Magnetism-induced solid solution effects in intermetallic Ni60Al40

In this study, experimental work on solute effects in an intermetallic alloy, NiAl, has been complemented by first-principles quantum mechanical calculations to investigate the effect of iron and cobalt solutes on lattice parameter and hardening. Ternary additions of iron and cobalt with similar atomic sizes were added to replace nickel in NiAl containing 40% Al. Cobalt solutes did not affect the lattice parameter or the hardening behavior of NiAl alloys. Iron solutes, on the other hand, substantially expanded the lattice, resulting in unusual solid solution softening. These results could not be explained from a consideration of the size mismatch based on the Goldschmidt radii for iron and cobalt atoms. From the contrasting behavior of the iron and cobalt solutes, magnetic interactions induced by iron atoms located on the aluminum sublattice have been identified as a new factor responsible for the unusual large lattice dilation and resultant solid solution softening in these intermetallic alloys. © 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.