THE INFLUENCE OF CR ADDITION ON THE ORDERED MICROSTRUCTURE AND DEFORMATION AND FRACTURE-BEHAVIOR OF A FE-28-PERCENT-AL INTERMETALLIC

Samples of Fe-28%Al and Fe-28%Al-4%Cr were recrystallized, and heat treated at 500-degrees-C to obtain B2 and DO3 ordering. While the material containing Cr was well ordered, the other material showed a two-phase ordered plus disordered microstructure with the degree of ordering, the domain size and the fraction of disordered phase depending sensitively on the experimental conditions. The material containing Cr was relatively soft, showed low work hardening and was fairly ductile: these properties are obtained by the ready movement of superdislocations. The other material was stronger and generally less ductile: these properties depended on whether single dislocations were present leaving APB trails and leading to low work hardening rates, or whether loosely-coupled superdislocations moved through a two-phase microstructure at a lower stress and with higher work hardening rates. This study emphasizes the need for complete microstructural characterization in order to understand the mechanical behaviour of such materials.