Influence Of Structural Evolution On Sliding Interface For Enhancing Tribological Performance Of Onion-Like Carbon Films Via Thermal Annealing

The onion-like carbon (OLC) possesses a micro-spherical structure with a diameter of approximately 7 nm consisting of 0.35 nm-spaced carbon layers, and the OLC film is capable of providing excellent solid lubrication performances because of the high content of sp(2)-bonded carbon phase. However, the unfavorable durability severely restricts the lubrication application in practice. For the purpose of addressing this issue, heat treatment is employed to improve the lubrication robustness of the loose OLC film. The wear resistance was significantly improved with a duration of 60,000 sliding cycles at least when the OLC-coated samples were annealed at 600 degrees C in vacuum. Furthermore, the systematic analyses, particularly providing deep insights into the microstructural characterization, indicate that the structural reinforcement of OLC and the net-like adhering structures formed on the steel substrates annealed at specific temperature can effectively promote lubrication characteristics in two different stages. We propose that annealing treatment can improve the stability of micro-spherical OLC structures, thereby increasing the duration of lubrication. The evolution mechanism of OLC structures at the sliding interface is the key factor for maintaining the lubrication duration in dry contact.