Medium-range order in Al-based liquid binary alloys

A short-to-intermediate range order of liquid Al-Cu binary alloys has been studied by X-ray diffraction and the reverse Monte Carlo modeling. The comprehensive analysis of three-dimensional models of the liquid Al-TM (TM = Co, Ni, Cu) binary alloys has been performed by means of Voronoi-Delaunay method. The existence of a prepeak in the S(Q) function of the liquid alloys reached with Al is caused by a specific arrangement of 3d-transition metal atoms in dense packed polytetrahedral clusters. It has been found that the icosahedral short-range order in dense polytetrahedral clusters and chemical short-range order lead to the formation of the medium range order in the investigated melts.