What is typically true regarding the mechanical properties of metals with fine grain structures?

Metals with fine grain structures generally exhibit higher strength due to a phenomenon known as the Hall-Petch relationship. This relationship states that as the grain size decreases, the yield strength of the material tends to increase. Fine grains provide more grain boundary area, which acts as obstacles to dislocation movement within the metal's crystal lattice. Dislocations are defects in the lattice that allow deformation to occur; when they meet the boundaries of fine grains, their movement is hindered, resulting in a stronger material.

In addition to increased strength, fine-grained metals can also maintain adequate ductility depending on the specific alloy and its processing. Therefore, while they can be stronger, they are not necessarily less ductile, and the impact resistance is contingent on several other factors beyond just grain size. This highlights why higher strength is the focus when considering the mechanical properties associated with fine grain structures.