BULK NANOSTRUCTURED OXIDE MATERIALS AND THE SUPERPLASTIC BEHAVIOR UNDER TENSILE FATIGUE AT AMBIENT ENVIRONMENT

Nano-sized yttria stabilized tetragonal zirconia polycrystal (Y-TZP) p owders were prepared by wet chemical process. Carefull charaterization and ways to avoid hard-agglomerate formation were discussed. Full den sification of large size samples was achieved with average grain size of 100+/-20 nm. Samples of the same chemical composition with submicro n grains were simultaneously prepared for comparison. Cyclic tensile f atigue studies on both types of specimens were pursued at ambient temp erature. If was first documented by AFM imaging that localized superpl astic deformation of the 100 nm grains at and near the fatigue fractur e surfaces was generated; while in the submicron grain-sized samples, the grains retained their original equiaxed morphology. The micromecha nisms underlying these phenomena were discussed. Grain boundary diffus ion is argued to be the major governing process in operation. (C) 1997 Acta Metallurgica Inc.