Development of High Adhesive α-Al₂O₃ Films Coated on Cemented Carbide Cutting Tools by VCD

Abstract

Cemented carbide cutting tools coated with a TiN layer, a MT-Ti(C, N) layer, a bonding layer and a α-A1₂O₃ layer in subsequent process steps in a hot wall Chemical Vapor Deposition (CVD) reactor have been developed, whose lifetime was about twice as long as that of the ordinary K-A1₂O₃ coated ones in cutting tests on a cast metal FC250 due to the improved adherence of α-A1₂O₃ 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 O, 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 the α-Al₂O₃ 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 the α-Al₂O₃ layer.