MICROSTRUCTURE AND MECHANICAL-PROPERTIES OF FE3AL ALLOYS WITH CHROMIUM

Alloys based on Fe3Al have an equilibrium DO3 Structure at low tempera tures and transform to a B2 structure above about 550-degrees-C. The i nfluence of different rates of quenching from the B2 region to room te mperature and of subsequent heat treatments on the microstructure and mechanical properties of powder metallurgy (P/M) alloys with two diffe rent chromium contents have been examined. Optimizing the processing t o maximize the amount of B2 order, without eliminating dislocations th at enhance both strength and ductility, yields room-temperature ductil ity approaching 20%, although the fracture mode is primarily brittle c leavage. The B2 structure generally has lower flow stress than the DO3 structure because of its lower strain-hardening rate, although B2 ord er actually has higher yield strength when the structure is free of di slocations. Increasing the chromium content from 2% to 5% has little e ffect on ductility, although the 2% Cr alloys generally have higher yi eld strengths and larger order parameters.