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

Abstract

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.

A novel approach to improve flexural strength of Al2O3‐20 wt% ZrO2 composites by oscillatory pressure sintering

“…Generally, mass transport during sintering under an external loading can be considered as analogous to that occurred in high‐temperature creep . In this process, the superplastic behavior can be often found in fine‐grained ceramics such as ZrO 2 , and Al 2 O 3 , etc . Concerning the superplastic deformation, the main mechanism was considered to be grain boundary sliding accommodated by diffusion and/or plastic deformation.…”

Surface segregation of 3 mol % yttria-doped tetragonal zirconia particle studied by atomic-resolution scanning transmission electron microscopy-energy-dispersive X-ray spectroscopy

“…The microstructures of zirconia ceramics have been widely studied so far, and it is generally accepted that Y prefer to segregate at the GBs. The GB Y segregation not only affects the grain growth behavior of zirconia ceramics, which is known as the GB segregation-induced phase transformation mechanism, 3) but also strongly influences the physical properties such as low-temperature superplasticity 4) and oxygen ionic conductivities. 2) It is, therefore, important to further investigate GB segregation for the development of next generation zirconia materials with better properties.…”

Effect of chemical composition and grain size on RT superplasticity of Zn-Al alloys processed by ECAP

“…All these requirements should be fulfilled so that the grain boundary sliding (GBS) can occur easily as the main deformation mechanism in superplastic region [3]. After the first report in 1912 [4], superplasticity-related studies have been one of the main topics among the material scientists and mechanical engineers, and various classes of materials including alloys [5][6][7][8][9][10][11][12][13][14][15][16][17][18], ceramics [19][20][21] and amorphous materials [22,23] have been addressed for this purpose.…”