1986 Volume 35 Issue 394 Pages 743-748
The WC-Co alloys coated with TiN by chemical vapour deposition process are substantially improved in their wear resistive properties, but are deteriorated in the failure resistance in comparison with those of the same alloys coated by physical vapour deposition process.
When the residual stress of WC-Co alloys coated with TiN by CVD or PVD process was measured by X-ray method, the residual stress of the CVD coated alloys was tensile, while that of the PVD coated alloys was compressive.
To estimate the effects of these residual stresses on the strength of the TiN-coated alloys, transverse-rupture strength was measured, and the crack sensitivity was also examined from the crack length around a Rockwell hardness indent. Owing to the residual stress of tension in the CVD coated alloys, the crack sensitivity increased and the fracture strength decreased.
When the PVD coated alloy was annealed at a temperature above 1173K, the residual stress of compression changed to tensile stress and the crack sensitivity increased. To make clear the cause of the change of these residual stresses in TiN-coated alloys, X-ray diffraction patterns were measured by use of Co Kα radiation monochromated by a graphite monochrometer, and furthermore, the crystalline states of the coated layer, the substrate and the interfacial phases were investigated by EPMA.