A dislocation mechanics-based crystallographic model of a B2-type intermetallic alloy

A crystallographic slip based model for cubic oriented NiAl single crystals is derived from an idealization of the dislocation network observed in the active slip systems, viz. {110} <110>. The crystallographic model successfully accounts for the cyclic steady-state behaviour of crystals subjected to strain histories within the range epsilon(<100>) = epsilon(m) +/- 0.5%, for epsilon(m) = 0 and 35%, at 750 and 850 degrees C. It accurately predicts the flow stress dependence on temperature, strain rate and dislocation density arising from the lattice resistance to dislocation motion and from discrete obstacle resistance due to dislocation interactions. The kinematic and isotropic hardening modes associated with defect trails left behind by gliding dislocations and dislocation storage, respectively, are properly represented. The average distance that dislocations have to glide for their density to increase beyond the level needed to balance dynamic recovery processes was predicted to be approximately 260 times the random forest dislocation spacing. Measured dislocation densities at different mean strains were found to be consistent with the predictions of the theoretical model.