Transmission electron microscopy study of a 3Y-TZP worn under dry and water-lubricated sliding conditions

A fine-grained 3-mol%-Y₂O₃-stabilized t-ZrO₂ (3Y-TZP) was worn under dry and water-lubricated sliding conditions against a magnesia-partially-stabilized zirconia (Mg-PSZ) counterface. Detailed transmission electron microscopy of cross sections of the worn surface indicated dramatic microstructural changes. The outer region of both test specimens consisted of randomly oriented, fine (6-8 nm) tetragonal zirconia crystals. Below this, the tetragonal grains had become elongated, corresponding to a 95% reduction in thickness from the starting material for the dry test. Transformation of tetragonal to monoclinic zirconia was first found at a depth of 1.0-2.2 μm (water-lubricated) and 2.2-3.5 μm (dry) and extended up to a maximum depth of approx. 6 μm. Evidence of dislocation flow was found in all phases. The mechanisms of the microstructural change are discussed.