1Toyota Central Research & Development Laboratories, Inc., Aichi
The Y2O3 doped PSZ and FSZ sintered ceramics were mechanically polished with SiC abrasive paper. The crystal structure of the abraded surface layer was examined by X-ray diffraction, and the flexural strength and the fracture toughness of PSZ subjected to polishing were measured, in order to clarify the influence of the surface modification on the structure and the mechanical properties of zirconia.
\noindent The results are summarized as follows:
(1) In the abraded surface layer, the cubic matrix phase (C-phase) was found to transform readily to rhombohedral phase (R-phase) having a distorted fluorite structure with respect to the specific  direction ( α'=89.5°). This structure was approximately similar to the rhombohedral phase ( α'=89.8°) induced by ion implantation.
(2) The C → R phase transformation is thought to be induced by a stress introduced by polishing. With increasing the roughness of the abrasive paper, the R-phase was formed more remarkably in PSZ than in FSZ. This can be explained by assuming that in FSZ, the stress imposed by the polishing is easy to relax by causing microcracks.
(3) By pulverizing and annealing, the R-phase disappeared to transform reversely to the original C-phase through stress relaxation. This suggests that the R-phase is metastable and exists only in the surface layer under stress.
(4) By forming the R-phase in the surface of PSZ, the flexural strength was found to increase by over 20% and the apparent fracture toughness by two to three times. The increases of the mechanical properties are thought to be caused by the surface compressive stress developed through the volume expansion associated with the C → R phase transformation.
fully stabilized zirconia, partially stabilized zirconia, mechanical polishing, surface modification, phase transformation, metastable phase, reverse transformation, mechanical properties
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