Microstructure evolution and mechanical properties of Al doped ta-C films prepared by filtered cathodic vacuum arc

Abstract

Al-doped tetrahedral amorphous carbon (ta-C) films were prepared by filtered cathodic vacuum arc technique. Effect of Al content on the structure and properties of the ta-C film were systematically investigated. Results showed that Al content in films increased from 0 to 39.5 at. % as the Al target current altered from 0 to 2 A. Without Al doping, ta-C film mainly presented amorphous characteristic with disordered arrangement and compact structure. With a small amount of Al doping, the film maintained the amorphous phase structure, and Al atoms mainly existed in the carbon tetrahedral interstitial space in the form of solid solution. At high Al doping content, the formed Al nanoparticles embedded in the carbon matrix network. Meanwhile, the addition of Al could promote the graphitization of films. The residual stress of ta-C films decreased gradually with increase of Al content. Furthermore, the hardness and elastic modulus of films also decreased with increasing Al content. That's ascribed to the reduction of residual stress and graphitization of the carbon structure. In addition, the ta-C film with Al addition could effectively improve the friction and wear properties of films at both room and high temperature. The friction coefficient decreased with the increase of Al content at room temperature (RT). At 400 °C, the film containing 7.6 at. % Al obtained the lowest friction coefficient and wear rate, corresponding to the values of 0.29 and 12.3 × 10−8 mm3/N⋅m, respectively.