Friction and wear property of a-CN x coatings sliding against Si 3N 4 balls in water

Abstract

Amorphous carbon nitride coatings (a-CN x ) were deposited on Si(1 0 0) wafers and Si 3N 4 disks using ion beam assisted deposition (IBAD), and their composition and chemical bonding were determined by X-ray photoelectron spectroscopy (XPS). The a-CN x coatings’ hardness was measured by nano-indentation and the friction and wear behavior of a-CN x coating sliding against a Si 3N 4 ball in water was investigated. The results indicated that the a-CN x coatings contained 12 at.% nitrogen and the major chemical bonding was sp 2 C N and sp 3 C–N. The nano-hardness of the a-CN x coatings was 29 GPa. At a sliding velocity of 0.16 m/s and after running-in, the mean steady-state friction coefficient varied around 0.02 when the normal load was lower than 3.5 N, and then decreased abruptly from 0.018 to 0.007 at 5 N. For self-mated Si 3N 4, the specific wear rate of a Si 3N 4 ball was a little higher than that of a Si 3N 4 disk, while for a-CN x /Si 3N 4, the specific wear rate of a Si 3N 4 ball was slightly smaller than that of a-CN x coating. Furthermore, the specific wear rate of Si 3N 4 ball sliding against a-CN x coating was reduced by a factor up to 35 in comparison to that against Si 3N 4 in water. This indicated that the wear mechanism of a-CN x coating/Si 3N 4 ball was the formation of a carbonaceous transfer film on the a-CN x coatings via a tribochemical reaction between a-CN x coatings and water induced by friction, while that of self-mated Si 3N 4 ceramics was the formation of silica gel on the contact zone via the reaction of silicon nitride and water.