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

Highlights: • Ni-Ti thin films have been deposited on Si substrate by dc-magnetron co-sputtering. • Austenite and martensite phases have been confirmed by XRD. • Mechanical properties of Ni-Ti thin films have been investigated before and after SHI irradiation. • Significant modifications in mechanical behavior have been observed after irradiation. - Abstract: 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).