Evaluation of Mechanical Properties of the Superficial Layer of CNx with Ultra Low Friction in N_2 Gas(Machine Elements, Design and Manufacturing)

Abstract

Carbon nitride (CNx) coating is one of the carbonaceous materials, which was reported to show superlow friction coefficient (μ<0.009) in Nitrogen environment. Therefore CNx coating is a promising material of solid lubricant for sliding interfaces to reduce friction. The superlow friction appeared after running in process of several hundreds of friction cycles and its mechanism has not been completely clarified yet. It was proposed that the soft thin layer generated on CNx coating after running-in process contributed to the superlow friction. However, the mechanical properties of the superficial layer of CNx coating such as hardness and Young's modulus have not been experimentally shown because of its small thickness estimated to be 10nm or less. So we carried out in-depth measurements of mechanical properties of the thin layer on CNx film by nanoscratching test using an atomic force microscope. Then the existence of thin, soft layer on the top of CNx coating after running-in process was experimentally shown.