Development of high adhesive -Al{sub}2O{sub}3 films coated on cemented carbide cutting tools by CVD

摘要

Cemented carbide cutting tools coated with a TiN layer, a MT-Ti(C, N) layer, a bonding layer and aα-A1{sub}2O{sub}3 layer in subsequent process steps in a hot wall Chemical Vapor Deposition (CVD) reactor have been developed, whose lifetime wasabout twice as long as that of the ordinaryκ-A1{sub}2O{sub}3 coated ones in cutting tests on a cast metal FC250 due to the improved adherence ofα-A1{sub}2O{sub}3 layer.The CVD coatings of the developed cutting tools have been investigated using X-ray diffraction, SEM, EPMA, TEM and TEM-EDX, and the following characteristics were found:(1) The bonding layer grains consisted of Ti, C, N and 0, or of Ti, C and O.(2) The crystal structure of the bonding layer phase were found to be face centered cubic with the lattice parameter of 0.431 nm.(3) The bonding layer grains grew epitaxially on the MT-Ti(C, N) layer grains.(4) No disorder of lattice fringes in some interfaces between the bonding layer grains and theα-A1{sub}2O{sub}3 layer grains could be found.The facts (3) and (4) among these were considered to be the causes for the improved lifetime or adherence of theα-A1{sub}2O{sub}3 layer.