HIGH-TEMPERATURE TENSILE DUCTILITY IN TZP AND TIO2-DOPED TZP

The role of TiO2 on the superplastic flow in tetragonal zirconia polyc rystal (TZP) stabilized by Y2O3 is examined with a special interest in tensile ductility at temperatures between 1200 and 1550 degrees C. Th e initial grain size of 0.66 mu m in TZP-5wt.% TiO2 is about twice as large as the size of 0.30 mu m in TZP, but the flow stress is lower in TZP-5wt.% TiO2 than TZP. The tensile elongation is improved by the ad dition of TiO2 at temperatures below about 1500 degrees C. The grain s ize at the time of failure, d(f) is much larger in TZP-5wt.% TZP than TZP at all temperatures. Assuming that d(f) is a parameter to describe a limit of an accommodation process for superplastic flow, the elonga tion to failure is estimated from the grain growth behavior during pla stic flow. The observed epsilon(f) vs. T relationship can reasonably b e expressed by the estimation. The present analysis reveals that there is an optimum temperature for superplastic flow at a certain strain r ate in each material. The temperature region of superplastic flow and the optimum temperature are mainly dependent on the activation energie s for superplastic flow and grain growth. The observed effect of 5 wt. % TiO2 addition on the tensile elongation is explained from a slight r eduction in the two activation energies. (C) 1997 Elsevier Science S.A .