Grain-size dependence of sliding wear in tetragonal zirconia polycrystals

Using a pin-on-plate tribometer with the reciprocating motion of SiC against yttria-doped tetragonal zirconia polycrystal (Y-TZP) plates, the friction and wear of Y-TZP ceramics were investigated as a function of grain size in dry N-2 at room temperature. The results showed that the overall wear resistance increased as the grain size of Y-TZP ceramics decreased, For grain sizes less than or equal to 0.7 mu m, the wear results revealed a Hall-Fetch type of relationship (d(-1/2)) between wear resistance and grain size, In this case, the main wear mechanisms were plastic deformation and microcracking. For grain sizes greater than or equal to 0.9 mu m, the wear resistance was proportional to the reciprocal of the grain diameter, In this regime, delamination and accompanying grain pullout were the main mechanisms, In this case, the phase transformation to monoclinic zirconia had a negative effect on the wear resistance of TZP ceramics. The coefficient of friction tended to be higher for fine-grained TZP-SiC couples than for coarse-grained TZF-SiC couples, whereas, for a specific regime of grain size, the coefficient of friction was almost independent of the grain size.