Pinning points

In a crystalline material, a dislocation is capable of traveling throughout the lattice when relatively small stresses are applied.

Pinning points in the material act to halt a dislocation's movement, requiring a greater amount of force to be applied to overcome the barrier.

Much like two particles of the same electric charge feel a repulsion to one another when brought together, the dislocation is pushed away from the already present stress field.

An alloying atom is by nature a point defect, thus it must create a stress field when placed into a foreign crystallographic position, which could block the passage of a dislocation.

The precipitation of a second phase within the lattice of a material creates physical blockades through which a dislocation cannot pass.