Study of thermal stability of some hard nitride coatings deposited by reactive magnetron sputtering

The thermal stability of Cr 2N x , CrN x , TiN and TiN x (B) y coatings was investigated in the temperature range of 300–1300 K, by characterization of their microstructural changes and oxidation behaviour. The microstructural changes were studied by high temperature X-ray diffraction under vacuum conditions (10 −3 Pa). The increase of temperature induces grain growth, crystallization of amorphous phase, phase decomposition and oxidation. All these phenomena appear at different temperatures depending on the coating material. The effects of annealing temperature on mechanical properties were characterized by means of the scratch test and Vicker's microhardness. Different evolutions of the critical load and microhardness were observed for each coating. Some relations between evolutions of the mechanical properties and the microstructure have been identified. The oxidation temperature of Ti-based coatings deposited on alumina substrates was determined by thermal gravimetric analysis. The highest thermal stability was observed for TiN x (B) y coatings, according to microstructure, oxidation resistance and mechanical properties.