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During grain growth, the boundaries between adjacent grains move towards their center of curvature because of the difference in the grain boundary energy. Grain boundaries act as barriers to the movement of atoms, and the boundary energy is directly proportional to the length of the boundary. Therefore, in order to minimize the total boundary energy, grains will grow by absorbing smaller neighboring grains with high boundary energy. As grains grow, they consume the smaller neighboring grains, and the boundaries between them shift towards their center of curvature. This movement is driven by the reduction in total boundary energy as the length of the grain boundary decreases.

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On the other hand, during recrystallization, the movement of grain boundaries is driven by the difference in the stored energy between the deformed and the recrystallized grains. During deformation, dislocations are generated, and the stored energy increases. This stored energy is reduced during recrystallization, and the grain boundary moves away from its center of curvature, resulting in the formation of new, strain-free grains. The movement of the grain boundaries during recrystallization is opposite to that during grain growth because the driving force for movement is different. In recrystallization, the movement is driven by the reduction in stored energy, whereas in grain growth, the movement is driven by the reduction in total boundary energy. ############

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Explanation:

Grain growth and recrystallization are two common phenomena that occur during the processing and deformation of materials. Grain growth refers to the increase in the average grain size of a polycrystalline material over time. It is driven by the minimization of the total boundary energy between adjacent grains. Recrystallization, on the other hand, refers to the formation of new, strain-free grains within a deformed material. It is driven by the reduction in the stored energy that results from the deformation. During grain growth, the boundaries between adjacent grains move towards their center of curvature because the grain boundary energy is directly proportional to the length of the boundary. As grains grow, they absorb smaller neighboring grains with high boundary energy, and the total boundary energy decreases as the length of the boundary decreases. This movement towards the center of curvature ensures that the new grain has a lower boundary energy than the original grain, and the process continues until the average grain size has increased. During recrystallization, the movement of grain boundaries is driven by the difference in stored energy between the deformed and the recrystallized grains. Deformation leads to the generation of dislocations, which increase the stored energy of the material. When the stored energy exceeds a certain threshold, new, strain-free grains are nucleated within the deformed material. The movement of the grain boundaries during recrystallization is away from their center of curvature because the movement is driven by the reduction in stored energy. The formation of new grains with a lower stored energy leads to a decrease in the overall stored energy of the material. In summary, the movement of grain boundaries during grain growth and recrystallization is driven by different factors. During grain growth, the movement is driven by the reduction in total boundary energy, and the boundaries move towards their center of curvature. During recrystallization, the movement is driven by the reduction in stored energy, and the boundaries move away from their center of curvature.

Final Answer:

In summary, the movement of grain boundaries during grain growth and recrystallization is driven by different factors. During grain growth, the movement is driven by the reduction in total boundary energy, and the boundaries move towards their center of curvature.

Explain why grain boundaries move towards their centre of curvature during grain growth but away from their centre of curvature during recrystallization.

Public Answer

Explain why grain boundaries move towards their centre of curvature
during grain growth but away from their centre of curvature
during recrystallization.