Experimental study of the mechanisms of brittle-to-ductile transition of cleavage fracture in Si single crystals

The micromechanisms of brittle-to-ductile transition (BDT) of cleavage fracture in Si single have been investigated using a recently developed novel experimental technique. The crack arrest tests were performed by propagating a cleavage crack with a quasi-steady state velocity against a temperature gradient. Constant K specimens with cracks on {111} and {110} cleavage planes were used. A laser imaging technique was used to measure the crack velocity. The crack arrest temperature (BDT temperature) was determined as a function of crack velocity. An etch-pitting technique was used to study the dislocation structure at or near the crack arrest front. The results indicate that high dislocation mobility and a high dislocation density are needed to arrest a running cleavage crack. Preliminary evidence has confirmed that for Si crystals, the rate-limiting mechanism for the BDT is dislocation motion rather than dislocation nucleation.