Deformation twinning in body-centered cubic metals and alloys

Deformation twinning is an important plastic carrier competing with the ordinary dislocation slip in a broad class of crystalline solids, which critically controls the mechanical properties, plasticity, and fracture of crystalline materials across different length scales. Compared with the well-established twinning theories in their close-packed metallic counterparts, a comprehensive understanding of twinning dynamics and twinning mechanisms in body-centered cubic (BCC) metals and alloys remains largely elusive, though some important progresses have been made in past few decades. In this review, we systematically summarize recent advances of deformation twinning in BCC metals and alloys in past few decades, by focusing on the various aspects of the most common {1 1 2}〈11$\overline{\text{1}}$〉 twins, including the atomic structures of twin boundaries, twin nucleation and growth mechanisms, asymmetry of twinning and anti-twinning, factors influencing the deformation twins, twin-induced fractures and some other unique properties. {3 3 2}〈11$\overline{\text{3}}$〉 and other types of high-index deformation twins that have been extensively observed in BCC alloys are also summarized and discussed. The comprehensive understanding of deformation twinning in BCC metals and alloys not only advances our knowledge of twinning in metallic materials, but also has broad implications for the design of high-performance BCC metals and alloys by regulating deformation twins.