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How can grain refinement increase the yield strength of a material?

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Figure 1: The position vector x and the velocity vector v of a material point, the body force fdV acting on an element dV of volume, and the surface force TdS acting on an element dS of surface in a Cartesian coordinate system 1, 2, 3 (see text).
mechanics of solids Figure 1: The position vector x and the velocity vector v of a material point, the body force fdV acting on an element dV of volume, and the surface force TdS acting on an element dS of surface in a Cartesian coordinate system 1, 2, 3 (see text).

Grain refinement increases the yield strength of a material by modifying its internal crystal or grain size. In metallurgy, a solid metal is composed of numerous small, randomly oriented crystallites known as grains, which meet at surfaces called grain boundaries.12

The yield stress of a metal is fundamentally determined by the resistance to the slipping of one plane of atoms over another. Grain boundaries act as significant barriers to this atomic slip. By refining the material to have a smaller grain size, the density of these grain boundaries increases, thereby creating more obstacles that impede the movement of dislocations within the crystal structure.3

Unlike other strengthening methods that may improve yield strength at the expense of other properties, grain refinement is unique because it can simultaneously increase both the strength and the toughness of an alloy.3