Sinter-Based Additive Manufacturing of Ni–Ti Shape Memory Alloy

Additive manufacturing (AM) of Shape Memory Alloys (SMA) is an emerging technology that can open the route for numerous new applications in the fields of actuation, sensing, energy harvesting, and heat management. Currently, most AM processes of SMA rely on liquid-state methods that locally melt the metallic feedstock. Recent advances in sinter-based AM have the potential to facilitate the control over the final microstructure and properties of the printed SMA. This article presents the production and characterization of Ni–Ti SMA using sinter-based Lithography-based Metal Manufacturing (LMM). We report a recoverable strain of up to 2.3% under compression, while the amount of irrecoverable plastic strain is smaller than 0.05% up to a stress of 800 MPa. The high strength with moderate recoverable strain is attributed to the carbon content that promotes the formation of Ti-carbides during high temperature sintering. We analyze the origin and role of the carbides in the thermo-mechanical response of the AM Ni–Ti and argue that this strengthening mechanism calls for further studies and can be beneficial for certain applications. Our results indicate that LMM is a feasible and promising method to produce net-shaped SMA and encourage future studies of other sinter-based AM processes.