Multiscale Study of the Thermodynamics and Kinetics of Vacancy–grain-boundary Interactions
Material type:
- 620 SUB
Item type | Current library | Call number | Status | Date due | Barcode | |
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JRD Tata Memorial Library | Available | ET00129 |
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PhD; 2022; Materials engineering
Grain boundaries (GBs) influence many physical and mechanical properties of crystalline materials. This is primarily because of their interactions with other kinds of defects, such as point and line defects. Such interactions are known to depend on the structure and properties of individual GBs, i.e. the GB character. Although much research has been done in this regard, an understanding of the effect of GB character on such interactions is still incomplete. The present study was undertaken to particularly understand the effect of GB character on vacancy--GB interactions in aluminium (Al). To achieve that, the study was done in five parts using a multiscale modelling approach which involved atomistic and continuum methods. First, using molecular statics (MS) simulations, Al bicrystals with symmetric [010]- and [101]-tilt GBs were constructed, and their stability was checked using molecular dynamics simulations. (A total of 32 boundaries were studied.) The GB structures were subsequently validated using the structural unit model (SUM). Second, vacancy formation and migration energies in the GBs were evaluated using MS simulations and the nudged elastic band method, respectively. These results were then used to obtain equilibrium vacancy concentrations and vacancy migration rates in the GBs. Third, using this data and the kinetic Monte Carlo (KMC) method, the anisotropic GB diffusivities were obtained by simulating random walks of a vacancy in the GBs with a focus on the role of the GB. Fourth, a multiple-site segregation equation was used to study the thermodynamics of vacancy segregation in cases where there is a supersaturation of vacancies, such as in-quenched or irradiated specimens. Segregation was studied as a function of GB character, grain size, temperature, and initial vacancy supersaturation. A phase-field method was then used to evaluate the kinetics of vacancy segregation at the GBs. Finally, quantities derived from the atomistic methods were used to evaluate differences in void nucleation and growth rates again in the presence of a vacancy supersaturation, and the role of GB character was explored.
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