EFFECT OF Mo CONTENT ON THE MICROSTRUCTURE AND PROPERTIES OF CrMoN COMPOSITE COATINGS

Ceramic coatings are usually used as protective coatings to improve performance and durability of tools and components now. Compared with conventional TiN based hard coating, CrN based coating like Cr-X-N (X=Ti, Al, Si, C, B, Ta, Nb, Ni) is a more interesting choice because of low friction coefficient, superior oxidation resistance and excellent corrosion resistance under severe environment conditions. The CrMoN is among these coatings and attractive since self-lubricating phase MoO(3)may be formed in tribological process. However the effect of Mo content on structure and tribological properties of CrMoN coatings is not still clear. In the present study, CrMoN composite coatings with different Mo content were deposited on M2 high speed steel (HSS) substrates by DC reactive magnetron sputtering. The effect of Mo content on the microstructure and properties was investigated systematically, including the chemical composition, phase structure, chemical valence, cross-section morphologies, microhardness and tribological properties. The results showed that the phase transformation of the as- deposited coatings occurred with the increase of Mo content. The phase structure changed to (Cr, Mo)N substitutional solid solution based on CrN-type firstly, and then to mixed phase with gamma-Mo2N as main phase, and a small amount of elemental bcc-Mo phase appeared when the Mo content is 69.3%. The microhardness of the CrMoN composite coatings always increased until the highest hardness when the Mo content reached to 45.4%, and then decreased; a relatively low friction coefficient was obtained compared with that of the CrN coating when more than 45.4%Mo content was doped. The reason is that the more MoO3 lubricant phase could be formed in tribological process.