Effect of substrate carburizing on properties of TiN (Ti) hard coatings deposited on Ti-6Al-4V alloy

Abstract:

Interface fracture often occurs in systems of soft substrate and hard coatings during the service process. That fracture is related to the weak interface strength and also the unstable expansion of cracks along the interface induced by the residual thermal stress. The residual thermal stress mainly comes from the mismatch of thermal physical properties between matrix and hard coatings. In this study, a gradient carburized layer was formed on TC4 substrate before the deposition of TiN(TiN) coatings using double glow plasma carburization. And then the mono- and multilayer TiN(Ti) coatings are synthesized on the carburized layer, forming composite hard coatings. The effect of substrate carburizing on properties of coatings is studied. The results showed that the composite coatings’ hardness could be increased nearly 2 times and the bonding strength was enhanced to over 80N, comparing with mono- and multilayer TiN(Ti) coatings. Also the interface brittle fracture tendency was restrained obviously by the harden substrate, and the coordinative deformation ability of coating at extra load was optimized. The composite coating composed of pre-carburized layer and TiN hard coating showed a higher strength and toughness.

Key words:carburized;layer, TiN/TiN;coating, interface;fracture, micro;hardness, bonding;strength