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978-3-8439-2033-9, Reihe Physik
Sascha B. Maisel
Characterization and optimization of multicomponent alloys based on quantum mechanics
223 Seiten, Dissertation Technische Universität Hamburg-Harburg (2014), Softcover, A5
Abstract The cluster-expansion method is a mathematical tool to condense the complicated many-body interaction inherent in any crystal into a few real numbers. When supplied with input derived from density functional theory calculations of sufficient accuracy, the resulting cluster-expansion models can describe energetics of different crystal structures to within a few meV. In this thesis, I exploit this concept to identify the energetically most favourable compounds (so-called ground-state structures) in various Ni-rich alloys. Using other, purely ab-initio-based techniques, the real-space geometries, elastic properties and the thermodynamic behaviour of these ground-state compounds are determined. These studies begin with the binaries Ni-Al, Ni-Ta, Ni-W and culminate in an effective Hamiltonian for the quaternary Ni-rich Al-Ni-Ta-W system. These alloys are important as building blocks of even more complex high-temperature materials and, in the case of the Al-Ni-Ta-W system, as a simplified model for the commercial CSMX-10 superalloy.
Abstract In a separate chapter, discuss the related beta-NiAl system as well. beta-NiAl is also a high temperature material and renowned for its ability to tolerate an exceedingly high amount of point defects. I treat the alloy as a ternary system composed of nickel, aluminium and vacancies. The different configurations reported in earlier works by Lerch et al. are used to predict the elastic properties as a function of both composition and configuration.
Abstract Finally, I attempt to raise awareness that such configurationally sensitive methods are crucial to make quantitative predictions for complex materials. This will be a theme throughout the work, but will become most evident in the last chapter, where I discuss the effect of local-order on the elastic properties of different alloys.