Intergranular corrosion primarily attacks which part of a metal?

Intergranular corrosion primarily attacks which part of a metal?

• A. Surface layer
• B. Defect sites
• C. Grain boundaries
• D. Center of grains

Answer: (C)

Intergranular corrosion travels along the interfaces between grains in a polycrystalline metal. Grain boundaries are high-energy, disordered regions where impurities and precipitates tend to segregate, and protective elements can become depleted. For example, in stainless steels, chromium carbides can precipitate at boundaries during certain heat treatments, creating chromium-depleted zones that are more anodic than the surrounding grain interiors. This makes the boundary regions preferential sites for corrosion and allows the attack to propagate along the network of boundaries rather than through the grain centers. So the attack is concentrated at the grain boundaries, not the surface layer, defect sites, or the centers of grains.

Intergranular corrosion travels along the interfaces between grains in a polycrystalline metal. Grain boundaries are high-energy, disordered regions where impurities and precipitates tend to segregate, and protective elements can become depleted. For example, in stainless steels, chromium carbides can precipitate at boundaries during certain heat treatments, creating chromium-depleted zones that are more anodic than the surrounding grain interiors. This makes the boundary regions preferential sites for corrosion and allows the attack to propagate along the network of boundaries rather than through the grain centers. So the attack is concentrated at the grain boundaries, not the surface layer, defect sites, or the centers of grains.