Iron aluminides are Fe–Al alloys with about 20–50 at.%Al. They are among the most widely studied intermetallic compounds due to their good oxidation resistance, low density compared to steels and their low manufacturing costs. Low room temperature ductility has been a major obstacle for mechanical processing of these materials, while a drop in strength above 600 °C limits their applications. Recent research indicates that doping and microstructure control can improve the mechanical properties of these alloys.
Iron aluminides exhibit order–disorder transformations and large concentrations of defects that depend on temperature and composition. In the Fe-rich portion of the Fe–Al binary diagram exist the disordered A2 and the ordered B2 (FeAl) and D03 (Fe3 Al) phases. The ordering transformations begin with the formation of small ordered nuclei, which grow until impingement, resulting in an anti-phase domain structure. Different types of anti-phase boundaries are present in the ordered alloys depending on their structure. In B2 ordered alloys only one type of anti-phase boundary is found, the B2-type APB (or APB1) that is formed through the A2→B2 ordering transformation and that has a fault vector a/2 (where a is the lattice parameter of the B2 unit cell). In ordered D03 two types of anti-phase boundaries can appear: the APB1 that forms as above, with a fault vector a0/4 (where a0 is the lattice parameter of the D03 unit cell) and the D03-type APB (or APB2) related to the B2→D03 transformation with a
fault vector a0/2 .