Computational investigation of interface structure and composition in cemented carbides at finite temperatures
Licentiate thesis, 2019
Atomic scale ab-initio calculations allow for accurately predicting interface energies for a given structure and composition. However, finding the ground-state interfacial structure and composition becomes a challenge as the search space is very large when considering all degrees of freedom. Furthermore, direct sampling of interfacial properties at finite temperature using density functional theory (DFT) often becomes computationally unfeasible as hundreds, thousands or even millions of calculations may be required. Therefore, employing atomic scale models based on DFT calculations is advantageous and allows for investigation of the interface structure, composition and free energy at finite temperatures. In this thesis the computational methods for calculating temperature dependent interfacial free energies are developed and applied to the WC-Co system.
An interfacial phase diagram for cubic thin films in undoped WC-Co is constructed. Here, configurational degrees of freedom are treated using cluster expansion models and Monte Carlo sampling. Vibrations are treated in the harmonic approximation using force constant fitting to significantly reduce the number of DFT calculations.
The temperature dependence of interface free energies for surfaces, grain boundaries and phase boundaries is using an analytic bond order potential. Here, multiple different free energy calculation methods are employed such as quasi-harmonic approximation, λ-integration, thermodynamic integration and surface tension calculation.
Molecular dynamics
Hard Metals
Interfacial free energies
Monte Carlo
Cemented carbides
Force constants
Cluster expansion
Author
Erik Fransson
Chalmers, Physics, Materials and Surface Theory
Sintring av inhomogena strukturer för förbättra prestanda. Materials Science 2015.
Swedish Foundation for Strategic Research (SSF) (RMA15-0062), 2016-05-01 -- 2021-06-30.
Flerskalsmodellering av plastisk deformation av hårdmetaller.
Swedish Research Council (VR) (2016-04342), 2017-01-01 -- 2020-12-31.
Infrastructure
C3SE (Chalmers Centre for Computational Science and Engineering)
Subject Categories
Other Physics Topics
Other Materials Engineering
Areas of Advance
Materials Science
Publisher
Chalmers
PJ-salen, Fysikgården 2, Göteborg
Opponent: Dr. Jochen Rohrer, Technische Universität Darmstadt