Antiphase domains or dispersed clusters? Neutron diffraction study of coherent atomic ordering in Fe3Al-type alloys

Abstract A combination of high-resolution and in situ real-time neutron diffraction was used to collect the experimental data concerning coherent atomic ordering in Fe3Al-type alloys in a wide temperature range. The analysis of the obtained data was carried out within the framework of two models: antiphase domains and dispersed clusters embedded in matrix. The second model, for which the atomic ordering is organized in the form of clusters of mesoscopic sizes (from ∼200 to ∼400 A) randomly distributed inside a less ordered matrix, provides a better fit of the data. For two chemically identical Fe3Al samples - the first was in the as-cast polycrystalline bulk state, and the second was grown as a single crystal - the initial state can be described as a partially ordered B2 structure (matrix) with dispersed clusters of the D03 ordered phase. The initial (quenched) state of the (Fe0.88Cr0.12)3Al polycrystalline sample is the disordered A2 phase with clusters of the partially ordered B2 phase. After heating and subsequent slow cooling, the structure of both binary and ternary alloys is B2 matrix with dispersed D03 clusters, whose dimensions are increased up to ∼900 A.