Grain boundary strengthening
![Figure 1: Hall–Petch Strengthening is limited by the size of dislocations. Once the grain size reaches about 10 nanometres (3.9×10−7 in), grain boundaries start to slide.](/Images/godic/202501/16/HallPetchLimit3747.png")
![This is a schematic roughly illustrating the concept of dislocation pile-up and how it affects the strength of the material. A material with larger grain size is able to have more dislocations pile up, leading to a bigger driving force for dislocations to move from one grain to another. Thus you will have to apply less force to move a dislocation from a larger than from a smaller grain, leading materials with smaller grains to exhibit higher yield stress.](/Images/godic/202501/16/Dislocation_pileup.svg3747.png")
Grain-boundary strengthening (or Hall–Petch strengthening) is a method of strengthening materials by changing their average crystallite (grain) size. It is based on the observation that grain boundaries impede dislocation movement and that the number of dislocations within a grain have an effect on how easily dislocations can traverse grain boundaries and travel from grain to grain. So, by changing grain size one can influence dislocation movement and yield strength. For example, heat treatment after plastic deformation and changing the rate of solidification are ways to alter grain size.