On the Effect of Process Parameters on Manganese Content and Shape Memory Behavior of LPBF-Fabricated Fe-Based Alloys

In this study, the effect of laser process parameters on Mn content and the shape memory behavior of Fe-20Mn-5Si-5Ni-9Cr-0.8V-0.2C-0.1N were studied. Laser Powder Bed Fusion (LPBF) method was employed to fabricate the parts using an EOS M290 system. The process aimed to achieve fully dense parts (>99.9%) with different Mn contents (between 15 to 20 wt%). Mn content measurements done with XRF revealed that scanning strategy (including stripe width, strip overlap, scan length, and rotation angle) significantly influence the Mn content in a part, despite being printed with identical power, speed, hatch spacing and layer thickness. The underlying causes were analyzed in the context of melt pool dynamics and vaporization tendencies of Mn during repeated scan path exposures. Next, differential scanning calorimetry (DSC) was employed to study the influence of Mn variation on shape memory transformation temperatures. Clear shifts in martensitic start (Ms), finish (Mf) and austenitic start (As), and finish (Af) temperatures were observed, with higher Mn content lowering the transformation range. Mechanical properties assessment showed that high-Mn samples had slightly reduced the strength, but improved ductility compared to low-Mn samples. Hardness measurements showed minor variation but aligned with the observed microstructural differences. Finally, the shape memory effect (SME) was assessed using a three-point bending recovery test. High-Mn samples exhibited significantly different behavior compared to low Mn samples, owing higher stability of Austenite in the high Mn samples. Moreover, in-situ heat treatment occurring due to high energy input in low-Mn samples resulted in formation of carbides and affected the shape memory behavior in the low Mn sample as compared to carbide free high Mn sample. This study highlights the sensitivity of Fe-Mn-Si shape memory alloys to Mn content and demonstrates how LPBF process parameters can be utilized to tailor chemical composition and mechanical behavior of this group of alloys.