| In crystallography, an area with surface energy, though it is within a material. This is due to some kind of disruption in lattice periodicity.
Enhanced diffusion occurs along these boundaries. They are also mobile at high temperatures. At these temperature, the materials on opposite sides of the boundary may slide, called (duh) grain boundary sliding, which contributes to creep. There are a few classifications of grain boundaries.
- High-Angle - These are boundaries with a large difference in grain direction. Usually, a large angle is considered to be 30 degrees or more.
- Low-Angle - A boundary with a lesser difference in directions, less than 50 degrees.
- Tilt - this occurs where edge dislocations line up with a spacing between them of D. It bends the planes to either side. tan θ = (b/D). If θ increases enough, it becomes a high-angle boundary.
- Twist - Actually a subset of low-angle boundary, it consists of two screw dislocations arrayed in a grid pattern, thus giving a simple rotation to the crystals.
This information was derived from my Materials Science and Engineering lecture notes.
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