Kinking in MgO single crystals under high confining pressure

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Abstract
Single crystals of MgO compressed in the [111] direction under high hydrostatic pressures at room temperature deformed abruptly at high stress by kinking on dodecahedral slip systems. In this orientation, only three of the (100)[110] slip systems were expected to be stressed, and the dodecahedral slip systems involved in the kinking are nominally unstressed. It is shown that only small local misorientations of crystal are required to throw critical resolved shear stresses on the dodecahedral slip systems to cause kinking. It was calculated that with approximately 2° of misorientation, the dodecahedral slip would persist to nearly 300° before cube-plane slip systems became active. It is suggested that the onset of brittle fracture below 350°c at atmospheric pressure follows the change in deformation mode. Residual stresses of 1·2 × 109 dynes cm−2 were measured in the kinks using stress-birefringence analysis.

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