The Microstructure and Mechanical Properties of Commercial Pure Titanium in Cold-Drawn Mg+B/CP-Ti/Cu Wires

In this study, the relationship between the microstructural evolution of a commercially pure titanium (CP-Ti) barrier during cold drawing and the variation in the cross-sectional area fraction of the materials constituting a Mg+B/CP-Ti/Cu wire was investigated. At a low drawing strain, deformation twins were observed inside the grains of the CP-Ti barrier, and it was confirmed that the {1122}1123 contraction and {1012}1011 extension twins operated as primary and secondary twin systems, respectively. The activated twins facilitated continuous plastic deformation in the drawing direction, thereby significantly reducing the cross-sectional area of the CP-Ti barrier compared to the Mg+B core and Cu sheath. At a high drawing strain, the twin fraction and grain size of the CP-Ti barrier decreased with increasing drawing strain. The CP-Ti barrier with high hardness by the Hall-Petch mechanism only operates the slip system in the drawing direction; thus, the cross-sectional area of CP-Ti is hardly reduced. In contrast, the cross-sectional area of the Cu sheath with relatively low hardness was rapidly reduced.