Oxidation behavior of Si-doped nanocomposite CrAlSiN coatings

Recently more and more hard coatings greatly emphasize the importance of oxidation characteristics. This study attempts to dope Si into conventional CrAlN to form the CrAlSixN coatings by RF magnetron sputtering on silicon wafers to investigate how Si content affects oxidation behavior. The oxidation resistance of the CrAlSixN coatings was evaluated after annealing at temperatures ranging from 800 to 1000 °C. The X-ray diffraction patterns revealed that the CrAlSixN (x = 0–10.2 at.%) coatings exhibited better oxidation resistance than that of traditional CrAlN coatings. As observed from SEM micrographs, the CrAlSixN coatings exhibited denser feature than CrAlN one. The columnar structure, typically existing in CrAlN coating and being harmful to oxidation behavior, was also eliminated. Doping certain Si content could indeed assist CrAlN coating in prolonging diffusion paths due to their reduced gain sizes, thereby effectively inhibiting outside oxygen from penetrating into the coatings. In addition, the dense oxide layers formed on the CrAlSixN coatings when oxidized could also serve as protective layers to enhance oxidation resistance by slowing oxygen diffusion. It was demonstrated that the overall antioxidation capability of the CrAlSixN coatings after doping Si was significantly improved at elevated temperature. The superior antioxidation behavior was due to the denser barriers and the said two fine protective layers prevented outside oxygen from diffusing into the coatings.