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Simulation of High-Entropy Materials

Anand, Gautam (2018) Simulation of High-Entropy Materials. PhD thesis, University of Sheffield.

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Abstract

Multicomponent materials containing a comparatively large number of different elemental components, yet exhibiting simple crystal structures have opened up a new era of materials design with the possibility of tuning properties of materials with greater degrees of freedom. This poses a formidable challenge in terms of design as the number of parameters involved in simulating such systems increase significantly with the increasing number of components. This work reports a sampling methodology based on hybrid genetic algorithm-molecular dynamics for sampling positional-disordered materials such as high-entropy systems. This investigation also demonstrates the influence of individual cationic species on the evolution of distortion in single-phase solid solution with the rock-salt structure, when oxides such as CoO, CuO, MgO, NiO and ZnO are mixed together. Additionally, the relationship between the number of atomic species and its effect on the lattice distortion has been presented. The influence of alloying elements on the evolution of lattice friction in substitutional alloys has been studied using Monte Carlo simulations with a continuum elasticity relation for dislocations. The spread in energy-range due to elastic properties and size-misfit of elements provides physical justification for friction stress being low in CoNi alloy, high in CoCrNi (medium entropy alloy), along with intermediate values in CoCrFeNi (High Entropy Alloy). A similar approach justifies strengthening due to dilute addition of Al into CoCrFeMnNi and CoCrFeNi. This approach is a computationally cheap method of screening a range of possible alloys with respect to their lattice friction stress. Spin-polarised density functional theory (DFT) calculations presented here were carried out to study the charge transfer among elements and evolution of distortion in substitutional alloys. To study the characteristics of the individual element, impurity-in- matrix type calculations were carried out. The charge transfer between impurity and matrix element is presented to determine issues with the electronegativity parameter of Miedema’s model for enthalpy calculations. The distortion in substitutional alloys, particularly due to Cr has been found to be related to interaction of electrons with complementary spins in their d-orbitals.

Item Type: Thesis (PhD)
Academic Units: The University of Sheffield > Faculty of Engineering (Sheffield) > Materials Science and Engineering (Sheffield)
Identification Number/EthosID: uk.bl.ethos.739892
Depositing User: Mr. Gautam Anand
Date Deposited: 23 Apr 2018 09:38
Last Modified: 25 Sep 2019 20:03
URI: http://etheses.whiterose.ac.uk/id/eprint/20063

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