Strain Hardening in Superplastic Codoped Yttria‐Stabilized Tetragonal‐Zirconia Polycrystals

The superplastic characteristics of 3‐mol%‐yttria‐stabilized tetragonal‐zirconia polycrystals (3Y‐TZP) were drastically improved by the combined addition of germanium oxide and other oxides (titanium, magnesium, and calcium), resulting in up to 1000% elongation under optimum conditions. Extensive work hardening of the codoped compositions for temperatures >1400°C was observed. Dynamic grain growth was not a sufficient mechanism to explain this anomalous high strain hardening. The appearance of a cubic phase that caused abnormal grain growth during testing may have resulted in increased flow stress, which resulted in exaggerated work hardening.