Sigma-Phase in Fe-Cr and Fe-V Alloy Systems and its Physical Properties

Abstract

This review addresses the physical properties of the σ -phase in Fe-Cr and Fe-V alloy systems as revealed both with experimental-mostly with the Mössbauer spectroscopy-and theoretical methods. In particular, the following questions relevant to the issue have been addressed: identification of σ and determination of its structural properties, kinetics of α-to-σ and σ -to-α phase transformations, Debye temperature and Fe-partial phonon density of states, Curie temperature and magnetization, hyperfine fields, isomer shifts and electric field gradients.

Ab Initio Study of Lattice Site Occupancies in Binary Sigma Phases Using a Single-Site Mean Field Model

“…The formation probability of the σ-phase in the Fe-V alloy is many times larger than in the Fe-Cr system due to a much wider temperature and compositional ranges, where this phase is stable [32]. Despite the fact that the σ-phase in the Fe-V system was found many years ago, the concentration and temperature ranges of its existence are still not precisely known.…”

“…Figure 5. The V site occupancies of the (A, B, C, D, E) sublattices versus the V composition, x V , at fixed T = 1,000 K. The full symbols denote the calculated results, the empty symbols represent the available experimental data (error bars within the symbol sizes) [28,32]. J Let us now consider the atomic site distribution in the Fe-V σ-phase with respect to the alloy composition, x V (see Figure 5).…”

“…In general it is difficult to accurately determine the phase boundaries due to several factors such as: the slow kinetics of the transformation, the dependence on the purity of the alloys, the mechanical state (strained or strain-free state) and the annealing temperature. According to the phase diagrams analyzed in [32] the upper temperature limit for the σ-phase stability equals to 1, 321…”

Twin nucleation in Fe-based bcc alloys—modeling and experiments

“…In the present work, the high temperature was selected in the cubic-α (bcc) region with subsequent quenching, and the room temperature microstructure is the α phase in its entirety. The formation of the σ phase requires incubation time in the σ region of the phase diagram [44][45][46][47]. Therefore, our theoretical analysis has been applied to the alloys where the predicted twinning stress is physically consistent with the microstructure.…”

Characterization of ODS Steels after Gamma Irradiation for Application in ALLEGRO Reactor

“…Hyperfine magnetic fields (B hf ) and isomer shifts (IS) at 57 Fe nuclei, are used for investigation of the changes in phase composition caused by X element in alloy structure by various authors [3][4][5][6].…”