Crack initiation and propagation in brittle-to-ductile transition regime of NiAl single crystals

The mechanisms of crack initiation and propagation in the brittle-to-ductile transition (BDT) regime were evaluated in double-notched tensile specimens of a stoichiometric NiAl single crystal. The crack initiation was found to occur by formation of stable microcracks in the localized slip bands that form in the vicinity of the notch. A study of the crack path revealed that the unstable crack prefers to propagate along the {511} planes. The results of this study suggest that the BDT in NiAl correlates with the onset of net-section yielding. Decreasing the displacement rate resulted in a reduction in BDT temperature to below room temperature. The effect of displacement rate on BDT temperature has been attributed to the higher probability of cross-slip at low strain rates.