ALUMINA COATED CUTTING TOOL

摘要

A coated cutting tool insert consisting of a substrate comprising cemented carbide, cermet, ceramics, steel or cubic boron nitride having deposited thereon a coating of a total thickness of a maximum of 60 μm comprising one or more layers comprising a wear resistant layer of α-Al2O3 of a thickness of 1 to 45 μm deposited by chemical vapour deposition (CVD), wherein when observed in a SEM microphotograph of a cross section of the α-Al2O3 layer, the α-Al2O3 layer comprises at least two portions, a first thickness portion and a second thickness portion immediately on top of the first thickness portion, the first thickness portion having an essentially columnar α-Al2O3 grain structure, and at the transition from the first thickness portion to the second thickness portion the grain boundaries of at least 1 out of 25 neighbouring grains, preferably of at least 5 out of 25 neighbouring grains, more preferable of at least 15 out of 25 neighbouring grains, of the α-Al2O3 grains undergo a directional change into a direction that is essentially perpendicular to the grain boundaries in the first thickness portion, wherein essentially perpendicular includes a directional change of 90 ± 45 degrees, preferably 90 ± 30 degrees.