Substrate heating and post-annealing effect on tungsten/tungsten carbide bilayers grown by non-reactive DC magnetron sputtering

Tungsten–tungsten carbide (W/WC) bilayers were produced by non-reactive DC magnetron sputtering at various substrate temperatures between room temperature and 300°C. The coatings were characterized in terms of morphology, structure and chemical composition using several techniques such as X-ray diffraction (XRD), Raman Spectroscopy, Auger Electron Spectroscopy (AES), Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS) and Scanning Probe Microscopy (SPM) in the Atomic Force Microscopy (AFM) mode. Bragg peaks corresponding to the (110) diffraction plane of the W phase and (111), (200), (220) and (311) peaks corresponding to the cubic WC phase were identified. From the XRD analysis, a strong influence of the substrate temperature on the grain size and crystallographic texture was observed; nevertheless, a poor influence on the lattice parameter and microstrain was detected. Furthermore, different vibrational modes of the W3C structure and characteristic peaks corresponding to O3W3O bonds were observed. Depth profile analysis was also carried out using AES, which revealed the presence of C, W, O and Fe. Initially, carbon and tungsten were observed in the WC layers. After the films were totally etched, Fe from the substrate was detected. However, the morphology was not significantly affected by temperature. An important result was the improvement in the coatings' adherence when an interlayer of W was inserted. In this work, the bilayers' behavior during annealing was also studied. The films were observed to oxidize at approximately 600°C.