Microstructure evolution and recrystallization during creep of MgO single crystals

Single crystals of MgO were deformed in compression parallel to 〈100〉, between 1573 and 1773 K and up to 69% strain. All samples deformed in the climb assisted dislocation glide regime, and dynamic recovery by sub-grain rotation is the main recrystallization mechanism. Deformation microstructures were analysed using electron backscatter diffraction (EBSD). At high strains sub-grain rotation recrystallization produces low (<10°), high (10° < θ < 40°) and very high (>40°) angle boundaries that show a continuous hierarchy of misorientations θ (the frequency of misorientation angles falls exponentially towards high values). Low angle boundaries are interpreted to be incidental dislocation boundaries and generally maintain low misorientations, while high angle boundaries may be geometrically necessary boundaries and rapidly rotate to large misorientations with increasing strain. Understanding these boundaries is fundamental if realistic models for recovery and recrystallization must be accomplished. Slip systems {1 1 0}〈110〉, {1 1 1}〈110〉, {1 0 0}〈110〉 and possibly {1 1 2}〈110〉 are proposed to be operative.