Observations and modelling ofa〈011〉 dislocations in NiAl at intermediate temperatures

Recent experimental evidence indicates that dislocations of the type a〈011〉 are prominent in microstructures following deformation in hard-oriented NiAl at intermediate temperatures (above the brittle-to-ductile transition temperature). The structure of a〈011〉 dislocations has been examined using diffraction-contrast transmission electron microscopy. Evidence has been found for the decomposition of a〈011〉 dislocations into two a〈001〉 dislocations. Analysis using both anisotropic elasticity and the embedded-atom method calculations has revealed that this decomposition process is energetically favourable, even though the net core energy increases upon decomposition. Based on microstructural evidence, additional decomposition occurs by a combination of climb and glide. A continuum-based dislocation model is introduced which incorporates these relevant microstructural features. The predictions of this model are compared with characteristics of deformation of NiAl in the hard orientation.