| An investigation of the mechanical properties of Fe-Al single crystals by tensile testing both at different strain rates (10−7 s−1 to 1 s−1) and in different environments (air, vacuum or oxygen), showed that moisture-produced hydrogen in Fe-Al dramatically lowers the ductility and the yield stress of Fe-Al single crystals. The critical resolved shear stress exhibits a strong orientation dependence at temperatures from room temperature to ∼800 K and at the yield stress peak temperature. At room temperature, fracture initiated from the surface of the specimen when it was tested in air or vacuum, but originated at the surface as well as inside the specimen when it was tested in oxygen. Doping with boron dramatically reduces the secondary cracking but produces only a small improvement in the elongation in air (only), possibly because it raises the yield strength.; Transmission electron microscopy showed the presence of antiphase boundary (APB) tubes in Fe-34Al, Fe-40Al, Fe-40Al-3Cu and Fe-40Al-3Cr but not in Fe-43Al, presumably due to the higher APB energy and thus, the narrower APB tube width in this material.; Both binary and ternary Fe-Al single crystals used in this study show a paramagnetic to ferromagnetic transition upon plastic deformation. The saturation magnetizations of the cold-rolled single crystals were measured in a vibrating sample magnetometer from 77 K to room temperature and the enthalpies associated with the removal of the APB tubes were measured in a differential scanning calorimeter. From the enthalpy measurement, the APB tube density and the number of Fe nearest neighbors were estimated. Hence, the saturation magnetizations were calculated. These were found to be in good agreement with the experimentally determined values. The calculation showed that the strain-induced saturation magnetization arises mainly from APB tubes. Consistent with this result, annealing at temperatures above ∼500 K leads to both the disappearance of the APB tubes and a reversion to paramagnetic behavior. |
