Friction and wear properties of CNx/SiC in water lubrication

Abstract

Amorphous carbon nitride coatings (a-CN x ) were deposited on SiC disk by ion beam assisted deposition (IBAD). The tribological behavior of a-CN x coating sliding against SiC ball in water was investigated and compared with that of SiC/SiC system at room temperature. The influences of testing conditions on friction coefficient and specific wear rate of both kinds of tribopairs were studied. The worn surfaces on disks were observed by scanning electron microscope (SEM). The results indicate that the running-in period of a-CN x /SiC was shorter than that of SiC/SiC system in water. At a sliding velocity of 120 mm/s, the mean steady-state friction coefficients of SiC/SiC (0.096) was higher than that of a-CN x /SiC (0.05), while at 160 mm/s, lower friction coefficient (0.01) was obtained for SiC/SiC in water. With an increment of normal load, the mean steady-state friction coefficients after running-in first decreased, reaching a minimum value, and then increased. For self-mated SiC, the specific wear rate of SiC ball was a little higher than that of SiC disk, while for a-CN x /SiC, the specific wear rate of SiC ball were 10 times smaller than that of a-CN x coating. Furthermore, the specific wear rate of SiC ball sliding against a-CN x coating was reduced by a factor up to 100$1000 in comparison to that against SiC in water. The wear mechanism of SiC/SiC system in water is related to micro-fracture of ceramic and instability of tribochemical reaction layer. Conversely, wear mechanism for a-CN x /SiC is related to formation and transfer of easy-shear friction layer.

Progress in Tribological Properties of Nano-Composite Hard Coatings under Water Lubrication

“…Zhou et al [53] confirmed the hydrophilic feature of a-CN x coatings and pointed out that the N atom in a-CN x coatings was prone to bond with the H atom in water during the friction process. In that way, the N atom easily left from the top surface of a-CN x coatings, and an sp 2 C=N rich layer with lower shear strength was built.…”

“…It has been reported that under the same load and sliding velocity, the friction coefficient of a-CN x /SiC tribopairs (0.02 to 0.05) was lower than that of a-C/SiC tribopairs (0.03 to 0.07) in water [52,53]. Zhou et al [53] confirmed the hydrophilic feature of a-CN x coatings and pointed out that the N atom in a-CN x coatings was prone to bond with the H atom in water during the friction process.…”

Tribological properties of a‐CNx coatings sliding against SiC balls in ethylene glycol aqueous solution

“…The ion beam assisted deposition (IBAD) machine (Hitachi Ltd, Ibaraki, Japan, as seen in Zhou et al 4 ) was used to deposit the a-CN x coatings. Prior to IBAD process, SiC disks (Φ30 mm × t 4 mm) were ultrasonically cleaned in acetone and ethanol for 30 min.…”

“…Due to insuffi cient strength and microstructure ageing, engineering plastics could not be applied to water lubrication system for longer period of time. 1 Although the Si 3 N 4 /Si 3 N 4 and SiC/SiC tribocouples in water all possess low friction coeffi cient(≤0.01), [2][3][4] , severe wear is easily observed for the self-mated SiC(Si 3 N 4 ) tribopair in water due to the longer running-in period for SiC/SiC tribo pairs in water and the easy occurrence of hydration reaction between SiC(Si 3 N 4 ) and water. An alternative approach is to take advantage of the hard coatings with good lubricity in water environment.…”

“…7 Recently, the a-CN x coatings have been found to enhance the wear resistance of SiC ball at lower or higher velocities in water lubrication. 4,8 When the a-CN x coatings slide against SiC or Si 3 N 4 balls at 5 N and 0.16 m s −1 in water, the low coeffi cient of friction of 0.01~0.02 is achieved, 9 and then the wear mechanism maps of the a-CN x /SiC(Si 3 N 4 ) tribo pairs in water have been established. 10,11 Under the same frictional conditions, the friction and wear properties of the a-CN x /SiC tribo-couple in water are superior to those of the a-C/SiC tribo-pair.…”