8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

P7.60Thu 811:10-14:00Crystal growth mechanism in the binary system Al 50 Ni 50 :formation of structural defectsPhilipp Kuhn 1 and Jürgen Horbach 21 German Aerospace Center, Linder Hoehe, 51147, Cologne, Germany2 Universität Düsseldorf, Duesseldorf, GermanyCrystal growth of intermetallic phases in binary metallic alloys proceeds at a considerably slowerpace than that of pure metals. In order to study the underlying mechanism, we perform MolecularDynamics Simulations of the growth of Al 50 Ni 50 . The crystal structure is a B2 lattice and thegrowth of a planar interface of (100) orientation proceeds by forming alternating layers of Nickeland Aluminum. To gain insight into the atomistics of this growth mode, we treat these layers asnatural structural units and monitor the evolution of each of them separately. The history of a singlelayer parallels the growth of the whole crystal, evolving from completely disordered to crystalline.Its state can be characterized by properly chosen quantities like composition and local bond orderparameters and by averaging over many layers we can extract a typical crystallization course. Asit turns out, the time evolution exhibits two overlapping dynamical aspects: The formation of theactual crystalline grid is preceded by a segregation process in which the two species accumulatein their respective layers. Since these two processes are not well separated in time the partitioninginto layers is not complete before crystallization freezes in the remaining deviations from crystalcomposition. The resulting structure contains defects such as vacancies and antisites, even forrelatively small undercooling.60