Diffusive and displacive phase transitions in Fe-Ga alloys

Abstract

Phase transitions between structurally ordered phases in Fe–Ga alloys have been studied upon their heating to 850 °C and subsequent cooling to room temperature by neutron diffraction in real-time mode. The transitions between four types of phases have been analyzed: D03 → L12 (both cubic phases), L12 ↔ D019 (cubic – hexagonal), D019 ↔ A2 (hexagonal – cubic). It has been established that all phase transitions include stage of the formation of a disordered state and have a combined, diffusive-displacive nature. The diffusion stages are necessary for the disordering and ordering of the structure, the displacive stage provides a change in the type of the crystal lattice. It can be concluded that the formation of an intermediate disordered state followed by a transition to the final equilibrium state is less energy-consuming than the direct transition to the final state. During the observed transformations, no traces of predicted intermediate structurally ordered tetragonal phases were found. These results may provide new insight into the microscopic basis for the formation of enhanced magnetostriction in Fe–Ga alloys.