A study of oxidation behavior of AlTiN-and AlCrN-based multilayer coatings

In this work, AlTiN/TiSiN and AlCrN/TiSiN multilayer coatings were deposited by arc ion plating on Al2O3 and cemented carbide substrates. The oxidation resistances of the coatings were studied under isothermal conditions up to1000°C. The oxidation behaviors of the multilayer coatings were studied by means of cross-sectional SEM (X-SEM), energy dispersive X-ray (EDX) maps analysis, X-ray diffraction (XRD) and EDX line-scanning after oxidation at 800 °C, 900 °C and 1000 °C in air for 2 h. The oxide scale formed on the surface region of the AlTiN/TiSiN coating illustrates a mixture of porous (Al, Ti)-Oxide scale. On the contrary, the oxide scale of the AlCrN/TiSiN coating mainly consists of a mixed (Ti, Al)-oxide scale outside layer and a dense (Al, Cr)2O3 inner layer. During the isothermal oxidation, the AlCrN/TiSiN coating exhibits lower weight increment. The oxidation result shows that the AlCrN/TiSiN multilayer coating exhibits more considerable oxidation resistance than that of the AlTiN/TiSiN coating. The formation of a dense protective mixed (Al, Cr)-oxide scale beneath the TiSiN layer acts as a barrier layer, blocking the outward diffusion of the Al, Ti and Cr atoms and retarding inward diffusion of oxygen into the AlCrN/TiSiN coating.