Creep of polycrystalline yttrium aluminum garnet (YAG) at elevated temperature in air and in steam

Abstract

Compressive creep of high-purity polycrystalline yttrium aluminum garnet (YAG, Y3Al5O12) was investigated at 1300°C and 50–200MPa in air and in steam. Compressive creep behavior of silica-doped polycrystalline YAG (Y3Al5O12–0.14wt% SiO2) was also studied. Creep specimens were microstructurally characterized by optical microscopy and TEM before and after creep. Steam slightly increased creep rates of material with grain size less than 1μm (the undoped YAG), but otherwise had little effect. The flow stress exponent was n≈1 for both SiO2-doped YAG and undoped YAG. Creep rates and microstructural observations are consistent with the Nabarro-Herring creep mechanism, with creep rate limited by lattice diffusion of yttrium cations (Y3+). Silica-doped YAG had a larger grain size of 2.41μm and lower creep rates than undoped YAG with 0.92μm grain size. However, creep rates normalized by grain size for Nabarro-Herring creep were higher in SiO2-doped YAG. Possible effects of SiO2 doping and steam on creep of YAG are discussed.