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 degrees C for 10 h and 150 nm in the 0.25 mol% GeO2-doped TZP sintered at 1100 degrees 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 degrees C1300 degrees C and initial strain rate range of 1.4 x 10(-5) s-1 to 1.0 x 10(-2) s-1. For instance, an elongation to failure in the Ge-doped TZP reached about 200% at 1150 degrees C and 1.4 x 10(-5) s-1. The nanocrystallization reduced the lower limit of the superplastic temperature of conventional, submicron-grain TZP materials by 150 degrees C. The improved ductility of the TZP at low temperatures was essentially attributed to the reduced grain size.