Mössbauer study of structural inhomogeneities formed upon the FCC–L10 transformation in equiatomic FePd alloy from different initial states

Abstract

ABSTRACTA comparative Mössbauer study of structural inhomogeneities that arise in the course of А1→ L10 phase transformation in nondeformed (as cast and quenched from 950°C and melt-spun from the ingot) and severely deformed samples of equiatomic FePd alloy upon ordering annealing at Т = 450°С has been performed. According to the known experimental works, the chosen temperature of annealing is optimal for achieving the highest coercive force Hc in both quenched and deformed samples. It is shown that in the high-coercivity state both quenched and deformed samples FePd possess an inhomogeneous tetragonal structure, which is preserved even after quite a prolonged (40–100 h) annealing. All the samples contain, along with the configurations of the nearest neighbourhood that are assigned to the ordered L10 phase, significant volume fractions of configurations typical of nonequiatomic compositions. This conclusion is inconsistent with the commonly accepted concept on single-phase L10 type alloys with maximal values of Hc. An inference is made that the structural inhomogeneities detected in the samples under study result from the mismatch of the position of the point of congruent А1→ L10 transformation (≈58 at.% Pd) in the phase diagram of the FePd system to equiatomic composition.