Mobility Transition at Grain Boundaries in Two-Step Sintered 8 mol% Yttria Stabilized Zirconia

TL;DR

This study investigates grain growth behavior in yttria-stabilized zirconia during two-step sintering, revealing microstructure bifurcation caused by inhomogeneous junction mobility, with implications for optimizing sintering processes.

Contribution

It uncovers a novel microstructure bifurcation phenomenon linked to junction mobility in two-step sintered zirconia, advancing understanding of grain growth control.

Findings

Grain growth obeys parabolic law above 1300°C.

Lowering temperature causes abrupt slowdown and microstructure bifurcation.

Inhomogeneous junction mobility explains microstructure bifurcation.

Abstract

Stagnation of grain growth is often attributed to impurity segregation. Yttria-stabilized cubic zirconia does not evidence any segregation-induced slowdown, as its grain growth obeys the parabolic law when the grain size increases by more than one order of magnitude. However, lowering the temperature below 1300 oC triggers an abrupt slowdown, constraining the average grains to grow by less than 0.5 ${\mu}$m in 1000 h despite a relatively large driving force imparted in the fine grains of ~0.5 ${\mu}$m. Yet isolated pockets of abnormally large grains, along with pockets of abnormally small grains, emerge in the same latter sample. Such microstructure bifurcation has never been observed before, and can only be explained by an inhomogeneous distribution of immobile four-grain junctions. The implications of these findings for two-step sintering are discussed.