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

Abstract 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.