Neutron diffraction studies of structures and phase transitions in ternary Fe-Ga-RE alloys (RE = Dy, Er, Pr, Sm, Tb, Yb)

Abstract

New data on the phase compositions and structural transformations in Fe₈₁Ga₁₉ and Fe₇₃Ga₂₇ alloys doped with trace amount (~0.1 − 0.5 at.%) of rare earth elements (RE) (Dy, Er, Pr, Sm, Tb, Yb) are presented. The structural data were obtained in neutron diffraction experiments performed with high resolution and in the continuous temperature scanning mode during heating to 900°C and subsequent cooling at a rate of ±2 °C/min. At a small amount of the RE element (≤ 0.2 at.%), structural rearrangements proceed in generally the same way both in the initial Fe₈₁Ga₁₉ and Fe₇₃Ga₂₇ alloys and in their alloyed analogs. On the contrary, in Fe₇₃Ga₂₇RE alloys with RE in the amount of ~0.5 at.%, both the sequence of forming and disappearing structural phases and the final state of the alloy depend on the type of rare earth element. In the initial (as-cast) state, the microstructure of Fe₈₁Ga₁₉RE alloys is predominantly a disordered matrix (phase A2) with regions of short-range order of the D0₃ type. The process of continuous slow heating leads to the formation of clusters of the ordered phase D0₃ with sizes in the range of (200 – 300) Å. The microstructure of most Fe₇₃Ga₂₇RE alloys with RE in the initial state is a structurally disordered matrix (phase A2) with dispersedly embedded clusters of the D0₃ phase with characteristic sizes of ~900 Å. During slow heating and cooling, a homogeneous state is formed in these alloys. The tetragonal phase L6₀, previously discovered in electron diffraction studies of surface layers of similar alloys, was not found in neutron diffraction spectra formed by the entire volume of samples in any of the studied Fe-Ga-RE alloys.