Microstructure, mechanical properties and corrosion behavior of additively-manufactured Fe–Mn alloys

In this paper, we describe the effects of different scanning speeds (600–900 mm/s) on the microstructure, mechanical properties and corrosion behavior of biodegradable bone-substitution alloys produced from 80:20 (by wt.) Fe:Mn powders using laser powder bed fusion (LPBF). Both the Mn content (18.9–15.1 wt% Mn) and density (7920–7730 kg/m3) of the LPBFed samples decreased slightly with increasing laser scanning speed, while the oxygen content increased (0.12–0.40 wt%). Increasing scanning speed also led to increased porosity (from 0.27% to 2.5%) and increased cracking. The specimen produced at the lowest scanning speed of 600 mm/s, which consisted of only the HCP ε-martensite phase, showed by far the highest yield strength (YS) at 644 MPa and the highest ultimate tensile strength (UTS) at 857 MPa, but the lowest elongation to failure (El) of only 13.7%. Specimens produced at higher scanning rates consisted of both BCC α′-martensite and ε-martensite phases. The sample fabricated at a scanning speed of 700 mm/s showed the best balance of mechanical properties with a YS of 330 MPa, a UTS of 839 MPa, and an El of 36.1%. Electrochemical testing showed corrosion rates from 0.09 mm/yr (600 mm/s specimen) to 0.22 mm/yr (700 mm/s specimen), which are higher than those of both pure Fe and most Fe–30Mn and Fe–35Mn alloys reported in the literature. The work demonstrates that the meso-/micro-scale structure, and, hence, the mechanical properties and corrosion rates of Fe–Mn alloys can be tailored by varying the scanning speed during LPBF processing. It also demonstrates the potential of LPBFed Fe–Mn alloys with low Mn content for use as biodegradable bone substitutes.