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 Fe 81 Ga 19 . The local BCC to ω phase transformation was observed at highly strained non-equilibrium state, where artificial-aging-induced tetragonal L6 0 intermediate phase and L1 2 equilibrium phase coexist with the BCC matrix. The mechanically harder L6 0 /L1 2 phases exert strong shear stress along 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.