Influence of Si-addition on wear and oxidation resistance of TiWSixN thin films

TiWSixN films were deposited using a magnetron co-sputtering system on silicon (111), 316L stainless steel, and M2 high-speed steel substrates. The silicon target current density was varied from 0 mA/cm(2) to 4.32 mA/cm(2) in order to modify the Si content in the films. The microstructure and chemical composition were determined by means of X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), respectively. The surface of the films was explored via scanning electron microscopy (SEM) and atomic force microscopy (AFM). Mechanical, tribological, and thermal properties were investigated by means of the nanoindentation, ball-on-disc, and cyclic oxidation tests, respectively. Our results indicated that as the silicon target current density was increased, the microstructure changed from crystalline to amorphous, and the hardness and elastic modulus improved from initial values of 7.5 +/- 0.3 GPa and 181 +/- 8 GPa to 15 +/- 1 GPa and 229 +/- 9 GPa, respectively. Furthermore, films deposited at high silicon target current exhibited better resistance to thermal oxidation. The failure mechanism of the WTiSixN thin films under cyclic oxidation was attributed to the microstructure of the films, WO(3 )sublimation, and the thermal coefficient mismatch between the film and the substrate.