Tailorable TiNiX (X = Cu, Hf) Shape Memory Alloy Thin Films from Recycled Sources for Next-Generation Microactuators

Freestanding and bimorph shape memory alloy (SMA) thin films offer a compelling pathway toward compact, low-power actuation in next-generation microsystems. However, developing such films remains challenging due to difficulties in achieving controlled composition, reliable release from substrates, and electrical insulation for device integration. This work demonstrates the first known fabrication of SMA thin films derived from recycled TiNi-based ingots, establishing a sustainable and economically viable pathway for future actuator manufacturing. TiNiCu and TiNiHf microfilms were fabricated using physical vapor deposition (PVD) from recycled SMA ingots TiNiCu (Ingpuls/ Khanjur) and TiNiHf (NASA Glenn), transformed into 3-in. sputtering targets as the source material. Energy-dispersive X-ray spectroscopy (EDX) confirmed that the film composition deviates from that of the target as a result of preferential sputtering during DC magnetron sputter deposition, producing Ni-rich (Ni > 50 at. %) film that results in superelastic or non-transforming characteristics. The recycled SMA targets were co-sputtered with a Ti source to adjust and tailor the composition within a promising transformation regime and subsequently annealed to yield functional transformation properties for future micro-actuation. Samples with promising compositions and thicknesses ranging from 300 nm-2 µm were deposited onto Si and Mo substrates. The phase transformation behavior of the co-sputtered films was characterized using differential scanning calorimetry (DSC), X-ray diffraction (XRD), and temperature-dependent resistivity measurements. These findings validate the feasibility of using recycled SMA ingots as sputter targets to produce functional thin films, and support Khanjur R&D’s industrial PVD process of TiNi-X thin-films for scalable production of next-generation SMA microactuators.