Local Displacive Phase Transformation in Large-Magnetostriction Alloy Fe₈₁Ga₁₉

Soluting nonmagnetic Ga into body-centered-cubic (BCC) Fe has been found to create over tenfold enhancement in magnetostriction—a fundamental property of ferromagnetic materials, but the underlying origin remains elusive. It was shown that such extraordinary magnetostriction enhancement is closely related to lattice softening, analogous to the scenario of displacive/martensitic phase transformation. In this work, we report the {111}_BCC collapse-induced hexagonal ω phase in the magnetostriction-peak alloy Fe₈₁Ga₁₉. The local BCC to ω phase transformation was observed at highly strained non-equilibrium state, where artificial-aging-induced tetragonal L6₀ intermediate phase and L1₂ equilibrium phase coexist with the BCC matrix. The mechanically harder L6₀/L1₂ phases exert strong shear stress along < 111 > _BCC direction on the mechanically softer BCC matrix, leading to the formation of ω phase at the phase interface. This study provides new evidence for the lattice softening of Fe–Ga alloys, adding important insight into understanding their extraordinary magnetostriction effect.