Comparative study of structural phase transitions in bulk and powdered Fe–27Ga alloy by real‐time neutron thermodiffractometry

• Published in: Journal of applied crystallography 2017-02, Vol.50 (1), p.198-210
• Main Authors: Balagurov, Anatoly M., Golovin, Igor S., Bobrikov, Ivan A., Palacheva, Valeria V., Sumnikov, Sergej V., Zlokazov, Victor B.
• Format: Article
• Language: English
• Subjects: Alloys; Bulk sampling; Crystallography; Diffraction; Ferromagnetism; Ferrous alloys; Fe–27Ga alloy; Microstrain; Neutron diffraction; Neutrons; Phase transformations; Phase transitions; Real time; real‐time neutron diffraction; structural phase transitions; Surface layer; Texture
• ISSN: 1600-5767; 0021-8898; 1600-5767
• DOI: 10.1107/S1600576716020045

Phase transformations in an iron–gallium alloy have been analyzed by in situ real‐time neutron diffraction in the temperature range from 293 to 1223 K. Two compositionally identical samples were studied: the first was in the as‐cast bulk state, and the second was ground into a powdered state. In both samples, the same sequence of structural transitions was recorded on heating with a constant heating rate (D03 → A2 → L12 → D019 → A2), and the same structural state (D03 + L12) was recorded after slow cooling to room temperature. Owing to strong texture in the bulk sample, only diffraction patterns of the powdered sample were treated with the Rietveld method to determine the volume fractions of the coexisting phases, the coefficients of thermal expansion, and the thermal and static atomic disorder parameters. The occupancy of Ga positions and the ordered iron magnetic moment were refined at selected temperatures. The level of microstrain in the crystallites in the initial as‐quenched state is small, but it sharply increases in the course of phase transitions when the alloy is heated. The microstrains are high and strongly anisotropic after slow cooling. Generally, phase transformations occur similarly in the powdered and bulk samples, but with a noticeable difference in details. The fulfilled analysis of the bulk and powdered samples allowed the real possibilities of the quantitative neutron diffraction analyses of phase transitions in ferromagnetic ordered alloys to be assessed. High‐resolution and high‐intensity neutron diffraction was applied to characterize the atomic and magnetic structure and microstructure of Fe–27Ga alloy in the as‐cast and powder states. Structural phase transformations occur with a noticeable difference in the as‐cast and powder states of the alloy.