Thermal stability and oxidation behavior of AlTiN, AlCrN and AlCrSiWN coatings

Al0.66Ti0.34N, Al0.66Cr0.34N and Al0.65Cr0.30Si0.04W0.01N hard coatings were fabricated by cathodic arc evaporation technology. WC-12Co-0.95Cr3C2-0.35VC cemented carbide with a grain size of 0.3 μm was used as the substrate. For the comparison research of the thermal stability and oxidation resistance, the coated cemented carbide specimens were treated in Ar and ambient atmosphere at 700, 800, 900 and 1100 °C for 2 h, respectively. The characteristics associated with the phase evolution were determined by scanning electron microscopy, energy dispersive spectroscopy, X-ray photoelectron spectroscopy, X-ray diffractometer and nanoindentation tester. The change in the composition on the cross section and the thickness of the oxidized layer were analyzed by electron probe micro-analysis. It is shown that among the three coatings, Al0.66Cr0.29Si0.04W0.01N exhibits the highest hardness (HV8 mN) of 33.96 GPa at ambient temperature, however it obtains the lowest hardness of 18.99 GPa at 1100 °C in Ar. At 900 °C in Ar, AlTiN acquires a maximum hardness of 29.48 GPa which is the highest among the three coatings. Oxidation resistance of the three coatings is evaluated in the following order: Al0.65Cr0.30Si0.04W0.01N > Al0.66Cr0.34N > Al0.66Ti0.34N. The reasons behind the differences in the properties are discussed.