Koch, Leonie (2015)
Computer simulations of ordering effects and dislocation structures in high entropy alloys.
Technische Universität Darmstadt
Masterarbeit, Bibliographie

Kurzbeschreibung (Abstract)

High entropy alloys constitute a new class of materials, which recently have attracted considerable attention in the field of high-performance materials [1]. Such materials are distinguished by their structural stability, resistance to external loads and a considerable strength, while preserving a sufficient ductility even at high temperatures. It is therefore not surprising that, since the principle of atomic-scale composites was first presented in 1995 [2, 1], an increasing scientific community focus on structure formation and mechanical deformation mechanisms. The concept of high entropy alloys is based on the combination and interaction of several chemical elements, where the number, by definition, amounts to at least five different components. All principal elements occur in an equimolar or a near equimolar ratio such that a distinction between a solvent and a solute is hardly possible. The almost unlimited diversity of compositions enables to use high entropy alloys in different industries, involving lightweight metal combinations for transportation or refractory alloys for high temperature applications [1]. However, currently most research focuses on only a small number of possible alloy systems [3]. According to Hammond et al. [4], the driving force in the development of new materials is the achievement of “revolutionary–rather than evolutionary–advances”. But why should exactly these multimaterial cocktails [5] be revolutionary? The origin of outstanding properties, such as durability and load capacity, have been extensively studied by theoreticians as well as experimentalists. A number of researchers reported that the high entropy of mixing facilitates the formation of random solid solutions, while preventing the formation of brittle intermetallic phases with complex microstructures [6, 2]. In addition, the use of differently sized atom types may cause lattice distortions, which greatly influence the deformation behavior. For this reason several recent studies have focused on phase competitions, composition dependence of phase stability, mechanical and magnetic properties or temperature effects on deformation [7, 8, 9, 10, 11]. Nevertheless, there has been some debate about phase selection rules for high entropy alloy production. Although most work has concentrated on the influence of parameters such as mixing enthalpy, atomic-size differences or valence electron concentrations, a complete determination of phase diagrams is still missing. Whereas properties like density, melting temperature and lattice parameter may be derived from simple “rules of mixture” [4], the final microstructure strongly depends on “inter-elemental reactions” [12]. Since the understanding of atomic structures is essential in order to predict material behavior, the generation of basis structures seems to be one of the first steps in this field of research. These generated structures might serve as a basis for the implementation of simulation-based mechanical tests.

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