Additive Manufacturing of Ni-Ti SMA by the Sinter-Based MoldJet Method

Additive Manufacturing (AM) of Shape Memory Alloys (SMA), and specifically Ni-Ti alloys, is an evolving field with significant potential to applications in actuation, energy harvesting, and refrigeration. Sinter-based AM technologies show promise in tailoring and controlling the microstructure and properties of Ni-Ti, because the metal particles remain in the solid-state throughout the process. Here, we report on the manufacturing and characterization of Ni-Ti produced using a novel sinter-based MoldJet method: a wax-based mold is deposited layer-by-layer using jet-printing, and its cavities are simultaneously filled with metallic paste. This additive process produces a green body that is sintered to form a dense metal part. The low content of organic binder in the metallic paste results in reduced carbon and oxygen contamination compared to other sinter-based AM methods. Consequently, the reduced formation of carbides and oxides enhances the thermomechanical properties. Here, we show that Ni-Ti produced via MoldJet exhibits a superelastic response with a substantial recoverable strain of 5.6% in tension and 4.5% in compression, and irrecoverable plastic strain below 0.2%. The results indicate that MoldJet is a promising method for AM of Ni-Ti for advanced applications. Specifically, we show that the obtained material properties are adequate for elastocaloric cooling devices.