Abstract
A titanium nitride layer was deposited mainly onto HIP-treated WC-10%Co substrate by ion plating (PVD) process at 773 K. The structure at an interface between substrate and layer, and the transverse-rupture strength (TRS) of the coated alloy were examined as a function of the layer thickness (\lesssim5 μm), the surface state of substrate (ground or polished) etc. The effect of annealing of the coated alloy on the structure and strength was also examined.
It was found that a foreign phase having no definite crystal structure formed generally at the interface. The thickness of this phase (\lesssim0.5 μm) did not vary with the layer thickness, but with the surface state of substrate. The foreign phase changed to η(Co3W3C) by annealing at 1073-1173 K. The foreign phase formation would be due to the diffusion of carbon atoms in the substrate near the interface into the coated layer. The TRS of the coated alloys decreased with increasing thickness of the layer, showing that the adhesion between substrate and layer was sufficient by the formation of non-equilibrium phase as above. The TRS was higher, when the substrate surface was in a ground state. When the coated alloys were annealed, the TRS decreased with increasing annealing temperature. It was shown that the fracture of the coated alloys generally took place at the moment of fracture of the coated layer, in other words, the TRS of the coated alloys was mainly controlled by the strength of layer.
