What does intergranular corrosion target?

Intergranular corrosion specifically targets the grain boundaries of the metal. This type of corrosion occurs along the boundaries between individual grains (or crystals) within a metal, often exacerbated by factors such as improper heat treatment or the presence of certain alloying elements.

When intergranular corrosion takes place, it can lead to significant weakening of the material because the bond between the grains is compromised. This can result in the metal losing its structural integrity without affecting the bulk of the grains themselves, which can ultimately lead to failure in applications where strength is critical.

The other options do not accurately describe the specific nature of intergranular corrosion. The surface layer of the metal is not the primary target, as this type of corrosion occurs beneath the surface, affecting the internal structure of the metal. The external coating or paint is a different area of concern, generally related to protective measures against corrosion rather than a target of it. General rust formation refers to uniform corrosion rather than the localized and specific nature of intergranular corrosion, which is focused on the distinct boundary regions between grains.