The effect of yttrium incorporation on the oxidation resistance of Cr–Al–N coatings

Cr–Al–N hard coatings exhibit considerable oxidation resistance due to the formation of stable, dense α-(Al,Cr)2O3 mixed oxide scales, which makes them promising candidates for advanced machining and other high temperature applications. Here, the effect of Y on the oxidation resistance of magnetron sputtered Cr–Al–N coatings with Al/Cr ratios close to 1.2 and Y-contents of 0, 1, 2, and 4 at.%, corresponding to YN mole fractions of 0, 2, 4, and 8% is studied. The oxidation resistance is investigated under isothermal and dynamic conditions up to 1400 °C. Structure and morphology of the oxidized films are studied by X-ray diffraction and electron microscopy. Based on our results we can conclude that Y incorporation has a considerable impact on the oxidation performance of the (Cr1 − xAlx)1 − yYyN films studied. Coatings with 2 and 4 mol% YN show significantly lower weight gains during isothermal oxidation and hence exhibit a higher oxidation resistance than Y-free Cr–Al–N films. However, YN-mole fractions > 4% are found to be detrimental to the oxidation resistance, as fast growing, porous oxide scales are formed.