Recently the concept of creating multi-layer and composite NiTi Shape memory actuators by joining of NiTi to itself and other materials has been explored to meet distinctive applications and improve its properties.  In this research, two NiTi layers with different composition, phase, and thickness were bonded to each other by diffusion bonding method.

Austenite (A) layer with Ni-rich composition and Martensite (M) layer with Cu-included Ti-rich composition were prepared by alloying using vacuum arc melting furnace. Both mating surfaces of two layers were prepared by the conventional grinding and polishing technique to obtain an optical finish. The pair of layers were kept in contact in a purpose-built fixture. Subsequently, the whole assembly was inserted in a vacuum chamber of 10^-4 mbar for 7.2Ks at 1000 ⁰C. 

The penetration at interface and microstructure of composite were characterized by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). An invisible interface with perfect bonding is obtained after diffusion bonding method. Also, phase interface moves from bonding interface as changing in atomic percent of elements. X-Ray Diffraction (XRD) analysis showed that A and M sides were almost fully Austenitic and Martensitic phase, respectively after diffusion bonding.