The effect of stress changes during creep of single-and polycrystalline MgO

Abstract

High-precision, constant-stress creep equipment has been used to study the strain/time behaviour following small stress changes during transient and steady-state creep of single-and polycrystalline MgO at 1596 K. In all cases, decreasing the stress by a small amount (∼5% of the applied stress) results in an incubation period of zero creep rate before the creep rate accelerates to a new positive value, suggesting that the same recovery process is rate-controlling throughout the creep curve with both single-crystal and polycrystalline MgO. A recovery model for creep is proposed in which the rate-determining process is the diffusion-controlled growth of the three-dimensional dislocation network to generate links which are sufficiently long to act as dislocation sources. Both subgrain boundaries and grain boundaries appear to act as obstacles to glide of dislocations generated at sources during high-temperature creep.