Effect of post-heat treatment on mechanical, microstructure, and thermal properties of Nitinol (NiTiNb) manufactured using laser direct metal deposition (LDMD) process

This study investigated the effect of annealing on the microstructure, mechanical properties, and thermal properties of Ti51.25Ni41.25Nb7.5 ternary nitinol alloy manufactured using the laser direct metal deposition (LDMD) technique. The mechanically pre-alloyed powder consisting of the composition of Ti52.5Ni42.5Nb7.5 was used as a feedstock to manufacture cubic samples on a Ti6Al4V base plate. The manufactured samples were subjected to post-heat treatment at temperatures of 700 degrees C and 900 degrees C. The produced samples were then characterized using scanning electron microscope (SEM), Vickers hardness, nano-indentation, Differential Scanning Calorimeter (DSC), and X-ray diffraction (XRD). SEM micrographs of both annealed samples showed dissolution of the eutectic phase that was present in the as-built sample into the matrix as beta-Nb phase, which resulted in the annealed samples having increased hysteresis. The Ni3Ti peaks' prominence increased with annealing temperature, leading to an increase in hardness.