The effect of ternary additions on vacancy hardening in near stoichiometric FeAl

The effect of transition metal ternary additions which replace iron on the variations in hardness and defect morphology with heat treatment of near stoichiometric FeAl has been studied. It was generally found that ternary additions of 1% have little effect on the vacancy-related hardening and softening which occurs in binary FeAl. The notable exception to this behaviour is the addition of nickel, which strongly hardens this alloy and dramatically changes the defect microstructure that develops during low temperature annealing. The hardening effect of nickel additions may be attributed to either this changed defect microstructure or the interaction of nickel atoms with the cores of glide dislocations. In contrast, ternary additions of 5% significantly harden FeAl, and it is believed that this is associated with the interaction of ternary atoms with thermal vacancies, in addition to conventional solute hardening. These ternary additions also strongly affected the defect microstructures which develop in FeAl during low temperature, vacancy-relieving heat treatments. Ternary additions resulted in the [001] dislocation structures becoming much wavier, and cobalt and vanadium additions induced the formation of [111] dislocations, in addition to the expected [001] defects. Furthermore, low-temperature heat treatment of Fe45Al50Cr5 led not only to the formation of FeAl2 particles, but also to localised disordered regions. Copyright (C) 1996 Elsevier Science Ltd