The microstructure and mechanical properties of nitinol manufactured by LPBF: differences between Ni-rich and Ti-rich compositions

The utilisation of laser powder bed fusion (LPBF) for nitinol alloys has garnered significant interest, owing to its capability to achieve a 4D response through the shape memory (SME) and superelastic (SE) effects. In this work, Ti-rich and Ni-rich nitinol parts have been additively manufactured by LPBF on Ti substrates to study their microstructure and mechanical response and their corresponding shape memory and superelastic effects. Various processing parameters were studied, including the use of post-printing heat treatments. Significant differences in printability were found between Ti-rich and Ni-rich nitinol. Generally speaking, Ti-rich nitinol showed a better printability and the manufactured parts offered a significant SME, independent of processing parameters and thermo-mechanical history. On the contrary, the printability of Ni-rich nitinol was seriously compromised by severe warping effects, and although the SE effect could be found for all conditions, the extent of SE was very dependent on processing parameters. Nevertheless, post-printing thermal treatments can improve the SE properties significantly.