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 t hat ternary additions of 1% have little effect on the vacancy-related hardening and softening which occurs in binary FeAl. The notable excep tion to this behaviour is the addition of nickel, which strongly harde ns this alloy and dramatically changes the defect microstructure that develops during low temperature annealing. The hardening effect of nic kel additions may be attributed to either this changed defect microstr ucture or the interaction of nickel atoms with the cores of glide disl ocations. In contrast, ternary additions of 5% significantly harden Fe Al, and it is believed that this is associated with the interaction of ternary atoms with thermal vacancies, in addition to conventional sol ute hardening. These ternary additions also strongly affected the defe ct microstructures which develop in FeAl during low temperature, vacan cy-relieving heat treatments. Ternary additions resulted in the [001] dislocation structures becoming much wavier, and cobalt and vanadium a dditions induced the formation of [111] dislocations, in addition to t he 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 Scie nce Ltd