Wear mechanism of thermally transformed CVD Al2O3 layer

Wear mechanism of the thermally transformed CVD α-Al2O3 that was produced from as-deposited κ-Al2O3 by different heat-treatment processes have been investigated. For alloy steel turning, the wear of the transformed α-Al2O3 produced by a heat-treatment through a cooling process after κ-Al2O3 deposition was uneven, that is, small chippings and flakings of the layer occurred on the wear surface, although its wear resistance was higher than that of as-deposited α-Al2O3 and as-deposited κ-Al2O3. On the other hand, the transformed α-Al2O3 produced by the heat-treatment without a cooling process but in connection to κ-Al2O3 deposition showed an excellent wear resistance without uneven wear. For the α-Al2O3 transformed without a cooling process, crack generation during the cooling is inhibited by the microcracks that have been generated before the cooling by a phase transformation of κ → α. Wear resistance is improved because the cooling cracks with a wide width, which will act as starting points of the uneven wear, decrease.