Structure and hardness of titanium carbide coatings on hard metals

Abstract

Commercial titanium carbide coatings on cemented carbide tools are usually prepared by chemical vapour deposition (CVD). The 3 – 6 μm coating formed produces an improvement in tool life of up to 400% over uncoated carbides. The CVD TiC coating is a result of a heterogeneous gas-solid reaction. During the deposition complicated diffusion processes take place. The uppermost layer of the substrate decarburizes and a layer of 6:6 ν carbide is formed below the coating. In the lower part of the coating an intermediate layer with a very small carbide grain size is found. In order to investigate the role of the binder phase at the beginning of the nucleation and growth of the coating layer, TiC was deposited on a cemented carbide, pure cobalt and a cobalt alloy having the same composition as the binder phase in WC-Co cemented carbides. The nucleation and growth of the TiC was found to be strongly affected by the crystallographic orientation and carbon content of the substrate.