COMPLEX FAULTS IN A B2 IRON ALUMINIDE ALLOY

摘要

Complex faults are present on {100} planes in a Fe-40Al-0.7C-0.5B alloy (all compositions are in atomic percent) but are not observed in a ternary Fe-40Al-0.6C alloy. These faults have a displacement vector of 1/2(001) lying in the plane of the fault. In addition, there is an aluminum layer missing at the fault and a recent study by Cadel et al. (Scripta Metall. 41(1999) 421) has claimed that there is boron segregation at these faults. Six variants of this fault can be present. The occurrence and configurations assumed by the fault depend on the heat-treatment temperature and cooling rate which are thought to influence the presence and migration of boron/vacancy complexes. The width of the complex fault also appears to be a function of the heat-treatment temperature (and hence boron in solid solution). In the quenched and annealed condition as well as in the material air-cooled from 1000 and 800 deg C, there is evidence for these complex faults being bound by partial dislocations that have a Burgers vector of 1/2(001). In several instances, when these faults are imaged edge-on, they exhibit a zig-zag appearance indicative of faceting on the cube planes. In addition to these complex faults, thermal antiphase boundaries are also observed in some heat-treatment conditions and are postulated to be a consequence of the recrystallized extruded structure.