Moderate temperature CVD of Ti-B-C-N on cemented carbide tools : Properties and metal-cutting tests

Moderate Temperature CVD (substrate temperature : 850°C) was used to deposit wear resistant coatings in the Ti-B-C-N system onto cemented carbides. The effects of various process parameters on composition, microstructure, hardness and wear resistance were investigated. X-ray diffraction studies of the coatings revealed an isomorphous mixture of cubic TiBCN. It was found that the C:N ratio in the coatings could be maintained constant by varying the precursor content in the gas phase. In addition the coating microstructure changed from columnar to fine grained when small amounts of B were introduced. Raising the B-content of the coatings increased the hardness from 2500 to 4300 HV. The decarburization effect (building of eta-phases) at the cemented carbide surface was also enhanced by higher B levels. Since the diffusion of the B is responsible for this decarburization effects, coatings of TiN or TiCN could act as diffusion barrier. Milling tests showed good abrasion wear resistance with coatings having low B content. Turning experiments were performed with monolayer and double layer coatings of TiBCN and TiCN/TiBCN. The dominant wear mechanism was crater wear