This work is concerned with the microstructural evolution in CVD κ-Al 2 O 3 coatings during high speed metal cutting. The wear characteristics and the κ-Al 2 O 3 to α-Al 2 O 3 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 κ-Al 2 O 3 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 κ-Al 2 O 3 of a more abrasive nature. On the rake face, a region of the κ-Al 2 O 3 coating was transformed to α-Al 2 O 3 , and the wear crater was positioned inside the transformed α-Al 2 O 3 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 κ-Al 2 O 3 to α-Al 2 O 3 , and the wear of the transformed α-Al 2 O 3 by plastic deformation, are characteristic of the rake face wear.