Ti-inducing sp2 nanocrystallites into amorphous carbon film for low-friction

We reported a low-friction performance of Ti-doped a-C film, which is Ti-inducing sp2 nanocrystallites embedded in a-C structure. Mechanical and tribological tests showed that Ti-inducing sp2 nanocrystallites softened the film hardness from 22.5 to 18.8 GPa and lowered the friction coefficient from 0.15 to 0.05. Friction interface char-acterization indicated that abundant sp2 nanocrystallites lay down on the contact surfaces. The low-friction was attributed to the interaction between sp2 C layers, which originated from original Ti-inducing and new Ti -promoting sp2 nanocrystallites. The Ti-promoting effect was speculated that Ti atoms with Ti-C bond reacted with O atoms to form Ti--O bond (TiO2), then some released C atoms turned to sp2 nanocrystallites at the friction interface.