Effect of precipitates on martensite formation and shape memory effect of FeMnSi-based shape memory alloys fabricated by laser powder bed fusion

The initial and evolving microstructure during the tensile test of two Fe-17Mn-5Si-10Cr-4Ni shape memory alloys, with and without V, C and fabricated by laser powder bed fusion are investigated and compared via electron backscattered diffraction, transmission electron microscopy and in-situ neutron diffraction. Tensile samples are fabricated from the two alloys in order to analyze their thermo-mechanical properties. The addition of V and C leads to the formation of a high area density of fine precipitates, mainly carbides, after heat treatment. The chemistry modifications caused by carbide precipitation cause a decrease in the stacking fault energy (SFE), promoting the formation of wider stacking faults and higher volume fractions of martensite phase under loading, which affect the pseudo-elastic properties and deformation behavior of the material. The carbide-containing alloy shows higher strength, work-hardening capability and pseudo-elasticity compared to the carbide-free alloy. However, the shape memory effect is reduced in the former. The present work sheds light on the crucial role of alloy composition, precipitation and SFE in shaping the mechanical and shape memory properties of Fe-based shape memory alloys. The findings hold potential implications for the design and optimization of materials for specific engineering applications, where either enhanced pseudoelasticity or shape memory effect is desired.