Effect of Laser treatment on the microstructure and mechanical properties of the surface of Ti-6Al-4V alloy fabricated by Powder Bed Fusion technology

Effect of Laser treatment on the microstructure and mechanical properties of the surface of Ti-6Al-4V alloy fabricated by Powder Bed Fusion technology | 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 Laser treatment on the microstructure and mechanical properties of the surface of Ti-6Al-4V alloy fabricated by Powder Bed Fusion technology Markéta Straková, Jonáš Divín, Jiří Kubásek, Drahomír Dvorský, and 5 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7472929/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 21 Apr, 2026 Read the published version in Progress in Additive Manufacturing → Version 1 posted You are reading this latest preprint version Abstract This study investigates the influence of laser surface treatment under different protective atmospheres (air, argon, and nitrogen) on the microstructure, mechanical, tribological, and biological properties of Ti-6Al-4V alloy produced by selective laser melting (SLM). A continuous-wave laser (200 W, 1070 nm) was used to remelt the surfaces of as-printed samples. Comprehensive characterization was performed using XRD, XPS, Raman spectroscopy, SEM/EDS, hardness testing, tribological measurements, and in-vitro cytotoxicity assays. The laser-treated samples exhibited a significant transformation of the surface microstructure from martensitic α′-Ti to a fine α + β phase mixture, along with the formation of hard compounds such as titanium oxides and nitrides. The depth of the remelted layer varied depending on the processing atmosphere, with the deepest and hardest layer observed for samples treated in air. All laser treatments substantially enhanced surface microhardness and dry sliding wear resistance compared to untreated samples. The most favorable combination of low friction, minimal wear, and surface uniformity was achieved with the argon-treated sample. In-vitro tests confirmed that all treated surfaces remained non-cytotoxic, supporting their potential for biomedical applications. Ti-6Al-4V SLM 3D-print laser Mechanical Properties Porosity Porous material 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 1 Introduction The Ti-6Al-4V alloy is one of the most widely used materials in the aerospace, medical, and automotive industries due to its high strength, low density, excellent corrosion resistance, and biocompatibility [ 1 – 6 ]. Due to the rapid development of the industry, the products have to be more complex [ 5 ]. Additive manufacturing (3D printing) is emerging as one of the key manufacturing techniques in the medical device industry. To produce medical devices with patient-specific geometries and complex porous structures, additive manufacturing of Ti-6Al-4V has become a leading method [ 7 – 9 ]. Selective laser melting (SLM) Ti-6Al-4V implants with interconnected porosity have become widely used in orthopaedic applications, where porous structures promote bone ingrowth, and the stiffness of the implant can be tuned to reduce stress shielding. The SLM technique allows high resolution control over the design. This includes the ability to introduce porosity with spatial variations in pore size, shape and connectivity [ 10 ]. Therefore, additive manufacturing technology for 3D printing includes LPBF (laser powder bed fusion) and EPBF (electric powder bed fusion). It offers the possibility of forming any special object with complex shape and/or porous structure in a single step. Especially compared to casting or forging, the mechanical properties of LPBF process are superior to others [ 5 , 10 , 11 ], it is inevitable to replace the traditional casting method in the future. The disadvantages of this technology include mainly very low production speed, internal stresses, surface roughness (caused by metal powder sticking to the hot surface) and porosity [ 12 ]. However, the mechanical properties and tribological properties of the 3D printed Ti-6Al-4V surface often do not meet the requirements for functional components. But these properties can be significantly improved by laser surface treatment [ 6 , 13 , 14 ]. Laser surface treatments, including nitriding, texturing, and peening, significantly enhance the tribological performance and mechanical properties of 3D-printed Ti-6Al-4V. These methods improve wear resistance and hardness, making the alloy more suitable for functional components. Additionally, optimizing laser power and heat treatment conditions can further refine the microstructure and mechanical properties, to overcome the limitations of 3D-printed Ti-6Al-4V [ 5 ]. To achieve the desired surface properties, the laser parameters must be carefully controlled. For instance, higher irradiance levels can provide a more uniform depth of processing, which is crucial for consistent surface modification [ 15 ]. The introduction of hard and brittle phases, such as martensite, can lead to crack formation and internal stress. These issues can be reduced by optimizing laser processing parameters, such as power and dwell time, to achieve a balance between hardness and ductility [ 16 ]. The laser surface treatment process is highly dependent on the type of inert gas atmosphere in use. In air, increased oxidation occurs, leading to the formation of hard oxide layers, such as TiO 2 ​, which can enhance hardness but may reduce ductility due to the brittle nature of oxides [ 14 ]. Lavisse et al. [ 17 ] investigated the chemical composition of similar laser-induced oxide layers on Ti substrates using a pulsed Nd:YAG laser. At low laser fluences (< 25 J/cm 2 ), the layers were colourless or pale yellow. A combination of XPS and Raman measurements identified titanium oxo-carbo-nitrides. At higher laser fluences, rough sample surfaces with purple and blue colouration were obtained, which showed increasing formation of anatase and rutile TiO 2 in Raman experiments. In another study, Ohtsu et al. [ 18 ] investigated the effects of pulsed Nd:YAG laser exposure in nitrogen and oxygen gases on Ti substrates as a function of gas pressure and laser parameters in the highly clean and well-controlled environment of a closed XPS/laser apparatus, which allowed in-situ analysis without the need to transfer the sample through ambient air. At low pressures of N 2 (< 13.3 kPa), only non-stoichiometric layers of titanium dioxide with a small amount of nitrogen were observed. At higher pressures, a layer of oxide and nitride was formed on top of the stoichiometric titanium nitride. Repeated laser shots promoted the formation of the oxide layer, but the oxide layer formed by the laser radiation was different from the layer that would naturally form on stoichiometric TiN in an atmosphere of high purity oxygen. Using an inert atmosphere like argon or helium minimizes interaction with the environment (oxidation), preserving the original alloy composition and producing a more uniform microstructure. This result is a more uniform microstructure and can extend the hardening zone, improve surface quality and reduce residual stresses [ 19 , 20 ]. Argon helps maintain a smoother surface profile and better weld quality compared to open atmospheric conditions [ 21 ]. In contrast, a nitrogen atmosphere can promote the formation of titanium nitrides (TiN), known for their high hardness and improved tribological performance. This can enhance the tribological performance of the treated surface [ 22 – 24 ]. Similarly, laser-assisted surface modification can adjust surface hardness by synthesizing different intermetallic phases [ 25 ]. The choice of atmosphere affects the surface morphology significantly. For instance, nitrogen can lead to the formation of humps due to the stacking of molten material, while argon results in a fine and flat melt pool surface [ 22 ]. Laser treatment in an oxygen-rich environment can create a dense passivation layer, improving corrosion resistance [ 20 ]. Laser surface modification can improve the biocompatibility of Ti-6Al-4V, making it more suitable for biomedical applications by enhancing osseointegration and reducing contamination [ 15 ]. This article aims to analyse the effects of different protective atmospheres (air, argon, and nitrogen) during laser treatment on the surface layer of 3D-printed Ti-6Al-4V alloy. Special attention is given to changes in microstructure, phase composition, and mechanical properties, particularly hardness and tribological performance, and a comparison with the bulk material. 2 Experiment details 2.1 Materials and processing For this study, Ti-6Al-4V bulk tensile samples with dog-bone geometry (70 × 5 × 3 mm, Fig. 1 ) were used as the reference material (labelled as AP – as printed). These samples were produced using the selective laser melting (SLM) technique and printed vertically in the SLM chamber. The reference material was analysed in as-built and laser-treated states. The samples were fabricated with a ConceptLaser M2 Cusing printer, which features a 200 W Yb:YAG fiber laser with a 200 µm laser spot size. Printing was carried out in a protective argon atmosphere containing below 0.5% oxygen by volume. The machine has a building volume of 250 × 250 × 280 mm³ and is operated in continuous mode during the process. The detailed printing parameters are provided in Table 1 . Based on these parameters, the volumetric energy density (VED) applied during SLM was calculated to be ~ 66.7 J/mm³, which is within the typical range reported in the literature for achieving high material density and good mechanical properties. The Ti-6Al-4V powder used in this study was prepared by gas atomization under an argon protective atmosphere, resulting in spherical particles with a narrow size distribution, typical for powders optimized for additive manufacturing. A more detailed description of the powder morphology, particle size distribution and chemical composition has been reported previously by Školáková et al. [ 26 ]. Table 1 – Parameters of the SLM 3D-printing process. Layer thickness [µm] Laser power [W] Scanning speed [mm/s] Hatching distance [µm] Volumetric energy density [J/mm 3 ] 30 200 1250 80 66 Laser remelting using a continuous laser was conducted. A 200 W laser with a wavelength of 1070 nm was utilized. The scanning speed was 400 mm/s, and the hatch spacing perpendicular to the build direction of the part was 25 µm. The calculated laser spot size was 130 µm, and the remelting rate was 11 mm²/s. There were three different atmospheres for laser modifications. Samples were processed on air (labelled as L-O), under a protective argon atmosphere (labelled as L-Ar), and under a protective nitrogen atmosphere (labelled as L-N) (Fig. 2 ). The energy input during laser remelting corresponded to a surface energy density of ~ 18.2 J/mm². 2.2 Methods of characterization The phase composition of the samples was analysed using X-ray diffraction (XRD) on a PANalytical X’Pert PRO device. The system operated with a Cu tube producing Kα radiation (λ = 0.15406 nm), a scanning range of 2θ between 5° and 89°, a step size of 0.039°, and generator settings of 30 mA and 40 kV. The chemical composition of the bulk material was analyzed using EDX. To further characterize the surface, X-ray photoelectron spectroscopy (XPS) was performed with a Kratos Analytical Axis Supra spectrometer (CEITEC). This instrument is equipped with a combined Al/Ag anode providing monochromatic X-ray sources with energies of 1486.6 eV and 2984.3 eV, respectively. The spectra were recorded with a step size of 0.1 eV and normalized to the C1s binding energy peak at 284.8 eV. Prior to analysis, the samples were carefully cleaned using distilled water, ethanol, and acetone. Data for evaluating the chemical states were referenced from the NIST X-ray Photoelectron Spectroscopy Database. Raman spectra were measured using a Thermo Scientific Raman Dispersive Spectrometer - Model DXR Microscope equipped with an Olympus confocal microscope. The excitation source was a laser with a wavelength of 532 nm and an input power of 10 mW. A grating with 900 notches/mm was used. The detector was a multi-channel thermoelectrically cooled CCD camera. The samples were measured at 50x magnification with a measurement area of approximately 1 µm 2 . Measurements were performed with a power of 9 mW, a measurement time of 10 s and 10 spectral accumulations. Omnic 9 software (Thermo Scientific) was used to process the spectra. For microstructure examination, a light optical microscope (Nikon) and scanning electron microscopes (SEM, Tescan Mira) with energy-dispersive spectroscopy (EDS) were utilized. Metallographic preparation involved the following steps: (i) cutting the samples using a precision cutting machine, (ii) grinding with silicon carbide (SiC) papers of grit sizes ranging from P400 to P2500, (iii) polishing with colloidal silica suspension (Eposil F, particle size 0.1 µm) mixed with hydrogen peroxide in a 4:1 ratio, and (iv) chemical etching with Croll’s solution (2 ml HNO 3 + 98 ml H 2 O). Vickers hardness testing was conducted using 1 kg (HV1) and 0.1 kg (HV0.1) loads. At least 20 hardness measurements were taken on cross-sections of bulk samples that had been ground to a P2500 finish, with the measurements aligned parallel to the building direction. Tribological properties were measured using the "ball-on-disc" method on a universal tribometer, TriboTester, manufactured by Tt-TRIBOtechnic. The test body were an Al 2​ O 3 ball and carbon steel ball, which performed a linear oscillating motion. The applied load was 5 N, and the ball did not rotate during the test. During testing, the ball travelled a total distance of 20 m at a speed of 5 mm/s. Tribological properties were measured on untreated surfaces in all cases, with two wear tracks created per test. The profiles of the wear tracks were measured using a profilometer, and these measurements were used to calculate the wear rate. The wear tracks and their surroundings were then analysed using SEM. 2.3 Biological evaluation: in-vitro cytotoxicity For the biological evaluation, indirect contact assays were conducted. The AP and the AP-machined samples were cut in half. The L-Ar, L-O, and L-N samples were cut in half, and the part with no laser application was removed. The resulting samples were disinfected with isopropanol (Centralchem, Slovakia) by being immersed in an ultrasonic bath for 3 minutes and sterilized by ultraviolet irradiation, with two cycles of 30 minutes, one for each side of the sample. Extraction was conducted according to ISO 10993-12, with an extraction ratio of 0.2 g∙mL − 1 . The disinfected and sterilized samples were immersed in Dulbecco′s Modified Eagle′s Medium (DMEM; Biosera, France) supplemented with 10% fetal bovine serum (FBS; Biosera, France), in closed and sterilized containers. The containers were incubated at 37 ºC, under the agitation of 180 rpm, for 24 hours. A container with only DMEM was used as a control. Once extraction was complete, the extracts were removed to new containers, under sterile conditions. In-vitro cytotoxicity was evaluated with an MTT assay according to ISO 10993-5 (Annex C), for 24 and 72 hours. The mouse-derived fibroblast L-929 cell line (NCTC clone 929: CCL-1™, American Type Culture Collection) was cultivated in DMEM with 10% FBS and seeded in a 96-well plate with a cell density of 1 × 10 5 cells∙mL − 1 . The plate was incubated at 37 ºC and 5% CO 2 . After one day of cultivation, the cells reached a semi-confluent state, and the medium was exchanged for the extracts. 6 wells were used as replicates for each sample, with the previously incubated DMEM used as a control. The plate was again incubated inthe same conditions as before. After 24 or 72 hours, the medium was again exchanged for an MTT solution: 3-(4,5-dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide (Sigma-Aldrich, USA) diluted in DMEM without phenol red (Lonza, Switzerland), at a concentration of 1 mg∙mL − 1 . During 2 hours of incubation at 37 ºC, the MTT was reduced by the viable cells into formazan crystals. Afterwards, the solution was discarded, replaced with isopropanol and incubated for an extra hour to dissolve the crystals into their fluorescent form. Lastly, the absorbance at 570 nm was measured using a microplate reader (BioTek Instruments, USA). Cell viability was expressed as a percentage of the absorbance of the control, and values above 70% were considered a viable response. 3 Results and discussion 3.1 Surface characterization Compacted samples were successfully prepared by SLM process. The surface of printed material is illustrated in Fig. 3 . It is rather rough as it contains unmelted or partially melted spherical powder particles. This phenomenon can be attributed to several factors: (a) thermal diffusion between the loose powder and the solidified material due to significant temperature differences, causing powder particles to adhere to the surface; (b) partial melting of boundary particles by the contour laser track, leading to their bonding at layer boundaries; and (c) the construction of curved struts in porous parts at varying inclined angles, where loose powder supports the structure, resulting in partial or complete melting of particles beneath each layer and subsequent bonding to the layer's underside [ 28 ]. These adhered particles negatively impact mechanical properties, particularly fatigue performance, and could potentially detach into biological systems after implantation, causing inflammation. For this reason, post-processing methods such as sandblasting, machining or chemical etching are commonly employed [ 29 ]. Another method for dealing with this phenomenon and smoothing the surface is laser treatment. Therefore, in this work, laser treated samples are compared with SLM and machined as-printed products in this work. Effect of the laser treatments on the quality of the surface is demonstrated on Fig. 4 . In all cases, the surface was smoothed compared to the AP samples. Nevertheless, the surface contained some visible cracks. Moreover, there were visible differences depending on the atmosphere during laser treatment [ 19 – 22 ]. Sample modified air (L-O) contained a significant number of cracks and a small dimple (Fig. 4 a). On the other hand, the sample modified under protective Ar atmosphere contained a lower number of cracks and the surface was much smoother (Fig. 4 b) as there was only limited access to oxygen. Surface of the sample modified under N atmosphere was something between those two as it contained lower number of cracks, however, it contained dimples (Fig. 4 c) as nitrogen could also react with Ti. Raman spectroscopy was used to characterize the surface of the samples. For each sample, 4–5 spectra were measured for evaluation of surface homogeneity (Fig. 5 ). In general, the spectra were quite homogeneous within each sample. For the laser modified samples, distinct bands of TiO 2 , mainly rutile, were identified (~ 250, 435 and 610 cm- 1 ). These are most pronounced in L-O samples, although they were also observed in minor amount for samples treated in N and Ar. The reason is that these gases also contain some portion of O 2 , therefore minor formation of oxides is expected. In addition to bands of oxidation products, bands of amorphous carbon (~ 1350 and 1580 cm − 1 ) and a broad spectral background can be seen in these samples. This is in agreement with the results of Lavisse et al [ 17 ], who at higher laser intensities obtained rough surfaces of purple and blue colored samples which showed increasing anatase and rutile TiO 2 formation in Raman experiments. The presence of amorphous carbon bands is most likely due to the decomposition of hydrocarbons adsorbed on the surface during laser processing or subsequent Raman measurement, rather than to changes in the bulk alloy. Similar carbonaceous surface features have been reported for laser-processed titanium alloys [ 30 ]. While this contamination does not affect the microstructure of the alloy, it may influence surface-related functional properties such as tribological behaviour or biological response. Therefore, it should be considered when interpreting surface chemistry. b) L-Ar and c) L-N. In the case of biomaterials, the surface composition is particularly important, because the biological environment at the interface between the implant/tissue and the biomaterial is interacting with the surface. The chemical composition of the surface layer, which can be several nanometres thick, therefore influences biocompatibility. Although the biocompatibility of the Ti-6Al-4V alloy is well known, it is possible that a part manufactured by SLM will have a different surface chemical composition than other parts manufactured with conventionally prepared material because the metal powder is rapidly melted and cooled [ 31 ]. The spectra obtained from the XPS analysis for all four samples are shown in Fig. 6 . The elements detected are C, N, O, Ti, and Al. The chemical composition of the surface evaluated from the spectra obtained from the measurements is given in Table 2 . The CasaXPS software, which allows the correction of errors due to carbon contamination, was used for the quantitative evaluation. However, as can be seen from the spectra for AP product (Fig. 6 c), carbon is partially presented in the form of titanium carbide, surface is also oxidised due to the high reactivity of molten titanium with residual oxygen in printing chamber, therefore, even a very small amount of oxygen is sufficient for this reaction [ 32 ]. Therefore, even laser-treated alloys must contain oxidised Ti. XRD and Raman spectroscopy confirmed the presence of TiO 2 , specifically rutile. Considering that XPS is used to analyse only a very thin surface layer, in the case of the AP samples the signal was dominated by the surface of the spherical particles adhering to the sample surface. Therefore, the results mostly reflect the chemistry of the atomised Ti-6Al-4V powder rather than the bulk material after SLM processing. The original powder was atomised in nitrogen atmosphere, which explains the relatively high nitrogen content detected by XPS (Table 2 ). The nominal composition of the Ti-6Al-4V alloy powder was 90.5 wt.% Ti, 5.6 wt.% Al and 3.9 wt.% V, as reported by our colleagues [ 26 ], with small but measurable nitrogen content originating from the atomisation process. Given the high affinity of Ti-6Al-4V powder to oxygen, surface oxidation is also inevitable and significantly contributes to the detected O and N signals in the XPS spectra [ 33 ].. Quantitative evaluation of the XPS data was carried out, and the elemental surface composition is presented in Table 2 . It should be noted that XPS is sensitive enough to distinguish between chemically bonded nitrogen in the alloy matrix and weakly adsorbed species on the powder surface. Interestingly, the Ti:Al ratio increased from 0.13 (AP) to 0.96 (L-O), 1.05 (L-Ar), and 1.93 (L-N). The higher relative concentration of aluminum in the SLM sample is probably due to its higher affinity for oxygen compared to titanium. Both metals have a high affinity for oxygen, but aluminum has a higher affinity for oxygen than titanium - because the formation of Al₂O₃ oxide is thermodynamically more favorable (more negative ΔG°) [ 33 , 34 ]. Preferential oxidation can be illustrated by the following reactions: $$\:4\:Al\left(s\right)+3\:{O}_{2}\left(g\right)\to\:2\:{Al}_{2}{O}_{3}\left(s\right)$$ $$\:Ti\left(s\right)+\:{O}_{2}\left(g\right)\to\:{TiO}_{2}\left(s\right)$$ According to thermodynamic calculations (ThermoCalc, FactSage), the standard Gibbs free energy of formation ΔG° at 1000 K is approximately − 960 kJ/mol O₂ for Al₂O₃, while for TiO₂ it is − 760 kJ/mol O₂. This clearly demonstrates that the oxidation of aluminum is energetically more favorable than the oxidation of titanium, which explains the enrichment of Al detected on the sample surface after laser processing. Although the SLM process was carried out in an argon atmosphere (containing below 0.5% oxygen by volume), some oxygen was presented and can reacted with Ti or Al. Since titanium is more prominent, it can be assumed that the surface layer is composed of titanium oxides and a smaller proportion of alumina. However, high resolution spectra were obtained to determine the oxidation states of the elements detected and to more accurately determine the chemical composition of the surface. Regardless, the study by Siblani et al. [ 33 ] found that the oxide scale on the powder surface is formed by a double layer with α-Al 2 O 3 in the outer part and TiO 2 in the inner part, which could explain the disproportion between the surface analysis of Ti and Al. Thermodynamic results showed that interstitial aluminium enters and rapidly diffuses into TiO 2 (rutile) to form Al 2 O 3 as a surface layer. In addition, α-Al 2 O 3 is a non-stoichiometric oxide with very little excess oxygen as a weight at high oxygen partial pressures. No nitridation was observed for the nitrogen atmosphere., while the surface was covered mainly by titanium oxides. The presence of titanium oxides forming a passive layer on the laser modified material is evident from a detailed spectrum (Fig. 6 ) showing the binding energies of titanium. TiO 2 is predominant, but Ti 2 O 3 , TiO and elemental Ti can also be identified. In the case of the SLM product, TiO 2 is greatly reduced in favour of stoichiometric oxides. This is due to the higher relevant aluminium concentration present in the form of alumina with a lower standard Gibbs energy [ 31 ]. Although carbon is introduced by atmospheric contamination in most cases of laser modification, the spectrum in Fig. 6 explains that it partially reacted to TiC during SLM for AP sample. Table 2 Surface composition determined by XPS. at. % Ti Al C O N AP 1.8 13.8 54.4 24.3 5.8 L-O 6.9 7.1 49.2 36.2 0.6 L-Ar 3.2 3.1 73.2 19.6 1.0 L-N 13.9 7.2 47.8 30.4 0.6 3.1 Microstructure In the case of laser remelting, the aim was to analyse the remelted layer also in depth. SEM images were taken of the layer cross-section. Initial microstructure of the Ti-6Al-4V alloy produced by SLM contained α’-martensitic needles (Fig. 7 ) due to the rapid heat dissipation from the laser site to the rest of the material (approximately 10 6 K/s, as reported [ 35 ]). Such high cooling rates are well above the critical threshold of ~ 410 K/s required for the diffusionless β→α′ transformation, explaining the fully martensitic character of the as-built material. With the volumetric energy density used here (approximately 66.7 J/mm³), the cooling conditions are consistent with the values reported in the literature for α′ formation. However, during subsequent laser remelting, the effective energy input (approximately 18.2 J/mm²) and slower local cooling rates may approach a regime in which partial α′ decomposition or α + β lamellar structure development can occur. This implies that martensite formation can be either promoted or suppressed depending on the applied parameters, which are consistent with observations for other laser-processed Ti-6Al-4V systems. Laser modifications altered microstructure in depth up to ~ 140 µm (Fig. 7 ). While the bulk material beneath this layer remained with martensitic structure, the surface layer, exposed to temperature fluctuations due to the laser treatment, has undergone a transformation to a fine-grained mixture of α and β phases (Fig. 8 ). Due to the extremely fine grain size, it was difficult to accurately distinguish the lamellae of the α and β phases by EDS. The presence of this two-phase structure was further confirmed by XRD analysis (Fig. 9 ). The individual laser treatment environments differ mainly in depth of the modified layer, with the thinnest layer formed under the Ar protective atmosphere, which goes somewhat against the claims in the literature [ 19 , 20 ], and the thickest layer formed under the protective N atmosphere (Table 3 ). The thickness of the remelted zone depends on the laser energy delivered per unit area and the efficiency of heat dissipation. In this study, the applied line energy (approximately 0.5 J/mm) and the high degree of overlap resulting from the small hatch distance (25 µm) led to the repeated reheating of adjacent tracks. This thermal accumulation reduces the effective cooling rate in the near-surface region, enabling decomposition of the α′ martensite into an α + β lamellar structure. This mechanism is consistent with observations in other laser-treated Ti-6Al-4V systems, in which a transition from martensitic to α + β morphology occurs when the local cooling rate falls below the critical threshold for β→α′ transformation [ 35 , 36 ]. The protective atmosphere also influences the remelting process; variations in the thermal conductivity and convective heat transfer of argon (Ar), nitrogen (N₂) and air can explain the different melt pool depths. In particular, the lowest modified depth in argon (Ar) may be attributed to its low thermal conductivity, which reduces convective transport and promotes faster solidification compared to nitrogen (N₂) or air. The chemical composition of the remelted layer was evaluated using EDS line scanning across the cross-section (see Fig. 9 ). The distribution of the main alloying elements (Ti, Al and V) was relatively uniform throughout the remelted zone, suggesting that macroscale segregation did not occur during the rapid solidification process. A clear enrichment in oxygen was detected in the near-surface region (0–80 µm), which is consistent with the Raman and XRD results that confirmed the presence of TiO₂. Additionally, traces of nitrogen were observed at the outermost part of the layer, suggesting limited incorporation of nitrogen from the processing atmosphere. Beyond ~ 120 µm, the oxygen and nitrogen levels decreased to background values, while the Ti, Al and V composition stabilised close to that of the bulk material. These results confirm that the chemical modifications induced by laser remelting are confined to the near-surface zone, correlating with the formation of refined α + β microstructures and oxygen/nitrogen-enriched phases. These phases contribute to the increased hardness and wear resistance of the treated samples. Table 3 – Variation of the depth of the modified layers produced by laser remelting under different conditions. Sample Depth of remelting layer [µm] L-O L-Ar 117 ± 2 79 ± 4 L-N 136 ± 5 The phase compositions of the sample surfaces were determined using XRD, see Fig. 10 . The analysis revealed that the as-printed sample consists of a single phase, α'-Ti, which corresponds to hexagonal martensite formed through rapid cooling from β-Ti. During laser surface modification in various atmospheres, the α' phase transforms into α-Ti and β-Ti phases in all samples. The α-Ti phase represents the HCP (hexagonal close-packed) allotropic form of titanium. This phase is challenging to differentiate from α'-Ti due to their nearly identical diffraction angle positions. It can be observed that the phase composition of the initial AP sample changed after laser treatment. Titanium martensite transformed into two phases, namely α-Ti and β-Ti. Additionally, there was also oxygen in the form of TiO and TiO 2 , where the more stable (TiO 2 ) was observed with higher intensity especially in L-O sample as it had access to oxygen from air. Otherwise, lower content of oxygen was present in L-Ar and L-N samples. 3.3 Mechanical properties The Vickers microhardness (HV0.1) of the surfaces was measured and the results are summarized in Table 1 . 4. The surface hardness of the AP sample (356 ± 20 HV0.1) was comparable to that of the inner structure (360 ± 20 HV0.1). By contrast, laser treatment in air dramatically increased the surface hardness to 873 ± 21 HV0.1, while leaving the bulk unaffected. This pronounced increase is associated with the formation of oxides, as detected by XRD and Raman spectroscopy, and with the high oxygen content, as measured by EDS line profiling. This shows the diffusion of oxygen into the remelted layer (up to ~ 30 wt.% near the surface). In the case of a nitrogen atmosphere, the hardness was slightly lower at 789 ± 27 HV0.1, which is consistent with reduced oxygen uptake compared to air. However, it was still higher than for the L-Ar sample due to the formation of nitrides and carbides (TiC was identified by XPS), which was confirmed by Raman spectroscopy. The lowest hardness increase was observed for the L-Ar sample (668 ± 21 HV0.1), where the inert atmosphere limited the incorporation of oxygen and nitrogen, and strengthening was mainly due to the α′→α + β transformation. Table 4 – Measured microhardness HV0.1 values of the starting material (AP) and the material modified by laser remelting. Sample Surface microhardness HV0.1 AP 356 ± 20 L-O 873 ± 21 L-Ar L-N 668 ± 21 789 ± 27 A plot of microhardness profile measurements from the surface of the sample to its center can be seen in Fig. 11 . The measurements were repeated four times. It was then fitted with a moving average curve. The depth of the melting region (read from the microstructural cross section through the sample) is marked in the graph. Considering that the decrease in hardness occurs beyond this region, the material has been affected deeper than can be seen from the microstructure in Fig. 7 . In their study, Bipasha et al. [ 37 ] investigated laser surface treatment (LST) of Ti-6Al-4V, which resulted in an increase in surface microhardness in nitrogen (839–1327 HV0.1) atmospheres compared to the printed sample (278 HV0.1). The reason for the higher microhardness values is the formation of titanium nitride (TiN and Ti 2 N) dispersed in the α-matrix after LST. Treatment in an argon atmosphere also enhances microhardness, though to a lesser extent than nitrogen, with values ranging from 435 to 630 HV0.1. Feng et al. [ 38 ] investigated the laser nitriding of Ti-20Zr-6.5Al-4V alloy surface, which led to an increase in surface microhardness under nitrogen atmosphere (917 HV0.1) due to the formation of TiN dendrites. In the present study, however, the increase in hardness can be attributed not only to nitride formation, but also to the presence of oxides and carbides, as confirmed by Raman, XRD, XPS and EDS analyses. Tribological tests are based on friction between the test body and the material under the test. In our case, an Al 2 O 3 sphere was used as the test body because its properties are close to those of human bone or ceramic parts of joint replacements, where the material to be tested is very useful [ 39 ]. The tribological tests were carried out in such a way that the test piece (Al 2 O 3 ball and carbon steel ball) travelled a distance of 20 m at a load of 5 N and a speed of 5 mm/sec. In all cases, 2 traces were made and further evaluated by SEM and EDS. The tests were carried out first on the starting material and then on the samples after laser modification. The SEM images are shown in Fig. 11 and the measured values after the tests are summarized in Table 5 . The materials after laser modification showed very different tribological properties compared to the starting material. All three laser surface treatments in different protective atmospheres resulted in improved dry sliding wear resistance. This was attributed to the increase in hardness and the formation of wear resistant compounds. Figure 12 shows the appearance of the grooves formed on the surface of each specimen. The mechanism of wear in the untreated titanium alloy was mainly by abrasion of the specimen surface. In addition, the AP specimen contained original powder particles on the specimen surface which were easily removed by vibrating both specimens (Al 2 O 3 and carbon steel). These particles were crushed in the process and acted as an abrasive, degrading the tribological properties (Table 5 ). For this reason, the AP specimen was machined (AP-M, Fig. 12 b), which rapidly reduced the surface roughness of the specimen from 3.2 µm to a value of 0.12 µm, which was even lower than that of the laser-treated specimens. Since the laser treatment was performed on the unmachined sample, the laser action melted the powder particles on the sample surface. The roughness values of all surfaces are shown in Table 5 . Contrary, laser treated materials were characterized by smoother surface without any powder particles, only with a few cracks. This resulted in smoother friction marks (Fig. 12 c,d, e). Despite having the higher surface hardness L-O material had the most visible scratches out of the laser treated materials. This might be associated with the small dimples observed on the surface that could be easily abraded, and loose hard particles may decrease the wear resistance. Thus, resulting wear resistance is the worst out of the laser treated material; however, it is still an order of magnitude better compared to AP sample. In case of L-Ar sample, the wear tracks are almost negligible as this material was characterized by the smoothest surface without any dimples, despite the surface hardness being lowest out of the laser treated samples. Therefore, this material reached the best wear resistance. Sample treated in nitrogen atmosphere had the wear resistance in between those samples due to the smooth surface, however, with dimples. However, in the laser treated cases, the material was removed by the formation and breaking of adhesive bonds. It is believed that the increased hardness changed the wear mechanism from ploughing to adhesion. The above results are confirmed by electron microscopy of the worn surfaces. The same conclusion was reached in a study S. Yerramareddy at all [ 6 ]. Using a corundum ball results in a significantly lower coefficient of friction and lower wear in laser samples. For carbon steel ball, laser processed samples are still advantageous in terms of wear, but may lead to an increase in friction, which is atypical and could be due to a different interaction with the steel material. The best combination of low roughness, low wear and low COF is with L-N or L-Ar with corundum. Bipasha Das et al. [ 37 ] processed the materials by laser melting in an argon atmosphere and nitrided the surface in a nitrogen atmosphere. For both melting and nitriding, the depth of the modified layer was found to vary depending on the laser parameters (232–1011 µm). The formation of TiN in nitrogen atmosphere not only increased the hardness but also significantly reduced the wear rate and offered higher wear resistance compared to other atmospheres. There was a marginal decrease in wear rate (against WC ball) due to laser surface melting (5.17–5.81 ×10 − 3 mm 3 /Nm) under argon and a substantial decrease in wear rate when melting was conducted under nitrogen atmosphere (1.91–4.94 × 10 − 3 mm 3 /Nm) as compared to Ti-6Al-4V (5.93 ×10 − 3 mm 3 /Nm). In both cases, the laser treatment has a positive effect on reducing wear. The best results are achieved when the laser is in a protective atmosphere (argon or nitrogen). The absolute values are not directly comparable between the sets because the counter-body (WC vs. corundum vs. carbon steel ball) and the sample/test conditions are different. On a relative scale, however, both experiments show the same trend: laser melting improves tribological properties, more significantly in inert or nitrogen atmospheres than in air. By way of comparison, the remelted depth in the present study was only ~ 140 µm. This difference is primarily due to the lower energy input: the volumetric energy density (VED) here was ~ 66.7 J/mm³, with a line energy of ~ 0.5 J/mm. Das et al., however, likely employed much higher effective energy densities due to their lower scan speeds (6 mm/s), higher laser power (500–1100 W) and potentially larger hatch distances. This higher energy input resulted in deeper melt pools and thicker modified layers in their work. Additionally, the very small hatch distance (25 µm) in the current study resulted in intense thermal overlap, causing the surface tracks to repeatedly reheat adjacent regions. This thermal accumulation limits the depth of penetration of the melt pool but enhances near-surface microstructural refinement and α′ decomposition. Similar effects of tight hatch spacing on the promotion of α + β lamellar structures via internal heat treatment have been reported by Barriobero-Vila et al., who observed intensive martensite decomposition and a very fine α + β microstructure in these conditions [ 35 ]. Thus, while the present study induces a shallower remelted zone, it still achieves significant microstructural transformation. Table 5 – Results of measurements of the tribological properties of the input material and the material after surface modification by laser remelting. Sample Ball Surface roughness [µm] Average wear track area [mm 2 ] Average coefficient of friction Average wear speed [mm 3 /N/m] AP Corund 3.20 1.44 \(\:\bullet\:\) 10 − 2 0.453 7.18 \(\:\bullet\:\) 10 − 4 AP-M 0.12 5.96 \(\:\bullet\:\) 10 − 3 0.397 2.98 \(\:\bullet\:\) 10 − 4 L-O 0.59 1.57 \(\:\bullet\:\) 10 − 3 0.269 7.84 \(\:\bullet\:\) 10 − 5 L-Ar 0.54 9.25 \(\:\bullet\:\) 10 − 4 0.171 4.63 \(\:\bullet\:\) 10 − 5 L-N 0.55 1.22 \(\:\bullet\:\) 10 − 3 0.138 6.08 \(\:\bullet\:\) 10 − 5 AP Carbon steel ball 3.20 1.59 \(\:\bullet\:\) 10 − 2 0.441 7.93 \(\:\bullet\:\) 10 − 4 AP-M 0.12 5.56 \(\:\bullet\:\) 10 − 3 0.382 2.78 \(\:\bullet\:\) 10 − 4 L-O 0.59 2.22 \(\:\bullet\:\) 10 − 3 0.530 1.11 \(\:\bullet\:\) 10 − 4 L-Ar 0.54 1.91 \(\:\bullet\:\) 10 − 3 0.640 9.56 \(\:\bullet\:\) 10 − 5 L-N 0.55 2.95 \(\:\bullet\:\) 10 − 3 0.435 1.47 \(\:\bullet\:\) 10 − 4 3.3 Biological properties The results from the MTT assay to evaluate the in-vitro cytotoxic response to the materials, for 24 and 72 hours of exposure, can be seen in Fig. 12 . DMEM with 10% FBS was used as a control and was set as 100% cell viability. Ti-6Al-4V samples without laser treatment (AP and AP-machined) were used as a reference material, since the biological response to the Ti6Al4V alloy is well known. According to ISO-10993-5, cell viability values above 70% are considered a non-cytotoxic response. For the 24-hour time point, all values for the different extracts, from the different tested materials, meet the threshold: AP – 88.31 ± 3.10%, AP-machined – 94.59 ± 4.94%, L-Ar – 76.72 ± 3.48%, L-O – 87.20 ± 2.13% and L-N – 72.94 ± 4.36%. However, the laser-treated materials L-Ar and L-N present a reduced cell viability value when compared with the control and with the reference materials, indicating that there may be an influence of these treatments on the cellular response. Hence, the assay was repeated for a 72-hour time interval to investigate if this reduction would persist with time. As a matter of fact, the results after 72 hours of exposure show values closer to the control, for all samples: AP – 99.30 ± 1.44%, AP-machined – 99.54 ± 4.05%, L-Ar – 88.31 ± 4.96%, L-O – 97.23 ± 5.47% and L-N – 101.50 ± 2.37%. These results may justify the differences measured before due to the characteristics of assay, with 24 hours not being enough time for the cells to adapt to the new environment, and not a real indicator of some cytotoxic potential. Notwithstanding, the benchmark from ISO-10993-5 is met, supporting the potential of these treatments in terms of biocompatibility. 4 Conclusions Laser surface treatment was applied to enhance the performance of SLM-manufactured Ti-6Al-4V alloy. The process parameters, especially the protective atmosphere, strongly influenced the resulting surface morphology, microstructure, and functional properties. The main conclusions are summarized below: Laser remelting improves surface smoothness, microhardness, and wear resistance. Air (L-O) increased hardness due to oxide formation, but surface cracking was observed. Argon (L-Ar) brings the best combination of smooth surface, wear resistance, and low friction. Nitrogen (L-N) increases hardness due to the formation of hard nitrides while minor surface cracking was observed. Remelted surface is characterized by transformed microstructure from α′ martensite to refined α + β phases. Surface hardness is increased by up to 250% after laser treatment. Wear resistance was improved by one order of magnitude: coefficient of friction decreased by up to 70%. Biocompatibility of laser threatened samples remained non-cytotoxic according to ISO 10993-5. In this study, the thickness of the modified layer (~140 µm) was significantly lower than values reported in the literature, due to the lower applied line energy and high track overlap. This processing strategy resulted in pronounced thermal accumulation near the surface, which promoted α′ martensite decomposition and refinement into α+β lamellae rather than deep melting. This demonstrates that the protective atmosphere, specific energy input, and scanning strategy are all crucial factors in achieving the desired balance of hardness, toughness, and wear resistance. Therefore, the results highlight the importance of optimising both the atmosphere and the energy delivery to achieve application-specific properties in additively manufactured Ti-6Al-4V. These findings confirm that laser surface modification under optimized conditions is a promising strategy for tailoring 3D-printed titanium alloy components for advanced engineering and biomedical applications. Declarations Author Contribution M.S. wrote the main text of the manuscript. F.S. wrote the chapter on biological testing. J.F. and D.S. performed the XPS measurements and analysis of the results. J.D., M.S., D. D., and J. K. measured the scientific data used. All authors reviewed the manuscript. Acknowledgement The authors would like to express their sincere gratitude to LASCAM Systems s.r.o. for their valuable support in the preparation of samples. The laser surface remelting of 3D-printed Ti-6Al-4V alloy specimens carried out by LASCAM significantly contributed to this work. Data Availability The data will be published in preprint mode on the Zenodo portal, but this process has not yet taken place. This is a condition of project No. CZ.02.01.01/00/22_008/0004634. References Pushp P, Dasharath SM, Arati C (2022) Classification and applications of titanium and its alloys. Materials Today: Proceedings, 54: pp. 537–542 Elitzer D et al (2022) Development of Microstructure and Mechanical Properties of TiAl6V4 Processed by Wire and Arc Additive Manufacturing. 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Rare Met 39(3):270–278 Kaur G et al (2019) Mechanical properties of bioactive glasses, ceramics, glass-ceramics and composites: State-of-the-art review and future challenges. Mater Sci Engineering: C 104:109895 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Published Journal Publication published 21 Apr, 2026 Read the published version in Progress in Additive Manufacturing → Version 1 posted 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. 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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-7472929","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":542123266,"identity":"cb4f76dd-6bd0-42c8-9f06-8bcb8a969134","order_by":0,"name":"Markéta 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16:14:27","extension":"xml","order_by":73,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":125075,"visible":true,"origin":"","legend":"","description":"","filename":"b1bbb529806f4b06958e4a71d16b5bcc1structuring.xml","url":"https://assets-eu.researchsquare.com/files/rs-7472929/v1/dd3539105e4c9b7c6478de1d.xml"},{"id":95557561,"identity":"64490446-0010-4598-9618-e88aeb09f58e","added_by":"auto","created_at":"2025-11-10 14:42:23","extension":"html","order_by":74,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":138010,"visible":true,"origin":"","legend":"","description":"","filename":"earlyproof.html","url":"https://assets-eu.researchsquare.com/files/rs-7472929/v1/49c533f3ca6a8d8e27ed7aab.html"},{"id":95654856,"identity":"9758f567-ff60-4ec1-9e9b-14895e187ca9","added_by":"auto","created_at":"2025-11-11 16:13:23","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":102384,"visible":true,"origin":"","legend":"\u003cp\u003eDimensions of 3D-printed samples for tensile tests (dimensions given in mm [27]).\u003c/p\u003e","description":"","filename":"Figure1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7472929/v1/4eb934534bfac037de9c1e23.jpg"},{"id":95797713,"identity":"d39e624c-3cef-4ab7-9f95-4818befcf07b","added_by":"auto","created_at":"2025-11-13 08:09:52","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":212688,"visible":true,"origin":"","legend":"\u003cp\u003eSamples after laser application: L-O, L-Ar, L-N samples.\u003c/p\u003e","description":"","filename":"Figure2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7472929/v1/11fa997dd5ae3e81907bcfe2.jpg"},{"id":95654620,"identity":"1fdc4c59-b66d-421f-baf3-1a9d54146cbb","added_by":"auto","created_at":"2025-11-11 16:12:36","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":662043,"visible":true,"origin":"","legend":"\u003cp\u003eSurface of the AP (as-printed) sample.\u003c/p\u003e","description":"","filename":"Figure3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7472929/v1/338740de92dde39bf60f79cf.jpg"},{"id":95654419,"identity":"b2659ca2-c5ab-46dc-a033-60891988330b","added_by":"auto","created_at":"2025-11-11 16:11:46","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":2972981,"visible":true,"origin":"","legend":"\u003cp\u003eSLM product surface after laser modification: a) L-O, b) L-Ar, c) L-N.\u003c/p\u003e","description":"","filename":"Figure4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7472929/v1/e2b6faaf607f1627812b4a37.jpg"},{"id":95557516,"identity":"f5b3132e-0f13-4a80-9e59-8c18f5082193","added_by":"auto","created_at":"2025-11-10 14:42:22","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":492134,"visible":true,"origin":"","legend":"\u003cp\u003eTypical Raman spectra of individual samples. Shown in offset. Photos from Raman microscope Nikon: a) L-O), b) L-Ar and c) L-N.\u003c/p\u003e","description":"","filename":"Figure5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7472929/v1/434f14c813a992a43156145e.jpg"},{"id":95655716,"identity":"0039994c-eaed-4e84-991b-7b5749f20fce","added_by":"auto","created_at":"2025-11-11 16:16:46","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":957769,"visible":true,"origin":"","legend":"\u003cp\u003eXPS element analysis: (a) Ti 2p, (b) Al 2p, (c) O 1s, (d) C 1s and (e) N 1s.\u003c/p\u003e","description":"","filename":"Figure6.png","url":"https://assets-eu.researchsquare.com/files/rs-7472929/v1/0c17b82959943c4b9136f05c.png"},{"id":95654943,"identity":"ef4f14c7-fa1c-48bd-b10b-2e2121817722","added_by":"auto","created_at":"2025-11-11 16:13:53","extension":"jpg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":2039394,"visible":true,"origin":"","legend":"\u003cp\u003eMicrographs of surface layer of (a) AP, and laser-modified products: (b) L-O, (c) L-Ar and (d) L-N.\u003c/p\u003e","description":"","filename":"Figure7.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7472929/v1/29e53d81db55477322446fa9.jpg"},{"id":95557503,"identity":"19803476-9440-4479-960c-b95e5bf3fd2e","added_by":"auto","created_at":"2025-11-10 14:42:22","extension":"jpg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":1164807,"visible":true,"origin":"","legend":"\u003cp\u003eLayer microstructure detail (a) L-O, (b) L-Ar and (c) L-N.\u003c/p\u003e","description":"","filename":"Figure8.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7472929/v1/b6bb6a3cbfb887e552daa876.jpg"},{"id":95557509,"identity":"167d99cd-d2a4-4c22-a363-9667c567e18f","added_by":"auto","created_at":"2025-11-10 14:42:22","extension":"jpg","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":579042,"visible":true,"origin":"","legend":"\u003cp\u003eEDS line scan across the remelted layer showing elemental distribution of Ti, Al, V, O and N. Increased oxygen concentration is visible in the near-surface region, while nitrogen incorporation is minor and confined to the outermost part of the layer.\u003c/p\u003e","description":"","filename":"Figure9.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7472929/v1/63a954bb7068e87e7b607145.jpg"},{"id":95655545,"identity":"6a0a5b02-6afd-44b5-a4d1-fcf87b7bef15","added_by":"auto","created_at":"2025-11-11 16:16:26","extension":"jpg","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":202662,"visible":true,"origin":"","legend":"\u003cp\u003eThe phase composition of the samples analyzed by X-ray diffraction.\u003c/p\u003e","description":"","filename":"Figure10.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7472929/v1/7bd07303cba1f3a753f35b9b.jpg"},{"id":95557512,"identity":"514fdea4-71bc-40da-ab55-e2cc31e6d7a9","added_by":"auto","created_at":"2025-11-10 14:42:22","extension":"jpg","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":228077,"visible":true,"origin":"","legend":"\u003cp\u003eHardness profile measured from the edge of the sample to the bulk for laser samples.\u003c/p\u003e","description":"","filename":"Figure11.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7472929/v1/f865fc71236b7b415670e903.jpg"},{"id":95655047,"identity":"1d5f6154-3a2c-438b-892c-7da27c7309e8","added_by":"auto","created_at":"2025-11-11 16:14:02","extension":"jpg","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":1808650,"visible":true,"origin":"","legend":"\u003cp\u003eSEM (BSE) images of traces after tribological testing of samples with both balls:(a) AP, (b) AP machined, (c) L-O, (d) L-Ar and (e) L-N.\u003c/p\u003e","description":"","filename":"Figure12.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7472929/v1/ac7317c87dd83b26de6dd72e.jpg"},{"id":95654673,"identity":"19602ab7-4102-40e3-a760-39ff33ae9974","added_by":"auto","created_at":"2025-11-11 16:12:44","extension":"jpg","order_by":13,"title":"Figure 13","display":"","copyAsset":false,"role":"figure","size":125099,"visible":true,"origin":"","legend":"\u003cp\u003e24 and 72 hours MTT assay results for the cytotoxic response of L929 cells to the laser-treated materials (L-Ar, L-O and L-N). Wells with cells cultured in medium only (DMEM with 10 % FBS) were used as a control, and their absorbance values were set as 100% of cell viability. Materials not submitted to laser treatment are presented as a reference (AP and AP-machined). According to ISO-10993-5, 70% is the threshold for the biological response to be considered non-toxic (represented in the graph with a dashed line). The data from the sextuplicate measurements are shown as mean ± standard deviation. Graph and statistical analysis were created with GraphPad Prism 10.\u003c/p\u003e","description":"","filename":"Figure13.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7472929/v1/21f2ae035f2f93d3c1b3e843.jpg"},{"id":107929298,"identity":"1803b4f7-a234-44cd-8bc9-78d33422602b","added_by":"auto","created_at":"2026-04-27 16:14:41","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":11780620,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7472929/v1/cede884e-3bb6-482f-bfc6-b7ae3c40d251.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Effect of Laser treatment on the microstructure and mechanical properties of the surface of Ti-6Al-4V alloy fabricated by Powder Bed Fusion technology","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003eThe Ti-6Al-4V alloy is one of the most widely used materials in the aerospace, medical, and automotive industries due to its high strength, low density, excellent corrosion resistance, and biocompatibility [\u003cspan additionalcitationids=\"CR2 CR3 CR4 CR5\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Due to the rapid development of the industry, the products have to be more complex [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. Additive manufacturing (3D printing) is emerging as one of the key manufacturing techniques in the medical device industry. To produce medical devices with patient-specific geometries and complex porous structures, additive manufacturing of Ti-6Al-4V has become a leading method [\u003cspan additionalcitationids=\"CR8\" citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. Selective laser melting (SLM) Ti-6Al-4V implants with interconnected porosity have become widely used in orthopaedic applications, where porous structures promote bone ingrowth, and the stiffness of the implant can be tuned to reduce stress shielding. The SLM technique allows high resolution control over the design. This includes the ability to introduce porosity with spatial variations in pore size, shape and connectivity [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. Therefore, additive manufacturing technology for 3D printing includes LPBF (laser powder bed fusion) and EPBF (electric powder bed fusion). It offers the possibility of forming any special object with complex shape and/or porous structure in a single step. Especially compared to casting or forging, the mechanical properties of LPBF process are superior to others [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e], it is inevitable to replace the traditional casting method in the future. The disadvantages of this technology include mainly very low production speed, internal stresses, surface roughness (caused by metal powder sticking to the hot surface) and porosity [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eHowever, the mechanical properties and tribological properties of the 3D printed Ti-6Al-4V surface often do not meet the requirements for functional components. But these properties can be significantly improved by laser surface treatment [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. Laser surface treatments, including nitriding, texturing, and peening, significantly enhance the tribological performance and mechanical properties of 3D-printed Ti-6Al-4V. These methods improve wear resistance and hardness, making the alloy more suitable for functional components. Additionally, optimizing laser power and heat treatment conditions can further refine the microstructure and mechanical properties, to overcome the limitations of 3D-printed Ti-6Al-4V [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. To achieve the desired surface properties, the laser parameters must be carefully controlled. For instance, higher irradiance levels can provide a more uniform depth of processing, which is crucial for consistent surface modification [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. The introduction of hard and brittle phases, such as martensite, can lead to crack formation and internal stress. These issues can be reduced by optimizing laser processing parameters, such as power and dwell time, to achieve a balance between hardness and ductility [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eThe laser surface treatment process is highly dependent on the type of inert gas atmosphere in use. In air, increased oxidation occurs, leading to the formation of hard oxide layers, such as TiO\u003csub\u003e2\u003c/sub\u003e​, which can enhance hardness but may reduce ductility due to the brittle nature of oxides [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. Lavisse et al. [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e] investigated the chemical composition of similar laser-induced oxide layers on Ti substrates using a pulsed Nd:YAG laser. At low laser fluences (\u0026lt;\u0026thinsp;25 J/cm\u003csup\u003e2\u003c/sup\u003e), the layers were colourless or pale yellow. A combination of XPS and Raman measurements identified titanium oxo-carbo-nitrides. At higher laser fluences, rough sample surfaces with purple and blue colouration were obtained, which showed increasing formation of anatase and rutile TiO\u003csub\u003e2\u003c/sub\u003e in Raman experiments. In another study, Ohtsu et al. [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e] investigated the effects of pulsed Nd:YAG laser exposure in nitrogen and oxygen gases on Ti substrates as a function of gas pressure and laser parameters in the highly clean and well-controlled environment of a closed XPS/laser apparatus, which allowed in-situ analysis without the need to transfer the sample through ambient air. At low pressures of N\u003csub\u003e2\u003c/sub\u003e (\u0026lt;\u0026thinsp;13.3 kPa), only non-stoichiometric layers of titanium dioxide with a small amount of nitrogen were observed. At higher pressures, a layer of oxide and nitride was formed on top of the stoichiometric titanium nitride. Repeated laser shots promoted the formation of the oxide layer, but the oxide layer formed by the laser radiation was different from the layer that would naturally form on stoichiometric TiN in an atmosphere of high purity oxygen.\u003c/p\u003e\u003cp\u003eUsing an inert atmosphere like argon or helium minimizes interaction with the environment (oxidation), preserving the original alloy composition and producing a more uniform microstructure. This result is a more uniform microstructure and can extend the hardening zone, improve surface quality and reduce residual stresses [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. Argon helps maintain a smoother surface profile and better weld quality compared to open atmospheric conditions [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. In contrast, a nitrogen atmosphere can promote the formation of titanium nitrides (TiN), known for their high hardness and improved tribological performance. This can enhance the tribological performance of the treated surface [\u003cspan additionalcitationids=\"CR23\" citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. Similarly, laser-assisted surface modification can adjust surface hardness by synthesizing different intermetallic phases [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. The choice of atmosphere affects the surface morphology significantly. For instance, nitrogen can lead to the formation of humps due to the stacking of molten material, while argon results in a fine and flat melt pool surface [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. Laser treatment in an oxygen-rich environment can create a dense passivation layer, improving corrosion resistance [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. Laser surface modification can improve the biocompatibility of Ti-6Al-4V, making it more suitable for biomedical applications by enhancing osseointegration and reducing contamination [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eThis article aims to analyse the effects of different protective atmospheres (air, argon, and nitrogen) during laser treatment on the surface layer of 3D-printed Ti-6Al-4V alloy. Special attention is given to changes in microstructure, phase composition, and mechanical properties, particularly hardness and tribological performance, and a comparison with the bulk material.\u003c/p\u003e"},{"header":"2 Experiment details","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003e2.1 Materials and processing\u003c/h2\u003e\u003cp\u003eFor this study, Ti-6Al-4V bulk tensile samples with dog-bone geometry (70 \u0026times; 5 \u0026times; 3 mm, Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) were used as the reference material (labelled as AP \u0026ndash; as printed). These samples were produced using the selective laser melting (SLM) technique and printed vertically in the SLM chamber. The reference material was analysed in as-built and laser-treated states.\u003c/p\u003e\u003cp\u003eThe samples were fabricated with a ConceptLaser M2 Cusing printer, which features a 200 W Yb:YAG fiber laser with a 200 \u0026micro;m laser spot size. Printing was carried out in a protective argon atmosphere containing below 0.5% oxygen by volume. The machine has a building volume of 250 \u0026times; 250 \u0026times; 280 mm\u0026sup3; and is operated in continuous mode during the process. The detailed printing parameters are provided in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. Based on these parameters, the volumetric energy density (VED) applied during SLM was calculated to be ~\u0026thinsp;66.7 J/mm\u0026sup3;, which is within the typical range reported in the literature for achieving high material density and good mechanical properties.\u003c/p\u003e\u003cp\u003eThe Ti-6Al-4V powder used in this study was prepared by gas atomization under an argon protective atmosphere, resulting in spherical particles with a narrow size distribution, typical for powders optimized for additive manufacturing. A more detailed description of the powder morphology, particle size distribution and chemical composition has been reported previously by Škol\u0026aacute;kov\u0026aacute; et al. [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e].\u003c/p\u003e\u003cp\u003e\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\u003e\u0026ndash; Parameters of the SLM 3D-printing process.\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\u003eLayer thickness [\u0026micro;m]\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eLaser power [W]\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eScanning speed [mm/s]\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eHatching distance [\u0026micro;m]\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eVolumetric energy density [J/mm\u003csup\u003e3\u003c/sup\u003e]\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e30\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e200\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e1250\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e80\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e66\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\u003eLaser remelting using a continuous laser was conducted. A 200 W laser with a wavelength of 1070 nm was utilized. The scanning speed was 400 mm/s, and the hatch spacing perpendicular to the build direction of the part was 25 \u0026micro;m. The calculated laser spot size was 130 \u0026micro;m, and the remelting rate was 11 mm\u0026sup2;/s. There were three different atmospheres for laser modifications. Samples were processed on air (labelled as L-O), under a protective argon atmosphere (labelled as L-Ar), and under a protective nitrogen atmosphere (labelled as L-N) (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). The energy input during laser remelting corresponded to a surface energy density of ~\u0026thinsp;18.2 J/mm\u0026sup2;.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003e2.2 Methods of characterization\u003c/h2\u003e\u003cp\u003eThe phase composition of the samples was analysed using X-ray diffraction (XRD) on a PANalytical X\u0026rsquo;Pert PRO device. The system operated with a Cu tube producing Kα radiation (λ\u0026thinsp;=\u0026thinsp;0.15406 nm), a scanning range of 2θ between 5\u0026deg; and 89\u0026deg;, a step size of 0.039\u0026deg;, and generator settings of 30 mA and 40 kV.\u003c/p\u003e\u003cp\u003eThe chemical composition of the bulk material was analyzed using EDX. To further characterize the surface, X-ray photoelectron spectroscopy (XPS) was performed with a Kratos Analytical Axis Supra spectrometer (CEITEC). This instrument is equipped with a combined Al/Ag anode providing monochromatic X-ray sources with energies of 1486.6 eV and 2984.3 eV, respectively. The spectra were recorded with a step size of 0.1 eV and normalized to the C1s binding energy peak at 284.8 eV. Prior to analysis, the samples were carefully cleaned using distilled water, ethanol, and acetone. Data for evaluating the chemical states were referenced from the NIST X-ray Photoelectron Spectroscopy Database.\u003c/p\u003e\u003cp\u003eRaman spectra were measured using a Thermo Scientific Raman Dispersive Spectrometer - Model DXR Microscope equipped with an Olympus confocal microscope. The excitation source was a laser with a wavelength of 532 nm and an input power of 10 mW. A grating with 900 notches/mm was used. The detector was a multi-channel thermoelectrically cooled CCD camera. The samples were measured at 50x magnification with a measurement area of approximately 1 \u0026micro;m\u003csup\u003e2\u003c/sup\u003e. Measurements were performed with a power of 9 mW, a measurement time of 10 s and 10 spectral accumulations. Omnic 9 software (Thermo Scientific) was used to process the spectra.\u003c/p\u003e\u003cp\u003eFor microstructure examination, a light optical microscope (Nikon) and scanning electron microscopes (SEM, Tescan Mira) with energy-dispersive spectroscopy (EDS) were utilized. Metallographic preparation involved the following steps: (i) cutting the samples using a precision cutting machine, (ii) grinding with silicon carbide (SiC) papers of grit sizes ranging from P400 to P2500, (iii) polishing with colloidal silica suspension (Eposil F, particle size 0.1 \u0026micro;m) mixed with hydrogen peroxide in a 4:1 ratio, and (iv) chemical etching with Croll\u0026rsquo;s solution (2 ml HNO\u003csub\u003e3\u003c/sub\u003e\u0026thinsp;+\u0026thinsp;98 ml H\u003csub\u003e2\u003c/sub\u003eO).\u003c/p\u003e\u003cp\u003eVickers hardness testing was conducted using 1 kg (HV1) and 0.1 kg (HV0.1) loads. At least 20 hardness measurements were taken on cross-sections of bulk samples that had been ground to a P2500 finish, with the measurements aligned parallel to the building direction.\u003c/p\u003e\u003cp\u003eTribological properties were measured using the \"ball-on-disc\" method on a universal tribometer, TriboTester, manufactured by Tt-TRIBOtechnic. The test body were an Al\u003csub\u003e2​\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e ball and carbon steel ball, which performed a linear oscillating motion. The applied load was 5 N, and the ball did not rotate during the test. During testing, the ball travelled a total distance of 20 m at a speed of 5 mm/s. Tribological properties were measured on untreated surfaces in all cases, with two wear tracks created per test. The profiles of the wear tracks were measured using a profilometer, and these measurements were used to calculate the wear rate. The wear tracks and their surroundings were then analysed using SEM.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\u003ch2\u003e2.3 Biological evaluation: \u003cem\u003ein-vitro\u003c/em\u003e cytotoxicity\u003c/h2\u003e\u003cp\u003eFor the biological evaluation, indirect contact assays were conducted. The AP and the AP-machined samples were cut in half. The L-Ar, L-O, and L-N samples were cut in half, and the part with no laser application was removed. The resulting samples were disinfected with isopropanol (Centralchem, Slovakia) by being immersed in an ultrasonic bath for 3 minutes and sterilized by ultraviolet irradiation, with two cycles of 30 minutes, one for each side of the sample. Extraction was conducted according to ISO 10993-12, with an extraction ratio of 0.2 g∙mL\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. The disinfected and sterilized samples were immersed in Dulbecco\u0026prime;s Modified Eagle\u0026prime;s Medium (DMEM; Biosera, France) supplemented with 10% fetal bovine serum (FBS; Biosera, France), in closed and sterilized containers. The containers were incubated at 37 \u0026ordm;C, under the agitation of 180 rpm, for 24 hours. A container with only DMEM was used as a control. Once extraction was complete, the extracts were removed to new containers, under sterile conditions.\u003c/p\u003e\u003cp\u003e\u003cem\u003eIn-vitro\u003c/em\u003e cytotoxicity was evaluated with an MTT assay according to ISO 10993-5 (Annex C), for 24 and 72 hours. The mouse-derived fibroblast L-929 cell line (NCTC clone 929: CCL-1\u0026trade;, American Type Culture Collection) was cultivated in DMEM with 10% FBS and seeded in a 96-well plate with a cell density of 1 \u0026times; 10\u003csup\u003e5\u003c/sup\u003e cells∙mL\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. The plate was incubated at 37 \u0026ordm;C and 5% CO\u003csub\u003e2\u003c/sub\u003e. After one day of cultivation, the cells reached a semi-confluent state, and the medium was exchanged for the extracts. 6 wells were used as replicates for each sample, with the previously incubated DMEM used as a control. The plate was again incubated inthe same conditions as before. After 24 or 72 hours, the medium was again exchanged for an MTT solution: 3-(4,5-dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide (Sigma-Aldrich, USA) diluted in DMEM without phenol red (Lonza, Switzerland), at a concentration of 1 mg∙mL\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. During 2 hours of incubation at 37 \u0026ordm;C, the MTT was reduced by the viable cells into formazan crystals. Afterwards, the solution was discarded, replaced with isopropanol and incubated for an extra hour to dissolve the crystals into their fluorescent form. Lastly, the absorbance at 570 nm was measured using a microplate reader (BioTek Instruments, USA). Cell viability was expressed as a percentage of the absorbance of the control, and values above 70% were considered a viable response.\u003c/p\u003e\u003c/div\u003e"},{"header":"3 Results and discussion","content":"\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\u003ch2\u003e3.1 Surface characterization\u003c/h2\u003e\u003cp\u003eCompacted samples were successfully prepared by SLM process. The surface of printed material is illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. It is rather rough as it contains unmelted or partially melted spherical powder particles. This phenomenon can be attributed to several factors: (a) thermal diffusion between the loose powder and the solidified material due to significant temperature differences, causing powder particles to adhere to the surface; (b) partial melting of boundary particles by the contour laser track, leading to their bonding at layer boundaries; and (c) the construction of curved struts in porous parts at varying inclined angles, where loose powder supports the structure, resulting in partial or complete melting of particles beneath each layer and subsequent bonding to the layer's underside [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. These adhered particles negatively impact mechanical properties, particularly fatigue performance, and could potentially detach into biological systems after implantation, causing inflammation. For this reason, post-processing methods such as sandblasting, machining or chemical etching are commonly employed [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. Another method for dealing with this phenomenon and smoothing the surface is laser treatment. Therefore, in this work, laser treated samples are compared with SLM and machined as-printed products in this work.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eEffect of the laser treatments on the quality of the surface is demonstrated on Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. In all cases, the surface was smoothed compared to the AP samples. Nevertheless, the surface contained some visible cracks. Moreover, there were visible differences depending on the atmosphere during laser treatment [\u003cspan additionalcitationids=\"CR20 CR21\" citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. Sample modified air (L-O) contained a significant number of cracks and a small dimple (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea). On the other hand, the sample modified under protective Ar atmosphere contained a lower number of cracks and the surface was much smoother (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb) as there was only limited access to oxygen. Surface of the sample modified under N atmosphere was something between those two as it contained lower number of cracks, however, it contained dimples (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec) as nitrogen could also react with Ti.\u003c/p\u003e\u003cp\u003eRaman spectroscopy was used to characterize the surface of the samples. For each sample, 4\u0026ndash;5 spectra were measured for evaluation of surface homogeneity (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). In general, the spectra were quite homogeneous within each sample. For the laser modified samples, distinct bands of TiO\u003csub\u003e2\u003c/sub\u003e, mainly rutile, were identified (~\u0026thinsp;250, 435 and 610 cm-\u003csup\u003e1\u003c/sup\u003e). These are most pronounced in L-O samples, although they were also observed in minor amount for samples treated in N and Ar. The reason is that these gases also contain some portion of O\u003csub\u003e2\u003c/sub\u003e, therefore minor formation of oxides is expected. In addition to bands of oxidation products, bands of amorphous carbon (~\u0026thinsp;1350 and 1580 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) and a broad spectral background can be seen in these samples. This is in agreement with the results of Lavisse et al [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e], who at higher laser intensities obtained rough surfaces of purple and blue colored samples which showed increasing anatase and rutile TiO\u003csub\u003e2\u003c/sub\u003e formation in Raman experiments.\u003c/p\u003e\u003cp\u003eThe presence of amorphous carbon bands is most likely due to the decomposition of hydrocarbons adsorbed on the surface during laser processing or subsequent Raman measurement, rather than to changes in the bulk alloy. Similar carbonaceous surface features have been reported for laser-processed titanium alloys [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. While this contamination does not affect the microstructure of the alloy, it may influence surface-related functional properties such as tribological behaviour or biological response. Therefore, it should be considered when interpreting surface chemistry.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cem\u003eb) L-Ar and c) L-N.\u003c/em\u003e\u003c/p\u003e\u003cp\u003eIn the case of biomaterials, the surface composition is particularly important, because the biological environment at the interface between the implant/tissue and the biomaterial is interacting with the surface. The chemical composition of the surface layer, which can be several nanometres thick, therefore influences biocompatibility. Although the biocompatibility of the Ti-6Al-4V alloy is well known, it is possible that a part manufactured by SLM will have a different surface chemical composition than other parts manufactured with conventionally prepared material because the metal powder is rapidly melted and cooled [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eThe spectra obtained from the XPS analysis for all four samples are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e. The elements detected are C, N, O, Ti, and Al. The chemical composition of the surface evaluated from the spectra obtained from the measurements is given in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. The CasaXPS software, which allows the correction of errors due to carbon contamination, was used for the quantitative evaluation. However, as can be seen from the spectra for AP product (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ec), carbon is partially presented in the form of titanium carbide, surface is also oxidised due to the high reactivity of molten titanium with residual oxygen in printing chamber, therefore, even a very small amount of oxygen is sufficient for this reaction [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. Therefore, even laser-treated alloys must contain oxidised Ti. XRD and Raman spectroscopy confirmed the presence of TiO\u003csub\u003e2\u003c/sub\u003e, specifically rutile. Considering that XPS is used to analyse only a very thin surface layer, in the case of the AP samples the signal was dominated by the surface of the spherical particles adhering to the sample surface. Therefore, the results mostly reflect the chemistry of the atomised Ti-6Al-4V powder rather than the bulk material after SLM processing. The original powder was atomised in nitrogen atmosphere, which explains the relatively high nitrogen content detected by XPS (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). The nominal composition of the Ti-6Al-4V alloy powder was 90.5 wt.% Ti, 5.6 wt.% Al and 3.9 wt.% V, as reported by our colleagues [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e], with small but measurable nitrogen content originating from the atomisation process. Given the high affinity of Ti-6Al-4V powder to oxygen, surface oxidation is also inevitable and significantly contributes to the detected O and N signals in the XPS spectra [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e].. Quantitative evaluation of the XPS data was carried out, and the elemental surface composition is presented in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. It should be noted that XPS is sensitive enough to distinguish between chemically bonded nitrogen in the alloy matrix and weakly adsorbed species on the powder surface. Interestingly, the Ti:Al ratio increased from 0.13 (AP) to 0.96 (L-O), 1.05 (L-Ar), and 1.93 (L-N). The higher relative concentration of aluminum in the SLM sample is probably due to its higher affinity for oxygen compared to titanium. Both metals have a high affinity for oxygen, but aluminum has a higher affinity for oxygen than titanium - because the formation of Al₂O₃ oxide is thermodynamically more favorable (more negative ΔG\u0026deg;) [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]. Preferential oxidation can be illustrated by the following reactions:\u003cdiv id=\"Equa\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e\n$$\\:4\\:Al\\left(s\\right)+3\\:{O}_{2}\\left(g\\right)\\to\\:2\\:{Al}_{2}{O}_{3}\\left(s\\right)$$\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equb\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equb\" name=\"EquationSource\"\u003e\n$$\\:Ti\\left(s\\right)+\\:{O}_{2}\\left(g\\right)\\to\\:{TiO}_{2}\\left(s\\right)$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eAccording to thermodynamic calculations (ThermoCalc, FactSage), the standard Gibbs free energy of formation ΔG\u0026deg; at 1000 K is approximately \u0026minus;\u0026thinsp;960 kJ/mol O₂ for Al₂O₃, while for TiO₂ it is \u0026minus;\u0026thinsp;760 kJ/mol O₂. This clearly demonstrates that the oxidation of aluminum is energetically more favorable than the oxidation of titanium, which explains the enrichment of Al detected on the sample surface after laser processing.\u003c/p\u003e\u003cp\u003eAlthough the SLM process was carried out in an argon atmosphere (containing below 0.5% oxygen by volume), some oxygen was presented and can reacted with Ti or Al. Since titanium is more prominent, it can be assumed that the surface layer is composed of titanium oxides and a smaller proportion of alumina. However, high resolution spectra were obtained to determine the oxidation states of the elements detected and to more accurately determine the chemical composition of the surface. Regardless, the study by Siblani et al. [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e] found that the oxide scale on the powder surface is formed by a double layer with α-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e in the outer part and TiO\u003csub\u003e2\u003c/sub\u003e in the inner part, which could explain the disproportion between the surface analysis of Ti and Al. Thermodynamic results showed that interstitial aluminium enters and rapidly diffuses into TiO\u003csub\u003e2\u003c/sub\u003e (rutile) to form Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e as a surface layer. In addition, α-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e is a non-stoichiometric oxide with very little excess oxygen as a weight at high oxygen partial pressures. No nitridation was observed for the nitrogen atmosphere., while the surface was covered mainly by titanium oxides.\u003c/p\u003e\u003cp\u003eThe presence of titanium oxides forming a passive layer on the laser modified material is evident from a detailed spectrum (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e) showing the binding energies of titanium. TiO\u003csub\u003e2\u003c/sub\u003e is predominant, but Ti\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, TiO and elemental Ti can also be identified. In the case of the SLM product, TiO\u003csub\u003e2\u003c/sub\u003e is greatly reduced in favour of stoichiometric oxides. This is due to the higher relevant aluminium concentration present in the form of alumina with a lower standard Gibbs energy [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]. Although carbon is introduced by atmospheric contamination in most cases of laser modification, the spectrum in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e explains that it partially reacted to TiC during SLM for AP sample.\u003c/p\u003e\u003cp\u003e\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\u003eSurface composition determined by XPS.\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"6\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eat. %\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eTi\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eAl\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eC\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eO\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003eN\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAP\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e1.8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e13.8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e54.4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e24.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e5.8\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eL-O\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e6.9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e7.1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e49.2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e36.2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e0.6\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eL-Ar\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e3.2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e3.1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e73.2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e19.6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e1.0\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eL-N\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e13.9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e7.2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e47.8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e30.4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e0.6\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=\"Sec8\" class=\"Section2\"\u003e\u003ch2\u003e3.1 Microstructure\u003c/h2\u003e\u003cp\u003eIn the case of laser remelting, the aim was to analyse the remelted layer also in depth. SEM images were taken of the layer cross-section. Initial microstructure of the Ti-6Al-4V alloy produced by SLM contained α\u0026rsquo;-martensitic needles (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e) due to the rapid heat dissipation from the laser site to the rest of the material (approximately 10\u003csup\u003e6\u003c/sup\u003e K/s, as reported [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]). Such high cooling rates are well above the critical threshold of ~\u0026thinsp;410 K/s required for the diffusionless β\u0026rarr;α\u0026prime; transformation, explaining the fully martensitic character of the as-built material. With the volumetric energy density used here (approximately 66.7 J/mm\u0026sup3;), the cooling conditions are consistent with the values reported in the literature for α\u0026prime; formation. However, during subsequent laser remelting, the effective energy input (approximately 18.2 J/mm\u0026sup2;) and slower local cooling rates may approach a regime in which partial α\u0026prime; decomposition or α\u0026thinsp;+\u0026thinsp;β lamellar structure development can occur. This implies that martensite formation can be either promoted or suppressed depending on the applied parameters, which are consistent with observations for other laser-processed Ti-6Al-4V systems.\u003c/p\u003e\u003cp\u003eLaser modifications altered microstructure in depth up to ~\u0026thinsp;140 \u0026micro;m (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e). While the bulk material beneath this layer remained with martensitic structure, the surface layer, exposed to temperature fluctuations due to the laser treatment, has undergone a transformation to a fine-grained mixture of α and β phases (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e). Due to the extremely fine grain size, it was difficult to accurately distinguish the lamellae of the α and β phases by EDS. The presence of this two-phase structure was further confirmed by XRD analysis (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e). The individual laser treatment environments differ mainly in depth of the modified layer, with the thinnest layer formed under the Ar protective atmosphere, which goes somewhat against the claims in the literature [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e], and the thickest layer formed under the protective N atmosphere (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eThe thickness of the remelted zone depends on the laser energy delivered per unit area and the efficiency of heat dissipation. In this study, the applied line energy (approximately 0.5 J/mm) and the high degree of overlap resulting from the small hatch distance (25 \u0026micro;m) led to the repeated reheating of adjacent tracks. This thermal accumulation reduces the effective cooling rate in the near-surface region, enabling decomposition of the α\u0026prime; martensite into an α\u0026thinsp;+\u0026thinsp;β lamellar structure. This mechanism is consistent with observations in other laser-treated\u003c/p\u003e\u003cp\u003eTi-6Al-4V systems, in which a transition from martensitic to α\u0026thinsp;+\u0026thinsp;β morphology occurs when the local cooling rate falls below the critical threshold for β\u0026rarr;α\u0026prime; transformation [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]. The protective atmosphere also influences the remelting process; variations in the thermal conductivity and convective heat transfer of argon (Ar), nitrogen (N₂) and air can explain the different melt pool depths. In particular, the lowest modified depth in argon (Ar) may be attributed to its low thermal conductivity, which reduces convective transport and promotes faster solidification compared to nitrogen (N₂) or air.\u003c/p\u003e\u003cp\u003eThe chemical composition of the remelted layer was evaluated using EDS line scanning across the cross-section (see Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e). The distribution of the main alloying elements (Ti, Al and V) was relatively uniform throughout the remelted zone, suggesting that macroscale segregation did not occur during the rapid solidification process. A clear enrichment in oxygen was detected in the near-surface region (0\u0026ndash;80 \u0026micro;m), which is consistent with the Raman and XRD results that confirmed the presence of TiO₂. Additionally, traces of nitrogen were observed at the outermost part of the layer, suggesting limited incorporation of nitrogen from the processing atmosphere. Beyond ~\u0026thinsp;120 \u0026micro;m, the oxygen and nitrogen levels decreased to background values, while the Ti, Al and V composition stabilised close to that of the bulk material. These results confirm that the chemical modifications induced by laser remelting are confined to the near-surface zone, correlating with the formation of refined α\u0026thinsp;+\u0026thinsp;β microstructures and oxygen/nitrogen-enriched phases. These phases contribute to the increased hardness and wear resistance of the treated samples.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\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\u003e\u0026ndash; Variation of the depth of the modified layers produced by laser remelting under different conditions.\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"2\"\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\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSample\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eDepth of remelting layer [\u0026micro;m]\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eL-O\u003c/p\u003e\u003cp\u003eL-Ar\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e117\u0026thinsp;\u0026plusmn;\u0026thinsp;2\u003c/p\u003e\u003cp\u003e79\u0026thinsp;\u0026plusmn;\u0026thinsp;4\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eL-N\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e136\u0026thinsp;\u0026plusmn;\u0026thinsp;5\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 phase compositions of the sample surfaces were determined using XRD, see Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e. The analysis revealed that the as-printed sample consists of a single phase, α'-Ti, which corresponds to hexagonal martensite formed through rapid cooling from β-Ti. During laser surface modification in various atmospheres, the α' phase transforms into α-Ti and β-Ti phases in all samples. The α-Ti phase represents the HCP (hexagonal close-packed) allotropic form of titanium. This phase is challenging to differentiate from α'-Ti due to their nearly identical diffraction angle positions.\u003c/p\u003e\u003cp\u003eIt can be observed that the phase composition of the initial AP sample changed after laser treatment. Titanium martensite transformed into two phases, namely α-Ti and β-Ti. Additionally, there was also oxygen in the form of TiO and TiO\u003csub\u003e2\u003c/sub\u003e, where the more stable (TiO\u003csub\u003e2\u003c/sub\u003e) was observed with higher intensity especially in L-O sample as it had access to oxygen from air. Otherwise, lower content of oxygen was present in L-Ar and L-N samples.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\u003ch2\u003e3.3 Mechanical properties\u003c/h2\u003e\u003cp\u003eThe Vickers microhardness (HV0.1) of the surfaces was measured and the results are summarized in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. 4. The surface hardness of the AP sample (356\u0026thinsp;\u0026plusmn;\u0026thinsp;20 HV0.1) was comparable to that of the inner structure (360\u0026thinsp;\u0026plusmn;\u0026thinsp;20 HV0.1). By contrast, laser treatment in air dramatically increased the surface hardness to 873\u0026thinsp;\u0026plusmn;\u0026thinsp;21 HV0.1, while leaving the bulk unaffected. This pronounced increase is associated with the formation of oxides, as detected by XRD and Raman spectroscopy, and with the high oxygen content, as measured by EDS line profiling. This shows the diffusion of oxygen into the remelted layer (up to ~\u0026thinsp;30 wt.% near the surface). In the case of a nitrogen atmosphere, the hardness was slightly lower at 789\u0026thinsp;\u0026plusmn;\u0026thinsp;27 HV0.1, which is consistent with reduced oxygen uptake compared to air. However, it was still higher than for the L-Ar sample due to the formation of nitrides and carbides (TiC was identified by XPS), which was confirmed by Raman spectroscopy. The lowest hardness increase was observed for the L-Ar sample (668\u0026thinsp;\u0026plusmn;\u0026thinsp;21 HV0.1), where the inert atmosphere limited the incorporation of oxygen and nitrogen, and strengthening was mainly due to the α\u0026prime;\u0026rarr;α\u0026thinsp;+\u0026thinsp;β transformation.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003e\u0026ndash; Measured microhardness HV0.1 values of the starting material (AP) and the material modified by laser remelting.\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"2\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSample\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eSurface microhardness HV0.1\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAP\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e\u003cp\u003e356\u0026nbsp;\u0026plusmn;\u0026nbsp;20\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eL-O\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e\u003cp\u003e873\u0026nbsp;\u0026plusmn; 21\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eL-Ar\u003c/p\u003e\u003cp\u003eL-N\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e\u003cp\u003e668\u0026nbsp;\u0026plusmn;\u0026nbsp;21\u003c/p\u003e\u003cp\u003e789\u0026nbsp;\u0026plusmn;\u0026nbsp;27\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\u003eA plot of microhardness profile measurements from the surface of the sample to its center can be seen in Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e. The measurements were repeated four times. It was then fitted with a moving average curve. The depth of the melting region (read from the microstructural cross section through the sample) is marked in the graph. Considering that the decrease in hardness occurs beyond this region, the material has been affected deeper than can be seen from the microstructure in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eIn their study, Bipasha et al. [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e] investigated laser surface treatment (LST) of Ti-6Al-4V, which resulted in an increase in surface microhardness in nitrogen (839\u0026ndash;1327 HV0.1) atmospheres compared to the printed sample (278 HV0.1). The reason for the higher microhardness values is the formation of titanium nitride (TiN and Ti\u003csub\u003e2\u003c/sub\u003eN) dispersed in the\u003c/p\u003e\u003cp\u003eα-matrix after LST. Treatment in an argon atmosphere also enhances microhardness, though to a lesser extent than nitrogen, with values ranging from 435 to 630 HV0.1. Feng et al. [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e] investigated the laser nitriding of Ti-20Zr-6.5Al-4V alloy surface, which led to an increase in surface microhardness under nitrogen atmosphere (917 HV0.1) due to the formation of TiN dendrites. In the present study, however, the increase in hardness can be attributed not only to nitride formation, but also to the presence of oxides and carbides, as confirmed by Raman, XRD, XPS and EDS analyses.\u003c/p\u003e\u003cp\u003eTribological tests are based on friction between the test body and the material under the test. In our case, an Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e sphere was used as the test body because its properties are close to those of human bone or ceramic parts of joint replacements, where the material to be tested is very useful [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eThe tribological tests were carried out in such a way that the test piece (Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e ball and carbon steel ball) travelled a distance of 20 m at a load of 5 N and a speed of 5 mm/sec. In all cases, 2 traces were made and further evaluated by SEM and EDS. The tests were carried out first on the starting material and then on the samples after laser modification. The SEM images are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e and the measured values after the tests are summarized in Table\u0026nbsp;\u003cspan refid=\"Tab5\" class=\"InternalRef\"\u003e5\u003c/span\u003e.\u003c/p\u003e\u003cp\u003eThe materials after laser modification showed very different tribological properties compared to the starting material. All three laser surface treatments in different protective atmospheres resulted in improved dry sliding wear resistance. This was attributed to the increase in hardness and the formation of wear resistant compounds. Figure\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e shows the appearance of the grooves formed on the surface of each specimen. The mechanism of wear in the untreated titanium alloy was mainly by abrasion of the specimen surface. In addition, the AP specimen contained original powder particles on the specimen surface which were easily removed by vibrating both specimens (Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e and carbon steel). These particles were crushed in the process and acted as an abrasive, degrading the tribological properties (Table\u0026nbsp;\u003cspan refid=\"Tab5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). For this reason, the AP specimen was machined (AP-M, Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003eb), which rapidly reduced the surface roughness of the specimen from 3.2 \u0026micro;m to a value of 0.12 \u0026micro;m, which was even lower than that of the laser-treated specimens. Since the laser treatment was performed on the unmachined sample, the laser action melted the powder particles on the sample surface. The roughness values of all surfaces are shown in Table\u0026nbsp;\u003cspan refid=\"Tab5\" class=\"InternalRef\"\u003e5\u003c/span\u003e.\u003c/p\u003e\u003cp\u003eContrary, laser treated materials were characterized by smoother surface without any powder particles, only with a few cracks. This resulted in smoother friction marks (Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003ec,d, e). Despite having the higher surface hardness L-O material had the most visible scratches out of the laser treated materials. This might be associated with the small dimples observed on the surface that could be easily abraded, and loose hard particles may decrease the wear resistance. Thus, resulting wear resistance is the worst out of the laser treated material; however, it is still an order of magnitude better compared to AP sample. In case of L-Ar sample, the wear tracks are almost negligible as this material was characterized by the smoothest surface without any dimples, despite the surface hardness being lowest out of the laser treated samples. Therefore, this material reached the best wear resistance. Sample treated in nitrogen atmosphere had the wear resistance in between those samples due to the smooth surface, however, with dimples.\u003c/p\u003e\u003cp\u003eHowever, in the laser treated cases, the material was removed by the formation and breaking of adhesive bonds. It is believed that the increased hardness changed the wear mechanism from ploughing to adhesion. The above results are confirmed by electron microscopy of the worn surfaces. The same conclusion was reached in a study S. Yerramareddy at all [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Using a corundum ball results in a significantly lower coefficient of friction and lower wear in laser samples. For carbon steel ball, laser processed samples are still advantageous in terms of wear, but may lead to an increase in friction, which is atypical and could be due to a different interaction with the steel material. The best combination of low roughness, low wear and low COF is with L-N or L-Ar with corundum.\u003c/p\u003e\u003cp\u003eBipasha Das et al. [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e] processed the materials by laser melting in an argon atmosphere and nitrided the surface in a nitrogen atmosphere. For both melting and nitriding, the depth of the modified layer was found to vary depending on the laser parameters (232\u0026ndash;1011 \u0026micro;m). The formation of TiN in nitrogen atmosphere not only increased the hardness but also significantly reduced the wear rate and offered higher wear resistance compared to other atmospheres. There was a marginal decrease in wear rate (against WC ball) due to laser surface melting (5.17\u0026ndash;5.81 \u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e mm\u003csup\u003e3\u003c/sup\u003e/Nm) under argon and a substantial decrease in wear rate when melting was conducted under nitrogen atmosphere (1.91\u0026ndash;4.94 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e mm\u003csup\u003e3\u003c/sup\u003e/Nm) as compared to Ti-6Al-4V (5.93 \u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e mm\u003csup\u003e3\u003c/sup\u003e/Nm). In both cases, the laser treatment has a positive effect on reducing wear. The best results are achieved when the laser is in a protective atmosphere (argon or nitrogen). The absolute values are not directly comparable between the sets because the counter-body (WC vs. corundum vs. carbon steel ball) and the sample/test conditions are different. On a relative scale, however, both experiments show the same trend: laser melting improves tribological properties, more significantly in inert or nitrogen atmospheres than in air.\u003c/p\u003e\u003cp\u003eBy way of comparison, the remelted depth in the present study was only\u0026thinsp;~\u0026thinsp;140 \u0026micro;m. This difference is primarily due to the lower energy input: the volumetric energy density (VED) here was ~\u0026thinsp;66.7 J/mm\u0026sup3;, with a line energy of ~\u0026thinsp;0.5 J/mm. Das et al., however, likely employed much higher effective energy densities due to their lower scan speeds (6 mm/s), higher laser power (500\u0026ndash;1100 W) and potentially larger hatch distances. This higher energy input resulted in deeper melt pools and thicker modified layers in their work. Additionally, the very small hatch distance (25 \u0026micro;m) in the current study resulted in intense thermal overlap, causing the surface tracks to repeatedly reheat adjacent regions. This thermal accumulation limits the depth of penetration of the melt pool but enhances near-surface microstructural refinement and α\u0026prime; decomposition. Similar effects of tight hatch spacing on the promotion of α\u0026thinsp;+\u0026thinsp;β lamellar structures via internal heat treatment have been reported by Barriobero-Vila et al., who observed intensive martensite decomposition and a very fine α\u0026thinsp;+\u0026thinsp;β microstructure in these conditions [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]. Thus, while the present study induces a shallower remelted zone, it still achieves significant microstructural transformation.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab5\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 5\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003e\u0026ndash; Results of measurements of the tribological properties of the input material and the material after surface modification by laser remelting.\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"12\"\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\u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c11\" colnum=\"11\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c12\" colnum=\"12\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e\u003cp\u003eSample\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003eBall\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003eSurface roughness [\u0026micro;m]\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e\u003cp\u003eAverage wear track area [mm\u003csup\u003e2\u003c/sup\u003e]\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c10\" namest=\"c9\"\u003e\u003cp\u003eAverage coefficient \u003c/p\u003e\u003cp\u003eof friction\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c11\"\u003e\u003cp\u003eAverage wear speed [mm\u003csup\u003e3\u003c/sup\u003e/N/m]\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"1\" nameend=\"c12\" namest=\"c12\"\u003e\u0026nbsp;\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e\u003cp\u003eAP\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" morerows=\"4\" nameend=\"c4\" namest=\"c3\" rowspan=\"5\"\u003e\u003cp\u003eCorund\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003e3.20\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e\u003cp\u003e1.44 \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\bullet\\:\\)\u003c/span\u003e\u003c/span\u003e 10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c10\" namest=\"c9\"\u003e\u003cp\u003e0.453\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c12\" namest=\"c11\"\u003e\u003cp\u003e7.18 \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\bullet\\:\\)\u003c/span\u003e\u003c/span\u003e 10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e\u003cp\u003eAP-M\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003e0.12\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e\u003cp\u003e5.96 \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\bullet\\:\\)\u003c/span\u003e\u003c/span\u003e 10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c10\" namest=\"c9\"\u003e\u003cp\u003e0.397\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c12\" namest=\"c11\"\u003e\u003cp\u003e2.98 \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\bullet\\:\\)\u003c/span\u003e\u003c/span\u003e 10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e\u003cp\u003eL-O\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003e0.59\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e\u003cp\u003e1.57 \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\bullet\\:\\)\u003c/span\u003e\u003c/span\u003e 10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c10\" namest=\"c9\"\u003e\u003cp\u003e0.269\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c12\" namest=\"c11\"\u003e\u003cp\u003e7.84 \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\bullet\\:\\)\u003c/span\u003e\u003c/span\u003e 10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e\u003cp\u003eL-Ar\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003e0.54\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e\u003cp\u003e9.25 \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\bullet\\:\\)\u003c/span\u003e\u003c/span\u003e 10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c10\" namest=\"c9\"\u003e\u003cp\u003e0.171\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c12\" namest=\"c11\"\u003e\u003cp\u003e4.63 \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\bullet\\:\\)\u003c/span\u003e\u003c/span\u003e 10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e\u003cp\u003eL-N\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003e0.55\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e\u003cp\u003e1.22 \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\bullet\\:\\)\u003c/span\u003e\u003c/span\u003e 10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c10\" namest=\"c9\"\u003e\u003cp\u003e0.138\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c12\" namest=\"c11\"\u003e\u003cp\u003e6.08 \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\bullet\\:\\)\u003c/span\u003e\u003c/span\u003e 10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e\u003cp\u003eAP\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" morerows=\"4\" nameend=\"c4\" namest=\"c3\" rowspan=\"5\"\u003e\u003cp\u003eCarbon steel ball\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003e3.20\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e\u003cp\u003e1.59 \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\bullet\\:\\)\u003c/span\u003e\u003c/span\u003e 10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c10\" namest=\"c9\"\u003e\u003cp\u003e0.441\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c12\" namest=\"c11\"\u003e\u003cp\u003e7.93 \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\bullet\\:\\)\u003c/span\u003e\u003c/span\u003e 10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e\u003cp\u003eAP-M\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003e0.12\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e\u003cp\u003e5.56 \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\bullet\\:\\)\u003c/span\u003e\u003c/span\u003e 10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c10\" namest=\"c9\"\u003e\u003cp\u003e0.382\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c12\" namest=\"c11\"\u003e\u003cp\u003e2.78 \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\bullet\\:\\)\u003c/span\u003e\u003c/span\u003e 10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e\u003cp\u003eL-O\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003e0.59\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e\u003cp\u003e2.22 \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\bullet\\:\\)\u003c/span\u003e\u003c/span\u003e 10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c10\" namest=\"c9\"\u003e\u003cp\u003e0.530\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c12\" namest=\"c11\"\u003e\u003cp\u003e1.11 \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\bullet\\:\\)\u003c/span\u003e\u003c/span\u003e 10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e\u003cp\u003eL-Ar\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003e0.54\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e\u003cp\u003e1.91 \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\bullet\\:\\)\u003c/span\u003e\u003c/span\u003e 10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c10\" namest=\"c9\"\u003e\u003cp\u003e0.640\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c12\" namest=\"c11\"\u003e\u003cp\u003e9.56 \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\bullet\\:\\)\u003c/span\u003e\u003c/span\u003e 10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e\u003cp\u003eL-N\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003e0.55\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e\u003cp\u003e2.95 \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\bullet\\:\\)\u003c/span\u003e\u003c/span\u003e 10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c10\" namest=\"c9\"\u003e\u003cp\u003e0.435\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c12\" namest=\"c11\"\u003e\u003cp\u003e1.47 \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\bullet\\:\\)\u003c/span\u003e\u003c/span\u003e 10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e\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=\"Sec10\" class=\"Section2\"\u003e\u003ch2\u003e3.3 Biological properties\u003c/h2\u003e\u003cp\u003eThe results from the MTT assay to evaluate the \u003cem\u003ein-vitro\u003c/em\u003e cytotoxic response to the materials, for 24 and 72 hours of exposure, can be seen in Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e. DMEM with 10% FBS was used as a control and was set as 100% cell viability. Ti-6Al-4V samples without laser treatment (AP and AP-machined) were used as a reference material, since the biological response to the Ti6Al4V alloy is well known. According to ISO-10993-5, cell viability values above 70% are considered a non-cytotoxic response.\u003c/p\u003e\u003cp\u003eFor the 24-hour time point, all values for the different extracts, from the different tested materials, meet the threshold: AP \u0026ndash; 88.31\u0026thinsp;\u0026plusmn;\u0026thinsp;3.10%, AP-machined \u0026ndash; 94.59\u0026thinsp;\u0026plusmn;\u0026thinsp;4.94%, L-Ar \u0026ndash; 76.72\u0026thinsp;\u0026plusmn;\u0026thinsp;3.48%, L-O \u0026ndash; 87.20\u0026thinsp;\u0026plusmn;\u0026thinsp;2.13% and L-N \u0026ndash; 72.94\u0026thinsp;\u0026plusmn;\u0026thinsp;4.36%. However, the laser-treated materials L-Ar and L-N present a reduced cell viability value when compared with the control and with the reference materials, indicating that there may be an influence of these treatments on the cellular response. Hence, the assay was repeated for a 72-hour time interval to investigate if this reduction would persist with time.\u003c/p\u003e\u003cp\u003eAs a matter of fact, the results after 72 hours of exposure show values closer to the control, for all samples: AP \u0026ndash; 99.30\u0026thinsp;\u0026plusmn;\u0026thinsp;1.44%, AP-machined \u0026ndash; 99.54\u0026thinsp;\u0026plusmn;\u0026thinsp;4.05%, L-Ar \u0026ndash; 88.31\u0026thinsp;\u0026plusmn;\u0026thinsp;4.96%, L-O \u0026ndash; 97.23\u0026thinsp;\u0026plusmn;\u0026thinsp;5.47% and L-N \u0026ndash; 101.50\u0026thinsp;\u0026plusmn;\u0026thinsp;2.37%. These results may justify the differences measured before due to the characteristics of assay, with 24 hours not being enough time for the cells to adapt to the new environment, and not a real indicator of some cytotoxic potential. Notwithstanding, the benchmark from ISO-10993-5 is met, supporting the potential of these treatments in terms of biocompatibility.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e"},{"header":"4 Conclusions","content":"\u003cp\u003eLaser surface treatment was applied to enhance the performance of SLM-manufactured Ti-6Al-4V alloy. The process parameters, especially the protective atmosphere, strongly influenced the resulting surface morphology, microstructure, and functional properties. The main conclusions are summarized below:\u003c/p\u003e\n\u003col\u003e\n \u003cli\u003eLaser remelting improves surface smoothness, microhardness, and wear resistance.\u003c/li\u003e\n \u003cli\u003eAir (L-O) increased hardness due to oxide formation, but surface cracking was observed.\u003c/li\u003e\n \u003cli\u003eArgon (L-Ar) brings the best combination of smooth surface, wear resistance, and low friction.\u003c/li\u003e\n \u003cli\u003eNitrogen (L-N) increases hardness due to the formation of hard nitrides while minor surface cracking was observed.\u003c/li\u003e\n \u003cli\u003eRemelted surface is characterized by transformed microstructure from \u0026alpha;\u0026prime; martensite to refined \u0026alpha; + \u0026beta; phases.\u003c/li\u003e\n \u003cli\u003eSurface hardness is increased by up to 250% after laser treatment.\u003c/li\u003e\n \u003cli\u003eWear resistance was improved by one order of magnitude: coefficient of friction decreased by up to 70%.\u003c/li\u003e\n \u003cli\u003eBiocompatibility of laser threatened samples remained non-cytotoxic according to ISO 10993-5.\u003c/li\u003e\n\u003c/ol\u003e\n\u003cp\u003eIn this study, the thickness of the modified layer (~140 \u0026micro;m) was significantly lower than values reported in the literature, due to the lower applied line energy and high track overlap. This processing strategy resulted in pronounced thermal accumulation near the surface, which promoted \u0026alpha;\u0026prime; martensite decomposition and refinement into \u0026alpha;+\u0026beta; lamellae rather than deep melting. This demonstrates that the protective atmosphere, specific energy input, and scanning strategy are all crucial factors in achieving the desired balance of hardness, toughness, and wear resistance. Therefore, the results highlight the importance of optimising both the atmosphere and the energy delivery to achieve application-specific properties in additively manufactured Ti-6Al-4V.\u003c/p\u003e\n\u003cp\u003eThese findings confirm that laser surface modification under optimized conditions is a promising strategy for tailoring 3D-printed titanium alloy components for advanced engineering and biomedical applications.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eM.S. wrote the main text of the manuscript. F.S. wrote the chapter on biological testing. J.F. and D.S. performed the XPS measurements and analysis of the results. J.D., M.S., D. D., and J. K. measured the scientific data used. All authors reviewed the manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eThe authors would like to express their sincere gratitude to LASCAM Systems s.r.o. for their valuable support in the preparation of samples. The laser surface remelting of 3D-printed Ti-6Al-4V alloy specimens carried out by LASCAM significantly contributed to this work.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eThe data will be published in preprint mode on the Zenodo portal, but this process has not yet taken place. This is a condition of project No. CZ.02.01.01/00/22_008/0004634.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003ePushp P, Dasharath SM, Arati C (2022) \u003cem\u003eClassification and applications of titanium and its alloys.\u003c/em\u003e Materials Today: Proceedings, 54: pp. 537\u0026ndash;542\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eElitzer D et al (2022) Development of Microstructure and Mechanical Properties of TiAl6V4 Processed by Wire and Arc Additive Manufacturing. Adv Eng Mater, 25\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eCarroll BE, Palmer TA, Beese AM (2015) Anisotropic tensile behavior of Ti\u0026ndash;6Al\u0026ndash;4V components fabricated with directed energy deposition additive manufacturing. Acta Mater 87:309\u0026ndash;320\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eDonachie M (2000) Titanium: A Technical Guide. 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Mater Sci Engineering: C 104:109895\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"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":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Ti-6Al-4V, SLM, 3D-print, laser, Mechanical Properties, Porosity, Porous material","lastPublishedDoi":"10.21203/rs.3.rs-7472929/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7472929/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis study investigates the influence of laser surface treatment under different protective atmospheres (air, argon, and nitrogen) on the microstructure, mechanical, tribological, and biological properties of Ti-6Al-4V alloy produced by selective laser melting (SLM). A continuous-wave laser (200 W, 1070 nm) was used to remelt the surfaces of as-printed samples. Comprehensive characterization was performed using XRD, XPS, Raman spectroscopy, SEM/EDS, hardness testing, tribological measurements, and in-vitro cytotoxicity assays. The laser-treated samples exhibited a significant transformation of the surface microstructure from martensitic α\u0026prime;-Ti to a fine α\u0026thinsp;+\u0026thinsp;β phase mixture, along with the formation of hard compounds such as titanium oxides and nitrides. The depth of the remelted layer varied depending on the processing atmosphere, with the deepest and hardest layer observed for samples treated in air. All laser treatments substantially enhanced surface microhardness and dry sliding wear resistance compared to untreated samples. The most favorable combination of low friction, minimal wear, and surface uniformity was achieved with the argon-treated sample. In-vitro tests confirmed that all treated surfaces remained non-cytotoxic, supporting their potential for biomedical applications.\u003c/p\u003e","manuscriptTitle":"Effect of Laser treatment on the microstructure and mechanical properties of the surface of Ti-6Al-4V alloy fabricated by Powder Bed Fusion technology","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-11-10 14:42:17","doi":"10.21203/rs.3.rs-7472929/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"6c31ab9f-5a32-4ee9-919d-d444c1120a2f","owner":[],"postedDate":"November 10th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-04-27T16:13:30+00:00","versionOfRecord":{"articleIdentity":"rs-7472929","link":"https://doi.org/10.1007/s40964-026-01662-3","journal":{"identity":"progress-in-additive-manufacturing","isVorOnly":false,"title":"Progress in Additive Manufacturing"},"publishedOn":"2026-04-21 15:56:55","publishedOnDateReadable":"April 21st, 2026"},"versionCreatedAt":"2025-11-10 14:42:17","video":"","vorDoi":"10.1007/s40964-026-01662-3","vorDoiUrl":"https://doi.org/10.1007/s40964-026-01662-3","workflowStages":[]},"version":"v1","identity":"rs-7472929","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7472929","identity":"rs-7472929","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}