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

ABSTRACT

A 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 H_c 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 H_c. 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.

KEYWORDS:

• Mössbauer spectroscopy
• FePd
• FCC–L1₀ phase transformation
• congruent ordering

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The research was carried out within the state assignment of FASO  of Russia [theme ‘Magnet’ No. АААА-А18-118020290129-5] and partially supported by the Russian Foundation for Basic Research [Project No. 17-52-45097].