Thermally Activated Deformation Mechanisms in MgO Investigated via High Temperature Scanning Indentation

ABSTRACT Magnesium oxide (MgO) serves as a model material for plastically deformable ceramics. In previous studies, it has mainly been investigated via uniaxial compression, with studies often focusing on a particular deformation mechanism and temperature range. In this work, the novel high temperature scanning indentation (HTSI) nanoindentation method is applied to characterize the mechanical properties of single‐crystalline MgO from room temperature to 800°C, allowing a quasi‐continuous measurement of hardness, elastic modulus, the coefficient of strain rate sensitivity, and the activation volume. Results show that the hardness is controlled by hard 1/2<110>{100} slip, while the activation parameters are influenced by both 1/2<110>{100} and 1/2<110>{110} slip systems. The temperature dependence of the hardness follows two linear regimes, while the strain rate sensitivity shows complex behavior with a maximum of m = 0.05 at a temperature of 675°C. In the same regime, the activation volume remains approximately constant at V = 10–20 b 3 . At higher temperatures, it increases to V = 100 b 3 . The combined hardness and activation parameter data enable the determination of transition temperatures between different deformation regimes. With increasing temperature, MgO first shifts from a kink‐pair to an obstacle‐controlled regime at 240°C, with long‐range dislocation interactions setting in at higher temperatures above 675°C.