Dopant Effect on the High-Temperature Grain Boundary Sliding in Alumina

摘要

High-temperature plastic flow in polycrystalline Al{sub}2O{sub}3 is often affected seriously by the doping of small amount of cations. For instance, a doping of either YO{sub}1.5 or ZrO{sub}2 in the level of 0.1mol% or less into Al{sub}2O{sub}3 increases very much the flow stress or drastically reduces the creep strain rate. Such a dopant effect is caused by grain boundary segregation of doped cation. The plastic flow in fine-grained, polycrystalline Al{sub}2O{sub}3 takes place mainly by grain boundary sliding or grain boundary diffusion. To make clear the effect of cation segregation on grain boundary sliding directly, we have examined the sliding behavior using undoped and Y{sup}(3+)-doped Al{sub}2O{sub}3 bicrystals with a random boundary at 1450°C under an applied stress of 15MPa. It was found that the grain boundary sliding rate was retarded in two orders of magnitude by Y{sup}(3+)-segregation in the random boundary. The result clearly indicates that the Y{sup}(3+)-segregation is an intrinsic effect to suppress the grain boundary sliding, The effect can be understood from the change in ionic bonding strength in the vicinity of grain boundaries with dopant segregation.