Influence of Iron Diffusion on the Oxidation Resistance of CrSiCN Hard Coatings

Abstract

Radiofrequency (RF) reactive magnetron sputtering was used to deposit thin SiCN and CrSiCN films on high-speed steel or silicon substrates. Nanoindentation, scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM-EDS), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) analyses were used to investigate the changes in the mechanical properties and microstructure of the CrSiCN films after annealing. The CrSiCN (37.6%Cr) film deposited on the Si substrate showed little change (¹12%) in the indentation hardness and microstructure after annealing in air at 800°C for 1 h. Comparatively, the hardness of the same films deposited on high-speed steel substrates was greatly degraded (¹36% to ¹50%). The microstructure of the films also changed remarkably after annealing in air or even under vacuum using the same temperature and time conditions. TEM/XPS analyses suggested that the mechanism of degradation of the CrSiCN films involved decomposition of the SiCN phase, induced by CrN and diffusion of Fe from the substrate. The diffusion of Fe formed FeSi in the films, while CrN generated CrC, which induced grain growth of the CrN phase and degraded the indentation hardness of the films. Thermodynamic calculations were performed to demonstrate the possibility of these reactions. The formation of crater wear faults in the CrSiCN hard coatings used for machining tools was also discussed.