Reassessing the biodegradation behavior of pure iron and iron-manganese alloys fabricated by laser powder bed fusion

This study investigates the biodegradation of pure Fe, Fe-25Mn, and Fe-30Mn alloys fabricated with laser powder bed fusion (LPBF). Unlike conventionally produced Fe-Mn alloys, in the scheme of LPBF, the addition of 25 wt.% and 30 wt.% Mn showed limited efficacy in enhancing the corrosion rates when compared with the LPBF-fabricated Fe. The rapid cooling during LPBF produced a refined grain structure in pure Fe, substantially increased the grain boundary density, and enhanced the corrosion rates. This effect resulted in a corrosion rate of LPBF-processed Fe (0.04mm/year) that matched the corrosion rate of the LPBF-fabricated Fe-25Mn (0.05mm/year) with enhanced galvanic corrosion due to a high ε-martensite to γ-austenite ratio. Whereas in the LPBF-fabricated Fe-30Mn alloy, a reduced corrosion rate (0.01mm/year) was determined because of its coarse columnar grains and constrained micro-galvanic effects derived from the low ε-martensite to γ-austenite ratio. These findings suggest that when LPBF is used to produce biodegradable Fe-based alloys, Fe could be a more optimal option than its Fe- (25 and 30 wt.%) Mn counterparts in terms of pursuing a faster degradation rate.