What is the grain boundary?

• A. The interface formed between grains
• B. A single crystal plane with uniform lattice
• C. A region of perfect order extending through the material
• D. A void in the crystal lattice

Answer: (D)

Grain boundary is the interface where two neighboring grains with different crystal orientations meet in a polycrystalline material. Because the grains are oriented differently, their lattice planes don’t line up perfectly at the boundary, creating a region of misfit and increased disorder compared with the grain interiors. This boundary influences material behavior by affecting how dislocations move, diffusion can be altered, and sites for segregation or corrosion can form. It is not a single crystal plane with uniform lattice, nor a region of perfect order extending through the material, nor a void in the crystal lattice. So, the grain boundary is specifically the interface between neighboring grains.