Cluster-Like Structure of Fe-Based Alloys with Enhanced Magnetostriction
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luster-Like Structure of Fe-Based Alloys with Enhanced Magnetostriction A. M. Balagurova, b, *, I. A. Bobrikova, S. V. Sumnikova, b, and I. S. Golovinc aFrank
Laboratory of Neutron Physics, Joint Institute for Nuclear Research, Dubna, Moscow oblast, 141980 Russia bMoscow State University, Moscow, 119991 Russia c National University of Science and Technology “MISIS,” Moscow, 119049 Russia *e-mail: [email protected] Received July 7, 2019; revised August 14, 2019; accepted August 17, 2019
Abstract—The microstructure of several Fe–xGa alloys with phase-separated structure have been studied by neutron diffraction with high Δd/d resolution. Analysis of diffraction data shows that the microstructure of these alloys is organized as nano-sized clusters with a better-ordered atomic structure coherently embedded in a disordered or less-ordered matrix. The characteristic size of the clusters depends on the Ga content and ranges from 100–2000 Å. Keywords: Fe–Ga alloys, neutron diffraction, structural phase transitions, dispersed clusters DOI: 10.1134/S1027451020070058
INTRODUCTION The discovery of a manyfold increase in the magnetostriction of Fe-xGa alloys at x ≈ 19 at. % (in this paper we use only atomic percent) compared to pure α-iron has stimulated many theoretical and experimental investigations. At present, their enhanced magnetostriction is associated with the formation of a heterogeneous state in ferromagnetic material. Several models exist for explanation of magnetostriction behavior in ordered Fe–xGa alloys, including the presence of tetragonally modified D03 (m-D03) nanoinclusions or small Ga-rich clusters of D03 phase in A2 matrix (for example, [1, 2]). In order to describe properly the inhomogeneous state in ordering alloys, it is desirable to identify the morphology of ordered regions, i.e., their size, shape and spatial organization, as well as the degree of order in them. The possibility of forming small clusters with an ordered atomic structure embedded within a disordered matrix for Cu–Au and Fe–Al alloys has been known since the early 1970s [3, 4]. Giant magnetostriction in Fe–xGa alloys has intensified the theoretical and experimental efforts to study their inhomogeneous cluster-like state. As a result, the mixed phase states A2 + D03 and B2 + D03 have been found in these alloys using techniques of transmission electron microscopy, scanning electron microscopy and energy dispersive spectroscopy [5–7]. In contrast with thin films or sample surface analysis, neutron diffraction studies are more effective for the analysis of bulk properties of metallic alloys. For
instance, the cluster state of FeαAl and (Fe,Cr)αAl, α ≈ 3, has been definitely established in our high-resolution neutron diffraction studies [8, 9]. In quenched samples, the matrix is a disordered A2 phase with clusters of the partially ordered B2 phase, whereas in the annealed samples the clusters of the ordered D03 phase are dispersedly distributed in the B2 matrix. The characteristic size of the clusters depends on the state of the alloy (as cas
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