Master thesis by Mathias Bjerre – Niels Bohr Institutet - Københavns Universitet

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Master thesis by Mathias Bjerre

Grain growth and coarsening in crystalline solids

In this thesis the dynamics of crystalline grain growth is investigated numerically using the Phase-Field Crystal model. The crystalline solid is in the model described through a periodic and continuous density field. By simulating the dynamics of this field it is possible to study how grain growth and coarsening in polycrystals proceed with time.

At first, growth of circular grains in simple crystalline matrices is studied varying both the model's temperature parameter and the surrounding matrix. The temperature parameter is varied such that the systems at all times are at their solid coexistence density. The grain area and orientation is obtained by tools developed to analyse the simulated density field during the course of this thesis. Using these tools the main mechanisms of grain growth is identified in which grain rotation is found to have an important role, especially at low temperature parameter values.

The coarsening dynamics in polycrystals is then investigated. Measuring the average grain area over time the dynamics is observed to obey a power law that depends on the temperature parameter. Comparing the obtained results to theory of grain growth the simulated coarsening proceeds rather slowly, while experimental results to some extent agree with the power law exponents identified. During the late stages of coarsening stagnating behaviour at low values of the temperature parameter is observed. Analysing the coarsening dynamics on grain level while taking into account the results from the simple crystalline matrix, it is concluded that grain rotation is an important factor for grain growth in polycrystals that display stagnant coarsening behaviour.