On the sintering and grain growth of 1.5 mol% yttria-stabilized zirconia

Low-yttria content tetragonal zirconia polycrystals have been proposed in 1980s with enhanced toughness over the popular 3 mol% yttria-stabilized zirconia (3YSZ). Along this direction, development of 1.5 mol% yttria-stabilized zirconia (1.5YSZ) is now possible with commercial powders from Tosoh, as reported by a few groups in Japan and Europe. Here, we seek to provide an independent evaluation on the sinterability and grain growth kinetics of Tosoh 1.5YSZ powders. We show that the green bodies formed by cold isostatic press can be readily sintered to full density at 1350°C for 2 h and with minimal monoclinic phase upon cooling. Too high sintering temperature, for example, 1500°C, leads to spontaneous formation of monoclinic phase upon cooling as detected by X-ray diffraction. Two-step sintering also works, producing 99.4% relative density and 253 nm average grain size first at 1225°C for 1 min and then at 1150°C for 20 h. The grain size is ∼40% smaller than that sintered by one step at 1350°C for 2 h. Isothermal grain growth experiments were conducted within the narrow kinetic window between 1200°C and 1300°C, high enough to enable substantial grow and low enough to suppress spontaneous monoclinic phase formation. The calculated grain boundary mobility from parabolic grain growth law is only 10 times higher than that of 3YSZ. The implications shall be discussed.