twin boundaries

Twin boundaries are internal features within a crystal structure where two regions are mirror images of each other, oriented differently but joined seamlessly. Imagine folding a paper strip so that one part lines up exactly as a mirror reflection of the other; the fold line is like the twin boundary. These boundaries occur naturally during the formation or deformation of materials, affecting their strength and properties. They help the crystal accommodate stress and can influence how the material responds to mechanical forces, often enhancing its durability or ductility.