Precision additive manufacturing of NiTi shape memory parts using micro-laser powder bed fusion

Nickel–titanium (NiTi) is a promising alloy for biomedical applications due to its unique combination of functional properties such as shape memory effect, superelasticity behavior and biocompatibility. In particular, additive manufacturing of complex NiTi parts containing micro features has received increased attention in bone tissue engineering. Micro-scale additive manufacturing using powder bed techniques such as laser powder bed fusion raises the need to develop new regimes of process parameters. In this research, micro-laser powder bed fusion (µLPBF) was served to fabricate single-phase austenitic nickel-titanium dense and porous materials. The focus of the first part of this study was on the phase transformation behaviour of µLPBF-built NiTi before and after various heat treatment cycles. Investigations revealed that post process age hardening heat treatment has a significant effect on phase transformation temperatures of µLPBF-built NiTi. In the second part of this study, a new strategy was employed to decrease the deviation of NiTi lattice structures with respect to the predesigned models. Results showed that precision additive manufacturing of single-phase NiTi is feasible through applying different µLPBF process parameters for border and hatching areas. With respect to nominal geometrical models, 13% and 24% deviations of pore diameter were calculated in NiTi lattice structures containing 580 µm and 380 µm pores, respectively.