Damage Produced by Moving Dislocations in MgO

Abstract

The dislocation substructures in single crystals of MgO deformed in four‐point bending at temperatures from –196° to 1300°C have been observed by transmission electron microscopy. Elongated edge dislocation pairs were found at all deformation temperatures. The majority of pairs originated where screw dislocations intersected grown‐in dislocations. Grown‐in dislocations always contained impurity precipitates along their length and often did not lie exactly in a slip plane. Because of either one or both of these factors, grown‐in dislocations remained immobile during deformation. The stability of dislocation pairs depended on the separation of the two dislocations and on the deformation temperature. Narrow pairs broke up into small prismatic loops at 750°C and above. The width of the largest observed pairs approached but never exceeded the calculated value: image