Combined Effect of Aluminum Content and Layer Structure on the Oxidation Performance of Ti1−xAlxN Based Coatings

Abstract

TiN, Ti1−xAlxN single layer coatings and TiN/Ti1−xAlxN multilayer coatings were deposited on SKH51 tool steel substrate by arc ion plating. The coatings were annealed in air to study the effect of aluminum and film structure on the oxidation performance. The surface morphology and structure were characterized by scanning electron microscopy and X-ray diffraction. The element distribution on the cross section was analyzed by electron probe microscopy. It is found that the oxidation resistance of these Ti1−xAlxN based coatings is mainly attributed to aluminum content in them. In comparison with the Ti1−xAlxN single layer coating, the TiN layer inserting into the Ti1−xAlxN in a multilayer coating increases the tendency of Ti diffusion toward the surface and forms a Ti-enriched top surface oxide layer, thus degrades the oxidation resistance. As far as the oxidation resistance is concerned in this study, Ti0.33Al0.67N single layer coating performs the best among all coatings. The kinetic of oxidation behavior of all coatings presents two definite stages. One is a slow oxidation growth which conforms to parabolic law, and the other presents severe mass gain with oxidation duration. The annealing time for severe oxidation initiation is responsible to Fe2O3 formation in the oxide scale.