Evolution of substructures in deformed NiAl single crystals oriented for single slip

We have examined the deformation behaviour of NiAl single crystals, oriented for single slip, at 77 and 300K and the resulting substructures. The macroscopic yield strength decreases by a factor of two when the deformation temperature is increased from 77 to 300 K. At 77 K, the work-hardening rate after yielding is very high, and the deformation-induced substructures consist of uniformly distributed, nearly straight edge dislocations, jogged screw dislocations and prismatic loops. The substructure observed after deformation at 300 K is comprised of walls consisting of prismatic loops and zigzag screw dislocations. We have rationalized the preceding observations in terms of the non-conservative motion of jogged screw dislocations. We have also argued that the observed microstructures may limit the motion of dislocations during additional deformation, implying that the limited ductility in NiAl at low temperatures may be 'acquired'.