Microstructure of highly adhesive TiN-Ti(C,N)-bonding layer-α-Al{sub}2O{sub}3 films coated by CVD on cemented carbide cutting tools

摘要

The microstructure of highly adhesive CVD coatedα-Al{sub}2O{sub}3 films on cemented carbide cutting tool inserts have been investigated. These inserts are coated with a TiN layer, a MT(moderate temperature)-Ti(C, N) layer, a bonding layer, and a α-Al{sub}2O{sub}3 layer by using CVD. SEM, TEM, and TEM-EDX were used to characterize the coatings, and following characteristics were found. (1) The bonding layer is composed of Ti, C, N, and 0 or of Ti, C, and 0. Its crystal structure is a face centered cubic one with a lattice parameter of 0.431 nm. (2) Each grain in the bonding layer continues crystallographically from the MT-Ti(C, N) layer grains. (3) There are crystalline planes running between a grain of the bonding layer and a grain of the α-Al{sub}2O{sub}3 layer. (4) Vertical-plane-shape projections are formed on the surface of bonding layer. The last three characteristics are considered to be the cause for improved α-Al{sub}2O{sub}3 layer adherence and longer tool life. A crystallographical model shows that the above mentioned microstructure is consistent to X-ray diffraction result which shows the (110) plane of α-Al{sub}2O{sub}3 layer is oriented to the parallel of the insert's surface.