, corrosion behaviour and biological property of hydroxyapatite/TiO2 coatings fabricated by plasma electrolytic oxidation,” Surf Coat Technol , vol. 386, Mar. 2020, doi: 10.1016/j.surfcoat.2020.125483. M. Molaei, A. Fattah-Alhosseini, and S. O. Gashti, “Sodium Aluminate Concentration Effects on Microstructure and Corrosion Behavior of the Plasma Electrolytic Oxidation Coatings on Pure Titanium,” Metall Mater Trans A Phys Metall Mater Sci , vol. 49, no. 1, pp. 368–375, Jan. 2018, doi: 10.1007/S11661-017-4405-2/FIGURES/11. M. Molaei, A. Fattah-Alhosseini, and M. K. Keshavarz, “Influence of different sodium-based additives on corrosion resistance of PEO coatings on pure Ti,” https://doi.org/10.1080/21870764.2019.1604609 , vol. 7, no. 2, pp. 247–255, Apr. 2019, doi: 10.1080/21870764.2019.1604609. L. Xu et al. , “Effect of oxidation time on cytocompatibility of ultrafine-grained pure Ti in micro-arc oxidation treatment,” Surf Coat Technol , vol. 342, pp. 12–22, May 2018, doi: 10.1016/J.SURFCOAT.2018.02.044. K. R. Shin, Y. S. Kim, H. W. Yang, Y. G. Ko, and D. H. Shin, “In vitro biological response to the oxide layer in pure titanium formed at different current densities by plasma electrolytic oxidation,” Appl Surf Sci , vol. 314, pp. 221–227, Sep. 2014, doi: 10.1016/J.APSUSC.2014.06.121. T. Wu et al. , “Role of phosphate, silicate and aluminate in the electrolytes on PEO coating formation and properties of coated Ti6Al4V alloy,” Appl Surf Sci , vol. 595, no. April, p. 153523, 2022, doi: 10.1016/j.apsusc.2022.153523. Q. Li, W. Yang, C. Liu, D. Wang, and J. Liang, “Correlations between the growth mechanism and properties of micro-arc oxidation coatings on titanium alloy: Effects of electrolytes,” Surf Coat Technol , vol. 316, pp. 162–170, 2017, doi: 10.1016/j.surfcoat.2017.03.021. C. ping YANG et al. , “Effect of electrolyte composition on corrosion behavior and tribological performance of plasma electrolytic oxidized TC4 alloy,” Transactions of Nonferrous Metals Society of China (English Edition) , vol. 33, no. 1, pp. 141–156, 2023, doi: 10.1016/S1003-6326(22)66096-5. V. Dehnavi, B. L. Luan, X. Y. Liu, D. W. Shoesmith, and S. Rohani, “Correlation between plasma electrolytic oxidation treatment stages and coating microstructure on aluminum under unipolar pulsed DC mode,” Surf Coat Technol , vol. 269, no. 1, pp. 91–99, 2015, doi: 10.1016/j.surfcoat.2014.11.007. M. Kaseem and H. C. Choe, “Simultaneous improvement of corrosion resistance and bioactivity of a titanium alloy via wet and dry plasma treatments,” J Alloys Compd , vol. 851, p. 156840, Jan. 2021, doi: 10.1016/J.JALLCOM.2020.156840. V. Dehnavi et al. , “Corrosion Behaviour of Electron Beam Melted Ti6Al4V: Effects of Microstructural Variation,” J Electrochem Soc , vol. 167, no. 13, p. 131505, Jan. 2020, doi: 10.1149/1945-7111/abb9d1. Cite Share Download PDF Status: Published Journal Publication published 04 Feb, 2026 Read the published version in The International Journal of Advanced Manufacturing Technology → Version 1 posted Editorial decision: Minor Revisions Needed 20 Nov, 2025 Reviewers agreed at journal 06 Oct, 2025 Reviewers invited by journal 06 Oct, 2025 Editor assigned by journal 06 Oct, 2025 First submitted to journal 02 Oct, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7716426","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":525406113,"identity":"a916a998-2031-4042-9d27-f857f1c906d0","order_by":0,"name":"Carlos A. Vargas","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA9ElEQVRIiWNgGAWjYHACxgNw5gcDMGVAUA9cC+MMAwMStTDzMBChhb/97IMDH/4cljfvX/z4s03Bn2gG9uZtEgw1Nji1SJxJNzg4s+2w4Zwbz8ykcwwMcht4jpVJMBxLw6nFgCGN4TBvQxrjDIkDZsxgLRI5ZhKMDYdxa+F/xnCY50+a/QyJ458/W4C0yL8hoEUCaAsPm03iDP4eA2kGsC08+LVI3HjGAPSLTfIMCZ4yyR4D49w2nrRiiwQ8fuHvT2N88OGPhO0M/uObP/z4I5fbz354440PeEIMyb4ECM0GIhKI0AC07wBRykbBKBgFo2AEAgBsqlEeC0qguwAAAABJRU5ErkJggg==","orcid":"","institution":"","correspondingAuthor":true,"prefix":"","firstName":"Carlos","middleName":"A.","lastName":"Vargas","suffix":""},{"id":525406114,"identity":"b67be25b-55fb-4f25-9d17-f566668e9fd5","order_by":1,"name":"Alejandro A. Zuleta","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Alejandro","middleName":"A.","lastName":"Zuleta","suffix":""},{"id":525406115,"identity":"11da9d57-092e-46d6-b39d-3370052071c6","order_by":2,"name":"Juan G. Castaño","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Juan","middleName":"G.","lastName":"Castaño","suffix":""},{"id":525406116,"identity":"2ef7aea2-b12f-4eff-adde-e932b1994d61","order_by":3,"name":"Maryory A. Gómez","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Maryory","middleName":"A.","lastName":"Gómez","suffix":""},{"id":525406117,"identity":"7478ecc6-8aed-4787-80d2-c9b30ab2f738","order_by":4,"name":"Carlos A. Botero","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Carlos","middleName":"A.","lastName":"Botero","suffix":""},{"id":525406118,"identity":"0ce1cbdb-edeb-4db0-bcfb-7a0fa40ad980","order_by":5,"name":"Jose A. Tamayo","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Jose","middleName":"A.","lastName":"Tamayo","suffix":""}],"badges":[],"createdAt":"2025-09-26 00:18:49","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7716426/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7716426/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s00170-025-17297-7","type":"published","date":"2026-02-04T15:57:31+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":93756849,"identity":"a677118b-e8ae-4871-9385-cd9b4f230ee0","added_by":"auto","created_at":"2025-10-17 08:54:12","extension":"xml","order_by":1,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":8669,"visible":true,"origin":"","legend":"","description":"","filename":"jamtJAMTD2505550.xml","url":"https://assets-eu.researchsquare.com/files/rs-7716426/v1/0423634816e8b90f59567d83.xml"},{"id":93757237,"identity":"acc9f50c-b295-4920-911d-920df8d4c2ca","added_by":"auto","created_at":"2025-10-17 09:02:11","extension":"xml","order_by":2,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":939,"visible":true,"origin":"","legend":"","description":"","filename":"JAMTD2505550157472.go.xml","url":"https://assets-eu.researchsquare.com/files/rs-7716426/v1/7c12a95eb3f69774ffef286e.xml"},{"id":93756837,"identity":"3ea14b60-4fe2-4bc9-9ea6-dc66d1ff7854","added_by":"auto","created_at":"2025-10-17 08:54:11","extension":"xml","order_by":3,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":922,"visible":true,"origin":"","legend":"","description":"","filename":"JAMTD2505550Import.xml","url":"https://assets-eu.researchsquare.com/files/rs-7716426/v1/33e757398d6375713c39775f.xml"},{"id":93756841,"identity":"c3cb4a8f-5533-456c-8cc6-f2488bf06f2f","added_by":"auto","created_at":"2025-10-17 08:54:11","extension":"xml","order_by":4,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":101155,"visible":true,"origin":"","legend":"","description":"","filename":"JAMTD25055500enriched.xml","url":"https://assets-eu.researchsquare.com/files/rs-7716426/v1/6e1559e621b16a920b90f7f7.xml"},{"id":93756890,"identity":"69136782-471d-4066-ae60-da914fb49248","added_by":"auto","created_at":"2025-10-17 08:54:14","extension":"jpeg","order_by":5,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":974986,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage1.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7716426/v1/cab3a36c223a1eadf94243f0.jpeg"},{"id":93757244,"identity":"d2a7cbab-5017-4300-ad66-d256d2bb15e3","added_by":"auto","created_at":"2025-10-17 09:02:12","extension":"jpeg","order_by":6,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":63910,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage10.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7716426/v1/36dd3a64721f32b2410ea872.jpeg"},{"id":93756850,"identity":"f37bf8db-3f94-4f0d-a0b5-35f1012fa8c2","added_by":"auto","created_at":"2025-10-17 08:54:12","extension":"jpeg","order_by":7,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":1549026,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage11.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7716426/v1/5252c8d0acda558d65c2da95.jpeg"},{"id":93756845,"identity":"0abf4d77-f117-426f-9319-6a01cac9a389","added_by":"auto","created_at":"2025-10-17 08:54:12","extension":"jpeg","order_by":8,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":1420334,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage12.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7716426/v1/a73fb4eeed3b4eafc61d3beb.jpeg"},{"id":93756840,"identity":"19fc06cf-5091-441f-b95e-17775a24a4a5","added_by":"auto","created_at":"2025-10-17 08:54:11","extension":"jpeg","order_by":9,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":131649,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage13.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7716426/v1/f0b2feca6bd9b3e3ad2a4554.jpeg"},{"id":93756851,"identity":"f9f0e7b8-255d-4322-97f9-6efafe716c14","added_by":"auto","created_at":"2025-10-17 08:54:12","extension":"jpeg","order_by":10,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":990318,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage14.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7716426/v1/0e5a45fa3c314c7365a22086.jpeg"},{"id":93757250,"identity":"8c83bb8a-a40f-4f69-8a44-87e334dcfe9c","added_by":"auto","created_at":"2025-10-17 09:02:12","extension":"jpeg","order_by":11,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":198082,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage15.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7716426/v1/063d2306fd791546dcd84d50.jpeg"},{"id":93756842,"identity":"e388568e-9049-420f-9b10-4e41d32c1174","added_by":"auto","created_at":"2025-10-17 08:54:12","extension":"jpeg","order_by":12,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":136365,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage16.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7716426/v1/d28b7eb90dcbcc11fd313ead.jpeg"},{"id":93756874,"identity":"77c1067a-f84a-4a24-9f9f-13b1d97b006f","added_by":"auto","created_at":"2025-10-17 08:54:13","extension":"jpeg","order_by":13,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":127546,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage17.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7716426/v1/7a3b771519c257fe7052604e.jpeg"},{"id":93758880,"identity":"523c3e28-f40b-491c-8b20-fd9b0a8d0210","added_by":"auto","created_at":"2025-10-17 09:19:10","extension":"jpeg","order_by":14,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":154376,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage2.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7716426/v1/b68f58f98e275199f6176ba4.jpeg"},{"id":93756858,"identity":"88cfbca6-1d97-4c1e-9595-e77b5ed106ac","added_by":"auto","created_at":"2025-10-17 08:54:12","extension":"jpeg","order_by":15,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":1098464,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage3.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7716426/v1/be5ca0025a6f0678726371b0.jpeg"},{"id":93758423,"identity":"a1dd0866-2c32-4925-a9c6-4ba84227b881","added_by":"auto","created_at":"2025-10-17 09:10:12","extension":"jpeg","order_by":16,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":943549,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage4.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7716426/v1/6d2f843f84ab3962d3444ac3.jpeg"},{"id":93757248,"identity":"d41797fd-3777-4832-a507-dcf6db63256f","added_by":"auto","created_at":"2025-10-17 09:02:12","extension":"jpeg","order_by":17,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":83012,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage5.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7716426/v1/8063bc9ec41a684b7742b1cb.jpeg"},{"id":93756879,"identity":"491e6383-094d-4efd-9720-bec6b431bd14","added_by":"auto","created_at":"2025-10-17 08:54:13","extension":"jpeg","order_by":18,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":434090,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage6.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7716426/v1/041d24318898fc69fe59b87d.jpeg"},{"id":93757254,"identity":"c4d367b4-9f02-4d65-aeda-5d33290de55b","added_by":"auto","created_at":"2025-10-17 09:02:13","extension":"jpeg","order_by":19,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":280618,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage7.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7716426/v1/06ab51941d336b0de9bdc6c4.jpeg"},{"id":93756857,"identity":"12ade79c-7f65-4262-b662-66933223c743","added_by":"auto","created_at":"2025-10-17 08:54:12","extension":"jpeg","order_by":20,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":108674,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage8.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7716426/v1/4fe568ecfb178eb8f18dc663.jpeg"},{"id":93756867,"identity":"09c08ded-c11c-4144-80ff-fbe1ad8cf670","added_by":"auto","created_at":"2025-10-17 08:54:12","extension":"jpeg","order_by":21,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":79560,"visible":true,"origin":"","legend":"","description":"","filename":"floatimage9.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7716426/v1/4807d6041332736a6959ef93.jpeg"},{"id":93756865,"identity":"1fcc783f-9953-41b9-b356-c3f659d558e2","added_by":"auto","created_at":"2025-10-17 08:54:12","extension":"png","order_by":22,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":60091,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-7716426/v1/b141505808f1af7dada2776b.png"},{"id":93757246,"identity":"60ac7fbf-6110-4a6f-a688-048fb359e0cc","added_by":"auto","created_at":"2025-10-17 09:02:12","extension":"png","order_by":23,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":25911,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage10.png","url":"https://assets-eu.researchsquare.com/files/rs-7716426/v1/93f0ab368d808cc9e24ecda4.png"},{"id":93756860,"identity":"c7e73437-320c-4c9d-81c1-29a978f19145","added_by":"auto","created_at":"2025-10-17 08:54:12","extension":"png","order_by":24,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":14090,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage11.png","url":"https://assets-eu.researchsquare.com/files/rs-7716426/v1/465ace882bd7b3377c241d51.png"},{"id":93757252,"identity":"c40dac51-e79a-42c9-9d7f-e20854553c03","added_by":"auto","created_at":"2025-10-17 09:02:13","extension":"png","order_by":25,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":17312,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage12.png","url":"https://assets-eu.researchsquare.com/files/rs-7716426/v1/201a9688decc6798fec17398.png"},{"id":93756877,"identity":"100b42a7-4f48-4a3d-a3db-4cf8cc7a1af3","added_by":"auto","created_at":"2025-10-17 08:54:13","extension":"png","order_by":26,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":71702,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage13.png","url":"https://assets-eu.researchsquare.com/files/rs-7716426/v1/0fa2712ad4169069cc2fa96f.png"},{"id":93756876,"identity":"844195c7-f1ba-4dab-a2cb-b67f3ea2d882","added_by":"auto","created_at":"2025-10-17 08:54:13","extension":"png","order_by":27,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":12845,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage14.png","url":"https://assets-eu.researchsquare.com/files/rs-7716426/v1/f4e8b935b334f4b7c980dcb0.png"},{"id":93757253,"identity":"5ff7a0a9-49a5-4986-89e4-5586d96b0f2b","added_by":"auto","created_at":"2025-10-17 09:02:13","extension":"png","order_by":28,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":145534,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage15.png","url":"https://assets-eu.researchsquare.com/files/rs-7716426/v1/346555ddc64c060ab4a50660.png"},{"id":93756862,"identity":"0e2d9fc1-2060-4afd-ba00-e64ed0e8286d","added_by":"auto","created_at":"2025-10-17 08:54:12","extension":"png","order_by":29,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":83216,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage16.png","url":"https://assets-eu.researchsquare.com/files/rs-7716426/v1/0c795b6b79cd64773633ae04.png"},{"id":93758427,"identity":"cc7a0373-2533-4c9f-978c-73768f5aede4","added_by":"auto","created_at":"2025-10-17 09:10:13","extension":"png","order_by":30,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":69020,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage17.png","url":"https://assets-eu.researchsquare.com/files/rs-7716426/v1/1803d27dada513f27bc4b754.png"},{"id":93756864,"identity":"f8a3264c-0bb2-4aad-b0d4-669f72adc3e4","added_by":"auto","created_at":"2025-10-17 08:54:12","extension":"png","order_by":31,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":124320,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-7716426/v1/6e6d86f2f180ed00cc485a99.png"},{"id":93756868,"identity":"005edaf3-dfe4-4456-99df-168343b55c29","added_by":"auto","created_at":"2025-10-17 08:54:12","extension":"png","order_by":32,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":416420,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-7716426/v1/274ff080734f02a56b71c3ff.png"},{"id":93756881,"identity":"7857ef67-44d0-4a9a-b68d-ce84bf6a38d0","added_by":"auto","created_at":"2025-10-17 08:54:13","extension":"png","order_by":33,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":849855,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-7716426/v1/d3c7e3ffcb194e03a7926e58.png"},{"id":93756875,"identity":"cfd2a2a0-f032-4362-a669-52b6c6e2dcd4","added_by":"auto","created_at":"2025-10-17 08:54:13","extension":"png","order_by":34,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":64753,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-7716426/v1/017f205d782827b77820e1a6.png"},{"id":93758869,"identity":"475c1030-3731-436f-a276-52553310bc99","added_by":"auto","created_at":"2025-10-17 09:18:12","extension":"png","order_by":35,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":328264,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-7716426/v1/1178a2effd86fc3766fe1f5a.png"},{"id":93756873,"identity":"51e6d7c4-478e-426a-ba89-28fdc104f6ca","added_by":"auto","created_at":"2025-10-17 08:54:13","extension":"png","order_by":36,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":217369,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-7716426/v1/2411385ba21eec5f6540d624.png"},{"id":93756880,"identity":"0a5d370f-13f7-481a-9f5e-3f6640a93a62","added_by":"auto","created_at":"2025-10-17 08:54:13","extension":"png","order_by":37,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":86239,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage8.png","url":"https://assets-eu.researchsquare.com/files/rs-7716426/v1/b9ce66e7a61892d8a148695d.png"},{"id":93756883,"identity":"ef255a37-fd52-4d59-9cc5-d52161085ea8","added_by":"auto","created_at":"2025-10-17 08:54:13","extension":"png","order_by":38,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":55551,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage9.png","url":"https://assets-eu.researchsquare.com/files/rs-7716426/v1/6e9201aaaf637de7eeb492b9.png"},{"id":93756886,"identity":"2f0fcb62-1c6b-4598-940e-1c83c0ed05e1","added_by":"auto","created_at":"2025-10-17 08:54:13","extension":"xml","order_by":39,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":100513,"visible":true,"origin":"","legend":"","description":"","filename":"JAMTD25055500structuring.xml","url":"https://assets-eu.researchsquare.com/files/rs-7716426/v1/095971d600ead815c0bc7808.xml"},{"id":93756889,"identity":"bc76a145-82d5-4c52-b4d1-133c6f95be6f","added_by":"auto","created_at":"2025-10-17 08:54:14","extension":"html","order_by":40,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":108748,"visible":true,"origin":"","legend":"","description":"","filename":"earlyproof.html","url":"https://assets-eu.researchsquare.com/files/rs-7716426/v1/4866fc57dd1ec5943adb1a0a.html"},{"id":93756835,"identity":"58701ef7-7ba4-4631-b074-a77c1909b89e","added_by":"auto","created_at":"2025-10-17 08:54:11","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":174682,"visible":true,"origin":"","legend":"\u003cp\u003eSubstrates obtained from additively manufactured specimens (bar part).\u003c/p\u003e","description":"","filename":"1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7716426/v1/1206d4e0abb8343d236d413b.jpg"},{"id":93757240,"identity":"80785016-46a2-41fa-a420-9261390bd0c7","added_by":"auto","created_at":"2025-10-17 09:02:12","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":561557,"visible":true,"origin":"","legend":"\u003cp\u003eVoltage–time curves for the PEO treatment on EB-PBF substrates: effect of current density for build direction (a) and transverse direction (b), and effect of build direction under different times and current densities (c–f).\u003c/p\u003e","description":"","filename":"2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7716426/v1/9c4836f54facbb806a5cc0fb.jpg"},{"id":93757236,"identity":"24622c84-a51a-4994-b1e1-3321f519749f","added_by":"auto","created_at":"2025-10-17 09:02:11","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":373693,"visible":true,"origin":"","legend":"\u003cp\u003eMicrostructure of bare Ti6Al4V: along the build direction at 1000X (a) and at 2000X (b); and transverse to the build direction at 1000X (c) and at 2000X (d).\u003c/p\u003e","description":"","filename":"3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7716426/v1/83870904b22ea5f56cd52b17.jpg"},{"id":93756884,"identity":"bd48c70f-73e5-4296-828c-c17cc6ade536","added_by":"auto","created_at":"2025-10-17 08:54:13","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":2701247,"visible":true,"origin":"","legend":"\u003cp\u003eMorphology and porosity of the obtained coatings.\u003c/p\u003e","description":"","filename":"4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7716426/v1/6fcb7659c12f5fa9b7870c92.jpg"},{"id":93756834,"identity":"64ac8fcc-3812-435f-bba4-a84b91239165","added_by":"auto","created_at":"2025-10-17 08:54:11","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":409273,"visible":true,"origin":"","legend":"\u003cp\u003ePorosity and pore size of coatings on EB-PBF substrates: build direction (a, c) and transverse to the build direction (b, d).\u003c/p\u003e","description":"","filename":"5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7716426/v1/12bab9f4fe837d9adb37900f.jpg"},{"id":93757239,"identity":"88107253-c44c-45e4-a6c5-e3ea59d52c8b","added_by":"auto","created_at":"2025-10-17 09:02:12","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":698373,"visible":true,"origin":"","legend":"\u003cp\u003eSEM images showing cracks generated during coating deposition: (a) L-600-50, (b) L-1000-100, (c) T-600-50, and (d) T-1000-100.\u003c/p\u003e","description":"","filename":"6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7716426/v1/0afa9d09e36810152257ede5.jpg"},{"id":93756839,"identity":"c15cc440-3b2b-407e-8037-4af2ea33229b","added_by":"auto","created_at":"2025-10-17 08:54:11","extension":"jpg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":728501,"visible":true,"origin":"","legend":"\u003cp\u003ePores or defects distributed throughout the coating thickness.\u003c/p\u003e","description":"","filename":"7.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7716426/v1/4a8e630a0a2f4b3f5a712aa9.jpg"},{"id":93757241,"identity":"52c8951f-d96d-4cb5-8e91-0fa524f793bf","added_by":"auto","created_at":"2025-10-17 09:02:12","extension":"jpg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":366456,"visible":true,"origin":"","legend":"\u003cp\u003eThickness of coatings obtained under different PEO treatment conditions.\u003c/p\u003e","description":"","filename":"8.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7716426/v1/bb2f8a5720854f5fe4f0753d.jpg"},{"id":93756848,"identity":"7a6967d5-c327-4e41-8fb8-2d8aea7ccc24","added_by":"auto","created_at":"2025-10-17 08:54:12","extension":"jpg","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":856411,"visible":true,"origin":"","legend":"\u003cp\u003eX-ray diffraction spectra of coatings obtained under different PEO treatment conditions.\u003c/p\u003e","description":"","filename":"9.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7716426/v1/e47a4da009b09ebc3fb2ac09.jpg"},{"id":93756856,"identity":"801e998b-5838-4f16-ac44-de90afaf0568","added_by":"auto","created_at":"2025-10-17 08:54:12","extension":"jpg","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":504401,"visible":true,"origin":"","legend":"\u003cp\u003eContents of anatase and rutile phases in coatings obtained under different PEO treatment conditions.\u003c/p\u003e","description":"","filename":"10.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7716426/v1/0a6e011da8bc304743634fea.jpg"},{"id":93758425,"identity":"42a73772-d5a6-4b8f-b3b0-8837d8903dcc","added_by":"auto","created_at":"2025-10-17 09:10:12","extension":"jpg","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":140272,"visible":true,"origin":"","legend":"\u003cp\u003eVoltage–time curves of PEO treatment under the (a) L-600-50 and (b) T-600-50 conditions.\u003c/p\u003e","description":"","filename":"11.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7716426/v1/134d3c04fd5e2ff028f1173f.jpg"},{"id":93756854,"identity":"4226f1da-6c4e-4f70-a1b9-9c45035c6881","added_by":"auto","created_at":"2025-10-17 08:54:12","extension":"jpg","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":144065,"visible":true,"origin":"","legend":"\u003cp\u003eVoltage–time evolution during PEO treatment under the (a) L-1000-100 and (b) L-600-50 conditions, and (c) a comparison of both conditions.\u003c/p\u003e","description":"","filename":"12.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7716426/v1/1c31d0a5c9ee0c2c692898e7.jpg"},{"id":93756846,"identity":"1bd2dc46-56f3-40ac-9cae-be508f7abc2f","added_by":"auto","created_at":"2025-10-17 08:54:12","extension":"jpg","order_by":13,"title":"Figure 13","display":"","copyAsset":false,"role":"figure","size":1514870,"visible":true,"origin":"","legend":"\u003cp\u003eNyquist and Bode plots of coatings obtained under different PEO treatment conditions.\u003c/p\u003e","description":"","filename":"13.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7716426/v1/c963503bf796de9e15435109.jpg"},{"id":93757245,"identity":"94a6073d-eeac-42b3-9405-23de7423b0ea","added_by":"auto","created_at":"2025-10-17 09:02:12","extension":"jpg","order_by":14,"title":"Figure 14","display":"","copyAsset":false,"role":"figure","size":88796,"visible":true,"origin":"","legend":"\u003cp\u003eEquivalent circuit defined to represent the electrochemical behavior of the coatings.\u003c/p\u003e","description":"","filename":"14.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7716426/v1/00103d0a16a53987a652db20.jpg"},{"id":93756859,"identity":"d27dd149-9e1e-4c9f-ae7e-6e9fd76c4bf6","added_by":"auto","created_at":"2025-10-17 08:54:12","extension":"jpg","order_by":15,"title":"Figure 15","display":"","copyAsset":false,"role":"figure","size":412631,"visible":true,"origin":"","legend":"\u003cp\u003eCorrosion parameters estimated based on the defined equivalent circuit, impedance, and polarization curves.\u003c/p\u003e","description":"","filename":"15.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7716426/v1/f0aff8f7b1deb41f809968ea.jpg"},{"id":93756885,"identity":"39580cf2-8053-46d8-b493-2b2ede9f82ad","added_by":"auto","created_at":"2025-10-17 08:54:13","extension":"jpg","order_by":16,"title":"Figure 16","display":"","copyAsset":false,"role":"figure","size":1651517,"visible":true,"origin":"","legend":"\u003cp\u003ePotentiodynamic polarization curves of coatings obtained under different PEO treatment conditions.\u003c/p\u003e","description":"","filename":"16.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7716426/v1/36f96705688ded1c00ec243d.jpg"},{"id":93756872,"identity":"3e39323e-eaf1-4a98-92e8-61e99ff84924","added_by":"auto","created_at":"2025-10-17 08:54:12","extension":"jpg","order_by":17,"title":"Figure 17","display":"","copyAsset":false,"role":"figure","size":1188539,"visible":true,"origin":"","legend":"\u003cp\u003eCorrosion rates of coatings obtained under different PEO treatment conditions.\u003c/p\u003e","description":"","filename":"17.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7716426/v1/740129f221f67bd2ba5cec3c.jpg"},{"id":102234718,"identity":"b025b906-5c40-46c2-b039-0d92822f949a","added_by":"auto","created_at":"2026-02-09 16:13:05","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":13325381,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7716426/v1/30e0cbc6-05b3-4e06-b55a-62bc12cde258.pdf"}],"financialInterests":"","formattedTitle":"Effect of build direction in Ti6Al4V alloy manufactured by EB-PBF on the corrosion performance of PEO coatings","fulltext":[{"header":"1. INTRODUCTION","content":"\u003cp\u003eTi6Al4V is a titanium alloy widely recognized for its exceptional balance of strength, low weight, and corrosion resistance. Because of this unique combination, it has become the material of choice for critical applications, including aerospace components (such as aircraft structures and engines), biomedical implants (due to its biocompatibility), marine equipment requiring resistance to saltwater, and high-performance automotive parts [1], [2], [3].\u003c/p\u003e\u003cp\u003eDue to the specific characteristics of applications using this alloy, manufacturing Ti6Al4V parts through powder bed Additive Manufacturing (AM) techniques, such as electron beam melting (EB-PBF) or laser melting (LPBF), has become increasingly important [4], [5]. Nevertheless, variations in the alloy\u0026rsquo;s cooling rate during AM along the build direction and transverse to it produce a differentiated microstructure of the material [6], [7], [8], [9]. As a result, anisotropy in the alloy\u0026rsquo;s properties may occur, as reflected in the mechanical and corrosion behavior of products made using these additive techniques [10], [11], [12], [13]. Given that materials used in aerospace and biomedical applications must meet high-performance demands, surface modifications are often applied to titanium alloy substrates [14], [15], [16].\u003c/p\u003e\u003cp\u003eAmong the available approaches, electrochemical surface modification techniques have emerged as excellent alternatives because they are easy to implement and produce coatings that combine good mechanical properties, improved corrosion resistance, and favorable biological responses [17], [18]. However, it remains necessary to analyze whether the differences in microstructure observed in alloys produced by AM could also lead to differentiated coatings, depending on the surface being modified. This involves considering both the build and transverse directions, as well as assessing whether there is an effect on the anisotropy of properties, similar to what has been observed in unmodified substrates.\u003c/p\u003e\u003cp\u003eAlthough previous studies have evaluated the effects of surface modification on additively manufactured titanium alloys\u0026mdash;particularly on coating properties and performance\u0026mdash;the influence of the anisotropic microstructure of the surface on the resulting coatings has not been systematically explored [19], [20], [21]. Furthermore, little research has addressed how these properties might vary depending on the build direction (longitudinal or transverse), especially in the context of critical applications such as aerospace and biomedical engineering. This gap makes it difficult to optimize coating processes and designs for achieving uniform and predictable performance.\u003c/p\u003e\u003cp\u003eIn this regard, Decha-umphai et al. [22] reported, through conventional anodizing, differential coating growth on the alpha (α) and beta (β) phases of Ti6Al4V substrates printed by LPBF. Similarly, Qing-bo Yan et al. [23] compared the surface characteristics and corrosion performance of Ti6Al4V substrates produced by LPBF and EB-PBF and modified using Plasma Electrolytic Oxidation (PEO). They observed differences in the phase composition and roughness of TiO\u003csub\u003e2\u003c/sub\u003e coatings, with LPBF samples exhibiting higher corrosion resistance.\u003c/p\u003e\u003cp\u003eDespite this, neither of these studies considered the effect of the build direction of parts produced by AM. By contrast, Liu et al. [24] conducted an initial evaluation of the differences in microstructure associated with build direction. They found that the pore size, film thickness, and roughness of PEO coatings were influenced by build direction when the Ti6Al4V alloy was modified by annealing.\u003c/p\u003e\u003cp\u003eAs observed in the literature, most studies have focused on characterizing coatings or substrate properties separately, without providing a comprehensive evaluation of how microstructural differences\u0026mdash;arising from the build direction of the printed substrate\u0026mdash;affect coating behavior. This issue is critical for ensuring stability and reliable performance in demanding applications. Therefore, further investigation into the anisotropy of microstructures obtained in alloys processed by AM is necessary.\u003c/p\u003e\u003cp\u003eAgainst this backdrop, this paper aims to evaluate the effect of build direction in Ti6Al4V alloys produced by Electron Beam Powder Bed Fusion (EB-PBF) on the properties of coatings deposited on them by PEO. For this purpose, substrates oriented along both the build and transverse directions were coated and subsequently characterized in terms of their microstructure, corrosion resistance, and crystalline phase composition.\u003c/p\u003e"},{"header":"2. MATERIALS AND METHODS","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003e2.1 Sample preparation\u003c/h2\u003e\u003cp\u003eA Ti6Al4V substrate was fabricated using an ARCAM S12 electron beam melting system (ARCAM, M\u0026ouml;lndal, V\u0026auml;stra G\u0026ouml;taland, Sweden). The build employed GE Additive\u0026rsquo;s standard Ti\u0026ndash;6Al\u0026ndash;4V alloy (grade 5) plasma-atomized powder (Arcam AB, M\u0026ouml;lndal, Sweden). During production, an acceleration voltage of 60 kV was applied, with a maximum beam power of 4 kW. The process took place under vacuum conditions at a pressure of about 10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e mbar, with the operational temperature ranging between 600 and 700\u0026deg;C. In addition, each layer of the build was consistently 50 \u0026micro;m thick.\u003c/p\u003e\u003cp\u003eFrom the additively manufactured specimens (bar part, Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), substrates were sectioned into pieces measuring10 mm in diameter and 3 mm in thickness along the transverse direction, and into 10\u0026times;10\u0026times;3 mm pieces along the build direction, for subsequent PEO treatment. To ensure uniform surface conditions, the substrates were first ground using silicon carbide paper of varying grit sizes (400, 600, 800, 1000, 1500, and 2500). They were then polished with diamond abrasive lapping fluid to achieve a mirror-like finish. Following polishing, the samples were thoroughly cleaned with distilled water and subsequently degreased ultrasonically in acetone for 5 min. Afterwards, they were rinsed, dried with a cool air stream, and finally stored in a desiccator until further processing.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003e2.2 PEO coating preparation\u003c/h2\u003e\u003cp\u003ePEO treatment was carried out by immersing the substrates into an electrolyte solution under specific process conditions, as detailed in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. A total of 0.4 L of electrolyte was held in a stainless-steel cell, which was placed in a cooled water bath to keep the temperature below 30\u0026deg;C. The titanium substrate served as the anode, while the cell itself acted as the cathode.\u003c/p\u003e\u003cp\u003eThe process was conducted in galvanostatic mode to generate the desired anodic coatings, employing a DC power supply (Kepco BHK 500\u0026ndash;0.4 MG). Voltage and current data were recorded using National Instruments LabVIEW 8.1 software to enable real-time monitoring of the process.\u003c/p\u003e\u003cp\u003eOnce the PEO treatment was completed, the samples were removed from the electrolyte, cleaned in an ultrasonic bath with deionized water for 15 min to prepare the surface and finally dried using cold air.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eProcess variables and bath composition for PEO treatment.\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"3\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colspan=\"3\" nameend=\"c3\" namest=\"c1\"\u003e\u003cp\u003eProcess conditions\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eFactors\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e\u003cp\u003eLevels\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eElectrolyte\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e\u003cp\u003eSi-P\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eTime [s]\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e600\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e1000\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCurrent density [mA/cm\u0026sup2;]\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e50\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e100\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSurface to coat\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eL: Build direction\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eT: Transverse to build direction\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colspan=\"3\" nameend=\"c3\" namest=\"c1\"\u003e\u003cp\u003e\u003cb\u003eBath composition\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eComponent (g/L)\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e\u003cp\u003e\u003cb\u003eSi-P\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eNa₃PO₄\u0026middot;12H₂O\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e\u003cp\u003e10.0\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eNa₂SiO₃\u0026middot;5H₂O\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e\u003cp\u003e2.0\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eEDTANa₂\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e\u003cp\u003e3.7\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eNaOH\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e\u003cp\u003e2.0\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\u003ch2\u003e2.3 PEO coating characterization\u003c/h2\u003e\u003cp\u003eScanning Electron Microscopy (SEM) was employed to analyze the surface characteristics and cross-sectional structure of the coated samples. These analyses were performed with a JEOL 6490LV microscope and a Thermo Fisher Scientific Apreo 2 field-emission scanning electron microscope, with the latter providing high-resolution imaging. In addition, SEM was used to study the microstructure of the samples prior to any surface modifications.\u003c/p\u003e\u003cp\u003eFor the preparation of mirror-polished surfaces, metallographic techniques were applied, including treatment with Kroll\u0026rsquo;s reagent. Subsequently, the cross-sectional morphologies of the PEO coatings were analyzed using an FEI QUANTA 3D FEG dual-beam SEM/FIB microscope. This setup enabled detailed observation of coating cross-sections to determine thickness and assess the morphology of pores throughout the layer. Furthermore, film thickness, pore size, and pore size distribution were accurately quantified from both top-view and cross-sectional SEM images, using their respective measuring scales together with the analysis tools provided by ImageJ software [25].\u003c/p\u003e\u003cp\u003eThe phase composition of the substrates and PEO coatings was then examined by X-ray Diffraction (XRD) using an Empyrean Alpha 1 diffractometer. The analysis employed Cu\u0026ndash;K radiation, with a step size of 0.02\u003csup\u003e\u0026deg;\u003c/sup\u003e/min and a scan range from 20\u0026deg; to 70\u0026deg; in 2θ. Finally, various phases were identified through Rietveld refinement in combination with several patterns included in the High Score Plus software.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\u003ch2\u003e2.4 PEO coating performance\u003c/h2\u003e\u003cp\u003eTo evaluate the protective behavior of the coatings and the kinetics (rate) of the associated corrosion reactions, Open Circuit Potential (OCP), Electrochemical Impedance Spectroscopy (EIS), and potentiodynamic linear polarization methods were employed. Simulated Body Fluid (SBF) was prepared following standard protocols so as to ensure consistency in testing conditions. The corrosion cell consisted of an Ag/Cl reference electrode and a graphite counter electrode, while the coated samples served as the working electrodes.\u003c/p\u003e\u003cp\u003eAll tests were analyzed using PSTrace software (PalmSens) and an Autolab potentiostat (Metrohm). Furthermore, electrochemical tests were conducted in SBF, the composition of which is provided in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. To stabilize the OCP, all samples were immersed in SBF for 1 h prior to polarization testing. For the linear polarization test in SBF, a voltage range of -1000 to 1000 mV was applied at a scan rate of 1 mV/s.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003ePreparation of 1000 ml of SBF (components, quantities, and preparation sequence).\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"3\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSequence\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eReactive\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eQuantity\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eNaCl\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e8.035 g\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eNaHCO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.355 g\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eKCl\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.225 g\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eK\u003csub\u003e2\u003c/sub\u003eHPO\u003csub\u003e4\u003c/sub\u003e3H\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.231 g\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eMgCl\u003csub\u003e2\u003c/sub\u003e6H\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.311 g\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1M-HCl\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e39 mL\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCaCl\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.292 g\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eNa\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.072 g\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eTris\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e6.118 g\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1M-HCl\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0\u0026ndash;5 mL\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e"},{"header":"3. RESULTS","content":"\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\u003ch2\u003e3.1 Plasma electrolytic oxidation\u003c/h2\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e presents the voltage\u0026ndash;time curves for the PEO treatment conducted on EB-PBF substrates under the conditions specified in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. As can be seen, the voltage trends for PEO durations of 600 and 1000 s were similar when tested under the same surface orientation and current density, thereby demonstrating good reproducibility of the process. However, at a higher current density (100 mA/cm\u0026sup2;), the voltage rose compared to that at 50 mA/cm\u0026sup2;, and the final voltage was also slightly higher (Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea and \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb). This increase is attributed to the greater energy input, which in turn affects the morphology and phase composition of the coatings [26]. Consequently, these results indicate that each PEO treatment reaches a maximum coating thickness at different rates, depending on the growth dynamics controlled by the specific process parameters [27], [28], as will be discussed later.\u003c/p\u003e\u003cp\u003eFigures \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec\u0026ndash;f illustrate the effect of build direction on the PEO treatment, indicating that higher voltages were observed along the build direction (L). Nevertheless, as the voltage stabilized, the levels became comparable for both substrates. This behavior suggests that microstructural differences associated with build direction may influence transport and energy dissipation during PEO treatment, potentially leading to variations in coating morphology between the build and transverse directions in EB-PBF substrates. Although few studies have assessed the effect of build direction on PEO-treated substrates, research has shown differential growth of PEO coatings due to microstructural variations, such as differences in grain size or the distribution of α, α\u0026rsquo;, and β phases induced by annealing heat treatments on substrate surfaces [24]. Other studies have also confirmed differential coating growth on the α and β phases of printed substrates in conventional anodizing, which represents the initial phase of the PEO process [22].\u003c/p\u003e\u003cp\u003eIn particular, Wu et al. [29] reported that discharge events tend to initiate in β-rich regions, commonly located along grain boundaries, resulting in a more porous and rapidly growing oxide layer. By contrast, areas dominated by the α phase yield a more compact and protective oxide film [29]. Therefore, a possible explanation for the higher voltages observed in the build direction is that, in the early stages of the process, microstructural effects such as grain boundaries and a higher presence of retained β phase within the grains (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e) influence coating growth, since the voltage reflects the resistance of the developing layer. Once a certain coating thickness is reached (where resistance to current flow becomes similar for both already-coated substrates), the voltage difference decreases, leading to the stabilization of the process.\u003c/p\u003e\u003cp\u003eFinally, it is noteworthy that the voltage gap between the coated substrates (build and transverse directions) became smaller at the highest current density of 100 mA/cm\u0026sup2; compared with 50 mA/cm\u0026sup2;. This trend could be linked to faster coating growth and process stabilization at 100 mA/cm\u0026sup2;.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\u003ch2\u003e3.2 Morphological characterization\u003c/h2\u003e\u003cp\u003eBefore analyzing the coating morphologies via SEM, the microstructure of the bare Ti6Al4V surface was examined. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, the SEM images depict the distribution of β and α phases both along and transverse to the build direction. Along the build direction, the grains appeared elongated, with significant propagation of α phases from the grain boundaries and a high presence of retained β phase within the grains (Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea and \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb). Conversely, in the transverse direction, the microstructure revealed grains with the typical equiaxed morphology as reported in the literature [7]. These grains correspond to prior β phases, with a fine distribution of α phases both inside the grains and along their boundaries (Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec and \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed). Overall, these observations confirm the microstructural anisotropy of Ti6Al4V substrates produced by EB-PBF.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eFigures \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e and \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e summarize the coating morphologies and porosity under different PEO treatment conditions. In general, higher current densities were found to increase porosity and pore size, particularly in treatments conducted for 1000 s. This effect can be explained by the greater energy input at higher voltages, as indicated by the voltage\u0026ndash;time curves in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. Under such conditions, the frequency of discharges rises, leading to a more significant increase in pore sizes [26], [30], [31]. During the intermediate stage between dielectric breakdown and voltage stabilization, discharges become more intense; however, once the voltage stabilizes, their intensity decreases [32], [33], [34]. Unlike the stage prior to voltage stabilization, this phase is characterized by fewer discharges, which persist at fixed points for longer periods. This behavior may be associated with the presence of discharge channels, which generate larger pores and even volcano-like pore structures, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e.\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e highlights the formation of cracks during PEO coating deposition. This can be attributed to the higher voltages reached during the process, which increase thermal stress and ultimately promote the formation of these defects [35], [36], [37].\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eIn addition, the Focused Ion Beam (FIB) cross-sectional images (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e) reveal that surface cracks can extend through the entire coating thickness, potentially reaching the titanium alloy substrate through pores or fissures present within the coating. This observation suggests that such defects may act as pathways for corrosive agents, thereby compromising the protective function of the coatings [38], [39]. Additionally, various pore types were observed:\u003c/p\u003e\u003cp\u003e\u003cul\u003e\u003cli\u003e\u003cp\u003ePores located near the interface with the alloy substrate (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ea).\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eLarge and small pores formed during intermediate stages of the process, later sealed by subsequently deposited layers during the PEO treatment (Figs.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eb and \u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ed).\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eInterconnected pores situated in the middle of the coating thickness, connected to cracks propagating from the external layer of the coating (Figs.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ec and \u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ee).\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eVariations in coating thickness caused by the presence of discharge channels expelling material around them (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ef).\u003c/p\u003e\u003c/li\u003e\u003c/ul\u003e\u003c/p\u003e\u003cp\u003eThese features are consistent with the typical microstructural characteristics of PEO coatings, where microdischarges during the process lead to the formation of pores and cracks, potentially affecting the coating\u0026rsquo;s protective properties.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eFinally, Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e shows that coating thickness increases with both current density and processing time, which is in line with observations reported in previous studies [40], [41]. This behavior is influenced by the irregular surface topography of the coatings, characterized by valleys and protuberances associated with pores generated by discharge channels (Figs.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ef and \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e). Furthermore, coatings formed in the longitudinal (L) direction of the Ti6Al4V substrate were slightly thicker than those in the transverse (T) direction. This difference is consistent with the higher voltage rise observed in the L direction during the intermediate stage of the PEO treatment\u0026mdash;between dielectric breakdown and voltage stabilization (Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec\u0026ndash;f and \u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\u003ch2\u003e3.3 Phase composition of coatings\u003c/h2\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e presents the XRD spectra of the coatings, revealing peaks corresponding to the anatase and rutile crystalline phases of TiO₂. Notably, no crystalline phases related to silica were detected, which agrees with previous studies reporting a predominance of amorphous phases even at high silicate concentrations [42]. Furthermore, it has been reported that silicon-rich electrolytes tend to inhibit the formation of anatase and rutile, whereas phosphorus-containing formulations promote their crystallization [42], [43], [44]. This observation is consistent with the present findings.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e lists the Miller indices of the peaks identified in the XRD spectra of the coatings, determined using HighScore software and based on reference standards 96-900-9087 (anatase) and 96-900-9084 (rutile). The most intense peaks clearly correspond to the characteristic reflections from which the contents of the anatase and rutile phases can be quantified.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eCrystallographic indices estimated from the XRD spectra of the PEO coatings.\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"5\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eIntensity [%]\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003ed-spacing [\u0026Aring;]\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003e2 Q [\u0026deg;]\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eh k l\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eAnatase/Rutile\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e100\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e3.51663\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e25.306\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0 0 1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eA\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e100\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e3.24822\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e27.436\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e1 1 0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eR\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e45.7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e2.48695\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e36.087\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0 1 1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eR\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e2.43086\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e36.949\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0 1 3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eA\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e19.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e2.37863\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e37.791\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0 0 4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eA\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e18.2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e2.18716\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e41.243\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e1 1 1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eR\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e27.9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1.89257\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e48.034\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0 2 0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eA\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e18\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1.70011\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e53.884\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0 1 5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eA\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e55.5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1.68733\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e54.325\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e1 2 1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eR\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e16.4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1.62427\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e56.62\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e2 2 0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eR\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e13.2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1.48097\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e62.682\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0 2 4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eA\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e7.7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1.47897\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e62.777\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0 0 2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eR\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1.45274\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e64.043\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e1 3 0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eR\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e6.6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1.33823\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e70.285\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e2 2 0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eA\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e2.8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1.25069\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e76.035\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0 3 1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eA\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eThe mass fractions of anatase (W\u003csub\u003eA\u003c/sub\u003e) and rutile (W\u003csub\u003eR\u003c/sub\u003e) in the PEO coatings were quantified by comparing the integrated areas of the diffraction peaks at 2θ values of 25.3\u0026deg; (anatase) and 27.4\u0026deg; (rutile), using the Spurr\u0026ndash;Myers equations (\u003cspan refid=\"Equ1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) and (\u003cspan refid=\"Equ2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$\\:{W}_{A}=\\frac{1}{\\left(1+0.88\\text{*}\\raisebox{1ex}{${A}_{A}$}\\!\\left/\\:\\!\\raisebox{-1ex}{${A}_{R}$}\\right.\\right)}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equ2\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ2\" name=\"EquationSource\"\u003e\n$$\\:{W}_{R}=\\frac{1}{\\left(1+1.26\\text{*}\\raisebox{1ex}{${A}_{R}$}\\!\\left/\\:\\!\\raisebox{-1ex}{${A}_{A}$}\\right.\\right)}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e2\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eIn these equations, A\u003csub\u003eA\u003c/sub\u003e and A\u003csub\u003eR\u003c/sub\u003e represent the integrated peak areas of anatase and rutile, respectively. The calculated values are presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e. As can be seen, the anatase content increased with process time and current density. This trend can be attributed to the stronger thermal effects of microdischarges, which favor crystallization from the amorphous phase.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eMoreover, the conversion of anatase to rutile was more pronounced under the L-600-50 and T-600-50 treatment conditions, characterized by shorter exposure times and lower current densities. In these cases, the voltage did not stabilize within the 600-second process duration (Figs.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003ea and \u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003eb). During the pre-stabilization phase, a high density of small, energetic microdischarges was observed, facilitating the transformation. As the process approached voltage stabilization, however, the discharges became less frequent, larger, and lower in energy, thereby reducing the efficiency of the conversion [33], [34], [36], [45].\u003c/p\u003e\u003cp\u003eAt a current density of 100 mA/cm\u0026sup2;, voltage stabilization coincided with the simultaneous formation of anatase and rutile phases. At this stage, the increased electrical resistance of the coating acted as a thermal barrier, restricting discharge intensity. The discharges evolved into spark-type events\u0026mdash;visually more intense but with lower effective energy dissipation\u0026mdash;potentially slowing the anatase-to-rutile conversion rate.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e shows the voltage profiles and microdischarges of the PEO treatments with the highest anatase and rutile content (L-1000-100 and L-600-50; see Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e). For L-1000-100, dielectric breakdown generated an initial stage of high discharge density and energy (483 s), followed by 517 s of stabilized voltage characterized by less frequent, larger, and lower-energy discharges, favoring the coexistence of both phases (Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003ea). In contrast, L-600-50 did not reach voltage stabilization and instead maintained a regime of high discharge density and energy for a longer duration, which also promoted the formation of both phases, although rutile predominated (Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003eb). Finally, the build direction did not have a significant effect on crystallization, suggesting the need for further analysis using complementary techniques.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\u003ch2\u003e3.4 Corrosion performance of coatings\u003c/h2\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig13\" class=\"InternalRef\"\u003e13\u003c/span\u003e presents the Nyquist plots from EIS measurements of coatings produced under different processing conditions. Overall, the highest impedance modulus was observed for PEO treatments at 50 mA/cm\u0026sup2; (600\u0026thinsp;\u0026minus;\u0026thinsp;50 and 1000-50), while the lowest value was recorded at the highest current density of 100 mA/cm\u0026sup2; (Figs.\u0026nbsp;\u003cspan refid=\"Fig13\" class=\"InternalRef\"\u003e13\u003c/span\u003ea and \u003cspan refid=\"Fig13\" class=\"InternalRef\"\u003e13\u003c/span\u003eb). This trend coincided with the Bode modulus plot at low frequencies, particularly for coatings generated in the build direction (Fig.\u0026nbsp;\u003cspan refid=\"Fig13\" class=\"InternalRef\"\u003e13\u003c/span\u003ec). According to these results, PEO coatings obtained at high current density exhibit lower corrosion resistance, resulting in reduced resistance to charge transfer and corrosion-related processes such as ion diffusion through coating pores, charge transfer across the interface, and chemical reactions.\u003c/p\u003e\u003cp\u003eThe Bode plots revealed two phase angles at lower and higher frequencies (Figs.\u0026nbsp;\u003cspan refid=\"Fig13\" class=\"InternalRef\"\u003e13\u003c/span\u003ee and \u003cspan refid=\"Fig13\" class=\"InternalRef\"\u003e13\u003c/span\u003ef). Notably, coatings produced under the 600\u0026thinsp;\u0026minus;\u0026thinsp;50 condition showed relatively high phase angles at both high and low frequency ranges, indicating superior corrosion resistance and a strong barrier effect across the entire structure. This behavior was observed consistently in both build directions (longitudinal and transverse), demonstrating that the chosen processing parameters provide robust protection regardless of substrate anisotropy.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe equivalent circuit in Fig.\u0026nbsp;\u003cspan refid=\"Fig14\" class=\"InternalRef\"\u003e14\u003c/span\u003e models the electrochemical behavior of PEO coatings on Ti6Al4V. In this model, R1 represents the resistance of the electrolyte; R2, the resistance of the porous layer; R5, the resistance of the dense inner layer; and R8, the charge transfer resistance\u0026mdash;a configuration previously applied in studies of PEO coatings on titanium [23], [37], [46]. Based on this model, and using the Nyquist and Bode plots together with the polarization curves (Fig.\u0026nbsp;\u003cspan refid=\"Fig15\" class=\"InternalRef\"\u003e15\u003c/span\u003e), the corrosion parameters were determined.\u003c/p\u003e\u003cp\u003eThe results indicate an increase in corrosion current density (Icorr) with both longer processing time and higher applied current density. In some cases, higher resistance in the porous and inner layers of the coatings correlated with lower Icorr values, as observed in samples T-600-50 and L-600-50. In contrast, lower resistance in these layers was associated with higher Icorr values, as seen in samples T-1000-100 and L-1000-100.\u003c/p\u003e\u003cp\u003eThis behavior could be explained by morphological variations within the coating, including the presence of internal pores, defects at the interface with the substrate, and cracks connected to pores throughout the coating thickness. As evidenced by the FIB images (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e), these features may influence the corrosion rate depending on their nature and distribution.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig16\" class=\"InternalRef\"\u003e16\u003c/span\u003e displays the potentiodynamic polarization curves of the coatings, along with a comparison to uncoated Ti6Al4V surfaces. In Fig.\u0026nbsp;\u003cspan refid=\"Fig16\" class=\"InternalRef\"\u003e16\u003c/span\u003ea, differences in corrosion behavior between the build direction (L) and the transverse direction (T) are observed for the uncoated Ti6Al4V alloy produced by EB-PBF, in terms of both corrosion potential and current density. Specifically, the polarization curves of uncoated samples revealed a higher corrosion rate on the surfaces along the build direction (L), as evidenced by a more negative Ecorr and higher Icorr compared to the transverse direction (T). This behavior, consistent with findings in earlier studies on corrosion in additively manufactured surfaces [11], [47], is attributed to the microstructural anisotropy of the titanium alloy. In particular, the higher β-phase content along the L direction (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e) increases its susceptibility to corrosion.\u003c/p\u003e\u003cp\u003eFor coated samples, the corrosion potentials shifted toward more positive values, indicating a reduced tendency for corrosion compared with uncoated surfaces. Additionally, the corrosion current density decreased (Figs.\u0026nbsp;\u003cspan refid=\"Fig16\" class=\"InternalRef\"\u003e16\u003c/span\u003eb and \u003cspan refid=\"Fig16\" class=\"InternalRef\"\u003e16\u003c/span\u003ec), confirming a lower corrosion rate, particularly for surfaces coated under PEO conditions at 50 mA/cm\u0026sup2; (samples 600\u0026thinsp;\u0026minus;\u0026thinsp;50 and 1000-50) (Figs.\u0026nbsp;\u003cspan refid=\"Fig17\" class=\"InternalRef\"\u003e17\u003c/span\u003ea and \u003cspan refid=\"Fig17\" class=\"InternalRef\"\u003e17\u003c/span\u003eb). This trend was consistent for surfaces oriented both along the build direction (L) and transverse to it (T).\u003c/p\u003e\u003cp\u003eWhen comparing the corrosion performance of coatings obtained in the L and T directions, no significant differences were observed, which suggests that build direction has no effect on the formation of PEO coatings. However, the PEO coating significantly reduced the corrosion rate of the surface in the L direction, thereby eliminating the pronounced difference in corrosion performance between the two directions observed in uncoated Ti6Al4V surfaces. In other words, PEO treatment removes the corrosion anisotropy introduced by the build direction in samples produced by EBM, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig17\" class=\"InternalRef\"\u003e17\u003c/span\u003ec.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e"},{"header":"4. CONCLUSIONS","content":"\u003cp\u003e\u003cul\u003e\u003cli\u003e\u003cp\u003eThe build direction of Ti6Al4V substrates produced by EB-PBF was found to exert a moderate influence on certain properties of ceramic coatings formed via the PEO technique. Although the anisotropic microstructure associated with the build direction affects some morphological characteristics of the coating, no pronounced differential growth of the anodic layer\u0026mdash;such as that typically reported in conventional anodizing processes\u0026mdash;was observed.\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eThe build direction of EB-PBF-manufactured substrates was found to influence the initial voltage response during PEO treatment. Higher values were observed in the L direction, primarily due to microstructural differences\u0026mdash;particularly the greater presence of the β phase in this orientation. At later stages, however, coating growth and the associated increase in thickness progressively reduced this effect. This attenuation became even more pronounced when a current density of 100 mA/cm\u0026sup2; was applied, which promoted faster coating growth and earlier stabilization of the process.\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eThe corrosion results demonstrate that PEO treatment effectively eliminates the anisotropic corrosion behavior of uncoated Ti6Al4V surfaces, thereby providing uniform protection regardless of build direction.\u003c/p\u003e\u003c/li\u003e\u003c/ul\u003e\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003ch2\u003eCompeting Interests\u003c/h2\u003e\u003cp\u003e\u003cem\u003eThe authors declare that they have no relevant financial or non-financial interests to disclose.\u003c/em\u003e\u003c/p\u003e\u003c/p\u003e\u003ch2\u003eFunding\u003c/h2\u003e\u003cp\u003eThe authors declare that no funds, grants, or other support were received during the preparation of this manuscript.\u003c/p\u003e\u003ch2\u003eAuthor Contributions\u003c/h2\u003e\u003cp\u003eAll authors contributed to the conception and design of the study. Data collection and analysis were carried out by Carlos A. Vargas, Alejandro A. Zuleta, and Jose A. Tamayo. Material preparation was performed by Carlos A. Botero. The first draft of the manuscript was written by Carlos A. Vargas, Maryory A. G\u0026oacute;mez, and Juan G. Casta\u0026ntilde;o. All authors provided feedback on earlier versions, and all read and approved the final version of the manuscript.\u003c/p\u003e\u003ch2\u003eACKNOWLEDGMENTS\u003c/h2\u003e\u003cp\u003eThe authors would like to thank the institutions that contributed to this research\u0026mdash;Instituto Tecnol\u0026oacute;gico Metropolitano, Universidad de Antioquia, Universidad Pontificia Bolivariana, and Mid Sweden University\u0026mdash;for providing access to equipment and laboratory facilities within the framework of the research project entitled \"\u003cem\u003eEvaluaci\u0026oacute;n del desempe\u0026ntilde;o superficial de piezas de Ti6Al4V obtenidas por manufactura aditiva para artroplastia de cadera y determinaci\u0026oacute;n de predictores de satisfacci\u0026oacute;n\u003c/em\u003e\u0026rdquo; (\u003cem\u003e\u0026ldquo;Evaluation of the surface performance of Ti6Al4V parts obtained by additive manufacturing for hip arthroplasty and identification of satisfaction predictors\u0026rdquo;\u003c/em\u003e). We also extend our gratitude to ITM Translation Agency ([email protected]) for their support in editing the manuscript in English\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eN. Ariyasu, S. Matsumoto, T. Kitaura, S. Nishiyama, and Y. Yonesho, \u0026ldquo;Manufacturing Technology of Titanium Products for Aerospace Industry,\u0026rdquo; 2021.\u003c/li\u003e\n\u003cli\u003eE. Marin and A. Lanzutti, \u0026ldquo;Biomedical Applications of Titanium Alloys: A Comprehensive Review,\u0026rdquo; \u003cem\u003eMaterials\u003c/em\u003e, vol. 17, no. 1, 2024, doi: 10.3390/ma17010114.\u003c/li\u003e\n\u003cli\u003eA. S. Oryshchenko, I. V Gorynin, V. P. Leonov, A. S. Kudryavtsev, V. I. Mikhailov, and E. V Chudakov, \u0026ldquo;Marine titanium alloys: Present and future,\u0026rdquo; \u003cem\u003eInorganic Materials: Applied Research\u003c/em\u003e, vol. 6, no. 6, pp. 571\u0026ndash;579, 2015, doi: 10.1134/S2075113315060106.\u003c/li\u003e\n\u003cli\u003eA. A. Salim, H. Bakhtiar, S. K. Ghoshal, and M. S. A. Aziz, \u0026ldquo;3D-printed titanium-aluminum-vanadium alloy produced at various laser powers: evaluation of microstructures and mechanical characteristics,\u0026rdquo; \u003cem\u003eThe International Journal of Advanced Manufacturing Technology\u003c/em\u003e, vol. 132, no. 7, pp. 3671\u0026ndash;3681, 2024, doi: 10.1007/s00170-024-13616-6.\u003c/li\u003e\n\u003cli\u003eT. Zhang and C. T. Liu, \u0026ldquo;Design of titanium alloys by additive manufacturing: A critical review,\u0026rdquo; \u003cem\u003eAdvanced Powder Materials\u003c/em\u003e, vol. 1, no. 1, p. 100014, Jan. 2022, doi: 10.1016/J.APMATE.2021.11.001.\u003c/li\u003e\n\u003cli\u003eW. Huang, X. Chen, X. Huang, H. Wang, and Y. Zhu, \u0026ldquo;Anisotropic Study of Ti6Al4V Alloy Formed by Selective Laser Melting,\u0026rdquo; \u003cem\u003eJOM\u003c/em\u003e, vol. 73, no. 12, pp. 3804\u0026ndash;3811, 2021, doi: 10.1007/s11837-021-04765-0.\u003c/li\u003e\n\u003cli\u003eH. K. Rafi, N. V. Karthik, H. Gong, T. L. Starr, and B. E. Stucker, \u0026ldquo;Microstructures and mechanical properties of Ti6Al4V parts fabricated by selective laser melting and electron beam melting,\u0026rdquo; \u003cem\u003eJ Mater Eng Perform\u003c/em\u003e, vol. 22, no. 12, pp. 3872\u0026ndash;3883, 2013, doi: 10.1007/s11665-013-0658-0.\u003c/li\u003e\n\u003cli\u003eA. A. Antonysamy, J. Meyer, and P. B. Prangnell, \u0026ldquo;Effect of build geometry on the \u0026beta;-grain structure and texture in additive manufacture of Ti6Al4V by selective electron beam melting,\u0026rdquo; \u003cem\u003eMater Charact\u003c/em\u003e, vol. 84, pp. 153\u0026ndash;168, 2013, doi: 10.1016/j.matchar.2013.07.012.\u003c/li\u003e\n\u003cli\u003eN. Hrabe and T. Quinn, \u0026ldquo;Effects of processing on microstructure and mechanical properties of a titanium alloy (Ti-6Al-4V) fabricated using electron beam melting (EBM), Part 2: Energy input, orientation, and location,\u0026rdquo; \u003cem\u003eMaterials Science and Engineering A\u003c/em\u003e, vol. 573, pp. 271\u0026ndash;277, Jun. 2013, doi: 10.1016/j.msea.2013.02.065.\u003c/li\u003e\n\u003cli\u003eV. Dehnavi \u003cem\u003eet al.\u003c/em\u003e, \u0026ldquo;Corrosion Behaviour of Electron Beam Melted Ti6Al4V: Effects of Microstructural Variation,\u0026rdquo; \u003cem\u003eJ Electrochem Soc\u003c/em\u003e, vol. 167, no. 13, p. 131505, Jan. 2020, doi: 10.1149/1945-7111/abb9d1.\u003c/li\u003e\n\u003cli\u003eX. Gong \u003cem\u003eet al.\u003c/em\u003e, \u0026ldquo;Building direction dependence of corrosion resistance property of Ti\u0026ndash;6Al\u0026ndash;4V alloy fabricated by electron beam melting,\u0026rdquo; \u003cem\u003eCorros Sci\u003c/em\u003e, vol. 127, pp. 101\u0026ndash;109, 2017, doi: 10.1016/j.corsci.2017.08.008.\u003c/li\u003e\n\u003cli\u003eY. Kok \u003cem\u003eet al.\u003c/em\u003e, \u0026ldquo;Anisotropy and heterogeneity of microstructure and mechanical properties in metal additive manufacturing: A critical review,\u0026rdquo; \u003cem\u003eMater Des\u003c/em\u003e, vol. 139, pp. 565\u0026ndash;586, Feb. 2018, doi: 10.1016/J.MATDES.2017.11.021.\u003c/li\u003e\n\u003cli\u003eH. M. Hamza, K. M. Deen, A. Khaliq, E. Asselin, and W. Haider, \u0026ldquo;Microstructural, corrosion and mechanical properties of additively manufactured alloys: a review,\u0026rdquo; \u003cem\u003eCritical Reviews in Solid State and Materials Sciences\u003c/em\u003e, vol. 47, no. 1, pp. 46\u0026ndash;98, 2022, doi: 10.1080/10408436.2021.1886044.\u003c/li\u003e\n\u003cli\u003eP. Pesode and S. Barve, \u0026ldquo;Surface modification of titanium and titanium alloy by plasma electrolytic oxidation process for biomedical applications : A review,\u0026rdquo; \u003cem\u003eMater Today Proc\u003c/em\u003e, vol. 46, pp. 594\u0026ndash;602, 2021, doi: 10.1016/j.matpr.2020.11.294.\u003c/li\u003e\n\u003cli\u003eJ. Alipal \u003cem\u003eet al.\u003c/em\u003e, \u0026ldquo;An updated review on surface functionalisation of titanium and its alloys for implants applications,\u0026rdquo; \u003cem\u003eMater Today Proc\u003c/em\u003e, vol. 42, pp. 270\u0026ndash;282, 2021, doi: 10.1016/j.matpr.2021.01.499.\u003c/li\u003e\n\u003cli\u003eM. Aliofkhazraei \u003cem\u003eet al.\u003c/em\u003e, \u0026ldquo;Review of plasma electrolytic oxidation of titanium substrates : Mechanism , properties , applications and limitations,\u0026rdquo; \u003cem\u003eApplied Surface Science Advances\u003c/em\u003e, vol. 5, no. January, p. 100121, 2021, doi: 10.1016/j.apsadv.2021.100121.\u003c/li\u003e\n\u003cli\u003eE. K. Baldin \u003cem\u003eet al.\u003c/em\u003e, \u0026ldquo;Copper incorporation by low-energy ion implantation in PEO-coated additively manufactured Ti6Al4V ELI: Surface microstructure, cytotoxicity and antibacterial behavior,\u0026rdquo; \u003cem\u003eJ Alloys Compd\u003c/em\u003e, vol. 940, 2023, doi: 10.1016/j.jallcom.2023.168735.\u003c/li\u003e\n\u003cli\u003eD. Madhuri \u003cem\u003eet al.\u003c/em\u003e, \u0026ldquo;Development and Characterization of High Emittance and Low-Thickness Plasma Electrolytic Oxidation Coating on Ti6Al4V for Spacecraft Application,\u0026rdquo; \u003cem\u003eJ Mater Eng Perform\u003c/em\u003e, vol. 30, pp. 4072\u0026ndash;4082, 2021.\u003c/li\u003e\n\u003cli\u003eZ. Mukhtar, A. Dey, and N. Kundan, \u0026ldquo;Optimized surface engineering of Ti-6Al-4V: Comprehensive coating evaluation for biomedical applications,\u0026rdquo; \u003cem\u003eSurfaces and Interfaces\u003c/em\u003e, vol. 56, no. December 2024, p. 105735, 2025, doi: 10.1016/j.surfin.2024.105735.\u003c/li\u003e\n\u003cli\u003eS. Demirci and M. M. T\u0026uuml;n\u0026ccedil;ay, \u0026ldquo;Surface engineering of additively manufactured Ti-6Al-4V alloys: A comparative study on micro/nanoscale topographies for biomedical applications,\u0026rdquo; \u003cem\u003eMater Today Commun\u003c/em\u003e, vol. 42, p. 111010, Jan. 2025, doi: 10.1016/j.mtcomm.2024.111010.\u003c/li\u003e\n\u003cli\u003eA. Kumar and G. Singh, \u0026ldquo;Surface modification of Ti6Al4V alloy via advanced coatings: Mechanical, tribological, corrosion, wetting, and biocompatibility studies,\u0026rdquo; \u003cem\u003eJ Alloys Compd\u003c/em\u003e, vol. 989, no. April, p. 174418, 2024, doi: 10.1016/j.jallcom.2024.174418.\u003c/li\u003e\n\u003cli\u003eD. Decha-umphai \u003cem\u003eet al.\u003c/em\u003e, \u0026ldquo;Effects of post-processing on microstructure and adhesion strength of TiO2 nanotubes on 3D-printed Ti-6Al-4V alloy,\u0026rdquo; \u003cem\u003eSurf Coat Technol\u003c/em\u003e, vol. 421, no. June, p. 127431, 2021, doi: 10.1016/j.surfcoat.2021.127431.\u003c/li\u003e\n\u003cli\u003eQ. Yan \u003cem\u003eet al.\u003c/em\u003e, \u0026ldquo;A comparative study of surface characterization and corrosion behavior of micro-arc oxidation treated Ti\u0026ndash;6Al\u0026ndash;4V alloy prepared by SEBM and SLM,\u0026rdquo; \u003cem\u003eJournal of Iron and Steel Research International\u003c/em\u003e, Jul. 2022, doi: 10.1007/s42243-022-00800-9.\u003c/li\u003e\n\u003cli\u003eY. C. Liu, T. W. Xu, S. S. Zhang, B. J. Lv, and H. B. Ji, \u0026ldquo;Effect of annealing and build direction on microarc oxidation coatings and its apatite induction ability of Ti6Al4VE alloy manufactured by selective laser melting,\u0026rdquo; \u003cem\u003eJ Mater Res\u003c/em\u003e, 2022, doi: 10.1557/s43578-022-00830-9.\u003c/li\u003e\n\u003cli\u003eC. A. Schneider, W. S. Rasband, and K. W. Eliceiri, \u0026ldquo;NIH Image to ImageJ: 25 years of image analysis,\u0026rdquo; \u003cem\u003eNat Methods\u003c/em\u003e, vol. 9, no. 7, pp. 671\u0026ndash;675, 2012, doi: 10.1038/nmeth.2089.\u003c/li\u003e\n\u003cli\u003eY. Yangi and H. Wu, \u0026ldquo;Effects of Current Density on Microstructure of Titania Coatings by Micro-arc Oxidation,\u0026rdquo; \u003cem\u003eJ Mater Sci Technol\u003c/em\u003e, vol. 28, no. 4, pp. 321\u0026ndash;324, Apr. 2012, doi: 10.1016/S1005-0302(12)60062-0.\u003c/li\u003e\n\u003cli\u003eG. Mortazavi, J. Jiang, and E. I. Meletis, \u0026ldquo;Investigation of the plasma electrolytic oxidation mechanism of titanium,\u0026rdquo; \u003cem\u003eAppl Surf Sci\u003c/em\u003e, vol. 488, pp. 370\u0026ndash;382, Sep. 2019, doi: 10.1016/J.APSUSC.2019.05.250.\u003c/li\u003e\n\u003cli\u003eS. Aliasghari, P. Skeleton, and G. E. Thompson, \u0026ldquo;Plasma electrolytic oxidation of titanium in a phosphate/silicate electrolyte and tribological performance of the coatings,\u0026rdquo; \u003cem\u003eAppl Surf Sci\u003c/em\u003e, vol. 316, no. 1, pp. 463\u0026ndash;476, Oct. 2014, doi: 10.1016/J.APSUSC.2014.08.037.\u003c/li\u003e\n\u003cli\u003eT. Wu \u003cem\u003eet al.\u003c/em\u003e, \u0026ldquo;Role of polymorph microstructure of Ti6Al4V alloy on PEO coating formation in phosphate electrolyte,\u0026rdquo; \u003cem\u003eSurf Coat Technol\u003c/em\u003e, vol. 428, no. November, p. 127890, 2021, doi: 10.1016/j.surfcoat.2021.127890.\u003c/li\u003e\n\u003cli\u003eI. Han, J. H. Choi, B. H. Zhao, H. K. Baik, and I. S. Lee, \u0026ldquo;Changes in anodized titanium surface morphology by virtue of different unipolar DC pulse waveform,\u0026rdquo; \u003cem\u003eSurf Coat Technol\u003c/em\u003e, vol. 201, no. 9\u0026ndash;11, pp. 5533\u0026ndash;5536, Feb. 2007, doi: 10.1016/J.SURFCOAT.2006.07.102.\u003c/li\u003e\n\u003cli\u003eZ. G. Karaji \u003cem\u003eet al.\u003c/em\u003e, \u0026ldquo;Effects of plasma electrolytic oxidation process on the mechanical properties of additively manufactured porous biomaterials,\u0026rdquo; \u003cem\u003eMaterials Science and Engineering: C\u003c/em\u003e, vol. 76, pp. 406\u0026ndash;416, Jul. 2017, doi: 10.1016/J.MSEC.2017.03.079.\u003c/li\u003e\n\u003cli\u003eG. Li \u003cem\u003eet al.\u003c/em\u003e, \u0026ldquo;Review of micro-arc oxidation of titanium alloys: Mechanism, properties and applications,\u0026rdquo; \u003cem\u003eJ Alloys Compd\u003c/em\u003e, vol. 948, p. 169773, 2023, doi: 10.1016/j.jallcom.2023.169773.\u003c/li\u003e\n\u003cli\u003eM. Petkovic, S. Stojadinovic, R. Vasilic, I. Belca, B. Kasalica, and L. Zekovic, \u0026ldquo;Plasma electrolytic oxidation of tantalum,\u0026rdquo; \u003cem\u003eSerbian Journal of Electrical Engineering\u003c/em\u003e, vol. 9, no. 1, pp. 81\u0026ndash;94, 2012, doi: 10.2298/sjee1201081p.\u003c/li\u003e\n\u003cli\u003eF. Jaspard-M\u0026eacute;cuson \u003cem\u003eet al.\u003c/em\u003e, \u0026ldquo;Tailored aluminium oxide layers by bipolar current adjustment in the Plasma Electrolytic Oxidation (PEO) process,\u0026rdquo; \u003cem\u003eSurf Coat Technol\u003c/em\u003e, vol. 201, no. 21 SPEC. ISS., pp. 8677\u0026ndash;8682, 2007, doi: 10.1016/j.surfcoat.2006.09.005.\u003c/li\u003e\n\u003cli\u003eW. Yao \u003cem\u003eet al.\u003c/em\u003e, \u0026ldquo;Micro‐arc oxidation of magnesium alloys: A review,\u0026rdquo; \u003cem\u003eJ Mater Sci Technol\u003c/em\u003e, vol. 118, pp. 158\u0026ndash;180, Aug. 2022, doi: 10.1016/J.JMST.2021.11.053.\u003c/li\u003e\n\u003cli\u003eY. liang Cheng, X. Q. Wu, Z. gang Xue, E. Matykina, P. Skeldon, and G. E. Thompson, \u0026ldquo;Microstructure, corrosion and wear performance of plasma electrolytic oxidation coatings formed on Ti\u0026ndash;6Al\u0026ndash;4V alloy in silicate-hexametaphosphate electrolyte,\u0026rdquo; \u003cem\u003eSurf Coat Technol\u003c/em\u003e, vol. 217, pp. 129\u0026ndash;139, Feb. 2013, doi: 10.1016/J.SURFCOAT.2012.12.003.\u003c/li\u003e\n\u003cli\u003eX. Zhang, Y. Wu, Y. Lv, Y. Yu, and Z. Dong, \u0026ldquo;Formation mechanism, corrosion behaviour and biological property of hydroxyapatite/TiO2 coatings fabricated by plasma electrolytic oxidation,\u0026rdquo; \u003cem\u003eSurf Coat Technol\u003c/em\u003e, vol. 386, Mar. 2020, doi: 10.1016/j.surfcoat.2020.125483.\u003c/li\u003e\n\u003cli\u003eM. Molaei, A. Fattah-Alhosseini, and S. O. Gashti, \u0026ldquo;Sodium Aluminate Concentration Effects on Microstructure and Corrosion Behavior of the Plasma Electrolytic Oxidation Coatings on Pure Titanium,\u0026rdquo; \u003cem\u003eMetall Mater Trans A Phys Metall Mater Sci\u003c/em\u003e, vol. 49, no. 1, pp. 368\u0026ndash;375, Jan. 2018, doi: 10.1007/S11661-017-4405-2/FIGURES/11.\u003c/li\u003e\n\u003cli\u003eM. Molaei, A. Fattah-Alhosseini, and M. K. Keshavarz, \u0026ldquo;Influence of different sodium-based additives on corrosion resistance of PEO coatings on pure Ti,\u0026rdquo; \u003cem\u003ehttps://doi.org/10.1080/21870764.2019.1604609\u003c/em\u003e, vol. 7, no. 2, pp. 247\u0026ndash;255, Apr. 2019, doi: 10.1080/21870764.2019.1604609.\u003c/li\u003e\n\u003cli\u003eL. Xu \u003cem\u003eet al.\u003c/em\u003e, \u0026ldquo;Effect of oxidation time on cytocompatibility of ultrafine-grained pure Ti in micro-arc oxidation treatment,\u0026rdquo; \u003cem\u003eSurf Coat Technol\u003c/em\u003e, vol. 342, pp. 12\u0026ndash;22, May 2018, doi: 10.1016/J.SURFCOAT.2018.02.044.\u003c/li\u003e\n\u003cli\u003eK. R. Shin, Y. S. Kim, H. W. Yang, Y. G. Ko, and D. H. Shin, \u0026ldquo;In vitro biological response to the oxide layer in pure titanium formed at different current densities by plasma electrolytic oxidation,\u0026rdquo; \u003cem\u003eAppl Surf Sci\u003c/em\u003e, vol. 314, pp. 221\u0026ndash;227, Sep. 2014, doi: 10.1016/J.APSUSC.2014.06.121.\u003c/li\u003e\n\u003cli\u003eT. Wu \u003cem\u003eet al.\u003c/em\u003e, \u0026ldquo;Role of phosphate, silicate and aluminate in the electrolytes on PEO coating formation and properties of coated Ti6Al4V alloy,\u0026rdquo; \u003cem\u003eAppl Surf Sci\u003c/em\u003e, vol. 595, no. April, p. 153523, 2022, doi: 10.1016/j.apsusc.2022.153523.\u003c/li\u003e\n\u003cli\u003eQ. Li, W. Yang, C. Liu, D. Wang, and J. Liang, \u0026ldquo;Correlations between the growth mechanism and properties of micro-arc oxidation coatings on titanium alloy: Effects of electrolytes,\u0026rdquo; \u003cem\u003eSurf Coat Technol\u003c/em\u003e, vol. 316, pp. 162\u0026ndash;170, 2017, doi: 10.1016/j.surfcoat.2017.03.021.\u003c/li\u003e\n\u003cli\u003eC. ping YANG \u003cem\u003eet al.\u003c/em\u003e, \u0026ldquo;Effect of electrolyte composition on corrosion behavior and tribological performance of plasma electrolytic oxidized TC4 alloy,\u0026rdquo; \u003cem\u003eTransactions of Nonferrous Metals Society of China (English Edition)\u003c/em\u003e, vol. 33, no. 1, pp. 141\u0026ndash;156, 2023, doi: 10.1016/S1003-6326(22)66096-5.\u003c/li\u003e\n\u003cli\u003eV. Dehnavi, B. L. Luan, X. Y. Liu, D. W. Shoesmith, and S. Rohani, \u0026ldquo;Correlation between plasma electrolytic oxidation treatment stages and coating microstructure on aluminum under unipolar pulsed DC mode,\u0026rdquo; \u003cem\u003eSurf Coat Technol\u003c/em\u003e, vol. 269, no. 1, pp. 91\u0026ndash;99, 2015, doi: 10.1016/j.surfcoat.2014.11.007.\u003c/li\u003e\n\u003cli\u003eM. Kaseem and H. C. Choe, \u0026ldquo;Simultaneous improvement of corrosion resistance and bioactivity of a titanium alloy via wet and dry plasma treatments,\u0026rdquo; \u003cem\u003eJ Alloys Compd\u003c/em\u003e, vol. 851, p. 156840, Jan. 2021, doi: 10.1016/J.JALLCOM.2020.156840.\u003c/li\u003e\n\u003cli\u003eV. Dehnavi \u003cem\u003eet al.\u003c/em\u003e, \u0026ldquo;Corrosion Behaviour of Electron Beam Melted Ti6Al4V: Effects of Microstructural Variation,\u0026rdquo; \u003cem\u003eJ Electrochem Soc\u003c/em\u003e, vol. 167, no. 13, p. 131505, Jan. 2020, doi: 10.1149/1945-7111/abb9d1.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"the-international-journal-of-advanced-manufacturing-technology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jamt","sideBox":"Learn more about [The International Journal of Advanced Manufacturing Technology](https://www.springer.com/journal/170)","snPcode":"170","submissionUrl":"https://submission.nature.com/new-submission/170/3","title":"The International Journal of Advanced Manufacturing Technology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Ti6Al4V alloy, electron beam melting (EB-PBF), Plasma Electrolytic Oxidation (PEO), build direction, microstructural anisotropy, corrosion resistance","lastPublishedDoi":"10.21203/rs.3.rs-7716426/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7716426/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis study investigates the influence of build direction in Ti6Al4V substrates manufactured by Electron Beam Powder Bed Fusion (EB-PBF) on the performance of Plasma Electrolytic Oxidation (PEO) coatings. Because of the inherent anisotropy of additively manufactured alloys, arising from differences in thermal history between the build and transverse directions, surface treatments and coating behavior may vary. To explore this, coatings were produced in a silicate\u0026ndash;phosphate (Si\u0026ndash;P) electrolyte under different current densities and treatment times. The resulting coatings were characterized in terms of morphology, crystalline phase composition, and corrosion performance. The results show that, although build direction affects the initial voltage response during PEO treatment, its influence on coating thickness and porosity is minimal. X-ray diffraction revealed the presence of both anatase and rutile TiO₂ phases, with anatase formation favored at lower current densities. Importantly, PEO treatment eliminated the corrosion anisotropy observed in uncoated Ti6Al4V manufactured by EB-PBF, leading to uniform protective behavior regardless of build direction. Overall, these findings demonstrate the potential of PEO to enhance the functional performance of additively manufactured titanium alloys for biomedical and aerospace applications. In addition, they underscore the importance of electrolyte composition and process optimization in tailoring surface properties.\u003c/p\u003e","manuscriptTitle":"Effect of build direction in Ti6Al4V alloy manufactured by EB-PBF on the corrosion performance of PEO coatings","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-10-17 08:54:06","doi":"10.21203/rs.3.rs-7716426/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Minor Revisions Needed","date":"2025-11-20T14:25:21+00:00","index":"","fulltext":""},{"type":"reviewerAgreed","content":"","date":"2025-10-06T13:33:20+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-10-06T13:20:17+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-10-06T04:06:13+00:00","index":"","fulltext":""},{"type":"submitted","content":"The International Journal of Advanced Manufacturing Technology","date":"2025-10-02T12:20:34+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"the-international-journal-of-advanced-manufacturing-technology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jamt","sideBox":"Learn more about [The International Journal of Advanced Manufacturing Technology](https://www.springer.com/journal/170)","snPcode":"170","submissionUrl":"https://submission.nature.com/new-submission/170/3","title":"The International Journal of Advanced Manufacturing Technology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"a0fb0914-d8e3-4f90-a67a-59fa73eed978","owner":[],"postedDate":"October 17th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2026-02-09T16:08:37+00:00","versionOfRecord":{"articleIdentity":"rs-7716426","link":"https://doi.org/10.1007/s00170-025-17297-7","journal":{"identity":"the-international-journal-of-advanced-manufacturing-technology","isVorOnly":false,"title":"The International Journal of Advanced Manufacturing Technology"},"publishedOn":"2026-02-04 15:57:31","publishedOnDateReadable":"February 4th, 2026"},"versionCreatedAt":"2025-10-17 08:54:06","video":"","vorDoi":"10.1007/s00170-025-17297-7","vorDoiUrl":"https://doi.org/10.1007/s00170-025-17297-7","workflowStages":[]},"version":"v1","identity":"rs-7716426","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7716426","identity":"rs-7716426","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}