The effect of annealing temperature on the structural, morphological, mechanical and surface properties of intermetallic NiTi alloy thin films

In this work, we report our studies on intermetallic NiTi thin films grown on silicon (1 0 0) substrates by glancing angle DC-magnetron sputtering technique using separate sputter targets Ni and Ti. The as prepared intermetallic NiTi thin films were vacuum annealed for one hour at four different temperatures, i.e. 350, 450, 550 and 650 °C. The crystallization and surface morphology were studied using X-ray diffraction technique (XRD), Field Emission Scanning Electron Microscopy (FESEM) and Atomic Force Microscopy (AFM). It was observed that the annealing temperatures had a significant influence on structural, morphological, mechanical and surface properties of intermetallic NiTi thin films. XRD studies revealed that the degree of crystallization increased with the increase in annealing temperature. The surface mean height (Ra), root mean square (RMS) and maximum peak to valley height (P-V) values have been obtained by AFM characterization. Nanoindentation tests on annealed intermetallic NiTi thin films were performed at room temperature. The hardness and elastic moduli increased from 8.32 to 10.24 GPa and from 154.60 to 164.49 GPa, respectively, with respect to the increase in annealing temperature. X-ray photo-electron spectroscopy (XPS) was used to study the composition and surface chemistry of the annealed films. From HR-XPS investigations, it was observed that intermetallic NiTi thin films had higher affinity to form Titanium dioxide (TiO2) layer on the film surface leaving a Nickel enriched matrix immediately behind the metal oxide layer.