Structure of liquid Al–Cu–Co alloys near the quasicrystal-forming range

Abstract

A local short-to-intermediate range order in liquid Al 63.9Cu 19.4Co 16.7, Al 71Cu 6Co 23, and Al 6oCu 29Co 11 alloys was investigated by X-ray diffraction technique and the reverse Monte Carlo modeling. A prepeak at Q ~ 17 nm − 1 originating from the unique bonding between the TM–TM pair (TM = Co, Cu) is observed in the structure factors of all investigated melts. The Voronoi–Delaunay analysis of RMC models indicates that a medium-range ordering of TM atoms in dense non-crystalline polytetrahedral clusters is associated with a chemical short-range order. The icosahedral short-range order is also closely related to the dense packing polytetrahedral clusters. A decrease of temperature leads to an enhancement of both chemical short-range order and icosahedral short-range order.