Isothermal Sintering Effects on Phase Separation and Grain Growth in Yttria‐Stabilized Tetragonal Zirconia Polycrystal

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The isothermal sintering behavior in 3 mol% yttria‐stabilized tetragonal zirconia polycrystal (Y‐TZP) was investigated to clarify phase‐separation and grain‐growth mechanisms during sintering. In the Y‐TZP sintered at 1300°C for 2 h, the Y3+ ion distribution of grain interiors in Y‐TZP was nearly homogeneous, but Y3+ ions segregated along grain boundaries within a width of about 10 nm. When the holding time increased from 2 to 50 h, the cubic‐phase regions with high Y3+ ion concentrations were clearly formed in the grain interiors adjacent to the grain boundaries, though the average grain size hardly increased. This result shows that the cubic‐phase regions were formed without grain growth, which can be explained by the grain‐boundary segregation‐induced phase transformation mechanism. In the Y‐TZP sintered at 1500°C for 2 h, the cubic‐phase regions were already formed, and both of the cubic‐phase region and average grain size increased with increasing holding time. This grain‐growth behavior can be interpreted by the third‐power growth low derived based on the solute drag theory, which indicates that the cubic‐phase regions do not effectively act as the pinning points.