Grain high-angle

If the weak bonding model is valid for high angle grain boundaries (>20°) it follows that diffusion in amorphous preparations of a given material should also show this measure of enhanced diffusion, when compared widr die crystalline material. 

Figure 12 An interface in 2212 showing atomically sharp high angle grain boundary with grain to grain connectivity. The diffraction pattern from the grains is inset. Grain B is 2212 phase and grain C is strontium-copper oxide.

A high-angle tilt grain boundary results when 6 > 15°. For 6 < 10°, a low-angle tilt grain boundary results, and Eq. (1.37) can be simplified to tmO 6 = b/h. In a similar manner, a twist grain boundary is a set of screw dislocations. 

H. Fang et al Atomistic simulations of Bauschinger effects of metals with high angle and low angle grain boundaries. Comp. Meth. App. Mech. Eng. 193, 1789-1802 (2004)... 

Finer-grained powders are used for portable firearms tubular powder is mostly employed for guns powders in the form of flakes and short tubes are employed for mortars, howitzers, and other high-angle firearms. 

Figure 8.37. Lattice-fringe image showing a high-angle grain boundary in a bicrystal of wet synthetic calcite (From Hay and Evans 1988.)...

Hay, R. S., Evans, B. (1988). Intergranular distribution of pore fluid and the nature of high-angle grain boundaries in limestone and marble. J. Geophys. Res.. 93, 8959-74. 

The result is a silicon ribbon with a typical dislocation density of less than 105 cm-2. The main defects in the central area of the ribbon are twins. High-angle grain boundaries occur at the edges due to heterogeneous nucleation. 

For coarse-grained metals, dislocation movement and twinning are well known primary deformation mechanisms. Ultrafine, equiaxed grains with high-angle grain boundaries impede the motion of dislocations and... 

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