On the Stability of Multilayer ZrN/SiN x and CrN/SiN x Coatings Formed by Magnetron Sputtering to High-Temperature Oxidation

Abstract

Multilayer ZrN/SiN_x and CrN/SiN_x coatings are formed using the method of magnetron sputtering by the consecutive sputtering of Zr (Cr) and Si₃N₄ targets upon a variation in the thickness of an individual layer from 2 to 10 nm at a substrate temperature of 300°C (ZrN/SiN_x system) and 450°C (CrN/SiN_x system). X-ray diffraction analysis demonstrates that multilayer ZrN/SiN_x and CrN/SiN_x coatings consist of nanocrystalline ZrN (CrN) layers with the preferred orientation (002) and amorphous SiN_x layers. The lattice parameters of the metal nitride phase for the ZrN/SiN_x and CrN/SiN_x films are greater than for monolytic ZrN and CrN layers, respectively, and, in the case of ZrN/SiN_x films, the lattice parameter increases upon a reduction of the ratio of ZrN to SiN_x elementary-layer thicknesses, which can be associated with the growth of compressive stress. As wavelength dispersive X-ray spectrometry of the film composition and scanning electron microscopy of the surface show, the multilayer ZrN/SiN_x and CrN/SiN_x coatings are more resistant to high-temperature oxidation (in the temperature range of 400–950°C) in comparison with the ZrN and CrN coatings. This resistance increases upon a decrease in the ratio of the thickness of the ZrN individual layer to that of the SiN_x individual layer as well as upon an increase in the quantity of layers in the film. However, these factors are not so deciding in the case of CrN/SiNx system. In general, CrN/SiN_x coatings are more stable than ZrN/SiN_x coatings under the conditions of high-temperature oxidation.