Deformation twinning in hexagonal materials

Due to the scarcity of “easy slip” systems in hexagonal materials with a hexagonal closepacked structure (hcp), deformation twinning plays a crucial role in determining mechanical properties and texture evolution. In this article, we highlight the current understanding of mechanisms and mechanics of the twinning system {1012}〈1011〉, which is commonly activated in all hexagonal materials for nucleation and propagation of deformation twins, twin-twin interactions, solute segregation at twin boundaries, and the development of constitutive models that account for the fundamental mechanisms of twinning/detwinning. Future directions such as characterizing the three-dimensional shapes of twins, the influence of solute atoms on twin propagation, and the influence of twin–twin junctions on mechanical properties of the hexagonal materials are discussed.