An Ab Initio Study of Thermodynamic and Mechanical Stability of Heusler-Based Fe2AlCo Polymorphs

Abstract

We use quantum-mechanical calculations to test a hypothesis of Glover et al. (J. Mag. Mag. Mater. 15 (1980) 699) that Co atoms in the Fe2AlCo compound have on average 3 Fe and 3 Co atoms in their second nearest neighbor shell. We have simulated four structural configurations of Fe2AlCo including the full Heusler structure, inverse Heusler polymorph and two other phases matching this idea. The highest thermodynamic stability at T = 0 K is indeed predicted for one of the phases with the distribution of atoms according to Glover and et al. However, small energy differences among three of the studied polymorphs lead to a disordered CsCl-structure-like (B2-like) phase at elevated temperatures. The fourth variant, the full Heusler phase, is predicted to be mechanically unstable. The global magnetic states are predicted to be ferromagnetic but local magnetic moments of Fe and Co atoms sensitively depend on the composition of the first and second coordination shells.

Creep of Heusler-Type Alloy Fe-25Al-25Co

“…The situation in the inverse-Heusler lattice is more complicated (due to the existence of four sublattices) but the Co atoms are expected [19] to occupy the sublattice at locations where the second nearest neighbors are only the Fe and Co atoms (and not the Al atoms). It was also shown previously by quantum-mechanical calculations of Heusler-based Fe 2 AlCo polymorphs, that the ordered full-Heusler structure is mechanically unstable and thermodynamically less stable than the inverse-Heusler lattice [13]. The energy differences between different polymorphs were found to be so small that partly disordered B2 and completely disordered A2 structures are predicted for elevated and high temperatures.…”

“…A very high Curie temperature of 857 • C was also found in the Fe 2 CoAl compound [12]. In the previous study, quantum-mechanical calculations were used to investigate properties of four different polymorphs of Fe 2 AlCo and the occurrence of structural multiplicity at elevated temperatures was predicted [13]. Very few studies have experimentally investigated mechanical properties of Heusler compounds [14].…”

“…The Fe 2 AlCo has, under 1000 K, a two-phase superalloy nanostructure with cuboids of a partly ordered phase coherently co-existing in a differently (or less) ordered matrix. The ordered phase has not the full-Heusler lattice (the L2 1 structure as a ternary analogue of D0 3 ) because quantum-mechanical calculations showed that it is mechanically unstable [13] and the inverse-Heusler structure, cf., Figure 1a, is both mechanically and thermodynamically more stable [10,13]. The inverse-Heusler is also in a better agreement with experiments (see, e.g., Ref.…”

Impact of Nano-Scale Distribution of Atoms on Electronic and Magnetic Properties of Phases in Fe-Al Nanocomposites: An Ab Initio Study

“…Next to the experimental research reported in the above mentioned papers, various Fe-Al-based materials were theoretically studied by quantum-mechanical calculations in the last three decades (see, e.g., Refs [18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33]). A surprising controversy has appeared in the case of first-principles prediction of the ground-state structure of Fe3Al.…”

Strength and Brittleness of Interfaces in Fe-Al Superalloy Nanocomposites under Multiaxial Loading: An ab initio and Atomistic Study

“…If it is not for this environmental embrittlement, Fe Al is seen in experiments to have decent ductility [ 8 , 9 ]. Recently, there is a renewed interest in Fe-Al-based materials containing higher number of chemical species and/or phases [ 1 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 ].…”