EXPERIMENTAL-STUDY OF THE MECHANISMS OF BRITTLE-TO-DUCTILE TRANSITIONOF CLEAVAGE FRACTURE IN SI SINGLE-CRYSTALS

The micromechanisms of brittle-to-ductile transition (BDT) of cleavage fracture in Si single crystals have been investigated using a recentl y developed novel experimental technique. The crack arrest tests were performed by propagating a cleavage crack with a quasi-steady state ve locity against a temperature gradient. Constant K specimens with crack s on {111} and {110} cleavage planes were used. A laser imaging techni que was used to measure the crack velocity. The crack arrest temperatu re (BDT temperature) was determined as a function of crack velocity. A n etch-pitting technique was used to study the dislocation structure a t or near the crack arrest front. The results indicate that high dislo cation 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 moti on rather than dislocation nucleation.