ON THE SHAPE OF EDGE-DISLOCATION LOOPS IN BETA-NIAL

The shapes of edge dislocation loops in P-NiAl have been studied. These loops have {001} habit planes, <001) Burgers vectors and exhibit two distinct forms. One of these is roughly square with segments nearly parallel to <010>; this corresponds to the equilibrium shape calculated on the basis of elastic anisotropy. The other form consists of segments aligned accurately parallel to <110>, which should be elastically unstable. It is proposed that this second shape is stabilized by dissociation of the perfect dislocation into three partial dislocations on the intersecting {110} planes for example <001>→1/4<TH>+1/2<001>+1/4<lTl> The consequences of such a dissociation for the plastic deformation of P-NiAl are discussed. © 1990 Taylor & Francis Group, LLC.