The difference in running-in period and friction coefficient between self-mated Si3N4 and SiC under water lubrication

Running-in periods and friction coefficients of Sic and Si3N4 sliding against themselves underwater lubrication were investigated with a pin-on-disk apparatus at sliding speed of 120 mm/s and a normal load of 5 N under ambient conditions. It was found that the running-in period of self-mated Si3N4 is much shorter than that of self-mated Sic, and also that the steady-state friction coefficient of self-mated Si3N4 was lower (less than or equal to0.0035) than that of self-mated Sic (0.01). The difference in mechanism was analyzed from the point of view of electronic structure and surface chemistry.