Repeated Impact Resistance of Stellite 6 Hardfacing Layer Produced by Gas Metal Arc Welding

Repeated Impact Resistance of Stellite 6 Hardfacing Layer Produced by Gas Metal Arc Welding | 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 Repeated Impact Resistance of Stellite 6 Hardfacing Layer Produced by Gas Metal Arc Welding Josef Daniel, Hana Šebestová, Libor Mrňa This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8156643/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 17 Mar, 2026 Read the published version in Progress in Additive Manufacturing → Version 1 posted You are reading this latest preprint version Abstract Cobalt-chromium-based alloys, such as Stellite 6, exhibit exceptional wear resistance, chemical stability, and thermal stability, making them suitable for demanding industrial applications. However, the manufacturing of components from Stellite 6 is challenging due to the alloy's high hardness and poor machinability. Hardfacing of enhancing layers on components made from a material with superior machinability and/or more desirable bulk properties has been identified as an effective solution to Stellite 6 manufacturing limitations. The advantages of hardfacing by gas metal arc welding include high deposition rates, cost-effectiveness, and the capability to fabricate large-area structures. Recent studies have characterised Stellite 6 produced by this method in terms of its resistance to external thermal, chemical, or certain mechanical factors. However, to date, limited research has investigated its behaviour under repeated impact loading conditions. The present study investigates the impact resistance of an alloy equivalent to Stellite 6 hardfaced by gas metal arc welding onto a steel substrate. Testing was performed in different positions – above the beads and above their overlaps – in order to evaluate potential differences in impact life. The results indicated that, despite minor variations in morphology and mechanical properties between the distinct positions, the impact lifetime was equivalent in both. The findings of this study provide valuable information for the design and utilisation of components hardfaced with Stellite 6 in applications where impact protection is crucial. Hardfacing Gas Metal Arc Welding Wire Arc Additive Manufacturing Impact test Stellite 6 Impact lifetime 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 1. Introduction Hardfacing by gas metal arc welding (GMAW) is a highly productive additive manufacturing technique well-suited for depositing relatively thick layers of material. The process, which utilizes gas metal arc welding technology, employs the heat generated by the arc to melt the filler wire and the surface of a component (substrate), thereby forming a clad bead. Successive, partially overlapping beads create a uniform layer, and multiple layers can be deposited to achieve the required thickness or to control the level of dilution. As the GMAW hardfacing is a specific instance of Wire Arc Additive Manufacturing (WAAM), some authors use the terms interchangeably [ 1 – 4 ]. One of the key hardfacing materials processed by GMAW is the alloy Stellite 6 [ 2 , 5 ]. This cobalt–chromium superalloy is well known for its exceptional wear resistance, corrosion resistance, and thermal stability [ 2 , 6 – 8 ]. The Stellite 6 is cobalt-based alloy; cobalt and chromium form cobalt–chromium dendrites, within which interdendritic carbides such as Cr 7 C 3 , Cr 3 C 2 , and Co–W–C are found [ 2 , 9 ]. These carbides give Stellite 6 its high hardness and resistance to mechanical loading. However, the carbide network also results in reduced fracture toughness, and the alloy tends to be prone to localized defects. For this reason, it is not suitable for fabricating bulk components [ 10 , 11 ]. Instead, Stellite 6 is primarily used in powder or wire form as a hardfacing material for surface treatments, such as plasma spraying, laser metal deposition, or GMAW [ 12 – 17 ]. In GMAW hardfacing, Stellite 6 is applied in a wire form. When wire is deposited via an electric arc, the Stellite 6 material becomes diluted with the substrate material, leading to the formation of additional phases. Steel of various types is one of the most typical substrates [ 13 ]. The resulting metallurgical bond between steel and Stellite 6 forms a multiphase alloy, where Stellite 6 incorporates iron and other elements from the steel substrate, while cobalt and chromium may diffuse into the steel [ 2 , 10 ]. The structural complexity is further complicated by the deposition method itself, in which successive partially overlapping beads thermally influence each other. Variations in thermal history lead to distinct diffusion behavior, microstructural transformations, and the formation of metallurgical interfaces [ 2 , 18 ]. When used as a hardfacing material, Stellite 6 is employed, for example, to enhance the surface properties of industrial turbines, pump impellers, engines, and similar moving parts [ 2 , 13 , 19 ]. Throughout the operational process, numerous components are exposed to recurrent dynamic and impact loads. Although the impact resistance of Stellite 6 produced by various technologies, such as high-velocity oxygen fuel (HVOF) and gas tungsten arc welding (GTAW), has been studied [ 20 , 21 ], no peer-reviewed research to date has addressed this property in Stellite 6 deposited by GMAW/WAAM. This gap is particularly relevant given the growing interest in GMAW hardfacing for manufacturing functional wear-resistant components that are exposed to repeated dynamic loading. The present study aims to address this gap by providing a comprehensive evaluation of the repeated impact resistance of wire-arc cladded Stellite 6 on steel substrate. The spatial variability research focuses on the influence of bead and bead-overlap regions, as well as the isotropy of the impact response within the plane of the surface. This research is supported by morphological, chemical, and mechanical analyses. The results obtained from this study contribute to a deeper understanding of the performance of GMAW-processed Stellite 6 in demanding operational conditions and provide insights for the optimisation of its application in critical industrial components. 2. Experimental The TPS 320i MIG/MAG source with WF60i Robacta Drive wire feeder (both from Fronius) was used in cold metal transfer (CMT) regime to melt the Co-based filler wire ALUNOX AX-FD Co6 (ERCCoCr-A, Stellite 6 equiv.) with a diameter of 1.2 mm. The ABB IRB 2400 robot holding the arc torch was employed to produce four 120 mm long linear overlapping beads with a 4 mm pitch on a ground 10 mm thick S355MC steel sheet substrate. The torch was angled at 30° from the substrate normal and pushed toward the melt pool. Figure 1 presents the scheme of the experimental setup. The beads were deposited at a welding speed of 20 mm/s. The average feeding rate, arc current, voltage, and power were 8.3 m/min, 267 A, 17.4 V, and 5.05 kW, respectively. Due to the complexity of the CMT regime, the arc power is not a simple product of electric current and voltage. It continuously changes as high-current and low-current phases take turns, and the heat source calculates the average power over time. Pure argon at a flow rate of 18 l/min prevented oxidation of the melt pool. After deposition, the cladded sample was cut perpendicularly to the deposition direction (y-z plane), and together with a reference substrate specimen, it underwent metallographic treatment on an MTH device. The surface of the cladded sample was ground to eliminate waviness induced by multiple bead deposition. Both specimens were then polished in x-y plane to achieve a uniform surface finish. The arithmetic mean surface roughness Ra was determined in accordance with ISO 13565-1 using the Keyence VK-X 1100 laser confocal microscope and reached (0.10–0.15) µm. The cross-section was polished and then etched with the Kalling 2 solution for 50 s to reveal the macrostructure and identify regions of interest for hardness and impact test measurements. Figure 2 illustrates the cladded specimen with the designated measurement regions “bead” and “overlap” located above the cladding depth maxima and minima, respectively. Vickers hardness of the machined surface was measured using the hardness tester Qness 60A + EVO at a load of 9.81 N. At first, two linear measurement series along the x-axis in x-y plane, each consisting of thirteen indents, were performed in both the bead and overlap regions identified in Fig. 2 . Due to the limited dimensions of the sample, hardness was measured at two different locations, each time in the same position relative to the bead and overlap. Then, a series of indents was made across all beads along the y-axis, 0.5 mm under the machined surface in y-z cross-section, located in the middle of the specimen length. The spacing of indents was 0.5 mm in each series. The samples were investigated using a ellectromagnetically driven dynamic impact tester. The tester operates at impact loads of 200 N, 400 N, and 600 N, which correspond to kinetic energies of 6.98 mJ/imp., 11.46 mJ/imp., and 17.42 mJ/imp., respectively. The impact frequency was set to 8 Hz. The impact indenter was a 5 mm tungsten carbide ball (Ceratizit CTF12E, with surface roughness G10 according to ISO 3290-1). Prior to each test, the indented ball was set to the same height and the ball itself was rotated so that it contacted the sample with the unworn side. The tested samples were subjected to all impact loads (i.e., 200 N, 400 N, and 600 N). Impact loads were utilised to devise a sequence of 1, 10, 100, 500, 1,000, 5,000, 10,000, 50,000, 100,000, and 250,000 impacts in x-y plane along the bead's length, both in the bead and overlap regions described in Fig. 2 . The impact load of 600 N was utilized in order to evaluate material isotropy in the plane of the sample surface. Each test condition (i.e., a given number of impacts at a specific impact load) was repeated multiple times to minimise random error. The testing of the reference substrate specimen (bare S355MC steel) involved only one series, as the in-plane anisotropy or structural inhomogeneity was not expected in bulk steel. The size and morphology of the impact craters were investigated with the Keyence VK-X 1100 laser confocal microscope. Volume of the impact craters was calculated as a rotational paraboloid [ 20 , 22 – 24 ]. The critical number of impacts, representing the impact lifetime, was estimated using the crater volume (including the variability of measured values) and crater dimensions according to Engel’s three-zone model [ 25 ]. In this model, the first zone corresponds to the initial deformation stage, during which the volume increases relatively rapidly as the number of impacts grows. This phase only lasts at the beginning of the process. After the first few to several dozen impacts, the system enters the second zone i.e. the zero wear zone. During this stage, the crater volume increases only slightly, and the energy delivered by the impact tester is dissipated within the material in other ways. Stress fields develop, gradually initiating the movement of material into pile-ups. The microstructure evolves under the influence of stress, which can lead to local hardening. Over time, an increasing proportion of the energy is dissipated through crack initiation and propagation. Once a critical number of impacts has been exceeded, the material can no longer withstand the incoming energy and undergoes impact fatigue. This process depends on the specimen being tested and may manifest as delamination, cohesive failure of the substrate, random material removal from the impact crater area, or uncontrolled crack propagation around the crater [ 20 , 24 – 27 ]. These processes result in a sudden increase in volume, marking the transition of the curve into the third zone. The chemical composition of the impact crater, as well as that of the non-impacted sample, was analysed using a scanning electron microscope FEI Magellan 400 XHR equipped with AMETEK EDAX Octane Elect Super energy-dispersive X-ray (EDX) detector for elemental analysis. 3. Results Figure 3 shows the cross-section of the ground hardfaced specimen in y-z plane. The clad beads have a casting microstructure. The different levels of etching might indicate varying dendrite spacing and different portions of eutectics, as the cooling rate varies within the bead and diffusion-related processes occur. The cladding exhibited a thickness of (1.74 ± 0.13) mm in the bead regions and a thickness of (1.00 ± 0.10) mm in regions of bead overlap. Black dots under the surface of the specimen are residual indents from the hardness measurement. The dark region under the clad bead represents the heat-affected zone, as was schematically shown in Fig. 2 . Prior to conducting the impact tests, hardness measurements were performed. Figure 4 presents the results of the hardness measured along y-axis in the x-y plane. Despite the presence of local inhomogeneities, which resulted in a scatter of values, no discernible trend appeared in the measurements. It can be stated that the hardness in the perpendicular direction fluctuated around a mean value of (369 ± 15) HV1. In the direction of specimen y-axis, eight impact tests were conducted under uniform conditions: an impact load of 600 N and a total of 10,000 impacts. These parameters were selected as they represent the maximum values at which the reference steel consistently yielded predictable results in repeated measurements (as discussed later). The number and spacing of the impact sites were chosen to prevent overlap of the impact-induced deformation zones around the craters. The resulting craters were labelled (a) to (h), as illustrated in Fig. 5 . Following the tests, the parameters of the craters were measured, and the crater volumes were calculated. A comparison of the crater volumes (see Fig. 5 a) revealed no significant trend; within the error margins, all craters exhibited comparable volumes. This similarity is further demonstrated in Fig. 5 b, which compares the selected crater profiles. For clarity, the comparison focuses on four representative craters, selected based on their positions: above a bead, above an overlap, between these two locations, and near the edge of the specimen. Figure 6 presents the crater from position (h) in Fig. 5 . A thorough observation of the crater reveals the presence of cracks on its outer periphery, specifically at the external edge of the pile-ups — the elevated, plastically deformed zones that envelop the crater rim. The pile-ups are also clearly visible in the profile comparison in Fig. 5 b. The occurrence of pile-ups can be attributed to the displacement of plastic material, a consequence of the progressive accumulation of shear stress that occurs during repeated impacts. The outward growth of the pile-ups induces tensile stresses on the outer rim of the crater [ 28 ]. This tensile stress is regarded as the most probable origin of the cracks observed in Fig. 6 . Similar cracks were present in several other craters. As is evident, cracks propagate along the dendrite boundaries. 3.2 Testing in positions “bead” and “overlap” As a preliminary step, hardness measurements were taken before the impact tests to ascertain potential differences between the bead and overlap positions. Figure 7 presents the results of the hardness measurement series for the bead and overlap positions in two different locations on the sample surface in x-y plane. No clear trend was evident in either position, with variability in hardness around the respective mean values. However, a discrepancy was observed between the measured means. As illustrated in Fig. 7 a, the bead position yielded a mean value of (367 ± 6) HV1, while the overlap position exhibited a slightly lower value of (357 ± 5) HV1. As illustrated in Fig. 7 b, comparable hardness values were obtained from the second location, with a range of (366 ± 10) HV1 in the bead position and (354 ± 5) HV1 in the overlap position. The hardness values measured in both positions were lower than those declared by the producer of the filler wire [ 29 ] and correspond to a relatively high level of dilution of the wire with the substrate material. The lower hardness of Stellite 6 produced by the GMAW hardfacing is consistent with the observations of other authors [ 2 , 30 ]. Although the hardness in the overlap position was lower than in both the bead position, this difference did not exceed 3% of the absolute value, which corresponds to the standard deviation measured within the one series. Moreover, the HV1 analysis revealed that the 9.81 N load resulted in an indentation depth of approximately 10–11 µm, as indicated by semi-empirical relationships derived from measured hardness [ 31 ]. This finding suggests that the observed variation in hardness is not attributable to the influence of the substrate, given that the substrate is situated at a depth at least 90 times greater than the indentation depth. The impact response of the Stellite 6 hardfacing layer was examined at two locations that were referred to as the bead and overlap positions. To evaluate this response, the relationship between crater volume and the number of impacts was analysed. This relationship is known as the loading curve. A comparison of loading curves obtained at both positions is shown in Fig. 8 . Figures 8 a, 8 b, and 8 c display the results for a load of 600 N, 400 N, and 200 N, respectively. This threezone distribution from Engel’s model is the most evident in the loading curve shown in Fig. 8 a. Both curves display firstzone behaviour up to ten impacts, after which they enter the second zone as the increase in impact crater volume slows down. This trend changes at around 5,000–10,000 impacts, when the crater volume starts to increase again. The expected impact resistance of GMAW hardfaced Stellite 6 on S355MC steel at 600 N lies within this range. As the impact load decreases, the transition to the third zone shifts towards higher numbers of impacts. For an impact load of 400 N, the critical number of impacts is around 10,000. For an impact load of 200 N, the critical number of impacts is unclear, but it is assumed to be greater than 50,000. Figure 8 shows that the crater volume after the first impact was approximately the same for both positions. However, from that point until the critical number of impacts was reached, the bead position exhibited slightly smaller crater volumes. This is because slightly smaller craters correspond to slightly higher hardness (see Fig. 7 a and 7 b), as higher material hardness results in lower deformation. The transition into the third zone is usually linked to the beginning of fatigue-related phenomena. In our case, however, no signs of fatigue, such as random crack propagation, crack networks surrounding the impact crater, or adhesive and cohesive failure, were observed. Therefore, the critical number of impacts was estimated based solely on the point at which a sharp increase in crater volume was first detected relative to the number of impacts. To refine this estimate, we also considered the values corresponding to the sudden growth in crater depth and diameter, since these parameters exhibit a similar trend to crater volume with increasing impact repetitions. Figure 9 shows an example of the evolution of crater depth and diameter with the number of impacts at a load of 600 N. Similar trends were observed for loads of 400 N and 200 N, but these are not displayed here for clarity. In addition to the bead and overlap positions, Fig. 9 a compares the crater depth on reference S355MC steel, and Fig. 9 b presents the evolution of crater diameters for all three samples. The estimated critical number of impacts is summarised in Table 1 . The overview shows that the dynamic impact lifetime was essentially identical in both positions. The only difference observed was at an impact load of 400 N, which is most likely due to sample inhomogeneities. However, as the values lie within the observed variability of the data, we consider them to be essentially the same. Furthermore, at all three impact load levels, the number of impacts corresponding to the onset of the sharp increase in crater size was higher than for the S355MC steel reference sample. Table 1 Critical number of impacts. 200 N 400 N 600 N Bead 80,000 ± 3,000 41,000 ± 3,000 10,000 ± 500 Overlap 80,000 ± 3,000 43,000 ± 3,000 10,000 ± 500 S355MC steel 45,000 ± 3,000 15,000 ± 1,500 8,000 ± 1,000 Figure 10 shows an example of impact craters corresponding to 100, 1,000, 10,000, and 100,000 impacts. For simplicity, only craters formed under an impact load of 600 N are shown. Figure 10 a shows impact craters from the bead position and Fig. 10 b shows craters from the overlap position. Figure 10 c depicts a series of craters produced under identical conditions on S355MC steel without a Stellite 6 hardfacing layer. Based on the images, the craters formed in the hardfaced sample from both positions were essentially the same. However, those formed in the uncoated steel substrate exhibited significantly greater deformation. This difference became more pronounced with increasing numbers of impacts and was most apparent at 100,000 impacts. Although the impact craters in the two examined locations appear visually similar and have similar parameters, e.g., 1,000 impacts at 600 N, they differ slightly in shape. As previously mentioned, the profile of the impact craters is that of a rotational paraboloid. This is due to imperfect plastic deformation. The Stellite 6 hardfacing layer on S355MC steel exhibits a non-zero component of elastic deformation. Furthermore, during unloading, the deformed material relaxes, and the residual stresses and the stresses that caused the transport of material into pile-ups influence the flow of material within the impact crater. To achieve a clearer and more rigorous quantification of these effects, a new parameter is introduced - the ratio of the actual crater volume (a rotational paraboloid) to the volume of an ideal spherical cap. This new parameter is denoted as Impact Volume Ratio (IVR). The closer the IVR is to one, the greater the plastic deformation exhibited by the sample upon impact, and the smaller the amounts of elasticity and material transported to pile-ups, as well as residual stress accumulation. Conversely, a lower IVR indicates less plastic deformation, as well as higher elasticity and material displacement. Figure 11 shows a comparison of the calculated IVR for the bead (red) and overlap (black) positions. The graphs also show the IVR results for the non-hardfaced S355MC steel sample (blue). At impact loads of 200 N (Fig. 11 a) and 400 N (Fig. 11 b), the sample exhibited a similar IVR value in both the bead and overlap positions. Furthermore, the IVR values calculated for the non-hardfaced steel at a load of 200 N were the same as those for the steel hardfaced by Stellite 6. A completely different situation was observed at an impact load of 600 N (Fig. 11 c). In this case, the behaviour of all three samples was different. The IVR calculated from the impact craters in the bead position remained almost unchanged from 1 to 250,000 impacts. The average IVR value in bead position was 0.41, varying only within a range of ± 10%. Conversely, the IVR value in the overlap position initially increased from 0.42 to a maximum of 0.55 with 100–1,000 impacts. After that, the IVR values decreased to values similar to those in the bead position. Finally, the IVR of the steel sample increased monotonically with the number of impacts, rising from 0.33 to 0.61. Some of the impact craters shown in Fig. 10 exhibit dark patches on the surface. A thorough analysis of these patches revealed that they are, in fact, isolated tribolayers. Initially, tribolayers formed as isolated patches following approximately 5,000–10,000 impacts. As the number of impacts increased, these patches merged to form continuous areas. These tribolayers are believed to form in regions where the movement of the impact ball induces friction and results in localised heating of the surface. This process can be further intensified by microscopic grains of material released from the sample during impact, which act as an abrasive. Figure 12 shows the chemical analysis of the tribo-layer. The analysis was performed on an impact crater in bead position resulting from 250,000 impacts at an impact load of 200 N. Figure 12 shows a detailed view of the tribolayer on the surface of such a crater. Two areas analysed by EDX are marked in the figure. The tribolayer at the base of the impact crater is denoted as position 1, while the crater's surface is denoted as position 2. The results corresponding to both positions are displayed below. 4. Discussion Minor differences in mechanical properties above the bead and overlap positions resulted in distinct deformations under repeated impact loading. These deformations were manifested in a divergent evolution of the parameter, designated as IVR. The impact volume ratio (IVR) parameter indicates the extent to which actual deformation deviates from ideal plastic deformation. In an ideal scenario, IVR would be equal to one and only a plastic deformation would occur. However, the real deformation of the impact crater comprises a combination of elastic recovery, material creep, and strain hardening, as well as the possible formation of tribolayers on the crater surface and material transport leading to pile-up formation, among other mass transports caused by residual stress [ 22 , 28 ]. The extent to which these parameters occur is indicative of the degree to which IVR is less than one. The observed difference in the IVR between overlap and bead positions at an impact load of 600 N (see Fig. 11 c) was likely caused by the lower hardness in the overlap region. According to the basic definition, hardness is the resistance of a material to plastic deformation; therefore, lower hardness leads to greater plastic deformation and, accordingly, to an increased IVR. Lin et al. [ 2 ] observed slightly lower hardness in the position over the overlap of the beads. This was discussed as a result of the difference in the cooling process, and thus in the grain size, in the area over the bead overlap. Furthermore, lower hardness may be related to iron dilution during deposition [ 2 ]. It is assumed that the combination of these phenomena will be most pronounced at greater depths, near the interface between the hardfacing Stellite 6 and the steel substrate. Therefore, differences in IVR related to hardness were only observed in analyses with the highest interaction volume, i.e., an impact load of 600 N; lower impact loads of 400 N and 200 N were influenced by iron dilution and grain size differences to a much lesser extent, resulting in minimal IVR differences (see Figs. 11 a and 11 b). Another parameter that influences IVR is the formation of tribolayer on the impact crater surface. As was shown in Fig. 12 , the tribolayer exhibited a noticeable amount of oxygen, consistent with an oxidic composition. Some authors attribute improved wear resistance to analogous oxide tribolayers, and these might even serve as a protective coating [ 10 , 24 , 32 , 33 ]. In comparison with non-oxidised surfaces, the oxidic tribolayer exhibited higher hardness but also higher brittleness [ 24 ]. The brittle behaviour of the oxide tribolayer in Fig. 12 is apparently the leading cause of the visible cracks. Figure 10 shows that impact craters formed by a higher number of impacts exhibited the formation of oxidic tribolayers. In the steel samples, these tribolayers tend to form preferentially at the centre of the impact craters. In the case of the hardfacing Stellite 6, tribolayer areas were observed to be evenly distributed across the entire impact crater, rather than primarily in the centre, as was the case with the steel sample. This evenly distributed protective tribolayer slows down further deformation more effectively than a protective tribolayer primarily distributed in the centre of the impact crater. This, coupled with the higher hardness of Stellite 6, is the primary reason why the hardfaced layer showed lower deformation and a smaller IVR than the steel substrate even after exceeding the critical number of impacts (see Fig. 11 ). Figure 10 thus confirms that the Stellite 6 hardfacing layer provides mechanical protection to S355MC steel under repeated dynamic loading. Comparing the impact life of wire arc cladded Stellite 6 with that of Stellite 6 prepared by the HVOF method and of comparable thickness reveals that the former has a longer impact life. Daniel et al. reported lower impact lifetimes for HVOF coatings—approximately 8,000 impacts at 400 N and 4,000 impacts at 200 N [ 20 ]—whereas our GMAW hardfacing layer endured longer under the same loading conditions. Even when the highest possible impact rates were applied, only visible cracks were observed outside the crater rim. Those cracks were probably caused by tensile stress induced by the pile-up growth. This distinguishes Stellite 6 hardfaced by GMAW from Stellite 6 samples with similar loadings that were prepared using other methods. Samples prepared by thermal spraying exhibited substantial cracking [ 20 ]. Furthermore, cracks were also observed in thicker Stellite 6 samples that were welded using the GTAW method [ 21 ]. Although minor local differences in IVR and deformation mechanisms—primarily associated with reduced hardness and variations in tribolayer development—were observed between the bead and overlap positions, these differences did not translate into a measurable difference in impact lifetime within the sensitivity of the present tests. On this basis, the Stellite 6 hardfacing layer produced by GMAW can be regarded as providing comparable macroscopic protection against repeated impact loading in both positions, and the overall impact response may therefore be considered effectively isotropic within the plane of the surface under the tested conditions. 5. Conclusion The hardness and dynamic impact resistance of the Stellite 6 layer deposited on S355MC steel substrate were investigated. Both tests were performed on the polished surface at positions of beads and their overlaps to evaluate the possible effect of bead remelting on the local mechanical properties of the layer. Marginally lower hardness was observed in the area of bead overlaps. From an impact behaviour standpoint, these phenomena affected the deformation of impact craters. It appears that the formation of a tribological oxide layer on the surface of the craters also played a significant role in repeated impact loading, which was most noticeable when comparing the cladding layer with the steel substrate. Despite these differences, it was found that the impact lifetime remained the same in both positions, even under several impact loads. Impact testing confirmed that the Stellite 6 hardfacing layer on S355MC steel component is in-plane isotropic and its presence significantly increases the component's impact lifetime. Declarations Author Contribution J.D. - impact testing and optical microscopy analysis, H. Š. - mechanical properties and electron microscopy analysis, L.M. - sample preparation; all authors discussed results and contributed to the manuscript preparation. 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Wear 250(1–12):391–400. https://doi.org/10.1016/S0043-1648(01)00601-9 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Published Journal Publication published 17 Mar, 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. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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08:40:21","extension":"xml","order_by":84,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":104673,"visible":true,"origin":"","legend":"","description":"","filename":"c44bdd4cc3614ba0a0fec8016edad0fa1structuring.xml","url":"https://assets-eu.researchsquare.com/files/rs-8156643/v1/91c64e249eb1535544eeb40a.xml"},{"id":97227651,"identity":"7ffe3dd3-69d3-4685-829d-f5a41a9c1287","added_by":"auto","created_at":"2025-12-02 08:40:21","extension":"html","order_by":85,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":114096,"visible":true,"origin":"","legend":"","description":"","filename":"earlyproof.html","url":"https://assets-eu.researchsquare.com/files/rs-8156643/v1/1ec811398aaf43257ed6ccc6.html"},{"id":97250302,"identity":"f9728d27-3b26-45c7-9f4d-5c34ac2c0a8c","added_by":"auto","created_at":"2025-12-02 13:14:13","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":148414,"visible":true,"origin":"","legend":"\u003cp\u003eThe scheme of the experimental setup\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-8156643/v1/24eb20e831e0071be2282d48.png"},{"id":97227550,"identity":"0e502e06-0780-4a1f-8569-3f6e9d6d83a1","added_by":"auto","created_at":"2025-12-02 08:40:15","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":275990,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic of the deposited layers with designated measurement regions\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-8156643/v1/4c4e26cb777da15cfcc0ae22.png"},{"id":97227554,"identity":"531ca20e-d781-4f0c-8407-5f040ae0bb14","added_by":"auto","created_at":"2025-12-02 08:40:15","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":377486,"visible":true,"origin":"","legend":"\u003cp\u003eThe macrostructure of the cladding's cross-section with indicated investigated regions\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-8156643/v1/8947b7f93ade194f5962caa3.png"},{"id":97227547,"identity":"380bbff8-47a7-463f-a335-b3363190d4db","added_by":"auto","created_at":"2025-12-02 08:40:14","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":61455,"visible":true,"origin":"","legend":"\u003cp\u003eVickers hardness along the y-axis\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-8156643/v1/cc4ea993572b31357985c651.png"},{"id":97227562,"identity":"b57aed19-874b-4382-a760-e48d44fd3d18","added_by":"auto","created_at":"2025-12-02 08:40:16","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":257659,"visible":true,"origin":"","legend":"\u003cp\u003eComparison of (a) the volumes and (b) profiles of the impact crater in the perpendicular direction\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-8156643/v1/113bb17a0813745a844a02c7.png"},{"id":97250477,"identity":"941af087-10d9-4f8f-8dea-83a2b55e1542","added_by":"auto","created_at":"2025-12-02 13:14:35","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":847462,"visible":true,"origin":"","legend":"\u003cp\u003eDetail view of the cracking outside the impact crater from the Position (h) in Figure 5\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-8156643/v1/9438c70ed4dc0f8cb71d0023.png"},{"id":97250948,"identity":"3b54f3f9-2891-42bf-93e3-ced364b89081","added_by":"auto","created_at":"2025-12-02 13:15:40","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":122208,"visible":true,"origin":"","legend":"\u003cp\u003eVickers hardness of bead and overlap series measured in x-y plane at two different locations (a, b) of the sample\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-8156643/v1/ee1dae3a4508536e2232515a.png"},{"id":97227558,"identity":"ac9949ba-c59b-4ef2-ae37-d7c051b288c3","added_by":"auto","created_at":"2025-12-02 08:40:16","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":184501,"visible":true,"origin":"","legend":"\u003cp\u003eComparison of load curves of the positions bead and overlap under the impact load of (a) 600 N, (b) 400 N, and (c) 200 N\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-8156643/v1/f41c37e8db8d9b344daf754e.png"},{"id":97251350,"identity":"e146ab5d-e3f5-44db-a167-5d4de2675bcf","added_by":"auto","created_at":"2025-12-02 13:16:50","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":188823,"visible":true,"origin":"","legend":"\u003cp\u003eComparison of the evolution of the impact crater (a) depth and (b) diameter of the cladding at the positions bead (red) and overlap (black), and of the S355MC steel substrate (blue), all after the impact with a load of 600 N. Dotted lines serve as an eye guide\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-8156643/v1/7cac92d49967f6200c084e5c.png"},{"id":97250084,"identity":"0a0bc004-5db4-4b05-9d5f-69a21d105070","added_by":"auto","created_at":"2025-12-02 13:13:54","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":692410,"visible":true,"origin":"","legend":"\u003cp\u003eComparison of impact craters from series bead (a) and overlap (b). For comparison impact craters from steel S355MC (c)\u003c/p\u003e","description":"","filename":"10.png","url":"https://assets-eu.researchsquare.com/files/rs-8156643/v1/068b374247b291f5330d3a71.png"},{"id":97250214,"identity":"584240a3-0450-4d51-8296-79cd776ee81e","added_by":"auto","created_at":"2025-12-02 13:14:06","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":184371,"visible":true,"origin":"","legend":"\u003cp\u003eComparison of impact volume ratio (IVR) calculated for the position bead (red), overlap (black), and for the S355MC steel (blue). The impact loads of 600 N (a), 400 N (b), and 200 N (c). Dotted lines serve as an eye guide\u003c/p\u003e","description":"","filename":"11.png","url":"https://assets-eu.researchsquare.com/files/rs-8156643/v1/13b16ae56337a04441637b62.png"},{"id":97250063,"identity":"7380f01c-e740-41df-a7a8-0c23805feb77","added_by":"auto","created_at":"2025-12-02 13:13:50","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":362113,"visible":true,"origin":"","legend":"\u003cp\u003eDetail view of the oxidic tribo-layer on the impact crater with marked places of EDX analysis and measured EDX spectra\u003c/p\u003e","description":"","filename":"12.png","url":"https://assets-eu.researchsquare.com/files/rs-8156643/v1/fc9ede91597173f7332ffdf9.png"},{"id":105224167,"identity":"53c69c52-7669-405c-82b8-a9038f66d166","added_by":"auto","created_at":"2026-03-23 16:12:56","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3925044,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8156643/v1/1c1cd6c7-92d3-440c-86ae-8d547f737f08.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Repeated Impact Resistance of Stellite 6 Hardfacing Layer Produced by Gas Metal Arc Welding","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eHardfacing by gas metal arc welding (GMAW) is a highly productive additive manufacturing technique well-suited for depositing relatively thick layers of material. The process, which utilizes gas metal arc welding technology, employs the heat generated by the arc to melt the filler wire and the surface of a component (substrate), thereby forming a clad bead. Successive, partially overlapping beads create a uniform layer, and multiple layers can be deposited to achieve the required thickness or to control the level of dilution. As the GMAW hardfacing is a specific instance of Wire Arc Additive Manufacturing (WAAM), some authors use the terms interchangeably [\u003cspan additionalcitationids=\"CR2 CR3\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eOne of the key hardfacing materials processed by GMAW is the alloy Stellite 6 [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. This cobalt\u0026ndash;chromium superalloy is well known for its exceptional wear resistance, corrosion resistance, and thermal stability [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan additionalcitationids=\"CR7\" citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. The Stellite 6 is cobalt-based alloy; cobalt and chromium form cobalt\u0026ndash;chromium dendrites, within which interdendritic carbides such as Cr\u003csub\u003e7\u003c/sub\u003eC\u003csub\u003e3\u003c/sub\u003e, Cr\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003e, and Co\u0026ndash;W\u0026ndash;C are found [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. These carbides give Stellite 6 its high hardness and resistance to mechanical loading. However, the carbide network also results in reduced fracture toughness, and the alloy tends to be prone to localized defects. For this reason, it is not suitable for fabricating bulk components [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. Instead, Stellite 6 is primarily used in powder or wire form as a hardfacing material for surface treatments, such as plasma spraying, laser metal deposition, or GMAW [\u003cspan additionalcitationids=\"CR13 CR14 CR15 CR16\" citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eIn GMAW hardfacing, Stellite 6 is applied in a wire form. When wire is deposited via an electric arc, the Stellite 6 material becomes diluted with the substrate material, leading to the formation of additional phases. Steel of various types is one of the most typical substrates [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. The resulting metallurgical bond between steel and Stellite 6 forms a multiphase alloy, where Stellite 6 incorporates iron and other elements from the steel substrate, while cobalt and chromium may diffuse into the steel [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. The structural complexity is further complicated by the deposition method itself, in which successive partially overlapping beads thermally influence each other. Variations in thermal history lead to distinct diffusion behavior, microstructural transformations, and the formation of metallurgical interfaces [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eWhen used as a hardfacing material, Stellite 6 is employed, for example, to enhance the surface properties of industrial turbines, pump impellers, engines, and similar moving parts [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. Throughout the operational process, numerous components are exposed to recurrent dynamic and impact loads. Although the impact resistance of Stellite 6 produced by various technologies, such as high-velocity oxygen fuel (HVOF) and gas tungsten arc welding (GTAW), has been studied [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e], no peer-reviewed research to date has addressed this property in Stellite 6 deposited by GMAW/WAAM. This gap is particularly relevant given the growing interest in GMAW hardfacing for manufacturing functional wear-resistant components that are exposed to repeated dynamic loading.\u003c/p\u003e\u003cp\u003eThe present study aims to address this gap by providing a comprehensive evaluation of the repeated impact resistance of wire-arc cladded Stellite 6 on steel substrate. The spatial variability research focuses on the influence of bead and bead-overlap regions, as well as the isotropy of the impact response within the plane of the surface. This research is supported by morphological, chemical, and mechanical analyses. The results obtained from this study contribute to a deeper understanding of the performance of GMAW-processed Stellite 6 in demanding operational conditions and provide insights for the optimisation of its application in critical industrial components.\u003c/p\u003e"},{"header":"2. Experimental","content":"\u003cp\u003eThe TPS 320i MIG/MAG source with WF60i Robacta Drive wire feeder (both from Fronius) was used in cold metal transfer (CMT) regime to melt the Co-based filler wire ALUNOX AX-FD Co6 (ERCCoCr-A, Stellite 6 equiv.) with a diameter of 1.2 mm. The ABB IRB 2400 robot holding the arc torch was employed to produce four 120 mm long linear overlapping beads with a 4 mm pitch on a ground 10 mm thick S355MC steel sheet substrate. The torch was angled at 30\u0026deg; from the substrate normal and pushed toward the melt pool. Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e presents the scheme of the experimental setup.\u003c/p\u003e\u003cp\u003eThe beads were deposited at a welding speed of 20 mm/s. The average feeding rate, arc current, voltage, and power were 8.3 m/min, 267 A, 17.4 V, and 5.05 kW, respectively. Due to the complexity of the CMT regime, the arc power is not a simple product of electric current and voltage. It continuously changes as high-current and low-current phases take turns, and the heat source calculates the average power over time. Pure argon at a flow rate of 18 l/min prevented oxidation of the melt pool.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eAfter deposition, the cladded sample was cut perpendicularly to the deposition direction (y-z plane), and together with a reference substrate specimen, it underwent metallographic treatment on an MTH device. The surface of the cladded sample was ground to eliminate waviness induced by multiple bead deposition. Both specimens were then polished in x-y plane to achieve a uniform surface finish. The arithmetic mean surface roughness Ra was determined in accordance with ISO 13565-1 using the Keyence VK-X 1100 laser confocal microscope and reached (0.10\u0026ndash;0.15) \u0026micro;m. The cross-section was polished and then etched with the Kalling 2 solution for 50 s to reveal the macrostructure and identify regions of interest for hardness and impact test measurements. Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e illustrates the cladded specimen with the designated measurement regions \u0026ldquo;bead\u0026rdquo; and \u0026ldquo;overlap\u0026rdquo; located above the cladding depth maxima and minima, respectively.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eVickers hardness of the machined surface was measured using the hardness tester Qness 60A\u0026thinsp;+\u0026thinsp;EVO at a load of 9.81 N. At first, two linear measurement series along the x-axis in x-y plane, each consisting of thirteen indents, were performed in both the bead and overlap regions identified in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. Due to the limited dimensions of the sample, hardness was measured at two different locations, each time in the same position relative to the bead and overlap. Then, a series of indents was made across all beads along the y-axis, 0.5 mm under the machined surface in y-z cross-section, located in the middle of the specimen length. The spacing of indents was 0.5 mm in each series.\u003c/p\u003e\u003cp\u003eThe samples were investigated using a ellectromagnetically driven dynamic impact tester. The tester operates at impact loads of 200 N, 400 N, and 600 N, which correspond to kinetic energies of 6.98 mJ/imp., 11.46 mJ/imp., and 17.42 mJ/imp., respectively. The impact frequency was set to 8 Hz. The impact indenter was a 5 mm tungsten carbide ball (Ceratizit CTF12E, with surface roughness G10 according to ISO 3290-1). Prior to each test, the indented ball was set to the same height and the ball itself was rotated so that it contacted the sample with the unworn side. The tested samples were subjected to all impact loads (i.e., 200 N, 400 N, and 600 N). Impact loads were utilised to devise a sequence of 1, 10, 100, 500, 1,000, 5,000, 10,000, 50,000, 100,000, and 250,000 impacts in x-y plane along the bead's length, both in the bead and overlap regions described in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. The impact load of 600 N was utilized in order to evaluate material isotropy in the plane of the sample surface. Each test condition (i.e., a given number of impacts at a specific impact load) was repeated multiple times to minimise random error. The testing of the reference substrate specimen (bare S355MC steel) involved only one series, as the in-plane anisotropy or structural inhomogeneity was not expected in bulk steel.\u003c/p\u003e\u003cp\u003eThe size and morphology of the impact craters were investigated with the Keyence VK-X 1100 laser confocal microscope. Volume of the impact craters was calculated as a rotational paraboloid [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e, \u003cspan additionalcitationids=\"CR23\" citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. The critical number of impacts, representing the impact lifetime, was estimated using the crater volume (including the variability of measured values) and crater dimensions according to Engel\u0026rsquo;s three-zone model [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. In this model, the first zone corresponds to the initial deformation stage, during which the volume increases relatively rapidly as the number of impacts grows. This phase only lasts at the beginning of the process. After the first few to several dozen impacts, the system enters the second zone i.e. the zero wear zone. During this stage, the crater volume increases only slightly, and the energy delivered by the impact tester is dissipated within the material in other ways. Stress fields develop, gradually initiating the movement of material into pile-ups. The microstructure evolves under the influence of stress, which can lead to local hardening. Over time, an increasing proportion of the energy is dissipated through crack initiation and propagation. Once a critical number of impacts has been exceeded, the material can no longer withstand the incoming energy and undergoes impact fatigue. This process depends on the specimen being tested and may manifest as delamination, cohesive failure of the substrate, random material removal from the impact crater area, or uncontrolled crack propagation around the crater [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e, \u003cspan additionalcitationids=\"CR25 CR26\" citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. These processes result in a sudden increase in volume, marking the transition of the curve into the third zone.\u003c/p\u003e\u003cp\u003eThe chemical composition of the impact crater, as well as that of the non-impacted sample, was analysed using a scanning electron microscope FEI Magellan 400 XHR equipped with AMETEK EDAX Octane Elect Super energy-dispersive X-ray (EDX) detector for elemental analysis.\u003c/p\u003e"},{"header":"3. Results","content":"\u003cp\u003eFigure \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e shows the cross-section of the ground hardfaced specimen in y-z plane. The clad beads have a casting microstructure. The different levels of etching might indicate varying dendrite spacing and different portions of eutectics, as the cooling rate varies within the bead and diffusion-related processes occur. The cladding exhibited a thickness of (1.74\u0026thinsp;\u0026plusmn;\u0026thinsp;0.13) mm in the bead regions and a thickness of (1.00\u0026thinsp;\u0026plusmn;\u0026thinsp;0.10) mm in regions of bead overlap. Black dots under the surface of the specimen are residual indents from the hardness measurement. The dark region under the clad bead represents the heat-affected zone, as was schematically shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003ePrior to conducting the impact tests, hardness measurements were performed. Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e presents the results of the hardness measured along y-axis in the x-y plane. Despite the presence of local inhomogeneities, which resulted in a scatter of values, no discernible trend appeared in the measurements. It can be stated that the hardness in the perpendicular direction fluctuated around a mean value of (369\u0026thinsp;\u0026plusmn;\u0026thinsp;15) HV1.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eIn the direction of specimen y-axis, eight impact tests were conducted under uniform conditions: an impact load of 600 N and a total of 10,000 impacts. These parameters were selected as they represent the maximum values at which the reference steel consistently yielded predictable results in repeated measurements (as discussed later). The number and spacing of the impact sites were chosen to prevent overlap of the impact-induced deformation zones around the craters. The resulting craters were labelled (a) to (h), as illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e.\u003c/p\u003e\u003cp\u003eFollowing the tests, the parameters of the craters were measured, and the crater volumes were calculated. A comparison of the crater volumes (see Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea) revealed no significant trend; within the error margins, all craters exhibited comparable volumes. This similarity is further demonstrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb, which compares the selected crater profiles. For clarity, the comparison focuses on four representative craters, selected based on their positions: above a bead, above an overlap, between these two locations, and near the edge of the specimen.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e presents the crater from position (h) in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e. A thorough observation of the crater reveals the presence of cracks on its outer periphery, specifically at the external edge of the pile-ups \u0026mdash; the elevated, plastically deformed zones that envelop the crater rim. The pile-ups are also clearly visible in the profile comparison in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb. The occurrence of pile-ups can be attributed to the displacement of plastic material, a consequence of the progressive accumulation of shear stress that occurs during repeated impacts. The outward growth of the pile-ups induces tensile stresses on the outer rim of the crater [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. This tensile stress is regarded as the most probable origin of the cracks observed in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e. Similar cracks were present in several other craters. As is evident, cracks propagate along the dendrite boundaries.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003e3.2 Testing in positions \u0026ldquo;bead\u0026rdquo; and \u0026ldquo;overlap\u0026rdquo;\u003c/h2\u003e\u003cp\u003eAs a preliminary step, hardness measurements were taken before the impact tests to ascertain potential differences between the bead and overlap positions. Figure\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e presents the results of the hardness measurement series for the bead and overlap positions in two different locations on the sample surface in x-y plane. No clear trend was evident in either position, with variability in hardness around the respective mean values. However, a discrepancy was observed between the measured means. As illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ea, the bead position yielded a mean value of (367\u0026thinsp;\u0026plusmn;\u0026thinsp;6) HV1, while the overlap position exhibited a slightly lower value of (357\u0026thinsp;\u0026plusmn;\u0026thinsp;5) HV1. As illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eb, comparable hardness values were obtained from the second location, with a range of (366\u0026thinsp;\u0026plusmn;\u0026thinsp;10) HV1 in the bead position and (354\u0026thinsp;\u0026plusmn;\u0026thinsp;5) HV1 in the overlap position.\u003c/p\u003e\u003cp\u003eThe hardness values measured in both positions were lower than those declared by the producer of the filler wire [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e] and correspond to a relatively high level of dilution of the wire with the substrate material. The lower hardness of Stellite 6 produced by the GMAW hardfacing is consistent with the observations of other authors [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e].\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eAlthough the hardness in the overlap position was lower than in both the bead position, this difference did not exceed 3% of the absolute value, which corresponds to the standard deviation measured within the one series. Moreover, the HV1 analysis revealed that the 9.81 N load resulted in an indentation depth of approximately 10\u0026ndash;11 \u0026micro;m, as indicated by semi-empirical relationships derived from measured hardness [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]. This finding suggests that the observed variation in hardness is not attributable to the influence of the substrate, given that the substrate is situated at a depth at least 90 times greater than the indentation depth.\u003c/p\u003e\u003cp\u003eThe impact response of the Stellite 6 hardfacing layer was examined at two locations that were referred to as the bead and overlap positions. To evaluate this response, the relationship between crater volume and the number of impacts was analysed. This relationship is known as the loading curve. A comparison of loading curves obtained at both positions is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e. Figures\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003ea, \u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003eb, and \u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003ec display the results for a load of 600 N, 400 N, and 200 N, respectively.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThis threezone distribution from Engel\u0026rsquo;s model is the most evident in the loading curve shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003ea. Both curves display firstzone behaviour up to ten impacts, after which they enter the second zone as the increase in impact crater volume slows down. This trend changes at around 5,000\u0026ndash;10,000 impacts, when the crater volume starts to increase again. The expected impact resistance of GMAW hardfaced Stellite 6 on S355MC steel at 600 N lies within this range. As the impact load decreases, the transition to the third zone shifts towards higher numbers of impacts. For an impact load of 400 N, the critical number of impacts is around 10,000. For an impact load of 200 N, the critical number of impacts is unclear, but it is assumed to be greater than 50,000.\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e shows that the crater volume after the first impact was approximately the same for both positions. However, from that point until the critical number of impacts was reached, the bead position exhibited slightly smaller crater volumes. This is because slightly smaller craters correspond to slightly higher hardness (see Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ea and \u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eb), as higher material hardness results in lower deformation.\u003c/p\u003e\u003cp\u003eThe transition into the third zone is usually linked to the beginning of fatigue-related phenomena. In our case, however, no signs of fatigue, such as random crack propagation, crack networks surrounding the impact crater, or adhesive and cohesive failure, were observed. Therefore, the critical number of impacts was estimated based solely on the point at which a sharp increase in crater volume was first detected relative to the number of impacts. To refine this estimate, we also considered the values corresponding to the sudden growth in crater depth and diameter, since these parameters exhibit a similar trend to crater volume with increasing impact repetitions. Figure\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e shows an example of the evolution of crater depth and diameter with the number of impacts at a load of 600 N. Similar trends were observed for loads of 400 N and 200 N, but these are not displayed here for clarity. In addition to the bead and overlap positions, Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003ea compares the crater depth on reference S355MC steel, and Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003eb presents the evolution of crater diameters for all three samples.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe estimated critical number of impacts is summarised in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. The overview shows that the dynamic impact lifetime was essentially identical in both positions. The only difference observed was at an impact load of 400 N, which is most likely due to sample inhomogeneities. However, as the values lie within the observed variability of the data, we consider them to be essentially the same. Furthermore, at all three impact load levels, the number of impacts corresponding to the onset of the sharp increase in crater size was higher than for the S355MC steel reference sample.\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\u003eCritical number of impacts.\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"4\"\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\u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003e200 N\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003e400 N\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003e600 N\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eBead\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e\u003cp\u003e80,000\u0026thinsp;\u0026plusmn;\u0026thinsp;3,000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e\u003cp\u003e41,000\u0026thinsp;\u0026plusmn;\u0026thinsp;3,000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e\u003cp\u003e10,000\u0026thinsp;\u0026plusmn;\u0026thinsp;500\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eOverlap\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e\u003cp\u003e80,000\u0026thinsp;\u0026plusmn;\u0026thinsp;3,000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e\u003cp\u003e43,000\u0026thinsp;\u0026plusmn;\u0026thinsp;3,000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e\u003cp\u003e10,000\u0026thinsp;\u0026plusmn;\u0026thinsp;500\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eS355MC steel\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e\u003cp\u003e45,000\u0026thinsp;\u0026plusmn;\u0026thinsp;3,000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e\u003cp\u003e15,000\u0026thinsp;\u0026plusmn;\u0026thinsp;1,500\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e\u003cp\u003e8,000\u0026thinsp;\u0026plusmn;\u0026thinsp;1,000\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\u003eFigure \u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e shows an example of impact craters corresponding to 100, 1,000, 10,000, and 100,000 impacts. For simplicity, only craters formed under an impact load of 600 N are shown. Figure\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003ea shows impact craters from the bead position and Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003eb shows craters from the overlap position. Figure\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003ec depicts a series of craters produced under identical conditions on S355MC steel without a Stellite 6 hardfacing layer. Based on the images, the craters formed in the hardfaced sample from both positions were essentially the same. However, those formed in the uncoated steel substrate exhibited significantly greater deformation. This difference became more pronounced with increasing numbers of impacts and was most apparent at 100,000 impacts.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eAlthough the impact craters in the two examined locations appear visually similar and have similar parameters, e.g., 1,000 impacts at 600 N, they differ slightly in shape. As previously mentioned, the profile of the impact craters is that of a rotational paraboloid. This is due to imperfect plastic deformation. The Stellite 6 hardfacing layer on S355MC steel exhibits a non-zero component of elastic deformation. Furthermore, during unloading, the deformed material relaxes, and the residual stresses and the stresses that caused the transport of material into pile-ups influence the flow of material within the impact crater.\u003c/p\u003e\u003cp\u003eTo achieve a clearer and more rigorous quantification of these effects, a new parameter is introduced - the ratio of the actual crater volume (a rotational paraboloid) to the volume of an ideal spherical cap. This new parameter is denoted as Impact Volume Ratio (IVR). The closer the IVR is to one, the greater the plastic deformation exhibited by the sample upon impact, and the smaller the amounts of elasticity and material transported to pile-ups, as well as residual stress accumulation. Conversely, a lower IVR indicates less plastic deformation, as well as higher elasticity and material displacement.\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e shows a comparison of the calculated IVR for the bead (red) and overlap (black) positions. The graphs also show the IVR results for the non-hardfaced S355MC steel sample (blue). At impact loads of 200 N (Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003ea) and 400 N (Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003eb), the sample exhibited a similar IVR value in both the bead and overlap positions. Furthermore, the IVR values calculated for the non-hardfaced steel at a load of 200 N were the same as those for the steel hardfaced by Stellite 6. A completely different situation was observed at an impact load of 600 N (Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003ec). In this case, the behaviour of all three samples was different. The IVR calculated from the impact craters in the bead position remained almost unchanged from 1 to 250,000 impacts. The average IVR value in bead position was 0.41, varying only within a range of \u0026plusmn;\u0026thinsp;10%. Conversely, the IVR value in the overlap position initially increased from 0.42 to a maximum of 0.55 with 100\u0026ndash;1,000 impacts. After that, the IVR values decreased to values similar to those in the bead position. Finally, the IVR of the steel sample increased monotonically with the number of impacts, rising from 0.33 to 0.61.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eSome of the impact craters shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e exhibit dark patches on the surface. A thorough analysis of these patches revealed that they are, in fact, isolated tribolayers. Initially, tribolayers formed as isolated patches following approximately 5,000\u0026ndash;10,000 impacts. As the number of impacts increased, these patches merged to form continuous areas. These tribolayers are believed to form in regions where the movement of the impact ball induces friction and results in localised heating of the surface. This process can be further intensified by microscopic grains of material released from the sample during impact, which act as an abrasive.\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e shows the chemical analysis of the tribo-layer. The analysis was performed on an impact crater in bead position resulting from 250,000 impacts at an impact load of 200 N. Figure\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e shows a detailed view of the tribolayer on the surface of such a crater. Two areas analysed by EDX are marked in the figure. The tribolayer at the base of the impact crater is denoted as position 1, while the crater's surface is denoted as position 2. The results corresponding to both positions are displayed below.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e"},{"header":"4. Discussion","content":"\u003cp\u003eMinor differences in mechanical properties above the bead and overlap positions resulted in distinct deformations under repeated impact loading. These deformations were manifested in a divergent evolution of the parameter, designated as IVR. The impact volume ratio (IVR) parameter indicates the extent to which actual deformation deviates from ideal plastic deformation. In an ideal scenario, IVR would be equal to one and only a plastic deformation would occur. However, the real deformation of the impact crater comprises a combination of elastic recovery, material creep, and strain hardening, as well as the possible formation of tribolayers on the crater surface and material transport leading to pile-up formation, among other mass transports caused by residual stress [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. The extent to which these parameters occur is indicative of the degree to which IVR is less than one.\u003c/p\u003e\u003cp\u003eThe observed difference in the IVR between overlap and bead positions at an impact load of 600 N (see Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003ec) was likely caused by the lower hardness in the overlap region. According to the basic definition, hardness is the resistance of a material to plastic deformation; therefore, lower hardness leads to greater plastic deformation and, accordingly, to an increased IVR. Lin et al. [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e] observed slightly lower hardness in the position over the overlap of the beads. This was discussed as a result of the difference in the cooling process, and thus in the grain size, in the area over the bead overlap. Furthermore, lower hardness may be related to iron dilution during deposition [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. It is assumed that the combination of these phenomena will be most pronounced at greater depths, near the interface between the hardfacing Stellite 6 and the steel substrate. Therefore, differences in IVR related to hardness were only observed in analyses with the highest interaction volume, i.e., an impact load of 600 N; lower impact loads of 400 N and 200 N were influenced by iron dilution and grain size differences to a much lesser extent, resulting in minimal IVR differences (see Figs.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003ea and \u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003eb).\u003c/p\u003e\u003cp\u003eAnother parameter that influences IVR is the formation of tribolayer on the impact crater surface. As was shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e, the tribolayer exhibited a noticeable amount of oxygen, consistent with an oxidic composition. Some authors attribute improved wear resistance to analogous oxide tribolayers, and these might even serve as a protective coating [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e, \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]. In comparison with non-oxidised surfaces, the oxidic tribolayer exhibited higher hardness but also higher brittleness [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. The brittle behaviour of the oxide tribolayer in Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e is apparently the leading cause of the visible cracks.\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e shows that impact craters formed by a higher number of impacts exhibited the formation of oxidic tribolayers. In the steel samples, these tribolayers tend to form preferentially at the centre of the impact craters. In the case of the hardfacing Stellite 6, tribolayer areas were observed to be evenly distributed across the entire impact crater, rather than primarily in the centre, as was the case with the steel sample. This evenly distributed protective tribolayer slows down further deformation more effectively than a protective tribolayer primarily distributed in the centre of the impact crater. This, coupled with the higher hardness of Stellite 6, is the primary reason why the hardfaced layer showed lower deformation and a smaller IVR than the steel substrate even after exceeding the critical number of impacts (see Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e thus confirms that the Stellite 6 hardfacing layer provides mechanical protection to S355MC steel under repeated dynamic loading. Comparing the impact life of wire arc cladded Stellite 6 with that of Stellite 6 prepared by the HVOF method and of comparable thickness reveals that the former has a longer impact life. Daniel et al. reported lower impact lifetimes for HVOF coatings\u0026mdash;approximately 8,000 impacts at 400 N and 4,000 impacts at 200 N [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]\u0026mdash;whereas our GMAW hardfacing layer endured longer under the same loading conditions. Even when the highest possible impact rates were applied, only visible cracks were observed outside the crater rim. Those cracks were probably caused by tensile stress induced by the pile-up growth. This distinguishes Stellite 6 hardfaced by GMAW from Stellite 6 samples with similar loadings that were prepared using other methods. Samples prepared by thermal spraying exhibited substantial cracking [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. Furthermore, cracks were also observed in thicker Stellite 6 samples that were welded using the GTAW method [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eAlthough minor local differences in IVR and deformation mechanisms\u0026mdash;primarily associated with reduced hardness and variations in tribolayer development\u0026mdash;were observed between the bead and overlap positions, these differences did not translate into a measurable difference in impact lifetime within the sensitivity of the present tests. On this basis, the Stellite 6 hardfacing layer produced by GMAW can be regarded as providing comparable macroscopic protection against repeated impact loading in both positions, and the overall impact response may therefore be considered effectively isotropic within the plane of the surface under the tested conditions.\u003c/p\u003e"},{"header":"5. Conclusion","content":"\u003cp\u003eThe hardness and dynamic impact resistance of the Stellite 6 layer deposited on S355MC steel substrate were investigated. Both tests were performed on the polished surface at positions of beads and their overlaps to evaluate the possible effect of bead remelting on the local mechanical properties of the layer. Marginally lower hardness was observed in the area of bead overlaps. From an impact behaviour standpoint, these phenomena affected the deformation of impact craters. It appears that the formation of a tribological oxide layer on the surface of the craters also played a significant role in repeated impact loading, which was most noticeable when comparing the cladding layer with the steel substrate.\u003c/p\u003e\u003cp\u003eDespite these differences, it was found that the impact lifetime remained the same in both positions, even under several impact loads. Impact testing confirmed that the Stellite 6 hardfacing layer on S355MC steel component is in-plane isotropic and its presence significantly increases the component's impact lifetime.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eJ.D. - impact testing and optical microscopy analysis, H. Š. - mechanical properties and electron microscopy analysis, L.M. - sample preparation; all authors discussed results and contributed to the manuscript preparation.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eThis work was co-funded by the European Union and the state budget of the Czech Republic under the project LasApp CZ.02.01.01/00/22_008/0004573. 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However, the manufacturing of components from Stellite 6 is challenging due to the alloy's high hardness and poor machinability. Hardfacing of enhancing layers on components made from a material with superior machinability and/or more desirable bulk properties has been identified as an effective solution to Stellite 6 manufacturing limitations. The advantages of hardfacing by gas metal arc welding include high deposition rates, cost-effectiveness, and the capability to fabricate large-area structures. Recent studies have characterised Stellite 6 produced by this method in terms of its resistance to external thermal, chemical, or certain mechanical factors. However, to date, limited research has investigated its behaviour under repeated impact loading conditions. The present study investigates the impact resistance of an alloy equivalent to Stellite 6 hardfaced by gas metal arc welding onto a steel substrate. Testing was performed in different positions \u0026ndash; above the beads and above their overlaps \u0026ndash; in order to evaluate potential differences in impact life. The results indicated that, despite minor variations in morphology and mechanical properties between the distinct positions, the impact lifetime was equivalent in both. The findings of this study provide valuable information for the design and utilisation of components hardfaced with Stellite 6 in applications where impact protection is crucial.\u003c/p\u003e","manuscriptTitle":"Repeated Impact Resistance of Stellite 6 Hardfacing Layer Produced by Gas Metal Arc Welding","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-12-02 08:40:09","doi":"10.21203/rs.3.rs-8156643/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":"97d6ff7f-12ea-4b01-abc8-c96ae1eeee1f","owner":[],"postedDate":"December 2nd, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-03-23T16:09:18+00:00","versionOfRecord":{"articleIdentity":"rs-8156643","link":"https://doi.org/10.1007/s40964-026-01628-5","journal":{"identity":"progress-in-additive-manufacturing","isVorOnly":false,"title":"Progress in Additive Manufacturing"},"publishedOn":"2026-03-17 15:58:33","publishedOnDateReadable":"March 17th, 2026"},"versionCreatedAt":"2025-12-02 08:40:09","video":"","vorDoi":"10.1007/s40964-026-01628-5","vorDoiUrl":"https://doi.org/10.1007/s40964-026-01628-5","workflowStages":[]},"version":"v1","identity":"rs-8156643","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8156643","identity":"rs-8156643","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}