Nobuhiko Shima

Microstructural investigation of α-Al2O3-epitaxially coated cemented carbide cutting tools

Cemented carbide cutting tools coated with a TiN layer, a Ti(C,N) layer, a bonding layer, and an α-Al2O3 layer by a chemical vapor deposition method have been developed. Epitaxial growth among the Ti(C,N) grains, the bonding layer grains, and the α-Al2O3 grains were observed by cross section transmission electron microscopy. X-ray diffraction results indicate that the epitaxial growth could be realized in many areas of the coating. This epitaxial growth can be considered as the origin for the improved close adherence of the layers and prolonged life of the developed cutting tools. It was also concluded that stepped surfaces of many vertical-plane shape protrusions in the bonding layer had promoted the epitaxial growth of the α-Al2O3 grains.