The effect of adding Ni to FeAl was investigated. The lattice parameter, density, vacancy concentration and hardness were measured for FeAl alloys (40, 45, 48, 50 or 51at%Al) to which was added up to 12%at%Ni. The samples were quenched from 700 or 1000C. It was found that Ni did not prevent the elimination of thermal vacancies, as had been previously suggested. However, the equilibrium vacancy concentrations were affected by the Ni additions. No clear evidence of solid-solution hardening by the Ni itself was found, but hardening seemed to arise via the effect of Ni upon the vacancy concentration. It was found that the hardness of most of the Ni-containing alloys could be directly correlated with the square root of the vacancy concentration.

Effect of Ni on Vacancy Concentrations and Hardness in FeAl Alloys L.M.Pike, C.T.Liu, Y.A.Chang: Metallurgical and Materials Transactions A, 1998, 29[7], 1911-6