Impact of SHI on structural and mechanical behavior of intermetallic NiTi thin films

In the present investigation, nanocrystalline thin films of NiTi are grown on Si substrate by dc-magnetron co-sputtering using Ni and Ti sputtering targets. These as- grown NiTi thin films are irradiated by 90 MeV Ni ions with fluences 1 × 1012, 3 × 1012, 9 × 1012 and 1 × 1013 ions/cm2, respectively. The elemental composition and depth profile of the pristine film are analyzed by Rutherford backscattering spectrometry. Further, structural, surface morphology and mechanical properties of these films are investigated by X-ray diffraction (XRD), atomic force microscopy (AFM) and nanoindentation techniques, respectively. X-ray diffraction result shows the presence of both austenite and martensite phases in the pristine film with the preferred growth of (110) orientation. The crystallite size is decreased with increase in the ion fluence as compared to pristine film. The AFM images confirm the variation in surface roughness values with the change in the incident ion fluence. The nanoindentation investigation has revealed the enhancement in the mechanical behavior of the NiTi films with ion fluences. The irradiated NiTi film at a fluence of 3 × 1012 ions/cm2 exhibits higher hardness, elastic modulus and depth recovery ratio and therefore better wear-resistance as compared to other films. This result of nanoindentation indicates the higher ductility of NiTi film in comparison of pristine film and their applicability for Micro-electromechanically system applications (MEMS).