The martensitic transformation in zirconia. Ph.D. Thesis
The metastable t-ZrO2 particles in both Y-TZP and Mg-PSZ can transform to m-ZrO2, and in the PSZ also to o-ZrO2, via a martensitic transformation. This research has demonstrated that the transformation is controlled by the thermally activated, stress-assisted nucleation of the martensite phase. The thermally activated character of the phase change was manifested as isothermal transformation kinetics in both materials: Residually stressed regions in indented Y-TZP`s underwent isothermal t = greater than m transformation during post-indentation anneals up to approximately equals 500 C In Mg-PSZ`s, slow isothermal t yields m and t yields o transformations occurred at room temperature after a short anneal at 1000 C, which reverses the room temperature aging. The phase transitions were accompanied by substantial transformation plasticity: Forward and reverse transformations during anneals in the residually stressed regions in the TZP caused large volume and shape changes, whose simulation with a finite element model was partially successful. In Mg-PSZ`s the transformation was induced by internal stresses during room temperature aging as well as by external stresses applied during stress-relaxation tests; again, ample transformation plasticity ensued. Furthermore, the effect of the indentation-induced transformation in Mg-PSZ on the growth of indent cracks during four-point bending was investigated, and the crystallographically oriented and autocatalytic deformation zones around indents in Y-PSZ single crystals were analyzed.
- Research Organization:
- Case Western Reserve Univ., Cleveland, OH (United States)
- OSTI ID:
- 147180
- Country of Publication:
- United States
- Language:
- English
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