Tribological characteristics of self-mated couples of Si3N4-SiC compositesin the range 22-700 degrees C

The tribological behaviour of self-mated pain of Si3N4, Si3N4/SiCp (platele ts) and Si3N4/SiCN (nanosized) hot pressed materials was studied in a pin-o n-disc configuration. Tests were performed without lubrication, at a fixed load of 5 N, using different temperatures (room temperature - 700 degrees C ) and sliding speeds (0.5-2 m s(-1)). Friction coefficients were usually ab ove 0.5, being almost independent of sliding speed and test temperature. Fo r all test conditions, the Si3N4/SiCp composite had the lowest friction coe fficient, due to the presence of SiC platelets with smooth cleavage planes oriented parallel to the sliding surface. Wear coefficients were above 10(- 6) mm(3) N-1 m(-1) denoting a generalised severe wear mode, controlled by s urface microcracking. No net differences were found between the wear behavi our of monolithic and composite materials under this wear regime. Wear decr eased with sliding speed due to the protective action of a coherent tribofi lm resulting from debris aggregation. Conversely, wear coefficients, showed a steep increase above room temperature, to values around 10(-4) mm(3) N-1 m(-1) at 700 degrees C. (C) 1999 Elsevier Science S.A. All rights reserved .