Mössbauer study of fine structure features of equiatomic FePd alloy after severe plastic deformation and ordering annealing

• New structure components are found upon transition А1 → L10 in deformed FePd alloy.
• Theirs structure is identified based on Mössbauer spectroscopy data.
• Effect of features of L10 ordering on coercivity of the FePd alloys is considered.

Using Mössbauer spectroscopy based on modern methods of processing spectra, new fine features of the structure of equiatomic alloy FePd, which is formed upon the А1 → L10 phase transformation in the course of severe plastic deformation by torsion and annealing for ordering at the temperature Т = 450 oС, have been studied. It is shown that the structure of the alloy in the as-deformed state cannot be treated as a homogeneous solid solution; it is more likely to consider it as an alternation of disordered regions that are different in composition and in the sign and degree of tetragonal distortions of the initial fcc lattice. Already at early stages of ordering annealing, there are detected low-symmetry regions, inhomogeneous in composition and in the degree of ordering, with tetragonal distortions of the same sign but essentially different in magnitude. These regions can be identified as the structure constituents of the A6 and L10 type with the tetragonal lattice. Such a multi-phase structure is retained even after a long-time (tann = 40 h) annealing. A conclusion is made that the equilibrium tetragonal L10 phase is formed as a result of long-term redistribution of Fe atoms between the initial cubic and newly formed tetragonal components. The effect of the fine-structure peculiarities on the coercivity of the FePd alloys is considered.