Low-Temperature Superplasticity in Nanocrystalline Tetragonal Zirconia Polycrystal (TZP)

Nanocrystalline tetragonal ZrO2 polycrystals (TZP) have been fabricated by the pressureless sintering of recently developed tetragonal ZrO2 powder containing 5.69 mol% YO1.5 and 0.60 mol% AlO1.5. The average grain sizes were 160 nm in the TZP sintered at 1150°C for 10 h and 150 nm in the 0.25 mol% GeO2‐doped TZP sintered at 1100°C for 100 h. The TZP and Ge4+‐doped TZP‐sintered bodies were essentially single‐phase materials, and neither the amorphous layer nor the second‐phase particle was observed along the grain boundary faces. High‐resolution transmission electron microscopy (HRTEM), scanning transmission electron microscopy (STEM), and nanoprobe energy‐dispersive X‐ray spectrometer (EDS) measurements revealed that the Y3+, Al3+ and Ge4+ cations tend to segregate in the vicinity of the grain boundaries in the TZP‐sintered bodies. The TZP and Ge4+‐doped TZP exhibited an elongation to failure of more than 100% in the temperature range of 1150°C–1300°C and initial strain rate range of 1.4 × 10−5 s−1 to 1.0 × 10−2 s−1. For instance, an elongation to failure in the Ge‐doped TZP reached about 200% at 1150°C and 1.4 × 10−5 s−1. The nanocrystallization reduced the lower limit of the superplastic temperature of conventional, submicron‐grain TZP materials by 150°C. The improved ductility of the TZP at low temperatures was essentially attributed to the reduced grain size.