Solid-solution hardening and softening by Fe additions to NiAl

Solid-solution hardening in the case of a ternary alloy addition to a B2 compound with the triple defect structure has been investigated. The fact that the ternary element may occupy either of two sublattices or may affect the concentration of other types of point defects present in the material makes this a very interesting problem to consider. Ni-rich (40 at% Al), stoichiometric (50 at% Al), and Al-rich (52at% Al) alloys were doped with up to 12at% Fe. Lattice parameter, bulk density and hardness measurements were performed on samples quenched from 100°C. It was found that solid-solution softening actually occurs in the Ni-rich alloys, while hardening was observed in the stoichiometric and Al-rich alloys. The vacancy concentration was determined from the experimental data, and the site occupancies of the Fe atoms were estimated from a thermodynamic model. Through careful consideration of all point defect concentrations the solid-solu-tion hardening and softening behaviors could be effectively rationalized. © 1997 Elsevier Science Limited.