High temperature oxidation of CrTiAlN hard coatings prepared by unbalanced magnetron sputtering

The present research aims to synthesize a multi-component CrTiAlN hard coating for the modification of high-temperature performance, as compared to the traditional TiN and TiAlN coatings. In this work, the quaternary CrTiAlN coatings were deposited on AISI M42 steel substrates by reactive unbalanced magnetron sputtering technique from Cr, Ti and Al elemental targets in Ar + N₂ mixture atmosphere, and their high-temperature oxidation behaviours as well as the oxidized structure were studied after static oxidation tests in air at different temperatures (500-900 °C). The structural, mechanical and tribological properties of the coatings were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), micro-indentation and pin-on-disc tribometer. The composition and depth profiles of the coatings after oxidation were investigated by X-ray photoelectron spectroscopy (XPS) with sputter profiling. The experimental results show that the CrTiAlN coatings outperform the other two conventional hard coatings (TiN and TiAlN) in terms of high-temperature oxidation resistance, structural stability, as well as wear resistance. The higher oxidation resistance is likely related to the formation of dense protective oxide layer consisting of Cr₂O₃ and Al₂O₃, suppressing the further diffusion and penetration of oxygen inside the coatings. After oxidation at 900 °C, the CrTiAlN coatings still retain basically their crystalline structure, surface morphology, hardness and wear resistance. It is expected that the CrTiAlN coating is a good candidate for industrial applications under harsh environments, such as dry high-speed machining. © 2009 Elsevier B.V. All rights reserved.