Mechanical Properties of WC-Co Cemented Carbides Coated with Titanium Carbonitride or Titanium Carbide by PVD Process

The HIP-treated WC-(10, 20) %Co alloys were coated with Ti(C,N) or TiC layer (up to 8 μm) at 773K by hollow cathode type ion-plating (PVD) process. The transverse-rupture strength (TRS) of coated alloys and hardness of layers were mainly measured as a function of layer thickness, cobalt contents of substrate and temperatures at which coated alloys were annealed, comparing with the previous results by the authors on coated alloy with TiN layer. The effects of the above factors on the strength of Ti(C, N) or TiC coated alloys as well as the interface structures between the layer and substrate were in common to the previous results on TiN coated alloy. The strength of Ti(C,N) or TiC coated alloys seemed to be somewhat higher than that of the TiN coated alloy. Hardness of the layers was in the order, TiC>Ti(C,N)>TiN, as expected. The formation of cracks in the layers at a low stress level below TRS was demonstrated for the coated alloys annealed at high temperatures, being a proof that the layers embrittled through annealing at high temperatures.