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Abstract
Conventional transmission and scanning electron microscopy were employed to investigate the structural state and phase transformations of the β(CsCl)-solid solution in rapidly quenched alloys of Al50Cu50− x Fe x with respect to the Cu/Fe ratio. We studied the alloys from the central (x = 17 and 13) and border areas (x = 6) of the β-solid solution homogeneity region. The structural state of the β-solid solution was characterized by premartensitic structural instability of the bcc lattice for x = 17 and 13, and the presence of combined short-range order accompanied by the intense diffuse scattering for x = 6. This short-range order can be described by the ordering of atoms and vacancies in the planes (111)β and ω-like atomic displacements (longitudinally polarized waves of displacement in the direction of the [111]β). The structural state of the β-solid solution with the combined short-range order was regarded as a pretransition state for the revealed transformation with homogeneous precipitation of the nanodispersed phase. The precipitation phase was attributed to an orthorhombic Al(Cu, Fe) η1-phase, belonging to the family of ordered β-based phases with orientation relationships of [100]η1 ||[110]β, [010]η1 ||[110]β, [001]η1 ||[001]β. We concluded that the atomic structure of the η1-phase is characterized by ordering, accompanied by ω-like atomic displacements of the adjacent layers in 3d metals (Cu, Fe) and aluminum.
Acknowledgements
The authors thank Dr A.N. Yksysnikov for technical assistance and N.G. Pomortseva for the help in preparing the English version of the manuscript. The TEM study was carried out in the Electron Microscopy Centre at the Ural Division of Russian Academy of Sciences. This work was supported by the 010-02-00602 RFBR grant.