Structural evolution of magnetron sputtered shape memory alloy Ni–Ti films

Abstract

Near equiatomic and Ti-rich Ni–Ti polycrystalline films have been deposited by magnetron co-sputtering using a chamber installed at a synchrotron radiation beamline. The in situ X-ray diffraction studies enabled the identification of different steps of the structural evolution during film processing. The depositions on a 140 nm amorphous SiO2 buffer layer heated at 520 °C (without applying bias voltage, Vb, to the substrate) led to a preferential growth of <100> oriented grains of the Ni–Ti B2 phase from the beginning of film growth until the end of the deposition. Films exhibiting a preferential growth of <110> oriented grains of the Ni–Ti B2 phase from the beginning of the deposition were obtained (without and with a Vb of −45 V) by using a TiN coating with a topmost layer formed by <111> oriented grains. Those trends have been observed for the growth of near equiatomic (≈50.0 at.% Ti–Ni) and Ti-rich (≈50.8 at.% Ti–Ni) Ni–Ti films. Additionally, an ion gun had been commissioned, which allows ion bombardment during sputter deposition or post-deposition ion irradiation. In this first series of experiments, a Ni–Ti film was irradiated with He ions after deposition (without exposing the film to the atmosphere, i.e., avoiding surface oxide formation), thus modifying deliberately the microstructure of the film locally.