Frictional performance of silicon carbide under different lubrication conditions

The frictional performance of materials used in face seals is critical to the sealing performance.Silicon carbide is commonly used in hard rings because of its abrasion resistance,corrosion resistance,and thermal shock resistance.In this study,the frictional performance of silicon carbide,including graphite-added silicon carbide,under water and lubrication-absent conditions was studied by using a Falex-1506 tribotester and different working parameters.In addition,the morphology of the worn surfaces was observed using scanning electron microscopy and the damage was characterized to understand the tribological behavior of different silicon carbides.The results suggest that the friction coefficients decrease with increasing pressure under water lubrication conditions because of the water within the holes on the surface of the materials.The percentage of water lubrication increases,whereas the percentage of solid friction decreases when the pressure increases.Under dry contact conditions,the friction coefficients change negligibly with increasing pressure and graphite-added silicon carbide shows better frictional performance.

Si_(3)N_(4)nanowires@pyrolytic carbon nanolayers coupled withhydroxyapatite nanosheets as reinforcement for carbon matrixcomposites with boosting mechanical and friction properties

Extensive attention has been drawn to the development of carbon-matrix composites for application in the aerospace and military industry,where a combination of high mechanical strength and excellent frictional properties are required.Herein,carbon-matrix composites reinforced by Si_(3)N_(4)nanowires@pyrolytic carbon nanolayers(Si_(3)N_(4nws)@PyCnls)coupled with hydroxyapatite nanosheets is reported.The Si_(3)N_(4nws)@PyCnls(SP)with coaxial structure could increase the surface roughness of Si_(3)N_(4nws)and promote the stress transfer to the carbon matrix,whereas the porous hydroxyapatite nanosheets favor the infiltration of the carbon matrix and promote the interfacial bonding between the SP and carbon matrix.The carbon matrix composites reinforced by SP coupled with hydroxyapatite nanosheets(Si_(3)N_(4nws)@PyCnls-HA-C)exhibit excellent mechanical strength.Compare with the conventional Si_(3)N_(4nws)reinforced carbon composites,Si_(3)N_(4nws)@PyCnls-HA-C(SPHC)have 162%and 249%improvement in flexural strength and elastic modulus,respectively.Moreover,the friction coefficient and wear rate decreased by 53%and 23%,respectively.This study provides a co-reinforcement strategy generated by SP coupled with hydroxyapatite nanosheets for effective improvement of mechanical and frictional properties of carbon matrix composites that are used for aerospace and military industry applications.