2-PHASE TIC/TIB2 HARD COATINGS

TiC/TiB2 coatings were deposited on cemented carbide tool bits by non-reactive magnetron sputtering using hot-pressed targets with different TiC:TiB2 molar ratios. In the as-deposited state, homogeneous cubic, hexagonal and amorphous layer structures were obtained depending on the composition. The layer constitution can be predicted by thermodynamic calculations taking into account the kinetics of deposition and film growth. Metastable homogeneous layer materials change their constitution after heat treatment to two-phase layer materials with grain sizes in the nanometer range. The properties and wear behaviour show a strong dependence on the conditions of heat treatment. This is mainly due to different amounts of interfaces formed in the coatings. The best properties and performance were obtained for coatings annealed for 2 h at 1100-degrees-C, showing a microstructure with TiC and TiB2 grains about 100 nm in size.