Structure and corrosion behaviour of CrxAl(Si)yC coatings fabricated by the vacuum arc discharge technique

Abstract

The composition, structure and corrosion behaviour of CrxAly(Si)C coatings fabricated by the arc discharge techniques using Cr-Al-Si and graphite cathodes were studied. X-ray photoelectron spectroscopy, X-ray energy-dispersive spectroscopy, nuclear reactions, and Rutherford backscattering methods were applied to determine composition of the coating, X-ray diffraction and transmission electron microscopy — to investigate the structure of the coating. Corrosion tests were performed in an electrochemical cell in a 3.5 % NaCl solution. Depletion of the cathode surface of chromium, screening of Cr+ by C+ in plasma, and selective etching of the coating upper layers are accompanied by a decrease of Cr / (Al + Si) ratio in the coatings compared to the cathode. The carbon content (CC) in CrxAl(Si)yC, determined by XPS, EDS and NR, differs by several times. The CC measured by NR correlates with the results of Raman spectroscopy and confirms the existence of a continuous carbon matrix in CrxAly(Si)C. Cr is chemical bonded with carbon, silicon — with carbon and aluminum. The Al-Si system provides the structure feature of CrxAl(Si)yC: a network of aluminum intersects the amorphous matrix. The mechanical mismatch and weak bond between the Al structures and the amorphous matrix may be the reason for the formation of defects in the form of cracks and microchannels along the boundaries.