Significant tensile ductility and toughness in an ultrafine-structured Ti68.8Nb13.6Co6Cu5.1Al6.5 bi-modal alloy

An important and effective strategy for ductility improvement of ultrafine-structured metallic materials is the development of multi-scale grain structures. Here we report about a new bi-modal Ti68.8Nb13.6Co6Cu5.1Al6.5 alloy with significantly improved tensile ductility and high static toughness. The alloy consists of an ultrafine-structured eutectic (B2 TiCo+bcc β-Ti) and coarse bcc β-Ti dendrites. The microstructure alteration upon tensile loading was studied in-situ by means of scanning electron microscopy. It is found that the ultrafine-structured eutectic exhibits a “slip”-like deformation behavior to accommodate the intensive plastic deformation of the dendrites. A detailed study of the microstructure by means of transmission electron microscopy revealed that this is due to a cube-on-cube orientation relationship of the eutectic (B2 TiCo+bcc β-Ti) and dendritic (β-Ti) phases.