Residual stress and tribological behavior of hydrogen-free Al-DLC films prepared by HiPIMS under different bias voltages

Hydrogen-free Al-DLC films were prepared by HiPIMS technology under different bias voltages through an Al-C composite target. Surface and cross-sectional morphologies, chemical composition, microphase structure and bonding state, residual stress, hardness and elastic modulus, friction coefficient and wear resistance of Al-DLC films were investigated to study the influences of substrate bias voltage. Results show that bias voltage decreased film roughness (Ra) from 3.83 nm to 1.16 nm through ion bombardment. The increase of negative bias voltage improved film disorder and altered the content of sp(3) bonds. However, the existence of sp(3) bonds should not be responsible for residual stress. Local distortions generated by film disorder together with the mismatch between film and substrate give rise to residual compressive stress in Al-DLC films. Film hardness is in the range of 10 GPa to 17 GPa which is affected by the content of sp(3) bonds and film disorder. The lowest wear rate of Al-DLC film is 6.07 x 10(-8) mm(3)/Nm. Besides graphitization, friction can also generate more sp(3) bonds at wear interface between Al-DLC film and the counterpart ball.