Low-temperature degradation in yttria-stabilized tetragonal zirconia polycrystal doped with small amounts of alumina: Effect of grain-boundary energy

Abstract Low temperature degradation (LTD) behavior was examined in 3 mol% Y 2 O 3 -stabilized tetragonal ZrO 2 polycrystals (Y-TZP) doped with 0–1.1 mol% Al 2 O 3 sintered at 1500 °C. 0.12 mol% Al 2 O 3 -doped Y-TZP exhibited monolithic microstructure without dispersion of Al 2 O 3 grain, while second-phase Al 2 O 3 particles were observed in the Y-TZP sintered bodies doped with 0.54–1.1 mol% Al 2 O 3 . In the Y-TZP doped with 0.12 mol% Al 2 O 3 , neither amorphous nor second phase was present along the grain boundaries, but Y 3+ and Al 3+ ions segregated in the vicinity of the grain boundaries. The tetragonal-to-monoclinic ( T  →  M ) phase-transformation rate during the accelerated LTD test significantly decreased at 0.12 mol% Al 2 O 3 , but the phase-transformation rate slightly increased with the increasing doping amount of Al 2 O 3 . The suppressed T  →  M phase-transformation in Al 2 O 3 -doped Y-TZP is explained in terms of decrease in grain-boundary free energy of tetragonal phase owing to Al 3+ ions’ grain-boundary segregation.