Comparison of TEM Observations with Dislocation Core Structure Calcuiations in B2 Ordered Compounds

ABSTRACTDislocation core structures have been calculated using atomistic computer simulations in NiAl and other B2 compounds. In the present work the calculated dislocation core structure are correlated with the known deforniatiorn behavior of B2 alloys. It is found that for the high ordering energy compounds <111> dislocations do not split in the simulations, in agreement with the experimental observations. It is also found that core structures for certain <111> and 1/2 <111> dislocations are spread in { 112} planes, which is consistent with the slip plane often reported for these dislocations. For the < 100> dislocations several orientations of the dislocation line produce sessile core configurations, whereas other orientations produce relatively more glissile cores. However, a structural transition of each of these dislocation cores may be required before < 100> dislocations become mobile, and this is consistent with the limited tensile ductility observed in NiAl “soft” single crystals below 200°C. Core structure simulations for < 110> dislocations are also reported and are discussed with respect to the importance of these dislocations in the deformation of NiAl.