Room temperature tensile properties of Fe-Al single crystals strengthened by excess vacancies

Effects of supersaturated excess vacancies on plastic deformation of Fe-Al were investigated by tensile testing at room temperature for three different single crystals (Fe-33, 41 and 44 mol% Al). Critical resolved shear stresses (CRSSs) of slowly-cooled specimens (as homogenized specimens) and well-annealed specimens (vacancy-eliminated specimens) were almost the same and did not show Al concentration dependence. On the other hand, the CRSS of vacancy-containing specimens (fast-cooled specimens) was significantly higher than that of the others, even for Fe-33 mol% Al, and showed strong Al concentration dependence. The fast-cooled specimens displayed serrated flow behavior during work-hardening at room temperature, and the serrated flow was more intensive at a higher Al composition. Deformation microstructures of Fe-44 mol% Al were examined by TEM, and it was found that dislocations in fast-cooled specimens were inhomogeneously distributed, suggesting jerky motion of slip dislocations. These dislocations were oriented along an unstable direction estimated from dislocation line tension. In addition, there were numerous dislocation loops. A dislocation mechanism of the excess vacancy strengthening is discussed on the basis of the experimental results.