Deformation of Polycrystalline MgO at Elevated Temperatures

Stress-strain curves for five types of polycrystalline MgO are presented as a function of temperature. All types were nominally dense and pure but differed in grain size, composition, and porosity. Above 1200°C deformation occurred by grain boundary shearing accompanied in some cases by slip; below 800°C, specimens fractured primarily by grain boundary parting with little permanent strain. Between 800° and 1200°C, one type deformed plastically by slip; the other four types were brittle. The observed behavior is analyzed in terms of the presence of mobile dislocations, the resistance to dislocation motion, and the strength of grain boundaries.