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Tribological tests were conducted in a ball on disk setup, using water as lubricant. A silicon nitride ball and alumina disk were used. The tests were conducted to investigate the effects of sliding speed, applied load and temperature on friction coefficient. The silicon nitride balls and alumina disks were characterized by determining density, Vickers hardness, elastic modulus and fracture toughness. The tests were conducted with initial roughness on the disk surface of 352 nm. The ultra low friction coefficient regime (ULFC, μ <0.01) was reached after a running-in period of approximately one hour and the friction coefficient remains in the range of μ = 0.008 to μ = 0.002 during this steady state regime. The results showed that this sliding system has hydrodynamic characteristics, because the friction coefficient decreased with increasing of the sliding speed. With an smooth variation of the applied load the system remained in the ULFC regime, when the applied load varied from 54 N up to 94 N. At temperatures below or equal to 11C the system did not reach the ULFC regime and the final friction coefficient was the order of hundredths. We observed the ULFC phenomenon at temperatures of 30 and 40C. However, at these temperatures, the water viscosity is low and should not allow the system to reach the ULFC regime. The data analysis allowed infer that during the ULFC regime the system slides with a mixed lubrication regime, hydrodynamic plus boundary, the first due to water film and the second due to the hydrated layer formed on the ceramics surfaces. The results showed the influences of temperature in the wear of ceramics. The results of the worn volume allowed to observe that during the tests alumina suffers less wear than the silicon nitride, and the ceramics wear increases with increasing temperature.

Ultra baixo coeficiente de atrito no deslizamento de Si3N4-Al2O3. Efeitos da força aplicada, velocidade de deslizamento e temperatura do ensaio.