Effect of surface roughness and wear in lubricated of self-mated alumina on friction reciprocating sliding contact

With increasing the possibilities of tribological applications for Al2O3 ceramic, much more attentions have been paid to researches on the tribological characteristics of Al2O3, such as compositions, microstructures, environments and other tribo-parameters. The effect of surface roughness of self-mated Al2O3 on friction and wear has been investigated at the present paper by varying the roughness parameters of samples under the conditions of reciprocating contact of cylinder-on-plate geometry lubricated by isooctane. In the tribotests, the roughness of plate samples were varied and they were ground by diamond grinding wheels. The surface of cylinders was, however, kept as delivered conditions. A dry air tribotest was also carried out to be as a reference test compared to lubricated tests. It has been found in this investigation that the increase of surface roughness results in high linear wear and friction coefficient of cylinder-plate tribopairs. It was observed that there exists a critical roughness about R-vk 1.89. High friction coefficient and linear wear will be got above this critical roughness. If the roughness of plate is below this critical value, friction coefficient and linear wear will be quite small after the test. It is also found by the SEM examinations of worn Surfaces that a thick third body layer is formed during the test with higher surface roughness of plates. The thin and compacted third body layer is formed with lower roughness of plates. Therefore, a carefully finished ceramic surface is extremely important to improve the tribological behaviours for engineering applications. It is interesting that the linear wear of as delivered cylinder-plate sample pairs is quickly levelled off in the dry air conditions even though their friction coefficient still keeps around 0.7. It can be concluded from this test that lubricant may have a negative effect on tribological behaviors.