Thermal Evolution of WC/C Nanostructured Coatings by Raman and In Situ XRD Analysis

Abstract

Abstract In this work, a series of WC/C nanostructured films were deposited on silicon substrates by changing the ratio of sputtering power applied to graphite and WC magnetron sources ( P C / P WC : 0, 0.1, 0.5, 1). The thermal stability of WC/C coatings was followed in situ by means of X‐ray diffraction measurements up to 1 100 °C in vacuum (10 −1 Pa). Initially, the film microstructure is composed of nanocrystalline WC 1− x and W 2 C phases. As the P C / P WC ratio increases the crystallinity decreases, and WC 1− x becomes the predominant phase from P C / P WC = 0.1. The results show that the structural evolution with temperature of all studied layers depends essentially on their initial phase and chemical composition (determined by the synthesis conditions: ratio P C / P WC ). The coating deposited at P C / P WC = 0 reveals a transformation of W 2 C phase into W and W 3 C phases at 400 °C. However, the samples with P C / P WC greater than 0 exhibits an improved thermal stability up to 600–700 °C where the WC 1− x begins to transform into W 2 C and WC phases. At 900 °C, WC is the predominant phase, especially for those coatings prepared with higher ratios. Further annealing above 1 000 °C yields W as the foremost phase. The thermal behaviour was later studied by means of Raman spectroscopy measurements at certain temperatures where the main changes in phase composition were observed. Particularly, a fitting analysis was carried out on the D and G bands typical of disordered and amorphous carbon. The changes induced during heating are discussed in terms of the positions of D and G lines, and full width at half maximum (FWHM).