Deformation of an ordered Fe-35·5 at. % Al alloy

The room-temperature deformation behaviour of a slowly cooled Fe-35·5 at.% Al alloy has been studied in some detail, particularly using transmission electron microscopy. The alloy has a high degree of B2 long-range order and some DO3 short-range order. A three-stage work-hardening curve is obtained, though the observed stage III is thought to be due more to the compression testing than to inherent properties of the material. Stage I, with its serrated flow, appears to be a yielding phenomenon associated with the formation of very coarse slip bands. It is probably related to the destruction of the DO3 short-range order. The stage ends when these bands cover the specimen. Stage II is characterized by a very high linear work-hardening rate (θII/G∼(1/50)) coupled with a comparatively low rate of increase in primary dislocation density with increasing stress and a very low secondary dislocation density (pf/pp-∼(1/100)). Present work-hardening theories of ordered alloys appear unable to explain these facts. The dislocation substructure in Stage II is similar to that observed in non-ordered b.c.c. alloys. Finally, some observations possibly due to APB tubes are also discussed.