Laser-beam powder bed fusion of Si-doped Fe-Mn alloys: manufacturing quality, phase transformation and biodegradation performance

Fe-Mn alloys have emerged as promising candidates for biodegradable implants due to their excellent mechanical properties and good biocompatibility. Unfortunately, Fe-Mn alloys still suffer from slow degradation. In this study, laser-beam powder bed fusion (LPBF) process combined with Si doping was proposed to fabricate Fe-Mn alloys with accelerated degradation. Firstly, an optimal process parameter (laser power of 150 W, scanning speed of 60 mm s^-1, and hatch distance of 0.08 mm) was identified based on the lowest surface roughness (2.61 μm) and the highest relative density (99.1 %). On this basis, the effects of varying Si contents (x = 0, 3, 6, and 9 wt %) on the phase composition and thereby the degradation behavior of LPBF-fabricated (LPBFed) Fe-25Mn-xSi alloys were systematically examined. Specifically, the extremely rapid cooling inherent to LPBF and the resulting expansion of Si solid solubility facilitated the phase transformation from γ-austenite to ε-martensite with increasing Si content, accompanied by a decrease of α-ferrite phase content. As a result, an accelerated corrosion rate (0.26±0.02 mm y^-1) was obtained for the LPBFed Fe-25Mn-6Si alloy, which was mainly attributed to the galvanic coupling corrosion occurring among the multiple phases, as well as to phase content variations induced by phase transformation. In summary, this study could offer a potential pathway for the development of biodegradable metals for implant applications.