Laser powder bed fusion of NiTiFe shape memory alloy via pre-mixed powder: microstructural evolution, mechanical and functional properties

High-cost pre-alloyed powder is the bottleneck problem that limits the widespread application of additive-manufactured shape memory alloys. In this work, the low-cost ternary NiTiFe shape memory alloy is fabricated by laser powder bed fusion (LPBF) technique via mechanically mixed pre-alloy NiTi powder and varying contents pure Fe powder (1, 2, 3 wt%). All NiTiFe alloys show a relative density of up to 99.8% by optimizing the LPBF processing parameters. Owing to the heterogeneous nucleation effect of micron-sized Fe particles, both grain refinement and texture weakening are generated in the NiTiFe alloys, accompanied by the reduction of dislocation density. For the room-temperature mechanical properties, the NiTi-3Fe alloy shows the highest microhardness of HV 370, but the fracture strength and elongation reduce to 1701 MPa and 23% simultaneously. The evolution of mechanical properties is attributed to the high internal defects, low dislocation density and the incoherent oxide. Moreover, the NiTi-3Fe alloy shows the quasi-linear superelasticity behavior; the superelastic recoverable strain of NiTi-1Fe and NiTi-2Fe decreased with the increase in Fe content. This study provided a new-fangled insight for the development of multi-component NiTi-based shape memory alloys by additive manufacturing.