Formation mechanism of tetragonal nanoprecipitates in Fe-Ga alloys that dominate the material's large magnetostriction

Up to now, the formation mechanism of tetragonal nanoprecipitates that may dominate the large magnetostriction of Fe-Ga alloys remains unclear. Here we found that both L6(0)- and D0(22)-type face-centeredtetragonal nanoprecipitates are precursors of the face-centered-cubic L1(2) equilibrium phase, as identified in the isothermally-aged Fe73Ga27 and Fe74Ga26 alloys, respectively. The L6(0) phase is formed due to Ga ordering along < 001 >-A2 direction and simultaneous lattice distortion. The D0(22) phase is formed via diffusionless lattice distortion when the D0(3) ordering degree is sufficient high. These findings may provide a microstructural basis for the large magnetostriction induced by soluting nonmagnetic Ga into bodycentered-cubic Fe. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.