Which term describes the formation of cavities or holes in a material surface?

Which term describes the formation of cavities or holes in a material surface?

• A. Pitting
• B. Cratering
• C. Erosion
• D. Chalking

Answer: (A)

Pitting is the formation of small cavities or pits on a surface caused by localized corrosion. It starts when a protective film or passive layer on a metal breaks down at specific spots, allowing aggressive species (often chlorides) to attack locally. Over time these tiny attack sites deepen into pits that can become quite pronounced relative to their width, compromising strength even if the rest of the surface looks relatively intact. This distinguishes pitting from other surface changes: cratering involves crater-like depressions that result from different processes like impacts or gas evolution and is not typically characterized by narrow, individual pits; erosion is the general removal of material by mechanical action of fluids or particulates; chalking is the formation of a loose, powdery layer from coating degradation, not holes.

Pitting is the formation of small cavities or pits on a surface caused by localized corrosion. It starts when a protective film or passive layer on a metal breaks down at specific spots, allowing aggressive species (often chlorides) to attack locally. Over time these tiny attack sites deepen into pits that can become quite pronounced relative to their width, compromising strength even if the rest of the surface looks relatively intact. This distinguishes pitting from other surface changes: cratering involves crater-like depressions that result from different processes like impacts or gas evolution and is not typically characterized by narrow, individual pits; erosion is the general removal of material by mechanical action of fluids or particulates; chalking is the formation of a loose, powdery layer from coating degradation, not holes.