Tribology of self-mated siliconized graphite under high pv factors in high-temperature and high-pressure water

To enhance the structural design reliability, certain operating conditions for the combination of high contact pressure and sliding velocity are desired in an advanced main coolant pump. The tribological properties of selfmated 22C-64SiC-14Si (vol%) siliconized graphite are investigated using a high-temperature and high-pressure water-lubricated tribometer on pin-on-disc configuration under high pv factors of 0.4-68.8 MPa center dot m/s at applied loads p of 500 and 1200 N with spindle speeds v of 100-6000 rpm in 50 degrees C and 1.5 MPa water environment. With the pv factor from 1.1 to 68.8 MPa center dot m/s, the wear depth decreases from 0.98 mu m to 0.12 mu m, the average COF declines from 0.030 to 0.010, and a smooth worn surface is noted, despite a slight increase in surface roughness Ra from 0.015 to 0.023 mu m. An oxidation layer is observed on the SiC of siliconized graphite by scanning electron microscope (SEM) and transmission electron microscopy (TEM) with energy dispersive spectroscopy (EDS) analysis. The abrasive wear of the SiC and Si asperities, in conjunction with the solid lubrication provided by graphite, is ascribed to boundary lubrication influenced by the high pv factor. The tribochemical wear under hydrodynamic lubrication occurs between the SiO2 layers on the SiC surface. The wear mechanism in mixed lubrication is contingent upon the contact ratio determined by the pv factor. In order to achieve the hydrodynamic lubrication regime of the siliconized graphite under high pv factor, it is necessary either to increase the sliding speed or to reduce the contact stress.