Effect of coating thickness on friction for carbon nitride films in repeated sliding against a spherical diamond with nano-scale asperities

The frictional behavior of carbon nitride coatings on silicon substrates repeatedly sliding against a spherical diamond is presented. The motivation is to clarify the coating thickness effect on friction with relation to applied normal load and repeated friction cycles. Repeated friction tests on silicon substrates with sputtered carbon nitride coatings of various thickness were conducted using a pin-on-disk type apparatus under a controlled environment. The results indicate that the maximum value of friction coefficient occurs around certain coating thickness with no relation to applied normal load. Considering the nano-scale sub-asperities on the tip of the diamond counter-face and the ratio of substrate to the coating hardness, the results from the experiments are favorably comparable to the results obtained with a contacting model proposed by Halling and Sherbiney .