TRANSMISSION ELECTRON-MICROSCOPY INSITU STRAINING OF MULTIPHASE NI-20 AT PERCENT AL-30 AT PERCENT FE

Transmission electron microscopy in situ straining experiments have been performed on the multiphase alloy Ni-20Al-30Fe (where the composition is in atomic per cent). This alloy consists of the B2 (ordered b.c.c.) phase Ni-30Al-20Fe and the phase Ni-12Al-40Fe which is fc.c. with fine L1(2) (ordered f.c.c.) particles. Slip in the B2 phase was by the movement of [100] dislocations occurring either on discrete slip planes or in bands and produced loops as debris behind the gliding dislocations. Slip in the f.c.c. L1(2) phase was by the glide of pairs of (a/2)[110] dislocations and occurred on discrete slip planes. The separation of the (a/2)[110] dislocation pairs increased with increasing distance from the head of the slip band, because of disordering of the L1(2) particles. Pile-ups occurred in both phases at the two-phase interface. Slip propagation was observed to occur across the interfaces both from the B2 phase to the f.c.c. L1(2) phase and vice versa; there was also some evidence that dislocations could be nucleated into both phases from the internal two-phase interfaces.