High-temperature creep and dislocation structure of MgO single crystals at low stresses

MgO single crystals oriented toward (100) have been compressively deformed to strains in the range of 0.04 to 0.09 at temperatures between 1948 and 2023 K using stresses under 6 MPa. Microstructural developments in the crept samples were monitored by etch pitting, SEM and HVEM. Optical microscopy revealed an equiaxed network of subgrains with 〈110〉 forming the framework for the formation of subgrains. Measurement of the dislocation density not associated with cells reveals that the stress dependence of the steady-state values of dislocation density can be described by the relationϱ ∫σ ^2.15. HVEM observations show that cell boundaries are formed by the process of knitting. Drastic unloading results in a fraction of the sub-boundaries straightening, but the majority of the boundaries are destroyed. It is concluded that creep of MgO at low stresses and high temperature is similar to those of fcc metals.