Grain boundaries are what type of defect?

• A. Point Defects
• B. Interfacial Defects
• C. Volume Defects
• D. Point and Line defects

Answer: (B)

Grain boundaries are planar defects: they form the interface between two differently oriented crystal grains in a polycrystal. Because they lie as a plane that extends through the material, they are a two-dimensional feature. Point defects are localized atoms missing or extra within the lattice, and line defects are dislocations that run through the crystal. Volume defects are three-dimensional features like voids or inclusions. Since grain boundaries are the boundary between grains and act as an interface rather than a localized point or a line, they are classified as interfacial (planar) defects.