Corrosion behavior of selective laser melting-manufactured bio-applicable 316L stainless steel in ionized simulated body fluid

339 RESEARCH ARTICLE Volume 10 Issue 1 (2024) International Journal of Bioprinting https://doi.org/10.36922/ijb.1416 *Corresponding author: Radim Kocich ([email protected]) Citation: Kocich R, Kunčická L, Benč M, Weiser A, Németh G. Corrosion behavior of selective laser melting-manufactured bio-applicable 316L stainless steel in ionized simulated body fluid. Int J Bioprint. 2024;10(1):1416. doi: 10.36922/ijb.1416 Received: July 30, 2023 Accepted: September 7, 2023 Published Online: January 5, 2024 Copyright: © 2024 Author(s). This is an Open Access article distributed under the terms of the Creative Commons Attribution License, permitting distribution, and reproduction in any medium, provided the original work is properly cited. Publisher’s Note: AccScience Publishing remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. Corrosion behavior of selective laser meltingmanufactured bio-applicable 316L stainless steel in ionized simulated body fluid Radim Kocich1,2*, Lenka Kunčická2,3, Marek Benč1, Adam Weiser3, and Gergely Németh4 1VŠB-Technical University of Ostrava, Faculty of Materials Science and Technology, 17. Listopadu 15, 70833 Ostrava 8, Czech Republic 2Brno University of Technology, Faculty of Mechanical Engineering, Technická 2896-2, 60200 Brno, Czech Republic 3Institute of Physics of Materials, Czech Academy of Sciences, Žižkova 22, 61662 Brno, Czech Republic 4Nuclear Physics Institute, Czech Academy of Sciences, Husinec - R ˇež 130, 250 68 R ˇež, Czech Republic (This article belongs to the Special Issue: 3D Bioprinting for Materials and Application) Abstract Additive manufacturing (AM) is gaining increasing popularity in various fields, including biomedical engineering. Although AM enables fabrication of tailored components with complex geometries, the manufactured parts typically feature several internal issues, such as unpredictable distribution of residual stress and printing defects. However, these issues can be reduced or eliminated by postprocessing via thermomechanical treatment. The study investigated the effects of combinations of AM and post-processing by the intensive plastic deformation method of rotary swaging (variable swaging ratios) on microstructures, residual stress, and corrosion behaviors of AISI 316L stainless steel workpieces; the corrosion tests were performed in an ionized simulated body fluid. The results showed that the gradual swaging process favorably refined the grains and homogenized the grain size. The imposed swaging ratio also directly influenced the development of substructure and dislocations density. A high density of dislocations positively affected the corrosion resistance, whereas annihilation of dislocations and formation of subgrains had a negative effect on the corrosion behavior. The first few swaging passes homogenized the distribution of residual stress within the workpiece and acted toward imparting a predominantly compressive stress state, which also favorably influenced the corrosion behavior. Lastly, the presence of the {111}||swaging direction texture fiber (of a high intensity) increased the resistance to pitting corrosion. Overall, the most favorable corrosion behavior was acquired for the AM sample subjected to the swaging ratio of 0.8, exhibiting a strong fiber texture and a high density of dislocations. Keywords: Additive manufacturing; Rotary swaging; 316L stainless steel; Electrochemical corrosion; Microstructure; Residual stress Corrosion behavior of SLM-prepared 316L steel 340Volume 10 Issue 1 (2024) https://doi.org/10.36922/ijb.1416 International Journal of Bioprinting 1. Introduction Additive manufacturing (AM), usually referred to as three-dimensional (3D) printing, involves several technologies, such as powder bed fusion (PBF), which comprises selective laser melting (SLM)1 and direct metal laser sintering (DMLS).2 The technologies are utilized based on a computer-generated model to fabricate a 3D product.3 Contrary to the conventional manufacturing methods, such as rolling, forging, extrusion, or drawing, AM technologies create the materials monolithically in a layer-by-layer fashion. The technologies are suitable to fabricate tailored components with complex geometries from various metals,4,5 polymers,6 and also ceramics.7,8 Over the recent years, AM has demonstrated success in fabrication of intricate components applicable in a variety of industrial fields, including aerospace, automotive, or biomedicine. For example, AM has already been used to fabricate complex bio-applicable structures, such as scaffolds, and patient-specific implants.9-11 Despite its indisputable advantage, i.e., the ability to create tailor-made geometries, AM also features several disadvantages, including residual porosity, surface roughness, inhomogeneous distribution of residual stress, and possible distortion of the final components12,13. In order to eliminate the printing defects, post-processing via a heat treatment, possibly combined with a high pressure (such as during the hot isostatic pressing [HIP] method)14, or processing via plastic deformation15, has been proven to be advantageous. Besides, optimized deformation (thermomechanical) treatment has been shown to also favorably enhance the mechanical properties of AMprepared materials (steels)15-17. The AISI 316L stainless steel is widely applicable in numerous commercial and industrial fields, from chemical and petrochemical industry18, through nuclear energetics19, transportation and marine20,21, to food industry and biomedicine22,23. Given its versatility, it has been the focus of numerous researchers working on the optimization of its production technologies and preparation processes. Its manufacturability by conventional production methods, as well as by modern and unconventional methods, such as hydroforming, electroforming, or severe plastic deformation (SPD) techniques, has been proven24-26. Recently, the 316L steel has also been gaining traction among researchers and manufacturers dealing with AM technologies27,28. As the selected processing parameters and particular AM technology directly influence the acquired microstructures and thus the mechanical properties, investigating the correlation of these variables has always been the main goal of numerous studies. Saboori et al.29 reviewed and summarized the effects of processing parameters of directed energy deposition (DED)-based AM methods on the microstructures and mechanical properties of the 316L steel. Guo et al.30, who used the high-power direct laser deposition (HP DLD) method, reported that the microstructures and properties depended significantly on the building direction. Regarding the optimized processing parameters, the therein achieved ultimate tensile strength (UTS) reached 900 MPa. Yin et al.31 documented that the thermal stability of the microstructures as-built by laser powder bed fusion (L-PBF) lasted for up to 400 h between 500°C and 600°C, and decreased significantly with increasing the temperature to 800°C. As the microstructures and possible presence of printing defects also affect the lifetime of the components, several research groups have examined the fatigue properties of AISI 316 steel prepared by AM32-34 and compared the results with those acquired for conventionally prepared steels35,36; such comparisons were also performed from the viewpoints of machinability37,38. Interestingly, Vinoth et al.39 reported that the wire arc additive manufacturing (WAAM) method can be used to fabricate steel plates that exhibit open pores after machining, which could be beneficial for a prospective bio-application. The 316L steel is one of the most commonly used, affordable materials for fabrication of various implants used in human body40. Examining the corrosion behavior of a bio-applicable material is of high importance because corrosion not only decreases the lifetime of the implant, but it also triggers release of ions from the implant materials, which can (negatively) affect the surrounding living tissues and cause inflammatory or anaphylactic responses27,41. Shih et al.42 documented that wrought 316L steel components are prone to exhibit localized corrosion and would gradually become cytotoxic as a result of the corrosion reactions. Majumdar et al.28 reported that almost 50% of 316L steel implantation failure is related to corrosion. To address this problem, various types of coatings (e.g., ZnO and TiO2 films) and surface treatments have been introduced to decrease the corrosion rate of the stainless steel43-45. As the corrosion behavior is dependent not only on the chemical composition of the material, but also on the microstructure and intrinsic properties, studies on AM-prepared 316L steel have been performed as well. Upon comparing the corrosion behaviors of 316L steel samples prepared conventionally and by AM+HIP in H2SO4 and HCl solutions, Fredriksson et al.46 found that the AM+HIP sample exhibited better resistance to pitting corrosion due to the formation of a thicker passive layer. The application of HIP has been shown to favorably enhance the corrosion resistance of AM-prepared steels47. However, HIP alone is not able to fully eliminate residual porosity, which tends to increase both the corrosion rate Corrosion behavior of SLM-prepared 316L steel 341Volume 10 Issue 1 (2024) https://doi.org/10.36922/ijb.1416 International Journal of Bioprinting and the depth of corrosion pits48. To enhance the corrosion resistance of AM-prepared 316L steel, one hypothesized solution is to combine AM and post-processing, which is a thermomechanical treatment15-17. The main focus of the present study was to correlate the microstructures and corrosion behaviors of 316L steel workpieces, prepared by a combination of the SLM methods and thermomechanical treatment performed with rotary swaging. The swaging method is highly favorable for the processing of powder-based and pre-sintered materials, mainly because it features predominantly compressive stress state during processing, which supports consolidation of the material and the elimination of possible printing defects and voids, and incrementally imparts shear strain, which supports shear mixing and gradual grain refinement16,49. In the current study, an original method was utilized to prepare the material, and electrochemical corrosion tests were performed in an ionized simulated body fluid (i-SBF)50-52 (as documented above, if the corrosion behavior of AM-prepared 316L steel for prospective bio-application has been examined, it has mostly been in NaCl-based solutions). The results of the electrochemical corrosion tests were correlated with the results of microscopic investigations of microstructure and substructure, as well as with the results of residual stress analyses performed by means of neutron diffraction. 2. Materials and methods 2.1. Materials The original workpiece of the AISI 316L stainless steel was prepared using SLM from a steel powder delivered by Renishaw, using a Renishaw AM400 machine (both by Renishaw company, Wotton-under-Edge, UK). The 3D printing was performed under an inert atmosphere (Ar of 99.998% purity). The powder featured the particle size distribution of 15–45 µm and the exact chemical composition as presented in Table 1. As for the building direction, we selected a vertical laser cladding strategy (based on the results of studies by Kunčická et al.16,17, who investigated the internal structures and intrinsic properties of AM-prepared AISI 316L workpieces lasercladded in the vertical and horizontal directions). The workpiece with a length of 100 mm and a diameter of ~26 mm (circular cross-section) was manufactured using a Meander printing strategy; the principle of which lies in cladding individual lines of the powder next to each other along the entire length of the designed workpiece16,53-56. The meander printing strategy is favorable as it represents a favorable trade-off between high deposition rate and low-temperature gradients. After the SLM, we applied a heat treatment at 900°C for 30 min, primarily to impart (partial) homogenization and relaxation of the residual stress. On the other hand, a relatively short dwell time was selected to avoid the risk of (negatively) affecting the utility properties, including the corrosion ones57,58. Having finished the preparation of the workpiece, thermomechanical post-processing via rotary swaging59-61 at the temperature of 900°C was applied. The swaging was performed in several consecutive passes to acquire swaged rods with diameters of 20 mm, 17 mm, and 15 mm. The applied swaging ratio in each consecutive pass can be calculated using Equation (I): ϕ = 0 n S S (I) where S0 and Sn are the cross-sectional areas of the workpiece at the input and output from the swaging dies, respectively. The swaging ratios for the individual samples were as follows: 0.5 for sample 20, 0.8 for sample 17, and 1.1 for sample 15. In the above mentioned works16,17, the authors documented that it is necessary to perform a few initial swaging passes to sufficiently increase the density and reduce the residual porosity of AM-prepared workpieces. Toward this end, we examined the samples subjected to the three last swaging passes. 2.2. Experiment 2.2.1. Neutron diffraction In order to examine the positive effects of rotary swaging on the residual stress, its distribution within the workpiece swaged to the diameter of 20 mm was investigated by means of neutron diffraction-strain scanning technique, which Table 1. Declared and experimentally measured chemical compositions of AISI 316L steel powder Element Cr Ni Mo Mn Si O N C S Fe Composition by manufacturer (wt.%) 16–18 10–14 2–3 <2 <1 <0.1 <0.1 <0.03 <0.03 bal. Measured composition (wt.%) 18.3 ± 0.5 11.2 ±1 .2 2.2 ± 0.1 1.9 ± 0.2 1.1 ± 0.2 0.05 ± 0.01 0.03 ± 0.01 0.02 ± 0.01 0.004 ± 0.001 bal. Corrosion behavior of SLM-prepared 316L steel 342Volume 10 Issue 1 (2024) https://doi.org/10.36922/ijb.1416 International Journal of Bioprinting is a highly efficient method for characterizing the stress distribution within the bulk of the material62,63. The analysis was performed using the SPN-100 25 diffractometer installed at NPL laboratory of CANAM infrastructure at Nuclear Physics Institute, Czech Academy of Sciences, Řež (Prague, Czech Republic)64. Figure 1A schematically depicts the cross-section of the analyzed workpiece and with the dimensions and the individual scanned lines. The scanning was performed along four lines crossing the geometrical axis of the workpiece (as depicted in the same figure). The distance between the individual measurement points was 1 mm, except the borderline of the workpiece, at which the spacing between the penultimate and last measured locations was 0.25 mm. Along all scanned lines, three scans were performed, individually for three mutually perpendicular orientations of the diffraction vector 𝑘 𝑑𝑖𝑓𝑓, which corresponded to three mutually perpendicular examined directions—radial, hoop, and axial (see Figure 1A). The axial and hoop directions were perpendicular to the line of scanning, whereas the radial direction aimed to the workpiece axis. Figure 1B shows a schematic depiction of a horizontal cut through the gauge volume, i.e., the material volume from which the diffracted neutrons were registered. Its shape was defined by the geometry of the used neutronoptical features, i.e., slits and radial collimator. For the radial and hoop scattering vector orientations, the width and height were 2.5 mm and 20 mm, respectively, whereas for the axial orientation, the dimensions were 2.5 × 2.5 mm2. For the examined {111} crystallographic planes, which are the most convenient to measure lattice strains for the stainless steel65, the diffraction angle 2ϴ111 was approximately 61.8°, and the neutron wavelength was 2.13 Å. The individual neutron diffraction measurements took 2400 s in the hoop and radial orientations, and 1 900 s in the axial orientation. The residual stress within the workpiece was evaluated by detecting the diffraction pattern from the examined {111} crystallographic planes. Using the Bragg’s Law, the inter-planar distance d111 can be calculated with the diffraction angle 2ϴ111. Acquiring the unconstrained lattice spacing, i.e., d0 111 parameter, is necessary to determine the strains and to acquire reliable results regarding the distribution of tensile/compressive residual stress. However, for AM-prepared metals, the d0 111 parameter acquired from the original powder is not reliable as repeated melting/solidification occurring during the manufacturing process imparts (minor) chemical changes in the matrix due to precipitation of additional phases66. Therefore, we determined the d0 111 parameter based on the equilibrium condition in the axial direction on the crosssection (see16,67). Consequently, the residual strain ε111 and residual stress σij were calculated using Equations (II) and (III), respectively, ε − = 111 111 111 0 111 0 dd d (II) Figure 1. (A) Schematic depiction of layout of neutron diffraction measurement (L1, L2, L3, and L4 depict the individual scanning lines). (B) Schematic characterization of gauge volume. Corrosion behavior of SLM-prepared 316L steel 343Volume 10 Issue 1 (2024) https://doi.org/10.36922/ijb.1416 International Journal of Bioprinting ( ) ( ) υ σ ε εεε υ υ  = + ++  − + 111 111 111 111 111 111 11 22 33 111 111 12 1 ij ij E (III) where E111 is 247.8 GPa, υ111 is 0.2468, d0 111 is the interplanar distance of {111} planes for original material with no residual stress, and ij are indices denoting stress tensor components (if principal stresses are considered, the nonzero stress components are 11 for hoop orientation, 22 for radial orientation, and 33 for axial orientation). Last but not least, spurious strains, which occurred in the vicinity of the workpiece periphery due to incomplete overlapping of the workpiece and gauge volume, were eliminated. These strains can cause aberration peak shifts and lead to misleading interpretation of the acquired data (the principles of the used method can be found in ref.69). The residual stress data was eventually depicted graphically as contour plots with five major and eight minor levels using the Origin Pro 8.1 software (OriginLab Corporation, Northampton, USA). 2.2.2. Electrochemical corrosion Biocompatibility of the AISI 316L stainless steel and (possible) effects of its usage within a human body on the surrounding tissues have been investigated by numerous researchers70-72. We performed the electrochemical corrosion testing in a simulated body fluid (SBF), which is a solution with ion concentrations closely similar to those in the human blood plasma. However, the mentioned correspondence is only an approximate. Thus, Oyane et al.50-52 introduced i-SBF, whose ion concentrations match those of the blood plasma in dissociated amounts. Besides, i-SBF is highly suitable to assess the in vitro activity of bio-applicable metallic materials. The preparation and chemical composition of the i-SBF used in this study were also inspired by other published works50-52. The pH of the used i-SBF was 7.40 ± 0.05 at 37°C. After preparation, the fluid was deaerated for 15 min with a flow of nitrogen gas at 5 ml/min. As for the experimental setup, we used standard three-electrode electrochemical cell supplemented with an SP-150 potentiostat (BioLogic Company, Inc., SeyssinetPariset, France) and a standard calomel reference electrode. Open circuit potential (OCP) measurement was performed for at least 60 min before the potentiodynamic scan was initiated. The potentiodynamic scan with 1 mV/s scan rate at 25°C started from -0.6 VSCE (below OCP) and ended at 1.2 VSCE (above OCP), or at the breaking current of 100 µA. The samples for the analyses were prepared from crosssectional cuts from the swaged workpieces acquired after each of the three last swaging passes; the exposed locations corresponded to the locations at which the microstructure observations were performed (see section 2.2.3). Each sample was then mechanically ground and polished using diamond solutions with the coarseness down to 3 µm, cleaned, and consequently rinsed in deionized water. 2.2.3. Structure observations The structure observations were performed on the cross-sectional cuts from the swaged pieces. Before the investigations, the feature of the rotary swaging process was considered (i.e., the fact that the shear strain is imposed from the periphery of the processed workpiece toward its axis; see ref.73). Therefore, microstructure analyses were performed in the mid-radius distance for each swaged workpiece. In other words, the observations for samples 20, 17, and 15 were performed in the distance of 5 mm, 4.25 mm, and 3.75 mm from the periphery of the workpiece, respectively. The examined locations corresponded to the locations in which the corrosion testing was performed. As for the methods, scanning and transmission electron microscopy (SEM and TEM) were used; for SEM, we applied the electron backscatter diffraction (EBSD) method. The used devices included a Tescan Lyra 3 XMU FEG/SEMxFIB microscope (Tescan Orsay Holding a.s., Brno, Czech Republic) equipped with a Symmetry EBSD detector (Oxford Instruments, Abingdon, United Kingdom), and a JEM-2100 TEM microscope (JEOL, Tokyo, Japan). The SEM-EBSD analyses were carried out on the transversely cut, cross-sectional samples prepared by manual grinding, manual polishing, and finally electrolytic polishing. In order to reliably assess the substructural features, such as low angle grain boundaries (LAGB) and local (Kernel) misorientations, the scan step was selected to be 0.4 µm. The TEM substructure analyses were performed on manually ground foils, which were then electrochemically etched. All the acquired data was then evaluated using the AZtecCrystal software (Oxford Instruments, Abingdon, United Kingdom). The considered limits for the grains and grain boundaries were 5° for LAGB and 15° for high angle grain boundaries (HAGB); the (ideal) texture orientations were evaluated with 15° maximum deviation. 3. Results 3.1. Residual stress The results of analyses of residual stress distribution within the sample 20 in the hoop, radial, and axial orientations are graphically depicted in Figure 2A–C), respectively. As can be seen, the residual stress distributions in the hoop and radial directions (Figure 2A and B), which were both oriented perpendicular to the axis of the workpiece (see Corrosion behavior of SLM-prepared 316L steel 344Volume 10 Issue 1 (2024) https://doi.org/10.36922/ijb.1416 International Journal of Bioprinting Figure 1A), were comparable. In other words, tensile stress prevailed within the bulk of the workpiece for both the orientations; its absolute values were generally relatively low and gradually decreased toward the workpiece periphery. The figures document that although the residual stress within the workpiece exhibited the tendency to homogenize during swaging, certain inhomogeneities in these two measured orientations were still evident for sample 20. On the other hand, the residual stress in the axial orientation, i.e., parallel to the workpiece axis, exhibited concentric regions of more or less homogenous residual stress values across the cross-section. Rotary swaging thus favorably influenced the stress state of the AM-prepared workpiece and imparted changes leading to a predominantly compressive stress state. Given the nature of the swaging process16,49, this effect is supposed to become more significant with increasing swaging ratio. 3.2. Texture Figures 3A–C depict the textures via pole figures (PF) for the swaged samples 20, 17, and 15, respectively. Kunčická et al.16 previously documented that AM-prepared and heat-treated 316L steel workpieces typically feature randomized texture with the maximum intensity of approximately two times random. The herein presented PFs show that the texture intensity was generally higher than that after swaging. The maximum texture intensity was comparable for the swaged samples 20 and 15 (up to four times random for both), whereas it was higher (up to seven times random) for sample 17. To confirm the results of the presented analyses and further determine, in a greater detail, the texture components occurring within the swaged microstructures, the presence of ideal shear texture orientations was further evaluated. Figures 3D–F show the intensities of the most prominent ideal texture orientations (||SD, i.e., shear direction) within the swaged samples. Particular orientations were examined based on the characteristic ideal texture orientations within FCC metals subjected to shear strain-based deformation processing, as identified by Beyerlein and Tóth74. The identified ideal orientations Figure 2. Distribution of residual stress within swaged sample 20. (A) Hoop orientation. (B) Radial orientation. (C) Axial orientation. Corrosion behavior of SLM-prepared 316L steel 345Volume 10 Issue 1 (2024) https://doi.org/10.36922/ijb.1416 International Journal of Bioprinting Figure 3. Textures within swaged workpieces via pole figures (PF): (A) sample 20, (B) sample 17, and (C) sample 15. Intensities of characteristic ideal texture orientations within (D) sample 20, (E) sample 17, and (F) sample 15. Corrosion behavior of SLM-prepared 316L steel 346Volume 10 Issue 1 (2024) https://doi.org/10.36922/ijb.1416 International Journal of Bioprinting were as follows: A1 and A2, belonging to the {111} fiber with constant Euler angles Φ = 45° and φ2 = 0°; Ab and A, belonging to the {111}<110> fiber with constant Euler angles Φ = 35.26° and φ2 = 45°; Bb and B, belonging to the <110> fiber with constant Euler angles Φ = 54.74° and φ2 = 45°; and C with the specific orientations of Euler angles of φ1 = 90°; Φ = 45°; and φ2 = 0°74,75. The analyses of the specific orientations confirmed that sample 20 featured no prevailing preferential texture orientation; the most prominent were the A1, A, and B orientations, but their intensities were comparable (volume fractions between 0.13% and 0.15%) and no single orientation dominated. On the other hand, swaging to the diameter of 17 mm resulted in the formation of a dominant ideal texture orientation; the intensity of the B orientation within sample 17 was more than twice as high as those of the other texture orientations, i.e., Ab, A, and Bb. In other words, almost 50% of the grains tended to acquire the ideal B orientation. Further swaging to the final diameter of 15 mm resulted in a decrease in the intensity of not only the B texture orientation (less than 25% volume fraction), but also the other Ab, A, and Bb orientations. A minor fraction of other ideal texture orientations, which were not observed within sample 17 but within sample 20, were present within sample 15, pointing to texture randomization, most probably caused by structure restoration (see also the following sections). 3.3. Microstructure The grain sizes were assessed via the area-weighted fractions of maximum Feret diameters (see Figure 4A–D for the graphical depictions of the results for the original workpiece and swaged samples 20, 17, and 15, respectively). The average grain size decreased with swaging from the original value of 31.4 µm to 14.6 µm the sample 20. After the subsequent swaging to 17 mm, the grain size further decreased to an average value of 11.0 µm, and then remained almost constant after the final pass (11.1 µm for sample 15). As can be seen, the grain size was also significantly homogenized during the swaging process. The sizes of the largest grains within the Figure 4. Grain size depicted with area-weighted fractions of maximum Ferret diameters for (A) AM-prepared workpiece, (B) sample 20, (C) sample 17, and (D) sample 15. Corrosion behavior of SLM-prepared 316L steel 347Volume 10 Issue 1 (2024) https://doi.org/10.36922/ijb.1416 International Journal of Bioprinting AM-prepared workpiece exceeded 300 µm. Sample 20 featured the greatest grain size inhomogeneity of all the swaged samples, as some of the grains were still relatively large and exceeded the diameter of 100 µm (although the majority of the grains was refined). Sample 17 featured the majority of refined grains, although the remnants of larger grains with the diameters of about 100 µm were still evident. The structure within sample 15, on the other hand, exhibited no evident traces of grains with sizes reaching up to 100 µm. The LAGB and HAGB fractions for the swaged samples 20, 17, and 15 are characterized in Figure 5A–C, which also depict the Kernel average misorientation (KAM) maps for the respective samples. The maximum limit for KAM was set to 5° to reliably depict relative densities of dislocations within the microstructures. The highest HAGB fraction (71.7 %) among the swaged microstructures was observed within sample 20. The occurrence of misorientations was relatively scarce within sample 20, which corresponded to the relatively low applied swaging ratio (Figure 5A). Increasing the imposed strain resulted in the accumulation of dislocations and development of substructure, i.e., the LAGB fraction increased at the expense of the HAGB one with continuing swaging (the HAGB fraction for sample 17 was 65.4%). Also, the occurrence of misorientations increased noticeably for this sample (Figure 5B), primarily by the effect of the increasing amount of the imposed shear strain59. The HAGB fraction then decreased with continuing swaging to 59.5% for sample 15. In other words, the LAGB fraction increased for this sample, and the microstructure also exhibited many misorientations (Figure 5C), collectively pointing to the development of substructure (as discussed in section 3.4). Figure 5. Kernel average misorientation (KAM) maps for structures of (A) sample 20, (B) sample 17, and (C) sample 15. Corrosion behavior of SLM-prepared 316L steel 354Volume 10 Issue 1 (2024) https://doi.org/10.36922/ijb.1416 International Journal of Bioprinting 39. Vinoth V, Sathiyamurthy S, Natarajan U, Venkatkumar D, Prabhakaran J, Prakash KS. Examination of microstructure properties of AISI 316L stainless steel fabricated by wire arc additive manufacturing. Mater Today Proc. 2022;66(7):702-706. doi: 10.1016/j.matpr.2022.04.011 40. Zach L, Kunčická L, Růžička P, Kocich R. Design, analysis and verification of a knee joint oncological prosthesis finite element model. Comput Biol Med. 2014;54:53-60. doi: 10.1016/j.compbiomed.2014.08.021 41. Pardo A, Merino MC, Coy AE, Viejo F. Pitting corrosion behaviour of austenitic stainless steels – combining effects of Mn and Mo additions. Corros Sci. 2008;50(6):1796-1806. doi: 10.1016/j.corsci.2008.04.005 42. Shih C-C, Shih C-M, Su Y-Y, Julie Su LH, Chang M-S, Lin S-J. Effect of surface oxide properties on corrosion resistance of 316L stainless steel for biomedical applications. Corros Sci. 2004;46(2):427-441. doi: 10.1016/S0010-938X(03)00148-3 43. Shahryari A, Omanovic S, Szpunar JA. Electrochemical formation of highly pitting resistant passive films on a biomedical grade 316LVM stainless steel surface. Mater Sci Eng C. 2008;28(1):94-106. doi: 10.1016/j.msec.2007.09.002 44. Tekdir H, Yetim T, Yetim AF. Corrosion properties of ceramic-based TiO2 films on plasma oxidized Ti6Al4V/316L layered implant structured manufactured by selective laser melting. J Bionic Eng 2021;18:944-957. 45. Yetim T, Tekdir H, Taftalı M, Turalıoğlu K, Yetim AF. Synthesis and characterisation of single and duplex ZnO/ TiO 2 ceramic films on additively manufactured bimetallic material of 316L stainless steel and Ti6Al4V. Surf Topogr Metrol Prop. 2023;11(2):024005. doi: 10.1088/2051-672X/accf6c 46. Fredriksson W, Petrini D, Edström K, Björefors F, Nyholm L. Corrosion resistances and passivation of powder metallurgical and conventionally cast 316L and 2205 stainless steels. Corros Sci. 2013;67:268-280. doi: 10.1016/j.corsci.2012.10.021 47. Geenen K, Röttger A, Theisen W. Corrosion behavior of 316L austenitic steel processed by selective laser melting, hot-isostatic pressing, and casting. Mater Corros. 2017;68(7):764-775. doi: 10.1002/maco.201609210 48. Hardes C, Pöhl F, Röttger A, Thiele M, Theisen W, Esen C. Cavitation erosion resistance of 316L austenitic steel processed by selective laser melting (SLM). Addit Manuf. 2019;29:100786. doi: 10.1016/j.addma.2019.100786 49. Canelo-Yubero D, Kocich R, Hervoches C, Strunz P, Kunčická L, Kratka L. Neutron diffraction study of residual stresses in a W–Ni–Co heavy alloy processed by rotary swaging at room and high temperatures. Met Mater Int. 2022;28(4):919-930. doi: 10.1007/s12540-020-00963-8 50. Oyane A, Onuma K, Ito A, Kim H-M, Kokubo T, Nakamura T. Formation and growth of clusters in conventional and new kinds of simulated body fluids. J Biomed Mater Res. 2003;64(2):339-348. doi: 10.1002/jbm.a.10426 51. Oyane A, Kim H-M, Furuya T, Kokubo T, Miyazaki T, Nakamura T. Preparation and assessment of revised simulated body fluids. J Biomed Mater Res. 2003;65(2): 188-195. doi: 10.1002/jbm.a.10482 52. Oyane A, Onuma K, Ito A, et al. Variation of clusters in simulated body fluids with time. Key Eng Mater. 2001; 218-220:629-632. doi: 10.4028/www.scientific.net/KEM.218-220.629 53. Kořínek M, Halama R, Fojtík F, et al. Monotonic tensiontorsion experiments and FE modeling on notched specimens produced by SLM technology from SS316L. Materials. 2020;14(1):33. doi: 10.3390/MA14010033 54. Pitassi D, Savoia E, Fontanari V, et al. Finite element thermal analysis of metal parts additively manufactured via selective laser melting. In: Finite Element Method - Simulation, Numerical Analysis and Solution Techniques. 2018. doi: 10.5772/intechopen.71876 55. Jin M, Piglione A, Dovgyy B, et al. Cyclic plasticity and fatigue damage of CrMnFeCoNi high entropy alloy fabricated by laser powder-bed fusion. Addit Manuf. 2020;36: 101584. doi: 10.48550/arXiv.2007.07043 56. Dovgyy B, Piglione A, Hooper PA, Pham M-S. Comprehensive assessment of the printability of CoNiCrFeMn in laser powder bed fusion. Mater Des. 2020;194:108845. doi: 10.1016/j.matdes.2020.108845 57. Elangeswaran C, Cutolo A, Muralidharan GK, et al. Effect of post-treatments on the fatigue behaviour of 316L stainless steel manufactured by laser powder bed fusion. Int J Fatigue. 2019;123:31-39. doi: 10.1016/j.ijfatigue.2019.01.013 58. Salman OO, Gammer C, Chaubey AK, Eckert J, Scudino S. Effect of heat treatment on microstructure and mechanical properties of 316L steel synthesized by selective laser melting. Mater Sci Eng A. 2019;748:205-212. doi: 10.1016/j.msea.2019.01.110 59. Kunčická L, Macháčková A, Krátká L, Kocich R. Analysis of deformation behaviour and residual stress in rotary swaged Cu/Al clad composite wires. Materials. 2019;12(21):3462. doi 10.3390/ma12213462 60. Zhang Q, Jin K, Mu D. Tube/tube joining technology by using rotary swaging forming method. J Mater Process Technol. 2014;214:2085-2094. doi: 10.1016/j.jmatprotec.2014.02.002 61. Strunz P, Kunčická L, Beran P, Kocich R, Hervoches C. Correlating microstrain and activated slip systems with Corrosion behavior of SLM-prepared 316L steel 355Volume 10 Issue 1 (2024) https://doi.org/10.36922/ijb.1416 International Journal of Bioprinting mechanical properties within rotary swaged WNiCo pseudoalloy. Materials. 2020;13(1):208. doi: 10.3390/ma13010208 62. Wang Z, Chen J, Besnard C, Kuncicka L, Kocich R, Korsunsky AM. In situ neutron diffraction investigation of texturedependent shape memory effect in a near equiatomic NiTi alloy. Acta Mater. 2021;202:135-148. doi: 10.1016/j.actamat.2020.10.049 63. Wang Z, Chen J, Kocich R, et al. Grain structure engineering of NiTi shape memory alloys by intensive plastic deformation. ACS Appl Mater Interfaces. 2022;14(27):3139631410. doi 10.1021/acsami.2c05939 64. Hervoches C, Mikula P, Vrána M. Recent instrumentation upgrades on the residual strain/stress diffractometer at NPI-Řež, in 53rd International Scientific Conference on Experimental Stress Analysis (EAN 2015), Czech Society for Mechanics, Český Krumlov. 2015;119-120. 65. Clausen B, Leffers T, Lorentzen T. On the proper selection of reflections for the measurement of bulk residual stresses by diffraction methods. Acta Mater. 2003;51:6181-6188. doi: 10.1016/j.actamat.2003.07.002 66. Zhong Y, Rännar LE, Liu L, et al. Additive manufacturing of 316L stainless steel by electron beam melting for nuclear fusion applications. J Nucl Mater. 2017;486:234-245. doi: 10.1016/J.JNUCMAT.2016.12.042 67. Martinez-Perez ML, Mompean FJ, Ruiz-Hervias J, et al. Residual stress profiling in the ferrite and cementite phases of cold-drawn steel rods by synchrotron X-ray and neutron diffraction. Acta Mater. 2004;52:5303-5313. doi: 10.1016/J.ACTAMAT.2004.07.036 68. Zhang Y, Chen W, McDowell DL, Y. Wang M, Zhu T. Lattice strains and diffraction elastic constants of cubic polycrystals. J Mech Phys Solids. 2020;138:103899. doi: 10.1016/j.jmps.2020.103899 69. Šaroun J, Rebelo-Kornmeier J, Gibmeier J, Hofmann M. Treatment of spatial resolution effects in neutron residual strain scanning. Phys/B. 2018;551:468. doi: 10.1016/J.PHYSB.2018.01.013 70. Li G, Song Y, Chen X, et al. Preparation, corrosion behavior and biocompatibility of MgFe-layered double hydroxides and calcium hydroxyapatite composite films on 316L stainless steel. Mater Today Commun. 2023;34:105195 71. Mejía-Caballero I, Palomar-Pardavé M, Martínez Trinidad J, et al. Corrosion behavior of AISI 316L borided and nonborided steels immersed in a simulated body fluid solution. Surf Coatings Technol. 2015;280:384-395 doi: 10.1016/j.surfcoat.2015.08.053 72. Karimzadeh N, Moghaddam EG, Mirjani M, Raeissi K. The effect of gas mixture of post-oxidation on structure and corrosion behavior of plasma nitrided AISI 316 stainless steel. Appl Surf Sci. 2013;283:584-589. doi: 10.1016/j.apsusc.2013.06.152 73. Kocich R, Kunčická L. Optimizing structure and properties of Al/Cu laminated conductors via severe shear strain. J Alloys Compd. 2023;953:170124. doi: 10.1016/j.jallcom.2023.170124 74. Beyerlein IJ, Tóth LS. Texture evolution in equal-channel angular extrusion. Prog Mater Sci. 2009;54(4):427-510. doi: 10.1016/j.pmatsci.2009.01.001 75. Toth LS, Gilorminis P, Jonas JJ. Effect of rate sensitivity on the stability of torsion textures. Acta Metall. 1988;36(12): 3077-3091. doi: 10.1016/0001-6160(88)90045-4 76. Li C, Liu ZY, Fang XY, Guo YB. Residual stress in metal additive manufacturing. Procedia CIRP. 2018;71(2): 348-353. doi: 10.1016/j.procir.2018.05.039 77. Macháčková A, Krátká L, Petrmichl R, Kunčická L, Kocich R. Affecting structure characteristics of rotary swaged tungsten heavy alloy via variable deformation temperature. Materials. 2019;12(24):4200 doi: 10.3390/ma12244200 78. Kunčická L, Kocich R. Optimizing electric conductivity of innovative Al-Cu laminated composites via thermomechanical treatment. Mater Des. 2022;215(10):110441. doi: 10.1016/j.matdes.2022.110441 79. Nazarov AA. Disclinations in bulk nanostructured materials: Their origin, relaxation and role in material properties. Adv Nat Sci Nanosci Nanotechnol. 2013;4:033002. doi: 10.1088/2043-6262/4/3/033002 80. Kong D, Dong C, Ni X, et al. Mechanical properties and corrosion behavior of selective laser melted 316L stainless steel after different heat treatment processes. J Mater Sci Technol. 2019;35(7):1499-1507. doi: 10.1016/j.jmst.2019.03.003 81. Abbasi Aghuy A, Zakeri M, Moayed MH, Mazinani M. Effect of grain size on pitting corrosion of 304L austenitic stainless steel. Corros Sci. 2015;94:368-376. doi: 10.1016/j.corsci.2015.02.024 82. Madrigal-Cano M, Hallen JM, Arce-Estrada EM, Le Manh T. Effect of crystallographic texture and microstructure on pitting corrosion behavior of low carbon steels: A Monte Carlo model. Comput Mater Sci. 2019;161:394-402. doi: 10.1016/j.commatsci.2019.02.016 83. Guo D, Kwok CT, Chan SLI. Spindle speed in friction surfacing of 316L stainless steel – How it affects the microstructure, hardness and pitting corrosion resistance. Surf Coatings Technol. 2019;361(2):324-341. doi: 10.1016/j.surfcoat.2019.01.055 84. Trisnanto SR, Wang X, Brochu M, Totis G. Effects of crystallographic orientation on the corrosion behavior of stainless steel 316L manufactured by laser powder bed fusion. Corros Sci. 2022;196:110009. doi: 10.1016/j.corsci.2021.110009 Corrosion behavior of SLM-prepared 316L steel 356Volume 10 Issue 1 (2024) https://doi.org/10.36922/ijb.1416 International Journal of Bioprinting 85. Zhang Y, Cheng F, Wu S. Improvement of pitting corrosion resistance of wire arc additive manufactured duplex stainless steel through post-manufacturing heat-treatment. Mater Charact. 2021;171:110743. doi: 10.1016/j.matchar.2020.110743 86. Kunčická L, Kocich R. Effect of activated slip systems on dynamic recrystallization during rotary swaging of electroconductive Al-Cu composites. Mater Lett. 2022;321(1):1013. doi: 10.1016/j.matlet.2022.132436