Dynamic formation of zircon during high temperature deformation of zirconia–silica composites with alumina additions

A three phase ceramic composite of 8 mol% Y2O3 stabilized ZrO2 (YSZ), SiO2, and Al2O3 was evaluated for potential high temperature superplasticity. The amorphous SiO2 content was 5 wt.%, and increasing additions of Al2O3 were made. The effect of varying the Y2O3 stabilizer concentration in ZrO2 was also studied. Samples sintered at 1200 C contained only YSZ, Al2O3, and amorphous SiO2, but ZrSiO4 formed in the samples above 1300 C. Mullite (3Al2O3 2SiO2) was not detected in any samples. Specimens of 1 wt.% Al2O3–YSZ/SiO2 had an anomalously high deformation rate of ~2 · 10–4 s–1 at 1200 C when compared to YSZ/SiO2 without Al2O3 (~4 · 10-5 s–1). Higher amounts of Al2O3 additions decreased the strain rate. Extensive deformation of Al2O3 doped YSZ/SiO2 at 1200 C induced the formation of ZrSiO4 due to enhanced reaction rates. This distributed, yet locally interconnected, zircon phase rapidly eroded the strain rate after ~60% deformation