Local atomic order in the Al-Cu-Fe melts corresponding to crystalline and quasicrystalline phases

Abstract

The local atomic order in the Al70Cu20Fe10 and Al61.9Cu25.4Fe12.7 melts that correspond to the tetragonal τ2 and quasicrystalline phases was studied. The structures of these ternary melts were investigated by high-temperature X-ray diffraction and Reverse Monte Carlo simulation at various temperatures. The structural models of the melts are analyzed using the Voronoi polyhedra and the Delaunay simplexes. The specific features in the structure factor curves were comprehensively discussed: a shoulder in the second maximum and a prepeak on the left side of the principal maximum. The prepeak in the structure factor curves in the diffraction vector range 11–22 nm−1 is shown to be caused by chemical local atomic ordering, and the shoulder on the right side of the second maximum is shown to result from the presence of icosahedral polytetrahedral clusters in the melts.