638 M. Hadad et al. /Wear 260(2006)634-641 Fig 4. SEM micrographs of wear debris collected after sliding test: (a)Si3 N4 bulk and (b)Si3N4-30%Tn composites Wear mechanism and friction at 300oC: literature data and velocities seems to lead a removal of the oxide layer suggests that the wear of Si3 N4/Si3 Na sliding pairs at 300C under mechanical action, which leads to an increase in wear is caused mainly by a thermomechanically dominated wear rate. The EDS analysis of the worn surface suggested oxy mechanism with grain boundary fatigue at the interface gen contents in the tenth of atomic percents. Despite the between B-Si3N4 and glass phase on and below the surface. semi-quantitative character of the EDs system in case of For the sliding pairs of Si3N4-TiN/Si3N4-TiN composites, non-planar surfaces and of the analysis of light elements, the tribochemically dominated wear mechanism was observed amount of oxygen indicated here is significant compared to [20]. The oxidation rate increases with increase in temper- ambient temperature results. This suggests on the one hand ature at the surface of contact. Increasing contact pressure that a tribochemical wear mechanism is active, which is in Bulk Si3N4 Si3N4-10%TiN composite g08 504 85 Time [min Time (min] Si3NA-20%TiN composite Si3N4-40%TiN composite 洲A L02 34578911121415 Time [min Time [min] Fig. 5. Friction coefficients of bulk and composites at ambient temperat638 M. Hadad et al. / Wear 260 (2006) 634–641 Fig. 4. SEM micrographs of wear debris collected after sliding test: (a) Si3N4 bulk and (b) Si3N4–30% TiN composites. Wear mechanism and friction at 300 ◦C: literature data suggests that the wear of Si3N4/Si3N4 sliding pairs at 300 ◦C is caused mainly by a thermomechanically dominated wear mechanism with grain boundary fatigue at the interface between -Si3N4 and glass phase on and below the surface. For the sliding pairs of Si3N4–TiN/Si3N4–TiN composites, tribochemically dominated wear mechanism was observed [20]. The oxidation rate increases with increase in temper￾ature at the surface of contact. Increasing contact pressure and velocities seems to lead a removal of the oxide layer under mechanical action, which leads to an increase in wear rate. The EDS analysis of the worn surface suggested oxy￾gen contents in the tenth of atomic percents. Despite the semi-quantitative character of the EDS system in case of non-planar surfaces and of the analysis of light elements, the amount of oxygen indicated here is significant compared to ambient temperature results. This suggests on the one hand that a tribochemical wear mechanism is active, which is in Fig. 5. Friction coefficients of bulk and composites at ambient temperature.