Which corrosion type forms along grain boundaries?

Which corrosion type forms along grain boundaries?

• A. Exfoliation Corrosion
• B. Pitting Corrosion
• C. Intergranular Corrosion
• D. Uniform Corrosion

Answer: (C)

Intergranular corrosion is indicated when the metal corrodes specifically along the interfaces between grains. Grain boundaries are high-energy regions where impurities or precipitates can segregate, creating paths of differing electrochemical potential. In sensitized materials like some stainless steels, chromium carbides form at these boundaries during heat exposure, depleting chromium in adjacent areas and making the boundaries anodic. This drives corrosion to travel along the boundaries rather than through the grain interiors, producing the characteristic pattern. Other forms described behave differently: uniform corrosion attacks the surface more or less evenly; pitting corrosion forms localized pits often at inclusions or defects; exfoliation corrosion occurs in some aluminum alloys where layers separate along grain boundaries, causing flakes.

Intergranular corrosion is indicated when the metal corrodes specifically along the interfaces between grains. Grain boundaries are high-energy regions where impurities or precipitates can segregate, creating paths of differing electrochemical potential. In sensitized materials like some stainless steels, chromium carbides form at these boundaries during heat exposure, depleting chromium in adjacent areas and making the boundaries anodic. This drives corrosion to travel along the boundaries rather than through the grain interiors, producing the characteristic pattern.

Other forms described behave differently: uniform corrosion attacks the surface more or less evenly; pitting corrosion forms localized pits often at inclusions or defects; exfoliation corrosion occurs in some aluminum alloys where layers separate along grain boundaries, causing flakes.