The influence of lutetium-doping effect on diffusional creep in polycrystalline Al2O3

High temperature compressive creep behavior in high-purity, undoped Al2O3 and 0.02 mol% LuO1.5-doped Al2O3 with an average grain size of about 5 μm was investigated under an applied stress of 10–100 MPa at 1250–1400 °C. Microstructure and chemical composition at the grain boundaries in the present materials were characterized with a high-resolution transmission electron microscopy (HRTEM) and an energy dispersive X-ray spectroscopy (EDS). The Lu-doping is effective for the improvement in the creep resistance in Al2O3 with the grain size of about 5 μm even at the dopant level of 0.02 mol%. Steady-state creep rate in undoped Al2O3 is in good agreement with theoretical creep rate of the grain boundary diffusion mechanism. On the other hand, in LuO1.5-doped Al2O3, the stress dependence of the creep rate is the same than in undoped one, but the activation energy for the creep deformation is much larger than that in undoped alumina. The large activation energy and the sluggish creep rate in Lu-doped alumina are caused by suppression of grain boundary diffusivity in alumina due to Lu3+ cations’ segregation. In fact, the effect of 0.02 mol% LuO1.5-doping in Al2O3 with the grain size of about 5 μm is very close to that of 0.1 mol% LuO1.5-doping in Al2O3 with the grain size of about 1 μm; owing to a similar grain boundary dopant content in the two materials.