Insights on high temperature friction mechanism of multilayer ta-C films

Abstract In this work, the high temperature friction mechanism of the tetrahedral amorphous carbon (ta-C) film was elucidated. The multilayer ta-C film with alternating hard and soft sub-layers exhibited a low friction coefficient of 0.14 at 400 °C before a sudden failure occurred at 4600 cycles. The wear failure was attributed to the gradual consumption of the ta-C film at the contact region. The design of a hard or soft top layer effectively regulated the high temperature friction properties of the multilayer ta-C. The addition of a hard top layer contributed to a low friction coefficient (0.11) and a minor wear rate (4.0 × 10−7 mm3/(N m)), while a soft top layer deteriorated the lubrication effect. It was proposed that the passivation of dangling bonds at the sliding interface dominated the low-friction mechanism of the ta-C film at high temperature, while the friction induced graphitization and the formation of sp2-rich carbonaceous transfer layer triggered C C inter-film bonding, resulting in serious adhesion force and lubrication failure. Moreover, the multilayer ta-C film with hard top layer obtained excellent friction performance within 500 °C, while the high temperature induced oxidation and volatilization of carbon atoms led to the wear failure at 600 °C.