On the plasticity of short-range ordered and long-range ordered alloys

The plastic behaviour of short-range ordered and long-range ordered alloys shows remarkable similarities but also differences, e.g. in the temperature dependence of the critical shear stress, in the work hardening of single and polycrystals, in the slip characteristics and in the development of dislocation microstructures. These features are compared and illustrated by experimental data on concentrated fcc alloys showing tendencies to short-range ordering (Cu–Al) and on bcc intermetallic (long-range ordered) compounds (CuZn, Fe3Al, Fe3Si). In spite of strong differences of the developed dislocation microstructures and fine structures of slip distribution on the micro scale due to different dislocation configurations in fcc and bcc lattices, quite similar patterns of local shear occur on larger scales, e.g. slip band evolution and instabilities of slip in certain temperature regimes, indicating more general reasons. Even the frequently discussed ‘stress anomaly’ in the temperature dependence of the critical shear stress shows striking similarities in short- and long-range ordered alloys suggesting that at least part of its causes may lie in the counteracting processes of a kind of obstacle destruction mechanism by gliding dislocations and a restoration process of diffusional origin.