Diffusion evaluation of Cu in NiTi Bi-layer thin film interface

Abstract

NiTi alloys are shape memory alloys (SMAs) which combine two very unique properties, shape memory effect and super-elasticity. These properties depend strongly on the composition and structure.In this research volume diffusion of Cu in bulk Ni50.8Ti49.2 alloy with B2 ordered structure has been measured and diffusion phenomenon on a bi-layer Ni–Ti thin film was also studied. The penetration profiles were determined by two techniques: secondary ion mass spectroscopy (SIMS) and energy dispersive X-ray analysis (EDS). Cu diffusivity in NiTi–Ni rich bulk was found to follow linear Arrhenius dependencies with the pre-exponential factor of 5.8±1×10−14m2/s and the activation energy of 40±4kJ/mol. Anti-site defect diffusion mechanism is suggested to provide diffusion of copper in NiTi alloy. The diffusion coefficient of Cu in Ni–Ti Ni-rich was used to estimate the gradient composition in the bi-layer thin film (Ni-rich/NiTiCu) after annealing. The bi-layer thin film was deposited on Si (111) using DC magnetron sputtering and annealed at 773K for 1h. The crystallization temperature and microstructure of the thin film were characterized using differential scanning calorimeter (DSC) and X-ray diffractometer (GIXRD). The results depicted that estimation of the concentration gradient in the bi-layer thin film using the diffusion equation obtained from the NiTi bulk samples shows good agreement with the measured concentration gradient in the bi-layer.