First Principles Investigation Of Mechanical Properties And Phase Stabilily Of Fe₃X（X=Al,Si,Ga）alloys

Ab initio alloy theory, formulated within the exact muffin-tin orbitals(EMTO) method was used to determine the elastic properties of Fe3X(Al,Si, Ga) alloys. The elastic parameters of Fe3 X alloys in disordered A2 structures, ordered DO3 and L12 structures were calculated. And further, the correlation between atomic order in bcc lattice and magnetism was analyzed.The results indicate that L12 is an unstable phase for Fe3 Al, and the stability of DO3 and A2 phases is strongly connected with its magnetic state.Nonmagnetic A2 structure of Fe3 X alloy is dynamically unstable, suggesting that the ferromagnetism stabilizes the disordered A2 phase. The C′ of nonmagnetic DO3 phase is a little larger than that of ferromagnetic phase,which indicating that the ferromagnetism destabilizes the DO3 phase. This characteristic is similar with that of Fe3 Ga alloys. For Fe3 Si alloys, DO3 phase is dynamically stable with very large C′, but the nonmagnetic DO3 has a negative C′, demonstrates that ferromagnetism stabilizes this ordered phase.Ferromagnetism increase the C′ of L12 compared with its nonmagnetic counterpart, and stabilize this phase. In Fe3 Ga alloys, L12 phase in low temperature ferromagnetic state is stable both thermodynamically and dynamically. This agrees with the findings in equilibrium phase diagram.Ferromagnetism destabilizes the ordered DO3 phase, but stabilizes L12 phase.In summery, the dynamical stability of Fe3X(Al,Si,Ga)alloys are correlated with the existence of strong coupling between magnetism and atomic order and structures, and which determines the stability of low temperature phase.