Revealing microstructure and magnetostrictive behavior of compositionally complex FeCoVGa alloys

The microstructure and magnetostrictive behavior of FeCoVGa multicomponent alloys were investigated by X-ray diffraction (XRD), electron backscatter diffraction (EBSD), transmission electron microscopy (TEM), and dilatometry. Fe-30Co, Fe-30Co-1V, and Fe-30Co-1V-xGa (x = 12, 16) alloys were analyzed after annealing and water quenching following arc melting. XRD revealed lattice expansion with V and Ga additions, while TEM confirmed the presence of an ordered B2 phase in the in the 12Ga alloy together with nanometric σ-phase precipitates. EBSD analysis showed that the binary Fe-30Co alloy develops a lamellar colony microstructure associated with the rapid A2 → B2 ordering transformation during cooling. Vanadium addition increased intragranular misorientation and refined the grain size, indicating diffusion-limited ordering. In FeCoVGa alloys, vanadium also promoted the formation of V-rich precipitates that may have contributed to abnormal grain growth. Ga addition stabilized a quaternary BCC phase with ordered B2 structure and further promoted grain coarsening. Magnetostriction measurements showed similar saturation magnetostriction values for Fe-30Co and Fe-30Co-1V (~28 × 10 -6 ), whereas Fe-30Co-1V-12Ga exhibited a reduced value (~17 × 10 -6 ) due to intrinsic Ga effects and texture contributions. The Fe-30Co-1V-16Ga alloy displayed highly anisotropic magnetostrictive behavior consistent with its quasi-single-crystal microstructure, yielding estimated magnetoelastic constants of λ 111 = −13.3 × 10 -6 and λ 100 = 30 × 10 -6 . The ordered FeCoVGa-B2 phase was estimated to exhibit a low saturation magnetostriction, λ s ≈ 4 × 10 -6 , substantially smaller than that of the binary alloy, making these alloys promising low-noise soft magnetic materials for AC motors and power transformers.