Even under the most ideal crystal growth conditions, metals are not crystallographically perfect. Instead, the lattice may contain many imperfections.On such imperfection is an edge dislocaition.Regions sorrounding the dislocation may be a perfect array of atoms; however, the core of the dislocation is shown as a localized distortion of the crystal lattice. While it may appear that this structure is unfavorable, dislocations are necessary in metals. For exmple, at grain boundaries, dislocation are “geometrically necessary” to allow the individual grains of different orientations to match.

1. crystallographically 结晶学的  

2. imperfection不完美

3. edge dislocaition刃型位错

4. distortion畸变

5. grain boundary晶界   

6. geometrically necessary 几何必需

7. orientation取向