Some discussion of grain growth can be found in Lecture 7 of a course on Metals and Alloys
Grain boundaries are defects associated with an excess energy per unit area. Grain coarsening is driven by this boundary energy. Large grains tend to grow at the expense of smaller ones, leading to an increase in the mean size and a net reduction in the total amount of grain boundary per unit volume of material.
The following computer simulations of grain growth in two-dimensions are by Y. Suwa and Y. Saito of Waseda University in Tokyo, Japan. They have been conducted using a technique known as "phase field" modelling. In this method, the boundary is treated as a continuous transition between adjacent grains across a thin layer of finite thickness. The value of a phase-field variable then identifies the location of the boundary and of each grain. The advantage of this method is that the boundary becomes a part of the system so that it does not have to be determined explicitly in the solution.
There are two movies, the first assuming a boundary energy that is independent of orientation. By contrast, the second deals with an orientation dependent boundary energy so that the grain structure evolves into an anisotropic form. The two cases have precisely the same starting configurations and yet they evolve into different grain structures. In the movies, the different colours represent different grain orientations. There is a pause for a few seconds after the title slide.
Two-dimensional grain growth with isotropic grain boundary energy.
Two-dimensional grain growth with orientation dependent grain boundary energy.
The same movies can be seen with higher time resolution on the following two icons. Bear in mind that these movies are necessarily larger (4 Mbytes compared with 600 kbytes above).
Two-dimensional grain growth with isotropic grain boundary energy.
Two-dimensional grain growth with orientation dependent grain boundary energy.
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