Improving wear resistance of yttria-stabilized tetragonal zirconia in air and high vacuum environments by multi-cycle annealing

To improve the wear resistance of yttria-stabilized tetragonal zirconia polycrystal (TZP), an effective multi-cycle annealing method was proposed. The effects of multi-cycle annealing temperature on the surface morphology, microstructure and mechanical properties of TZP were investigated. The dry friction and wear behaviors of original and annealed TZP against TZP balls both in air and high vacuum conditions were further explored. During multi-cycle annealing at 1100-1300 degrees C, recrystallization takes place in TZP polished surface, inducing an average surface grain size ranging from 0.11 mu m to 0.21 mu m. With the rise of annealing temperature, the zirconia transforms from monoclinic phase into tetragonal phase, and the surface machining traces of TZP gradually fade away, while the surface grain morphology becomes prominent. However, when the annealing temperature reaches to 1500 degrees C, zirconia grains excessively grow to 0.58 mu m, resulting in an evident reduction in mechanical properties. The Y-TZP annealed at 1300 degrees C (TZP1300) has the optimal wear resistance. In comparison with the original TZP, its average wear rates in air and high vacuum environments significantly decreased by about 65.7 % and 70.7 %, respectively. This is mainly attributed to the increase of tetragonal phase zirconia, and the appropriate growth of surface grains, which not only maintains the excellent mechanical properties, but also promotes the repairing of surface processing defects.