Tribological Properties of Plasma-sprayed Cr_3C_2-NiCr Coating against Toughened SiC Ceramics under Water-lubricated Sliding

The tribological properties of plasma sprayed Cr 3C 2 NiCr coating sliding against toughened SiC ceramics under water lubricated condition were investigated on an MM 200 friction and wear tester. The morphology of the worn surface and the elemental composition of the wear debris were examined by means of electron probe micro analysis and (Fourier transformed infrared) spectroscopy. It has been found that the friction pair records a friction coefficient below 0.2 and wear rates less than 10 -6 mm 3(Nm) -1 . Under water lubricated condition at a relatively low load, tribochemical oxidation of SiC took place, with the generation of the protective film composed of SiO 2 and SiO 2.nH 2O formed on the worn surface. This contributes to decrease the friction coefficient and wear rate. While under a relatively high load, local grain fracture of SiC ceramics occurred, which accounts for the fluctuation in the friction coefficient and the increase in the wear rates of the Cr 3C 2 NiCr coating.