Microstructural changes in CVD κ-Al2O3 coated cutting tools during turning operations

This work is concerned with the microstructural evolution in CVD kappa-Al2O3 coatings during metal cutting. The wear characteristics and the kappa-Al2O3 to alpha-Al2O3 phase transformation during metal cutting have been studied in detail by means of transmission electron microscopy and scanning electron microscopy. Based on the results of these investigations, the different wear mechanisms of kappa-Al2O3 coated cemented carbide tools in metal cutting are discussed. Under the cutting conditions studied, flank wear depth developed at about twice the speed of rake face wear. No phase transformation occurred on the flank face, leading to wear of the non-transformed kappa-Al2O3 of a more abrasive nature. On the rake face, a region of the kappa-Al2O3 coating was transformed to alpha-Al2O3, and the wear crater was positioned inside the transformed alpha-Al2O3 area. The surface zone in the crater displayed a higher dislocation density, an indication of the occurrence of plastic deformation. It is concluded that the transformation from kappa-Al2O3 to alpha-Al2O3, and the wear of the transformed alpha-Al2O3 by plastic deformation, are characteristic of the rake face wear. (C) 1999 Elsevier Science S.A. All rights reserved.