Study on high-temperature oxidation resistance of CrAlN coatings

The effect of bias voltage on the oxidation behavior of CrAlN coatings was studied, in air for 20 h at 900C. The structures and the surface morphologies of CrAlN coatings before and after oxidation were examined by X-ray diffraction (XRD) and Field Emission Scanning Electron Microscopy (FESEM). Mass gain was measured every 4 h. The results show that Al concentration in coatings increases and the oxidation resistance of the CrAlN coatings is improved as the increase of the bias voltage. The following conclusions are drawn: 1) more mixed Cr and Al oxide form with the increase of the bias voltage, this mixed oxide layer can act as an effective diffusion barrier slowing down the inward diffusion of the oxygen at high temperatures; 2) Al and N atoms are covalently bonded which will improve the thermal stability of coatings. © 2009, Northwest Institute for Nonferrous Metal Research. Published by Elsevier BV. All rights reserved.