Fabrication of multi-functional Ni–Ti alloys by laser powder bed fusion

Ni–Ti alloys with multiple transformation temperatures for a single component can be called multi-functional Ni–Ti alloys. Multi-functional Ni–Ti alloys can increase the flexibility of designing complex systems and have broad application prospects. Existing research mainly focuses on manufacturing multi-functional Ni–Ti alloys through welding or changing the local Ni/Ti ratio. However, the above-mentioned methods have problems such as the low connection strength of the welded part, difficulty of precisely controlling the Ni–Ti ratio, and poor design flexibility. In this paper, laser powder bed fusion (LPBF) was used to successfully fabricate multi-functional Ni–Ti alloys. Ni-rich (Ni53.4-Ti46.6 (at.%)) powders and Ti–rich (Ni46.4-Ti53.6 (at.%)) powders were prepared. The Ni-rich powder was first used to fabricate super-elasticity (SE) parts with a high relative density. The Ti–rich powder was then used to manufacture shape memory effect (SME) parts with different process parameters based on the SE parts. These integrated components were processed into dog-bone shapes and subjected to tensile tests. The sample that had the highest ultimate tensile strength while manufactured at a relatively low energy density was selected for further analysis. The properties of the sample, such as the microstructure and transformation temperature, were analysed through a series of tests. The results confirm that LPBF is a suitable method to fabricate multi-functional Ni–Ti alloys.