Plastic Deformation on the Fracture Surfaces of Germanium Crystals Cloven at Room Temperature

Abstract

The fracture surfaces of germanium crystals cloven at room temperature have been examined by optical and electron microscopes and also by X-ray diffraction. These observations give evidences that plastic deformation takes place in thin surface zones of fracture surfaces. It is proposed that the surface zones were deformed by imperfect deformation twinning which would take place along {123} Plane in the ideal case. The deviation of the twin boundary from the ideal one is attributed to the high Peierls force in germanium. These deformation twins may be formed through the large stress concentration at the tip of crack. The most significant group of twins is formed along the fracture surface so as to cover it, and the twinning dislocations are created at the tip of crack. Another significant group of twins is formed at the step of crack where large shear stress exists.