DISLOCATION CORE STRUCTURES IN B2-NIAL ALLOYS

Single crystals of Ni-48Al, Ni-50Al and Ni-52Al have been deformed in the [101] orientation. Slip trace and diffraction contrast Burger's vector analyses have been used to characterize the deformation characteristics of these alloys. Ni-50Al was found to display predominantly [001]{100} slip with some limited [001]{100} slip while the non-stoichiometric Ni-48Al and Ni-52Al exhibited a predominance of [001]{100} slip with limited [001]{110} dislocation motion. Direct imaging of the [001]{100} edge dislocation cores by high resolution electron microscopy revealed differences between Ni-50Al and Ni-48Al. Cores in the Ni-48Al were found to display significantly greater spreading of the cores, both within and normal to the slip plane, than for Ni-50Al. The mechanical behavior of these alloys is rationalized in terms of these observations. Comparison of the experimental core images with simulated images based on embedded atom models of the cores indicates that the models are able accurately to predict core structures in stoichiometric alloys, but may have some limitations in predicting structures in non-stoichiometric alloys.