Structure evolution of as-cast metastable Fe-38Ga alloy towards equilibrium

Abstract The evolution of the structural phases of the Fe-38.4 at%Ga alloy was studied in neutron diffraction experiments performed with high-intensity continuous scanning in a wide temperature range. The as-cast alloy consists of ~70% Fe13Ga9 intermetallic and ~30% bcc-based disordered A2 solid solution (or its partially ordered/short-range ordered B2 variant). The research proves that during the first heating of the cast alloy, the Fe13Ga9 phase is stable up to T ≈ 550 °C, then it transforms into α-Fe6Ga5, fcc-based L12 and B2 phases. At the same temperature, the disorder-order transition A2 → B2 begins, ending at T ≈ 720 °C. The Fe13Ga9 phase does not restore during subsequent cooling and next heating and cooling cycles. The structural parameters of the identified phases are refined. The research also shows that the transition temperatures depend on the alloy prehistory.