Intergranular fracture of magnesium oxide bi-crystals

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Abstract
Intergranular fracture of magnesium oxide bi-crystals of certain mis-orientations without showing macroplasticity has been observed during three-point bend tests. In the absence of large pile-ups of dislocations at the grain boundary, the cause of failure is other than that suggested by Zener, and the role of impurities and defects in the grain boundary in determining the mechanical behaviour of the crystals has been investigated. Electron probe analysis of the fracture surfaces and microscopic studies of the grain boundaries under transmitted light show the existence of a silicate phase associated with pores and cavities at the grain boundary. These seem to be the major sources of weakness as cavities evidently propagate as Griffith cracks during the deformation of the bi-crystals.

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