Sulfur containing alpha-alumina coated cutting tool

The present invention relates to A cutting tool insert consisting of a substrate of cemented carbide, cermet, ceramics, steel or a superhard material such as cubic boron nitride (CBN) and a coating with a total thickness of 5 to 40 µm, the coating consisting of one or more refractory layers of which at least one layer is an ±-Al 2 O 3 layer having a thickness of 1 to 25 µm characterized in that the at least one ±-Al 2 O 3 layer having a sulphur content of more than 100 ppm analysed by Secondary Ion Mass Spectroscopy (SIMS) and the at least one ±-Al 2 O 3 layer having a texture coefficient TC (0 0 12) > 4 for the (0 0 12) growth direction, the TC (0 0 12) being defined as follows: TC 0 0 12 = I 0 0 12 I 0 0 0 12 ¢ 1 n ˆ‘ n - 1 n I hkl I 0 hkl - 1 (hkl) = measured intensity of the (hkl) reflection l 0 (hkl) = standard intensity of the standard powder diffraction data according to JCPDF-card no. 42-1468 n = number of reflections used in the calculation, whereby the (hkl) reflections used are: (012), (104), (110), (113), (116), (300) and (0 0 12). The invention also relates to a method of manufacturing a cutting tool insert of any of the previous claims wherein said at least one ±-Al 2 O 3 layer is deposited by chemical vapour deposition (CVD) the reaction gas of the CVD process comprising H 2 , CO 2 , AlCl 3 and X, with X being H 2 S, SO 2 , SF 6 , or combinations thereof, and optional additions of N 2 and Ar, wherein the X is present in the reaction gas mixture in an amount of at least 1.0 vol-% of the total volume of gases in the CVD reaction chamber and wherein the volume ratio of CO 2 and X in the CVD reaction chamber lies within the range of 1 ‰¤ CO 2 / X ‰¤ 7 during deposition of the at least one ±-Al 2 O 3 layer.