Transmission electron-microscopic studies on surface effect upon dislocation and friction stress in MgO

Abstract

Deformed magnesium oxide single crystals have been studied by transmission electron microscopy and it has been found that there are two sources of the surface effect upon dislocation configurations : the mirror image force and the line tension of a dislocation. The effect of the image force reaches as deep as 3200 Å for commercially pure crystals and in addition to this, the effect of the line tension is realized when the specimen thickness is less than a certain critical value. In this case, dislocation configurations observed are totally influenced by the surface and far from those in bulk. From quantitative studies of the critical thickness for pure and doped crystals with various hardnesses, the friction stress for an edge dislocation has been determined and is in good agreement with the flow stress.