Microstructure and mechanical properties of Fe3Al alloys with chromium

Alloys based on Fe₃Al have an equilibrium DO₃ structure at low temperatures and transform to a B2 structure above about 550°C. The influence of different rates of quenching from the B2 region to room temperature and of subsequent heat treatments on the microstructure and mechanical properties of powder metallurgy (P/M) alloys with two different chromium contents have been examined. Optimizing the processing to maximize the amount of B2 order, without eliminating dislocations that enhance both strength and ductility, yields room-temperature ductility approaching 20%, although the fracture mode is primarily brittle cleavage. The B2 structure generally has lower flow stress than the DO₃ structure because of its lower strain-hardening rate, although B2 order actually has higher yield strength when the structure is free of dislocations. Increasing the chromium content from 2% to 5% has little effect on ductility, although the 2% Cr alloys generally have higher yield strengths and larger order parameters.