ANS:C - erosion

Damage to a metal surface by mechanical action is called erosion. Explanation: Erosion refers to the gradual wearing away or removal of material from a solid surface due to the mechanical action of external forces. These forces can include the impact of abrasive particles, the flow of fluids (such as water or air), or the movement of solid objects against the surface. In the context of metals, erosion commonly occurs in environments where there is high-velocity fluid flow, such as in pipelines, channels, or machinery components exposed to moving fluids. The impact of particles suspended in the fluid or the flow of the fluid itself can cause the metal surface to wear away over time, resulting in loss of material and changes to the surface morphology. Pitting and corrosion, on the other hand, are forms of chemical degradation rather than mechanical damage:

• Pitting refers to localized corrosion damage that occurs in the form of small pits or craters on the metal surface. It is typically caused by chemical reactions, such as the breakdown of protective surface films or the concentration of corrosive agents in localized areas.
• Corrosion is the degradation of a metal due to chemical or electrochemical reactions with its environment. It can occur through various mechanisms, including uniform corrosion, galvanic corrosion, crevice corrosion, and stress corrosion cracking. Unlike erosion, corrosion does not necessarily involve mechanical action but rather chemical processes that lead to the deterioration of the metal.