Effects of anelastic deformation on high-temperature stress relaxation of polycrystalline MgO and Al2O3

High-temperature (1160 to 1450 C) deformation of dense polycrystalline (10 to 90 m) Al₂O₃ and MgO doped with Fe (up to 2.65 cation %) was studied by stress relaxation, dead-load creep and creep recovery. In some cases, all three deformation tests were conducted on a single specimen. A comparison of strain rate-stress data calculated from both stress relaxation and dead-load creep experiments revealed discrepancies in both the magnitude of the strain rates and the dependence between the strain rate and stress. These differences were attributed to the existence of anelastic deformation effects. The correction of stress relaxation data in the low stress regime for linear anelasticity led to strain rate-stress data in reasonably close agreement with results obtained from dead-load creep tests conducted in the viscous creep regime. Creep recovery experiments indicated that anelastic deformation in these ceramic materials was relatively insensitive to changes in temperature and grain size over the range of variables studied.