OBSERVATIONS AND MODELING OF A(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-o riented NiAl at intermediate temperatures (above the brittle-to-ductil e transition temperature). The structure of a[011] dislocations has be en examined using diffraction-contrast transmission electron microscop y. Evidence has been found for the decomposition of a[011] dislocation s into two a[001] dislocations. Analysis using both anisotropic elasti city 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 ev idence, additional decomposition occurs by a combination of climb and glide. A continuum-based dislocation model is introduced which incorpo rates these relevant microstructural features. The predictions of this model are compared with characteristics of deformation of NiAl in the hard orientation.