Weak beam observations of dissociation of pure screw dislocations in Ni3Al

The dissociation of superdislocations in Ni₃Al, which have a pure screw character, has been recorded on weak beam images at the g(5g) imaging condition. All screws were observed to dissociate on an {001} habit plane bounding APB faults. By computer modelling, the dissociation distance (d^CSF) of the Shockley partial dislocations that bound a complex stacking fault is shown to be less than 1.5 nm. This is the first reported case of fourfold dissociation bounding CSF + APB + CSF faults with a non-planar configuration and pure screw character. The energy values deduced from the measured spacing show quite large difference from the results obtained from dissociation with a planar system. It is questionable to use the linear anisotropic elasticity theory for such small splitting and nonplanar configuration. In addition our simulations demonstrate that a g(ng) condition is a wise choice for imaging partial separation.