In Situ Alloyed NiTiCu by Laser Powder-Bed Fusion for Biomedical Applications

In-situ alloying by additive manufacturing (AM) or three-dimensional (3D) printing of pre-mixed powders has been recognised as a promising low-cost method for creating complex-shaped intermetallic parts. This work preliminarily addresses several technical concerns with the laser powder-bed fusion (L-PBF) in-situ alloyed NiTiCu for biomedical applications. The influences of heat treatment temperature and duration on the microstructural homogeneity, phase transformation temperatures and sequences of the NiTiCu alloy are studied. Heat treatments with elevated temperatures and long duration cause a significant increase in porosity. To achieve sufficiently good microstructural homogeneity with low porosity, an optimum post homogenization heat treatment scheme is determined. All heat treatments lead to the formation of secondary phase Ti₂(Ni,Cu), along with precipitates dispersed throughout the matrix, which induces two-step phase transformations to occur. Moreover, the Cu addition into NiTi shape memory alloy is found to increase the wear resistance of the alloy under lubrication conditions. Conversely, under dry conditions it had an adverse effect on the tribological properties. Overall, AM is shown to have a positive impact on the wear behaviour of the alloy under both testing environment.