Bias-graded deposition and tribological properties of Ti-contained a-C gradient composite film on Ti6Al4V alloy

Ti-contained a-C gradient composite film with a thickness 1.5 μm was deposited on medical Ti6Al4V alloy substrate using a closed field unbalanced magnetron sputtering with bias-graded voltage through −20 V to −150 V. The mechanical and tribological properties were evaluated from nanoindentation, scratch test and ball-on-disk tribometer. Compared with the constant-bias film deposited at −150 V, the bias-graded film has the approximate hardness (19 GPa) but high toughness and adhesion strength. At a normal load of 10 N, the bias-graded composite film shows a low friction coefficient of 0.08 and wear rate of 2.89 × 10−16 m3 N−1 m−1 in ambient air. While in Hanks' solution, the film has the same low friction coefficient but low wear rate of 4.63 × 10−17 m3 N−1 m−1. Excellent wear resistance in Hanks' solution may bring about a biological application for the Ti-contained a-C gradient composite film.