Influence of Vacancies on Isochronal Ordering in FeCo Alloy

Kinetics of isochronal ordering and behavior of vacancies in an FeCo alloy have been investigated with the measurement of temperature derivative of electrical resistivity αR. A part of αR caused by the ordering or disordering, ΔαR, was estimated by eliminating other effects such as magnetic and phonon scattering effect. The data on ΔαR revealed that the homogenious and heterogeneous orderings occur concurrently in the temperature range 650-773 K, whereas only the homogenious ordering occurs above 773 K.On the other hand, the kinetic equation of ordering derived in our previous work was expanded, by assuming that the ordering takes place by the migration of vacancies. The variations of ΔαR of the alloy were analysed using the expanded rate equation. It was shown that the two types of homogenious ordering proceed continuously in the range of low temperatures. The one is the ordering due to the quenched-in excess vacancies, about 15% of the equilibrium concentration for the quenched temperature, and the other is due to the thermal ones. The kinetic behavior of ΔαR and vacancies were interpreted satisfactorily by the present expanded rate equation.