The brittle-to-ductile transition in germanium

Abstract

The brittle-to-ductile transition in precracked germanium crystals has been studied experimentally. Germanium undergoes a “smooth” brittle-ductile transition, where the stress to fracture rises steadily with temperature, associated with dislocation activity around the crack front at temperatures well below the transition temperature. The variation in transition temperature with strain rate yields an activation energy of 1.54 eV, suggesting, as in silicon, that dislocation mobility controls the brittle-ductile transition. Modelling of the experiments, using a computer simulation of the shielding effect of an evolving crack tip dislocation array, fits best with a small distance (∼0.1–0.5 μm) between the dislocation sources at the crack tip. This corresponds to the experimental observation that the dislocations reach the crack during the early stages of the tests and multiply along the crack front to form many crack tip sources.