Which type of cracking is environmentally induced and worsened by progressive corrosion, common at atomic boundaries in alloys?

• A. Crevice corrosion
• B. Pitting corrosion
• C. Stress corrosion
• D. Microbiologic corrosion

Answer: (C)

Cracking that occurs when a material is under tensile stress in a corrosive environment is stress corrosion cracking. The environment facilitates metal dissolution and weakening at the crack tip, while the applied or residual stress drives crack opening and propagation. In alloys, atomic boundaries such as grain boundaries are common weak spots where diffusion and dissolution concentrate, making cracks start and grow along these boundaries as corrosion progresses. This combination—environmentally induced cracking that worsens with ongoing corrosion—is what allows cracks to form and advance under the right conditions.

Other forms of corrosion involve surface attack without the induced cracking under sustained stress, such as crevice corrosion or pitting, or are driven by biological factors, rather than by the synergistic effect of environment plus tensile stress that produces crack growth.