Deposition of Ti _x C layers on TiC hardmetals

Abstract

The chemical vapour deposition of Ti _x C layers on nickel-containing hardmetals is often connected with the formation of small inclusions within the layers depending on the stoichiometryx. The inclusions were identified as the Ni₃ Ti intermetallic compound, which is formed ifx exceeds 1.03. It was found that the deposition of high stoichiometric and, consequently, inclusion-free Ti _x C layers is difficult in the kinetically controlled region of the hydrocarbon decomposition used as carbon carrier in the gas phase (for example C₆H₆, CH₄). It was shown by special experiments, that the intermetallic phase is formed by chemical reaction between the gas phase and solid nickel, which comes into contact with the gaseous components by surface and grain-boundary diffusion processes through the layer. It is possible to reduce or to avoid the formation of inclusions by the substitution of nickel by cobalt or iron as binding metals due to the decreasing thermodynamic stability of the metal-rich intermetallic phases.[/p]