Variation of Lattice Constant in FeCo Alloys on Isothermal Annealing

Abstract

The effect of isothermal annealing on the lattice constant of FeCo alloys, quenched from a disordered state, was observed by means of X-ray diffraction. It was found the lattice constant increases in two stages, which indicates the ordering takes place by a vacancy mechanism, first with quenched-in excess vacancies and then with equilibrium ones. A set of phenomenological rate equations, which describe the ordering and the change in vacancy concentration, were applied to analyse the experimental results, and the values for formation and migration energies of vacancies in FeCo were estimated at 91 and 139 kJ/mol, respectively.