The Microstructure and Cutting Performance of TiN-Ti (C, N) -a Bonding Layer-α-Al2O3 Films Coated Cutting Tools

We developed cemented carbide cutting tools coated with a layer of TiN, moderate temperature-Ti (C, N), bonding, and α-Al2O3 by chemical vapor deposition (CVD). Tool life is about twice that of ordinary TiN-Ti (C, N) -TiC-κ-Al2O3 coating in cutting tests on a cast metal FC 250 due to improved α-Al2O3 layer adherence. CVD coatings of cutting tools were studied using X-ray diffraction, SEM, EPMA, TEM, and TEM-EDX, with the following results: (1) Bonding layer grains consisted of Ti, C, N, and O, or of Ti, C, and O. (2) The crystal structure of the bonding layer phase was face-centered cubic with a lattice parameter of 0.431nm. (3) Bonding layer grains grew epitaxially on moderate temperature-Ti (C, N) layer grains. (4) No disorder of lattice fringes in interfaces between bonding layer grains and α-Al2O3 layer grains was seen. (3) and (4) are considered to be the reason for improved tool life and α-Al2O3 layer adherence.