Hongjian Zhao

Structure and mechanical properties of reactive sputtered WCN films

The WCN films with different C contents were deposited under different substrate bias by a sputtering system. The composition, structure and mechanical properties were characterised by X-ray photoelectron spectroscopy, X-ray diffraction, high resolution transmission electron microscopy, scanning electron microscopy, atomic force microscopy and nanoindentation. Results showed that the WCN films consisted of WCN, W2N, amorphous C and CNx phases. With the incorporation of C content, the growth pattern changed from continuous columnar to discontinuous columnar due to grain refinement. By applying substrate bias to the films, the growth pattern changed from discontinuous columnar to fine grained structure because the bias could enhance the mobility of impinging ions or atoms leading to film densification. As increasing the C content, the hardness first increased and then decreased due to the effect of solid solution strengthening and grain refinement. However, the substrate bias had little influence on the hardness because of the co-action of the dense structure and residual stress induced by bias.

Influence of yttrium addition on reactive sputtered W–Y–N coatings

W–Y–N coatings with yttrium content ranging from 0 to 8.2 at.-% were deposited by reactive magnetron sputtering technique. The influence of yttrium content on the structure, oxidation resistance and mechanical properties was investigated. The results show that yttrium atoms substitute tungsten atoms forming the solid solution W–Y–N coatings. All the coatings exhibit a single-phase face-centered cubic structure and the preferred orientation changes from (200) to (111) with yttrium addition. The grain size of W–Y–N coatings decreases with the increase of yttrium content. The oxidation resistance temperature of W–Y–N coatings increases from 500°C at 0 at.-% Y to 730°C at 8.2 at.-% Y. All coatings are in compressive stress state. The hardness, elastic modulus and compressive stress of W–Y–N coatings increase gradually from 28.0, 320 and 1.1 GPa at 0 at.-% Y to 36.0, 385 and 2.1 GPa at 8.2 at.% Y, respectively. The improvement of hardness was attributed to the effect of solid solution strengthening and the grain refinement. In addition, the addition of yttrium content into WN coating also improves its resistance against elastic strain and plastic deformation to failure.

The structure and mechanical properties of magnetron sputtered VSiN coatings

VSiN coatings with silicon content ranging from 0 to 19.8 at-% were deposited by reactive magnetron sputtering technique. The structure and mechanical properties were investigated by X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, atomic force microscopy and nano-indentation CSM. The results show that the incorporation of silicon does not affect the cubic structure. VSiN coatings consist of a mixture of fcc-VN, hcp-V2N and amorphous Si3N4 phases. The incorporation of silicon results in the crystallite size refinement and the decrease of the average roughness. With the incorporation of silicon content, the growth pattern changed from continuous columnar to discontinuous columnar due to the grain refinement. The H, H/E and H3/E2 ratios of VSiN coatings first increase and then decrease and the maximum values are 27 GPa, 0.098 and 0.265 GPa, respectively, at 10.2 at-% Si. All the H, H/E and H3/E2 ratios of VSiN coatings are higher than that of vanadium nitride coating.