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The tribological behaviour of different monolithic and composite ceramics was evaluated in the temperature range between room temperature and 750°C. The test method was oscillating sliding with a ball-on-disk arrangement in an SRV machine. Alumina balls were used as counter body. The friction behaviour was determined on-line, and the wear behaviour was determined from calculations on the basis of wear scar dimensions and profilometric measurements. The friction depends on temperature and shows an increase for most materials for increasing temperature; the smallest friction at all temperatures is found for monolithic TiC. The wear behaviour shows different trends for the different materials. In tests against SiC a maximum of wear is found at 500°C, for TiC at 200°C and for TiB2 at 750°C. The composite ceramics suffer the smallest wear of all materials in the range from 200°C to 500°C.
Contact formation and development are the basis of friction and wear modelling and understanding. Unanimously topography formation and development in friction contacts are regarded of highest importance for understanding and modelling friction processes. The frequently found running in behaviour of sliding contacts is—aside from the build up of reaction and transfer layers-at least partly caused by the topography development due to friction processes until a stable equilibrium state is reached.
Experimental results of friction and topography measurements are presented which demonstrate the mutual modification of friction and contact topography.
A special experimental set up with an AFM allowed to correlate the measured friction forces with the contact position and the topography at this point. In this way, friction force transitions and changes can be assigned to topography changes due to abrasion, adhesion and wear particle agglomeration.
Contact surfaces with artificial regular structures have been prepared to avoid problems with topography and friction correlation due to the statistical nature of roughness on technical contact surfaces. The friction effects of roughness were simulated by etched ditches of defined width, depth and distance on silicon or metal surfaces. This allowed to explain the mutual influences of topography and friction. The effect of a single asperity and of the 'roughness structures' could be demonstrated.
Topography measurements with an AFM correlated with the friction force could help to understand friction changes without changing any parameter.
The friction and wear behaviour of SiC, Si3N4 and SiC/Si3N4 composite ceramics were investigated with oscillating sliding (gross slip fretting) at room temperature. The influence of counter body material and the humidity of the surrounding air was studied with a ball-on-disc configuration with different ball materials (1000Cr6, Al2O3 SiC and Si3N4). The effect of RH on friction is marginal with exception of SiC (low friction) as counter body material. The wear behaviour, however, is strongly affected by humidity, showing inverse trends for different counter body materials. Consequently, the wear behaviour of a tribo couple can be improved by selecting an adequate mating material. The results reveal the necessity to control RH in tribological tests. For estimation of the performance of tribo couples under varying environmental conditions, a variation of RH is required. In tribo couples with single phase SiC, either as ball or disc, the tribological behaviour of the system is dominated by SiC. The friction behaviour of the composite material is in between the behaviour of the two single phase materials, Si3N4 and SiC, whereas the wear behaviour is very similar to that of single phase Si3N4.