Electrical and tribological characteristics of copper containing diamond-like carbon nanocomposite coating on brass substrate sliding against brass ball

With the market growth of electrical and hybrid vehicles, demands for innovative technology on sliding contacts for vehicles have been increasing. Reducing the electrical contact resistance and the coefficient of friction are major technological requirements. This report provides electrical and tribological characteristics of a Copper containing Diamond-like Carbon (Cu-DLC) nanocomposite coating deposited on a brass plate, investigated with a ball-on-flat linear-reciprocating tribometer. The counterpart was a brass ball. While the initial electrical contact resistance was hundreds of milliohms, it gradually decreased with cycles and reached approximately 2 milliohms after 600 cycles. Coefficient of friction started below 0.35 and decreased progressively, stabilizing around 0.25 after 600 cycles. Sliding surfaces after different number of cycles were analyzed by optical microscope, energy dispersive X-ray spectroscopy, transmission electron microscopy and nanoindentation. The results of analyses revealed that a copper-rich tribofilm was built up on the ball and it grew and hardened as the sliding cycle increased. The Cu-DLC coating wore gradually and was almost worn out after less than 1000 cycles. However, detrimental effects were not observed either on electrical contact resistance or on coefficient of friction. Therefore, the tribofilm on the ball should have a key role in achieving and maintaining the good electrical-tribological characteristic.