Effects of Grain Size and Humidity on Fretting Wear in Fine-Grained Alumina, Al2O3/TiC, and Zirconia

Friction and wear of sintered alumina with grain sizes between 0.4 and 3 μm were measured in comparison with Al2O3/TiC composites and with tetragonal ZrO2(3 mol% Y2O3). The dependence on the grain boundary toughness and residual microstresses is investigated, and a hierarchical order of influencing parameters is observed. In air, reduced alumina grain sizes improve the micromechanical stability of the grain boundaries and the hardness, and reduced wear is governed by microplastic deformation, with few pullout events. Humidity and water slightly reduce the friction of all of the investigated ceramics. In water, this effect reduces the wear of coarser alumina microstructures. The wear of aluminas and of the Al2O3/TiC composite is similar; it is lower than observed in zirconia, where extended surface cracking occurs at grain sizes as small as 0.3 μm.