High strength nano-structured Ti-Nb-Zr-Sn alloy

To obtain fully dense nano-structured metallic materials, severe plastic deformation technique usually has to be used because normal deformation mechanisms, such as dislocation interaction, deformation twins and/or martensitic transformation, are ineffective in grain refinement. Recently we found localised unstable plastic deformation in a beta type Ti-Nb-Zr-Sn titanium alloy that is very effective in grain refinement. By taking advantage of this deformation mechanism, grain size less than 50 nm can be easily achieved in conventionally cold-rolled sheet with thickness of 1.5 mm. In this paper we examine the conditions under which such an unusual deformation mechanism can be realised and report further strengthening of the nano-structured alloy by aging treatment. The origin of this deformation mechanism will be discussed.