Effect of Addition of Magnesia and Zirconium Oxide on High Temperature Deformation of Fine-grained Alumina Polycrystals

Abstract

For alumina polycrystals doped with MgO and ZrO₂ (1000 ~ 10000 ppm), compression and four-point bending tests were carried out. In the early stages of deformation of alumina doped with MgO, diffusional creep controlled by the grain boundary diffusion was dominant deformation mechanism at higher stresses with the stress exponent n ⋍ 1. At lower stresses, on the other hand, deformation with n ⋍ 2 was observed, suggesting that the interface-reaction seemed to control the creep deformation. Strain hardening, resulting from grain growth of Al₂O₃, was observed during creep tests. Furthermore, Al₂O₃ doped with higher amounts of dopant deformed at lower stresses, because the strain hardening effect decreased with increasing amount of secondary phase, which suppressed the dynamic grain growth. Although Al₂O₃ doped with ZrO₂ had the same deformation mechanism as MgO dopant, the strain rates of Al₂O₃ doped with ZrO₂ were nearly one-tenth slower than Al₂O₃ doped with MgO due to the segregation of Zr⁴⁺ at the grain boundaries.