Twin boundaries are planar defects within a crystal structure where the lattice is mirrored, creating a symmetrical interface that can enhance material properties like strength and ductility. They play a crucial role in deformation mechanisms and can influence the mechanical and physical properties of materials by acting as barriers to dislocation movement.
Grain boundary strength refers to the resistance against deformation or fracture at the interfaces between crystalline grains in a material. It plays a critical role in determining the overall mechanical properties and durability of materials, particularly in metals and ceramics.
Brittle materials fracture without significant deformation when subjected to stress, while ductile materials can sustain substantial deformation before breaking. This fundamental difference arises from the material's ability to absorb energy and accommodate structural changes under stress, which determines its applications and failure modes.