Dislocations (lines of atoms that are in the wrong place) are present
in all materials and components and they weaken materials by moving
through grains. However, their motion is held-up at grain boundaries.
If we give the material a smaller grain size (for example, by cooling
it more quickly), we provide more obstacles (grain boundaries) to
dislocation movement and so increase the strength of the material.
Now return to the main text.