EFFECTS OF Mo CONTENT ON THE MICROSTRUCTURE AND TRIBOLOGICAL PROPERTIES OF CrMoAlN FILMS

In recent decades, CrAlN coatings have been widely used for cutting tools due to their high hardness, good wear resistance, especially excellent thermal stability and oxidation resistance. However, the rapid development in high speeds and dry cutting applications demands further improvement in hardness and wear properties of CrAlN coatings. Mo nitrides coatings are commonly used as protective surface layers against wear and corrosion. The combination of CrAlN and Mo may lead to the development of new composite coatings with superior wear properties. In this study, the CrMoAlN multilayer coatings with different Mo contents were deposited on M2 tool steel and silicon wafers substrates by closed-field unbalanced magnetron sputtering ion plating (CFUMSIP) technique in a gas mixture of Ar+N-2. The chemical composition, surface and cross sectional morphologies, microstructure, mechanical and tribological properties of coatings were studied by EDS, SEM, XRD, XPS, nano-indentation and pin-on-disk tribometer, respectively. The results indicate that the CrMoAlN coatings exhibit fcc structure. Mo atoms substitute Cr and/or Al atoms in CrAlN lattice forming the solid solution CrMoAlN coatings. The surface and cross-sectional morphologies of the CrMoAlN coatings show that the grain size and the column width decrease with the increasing of Mo content. Nano-indentation result reveals a promoted hardness and elastic modulus of the CrMoAlN coatings with enhanced Mo content from 0 to 19.47% (atomic fraction) due to the solid solution strengthening and grain size diminishment. A maximum hardness and elastic modulus of the coatings are found to be 29.70 GPa and 427.53 GPa when the Mo content reached to 19.47%. The average friction coefficient and wear rate were observed to decrease with the increase of Mo content and the lowest values were 0.271 and 1.2x10(-16) m(3)/(N.m), respectively, at 19.47%Mo.