Short and Medium-Range Order in Liquid Ternary Al_(80)Co_(10)Ni_(10),Al_(72.5) Co(14.5a)Nni_d(1 3A),land Al_(65)Co_(17.5)Ni_(17.5) Alloys

摘要

A local short-to-intermediate range order of liquid Al_(80)Co_(10)Ni_(10),Al_(72.5)Co_(14.5)Ni_(13),and Al_(65)Co_(17.5)Ni_(17.5) alloys was examincd by X-ray difraction and the reverse Monte Carlo modeling. The comprehensive analysis of three-dimensional models of the liquid ternary alloys was performed by means of the Voronoi-Delaunay method. The existence of a prepeak on the S(Q) function of the liquid alloys is caused by medium range ordering of 3d-transition metal atoms in dense-packed polytetrahedral clusters at temperatures close to the liquidus. The non-crystalline clusters, represented by aggregates of pentagons that consist of good tetrahedra, and chemical short-range order lead to the formation of the medium range order in the liquid binary Al-Ni, Al-Co and ternary Al-Ni-Co alloys.