Twinning is a critically important deformation mode in hexagonal close-packed metals. Twins are three-dimensional (3D) domains, whose growth is mediated by the motion of facets bounding the 3D twin domains and influences work hardening in metals. An understanding of twin transformations therefore necessitates that the atomic-scale structure and intrinsic mobilities of facets be known and characterized. The present work addresses the former point by systematically characterizing the boundary structures of 3D {1¯012} twins in magnesium using high-resolution transmission electron microscopy (HRTEM). Eight characteristic facets associated with twin boundaries are reported, five of which have never been experimentally observed before. Further, molecular dynamics simulations suggest that the formation and motion of these facets is associated with the accumulation of twinning dislocations. This work provides insights into understanding the structural character of 3D twins and serves to develop strategies for modulating twin kinetics by modifying twin boundaries, such as solute segregation.

This review provides an overview of recent advancements in Cu-Ni-Co-Si alloys, focusing on their processing methods, microstructures, and properties. Due to their non-toxic composition, enhanced mechanical properties, and excellent electrical conductivity, Cu-Ni-Co-Si alloys have emerged as a promising alternative to traditional Cu-Be alloys in the electrical and electronics industry. This review discusses various synthesis techniques, including casting, vacuum induction melting, and additive manufacturing, and evaluates their effects on the formed microstructures. In addition, it explores the influence of different elements and thermal treatments on the alloys’ microstructures and properties, discussing strategies to enhance the properties of Cu-Ni-Co-Si alloys. Key strengthening mechanisms—including precipitation hardening, grain boundary strengthening, and solid solution hardening—are examined in detail, with particular emphasis on their synergistic effects in optimizing alloy performance. Furthermore, future research directions are highlighted, focusing on the optimization of alloying element concentrations and heat treatment protocols to achieve an enhanced balance between strength and electrical conductivity. These improvements are critical for meeting the demanding requirements of advanced applications in electronics and high-reliability components.