The lifting or flaking of the metal at the surface due to delamination of grain boundaries caused by corrosion residual product buildup is called

• A. Spalling
• B. Pitting
• C. Exfoliation
• D. Erosion

Answer: (C)

Exfoliation is the lifting or flaking of metal surface that occurs when corrosion products build up between grain boundaries and pry the layers apart. The corrosion byproducts create pressure between grains, causing delamination and peeling of surface layers. This is distinct from pitting, which forms localized holes; erosion, which wears away material by moving fluids or particles; and spalling, which is surface flaking from mechanical or thermal stresses not specifically tied to grain-boundary delamination from corrosion products.