Nanostructured β-type titanium alloy for biomedical application

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 martensitic transformation, are ineffective in grain refinement. Recently we found localized, unstable plastic deformation in a beta-type Ti-Nb-Zr-Sn titanium alloy developed for biomedical application that is very effective in grain refinement but contributes little to strength. By taking advantage of this deformation mechanism, grain size less than 50 rim. can be easily achieved in conventionally cold-rolled sheet after only 90% thickness reduction. We call this alloy soft nanostructured metallic materials (NMMs) because the flow stress increases by only similar to 5.5% when coarse grains are refined to less than 50 nm, in contrast with several times increase for previously-reported NMMs. The reported titanium alloy with nano-size grains enables investigation of the intrinsic effect of nanostructured grains on properties related to biomedical applications. In this paper we examine the conditions under which such an unusual deformation mechanism can operate and report further strengthening of the nanostructured alloy by aging treatment. A technique to produce submicron porous surface of cold-rolled sheet after solution treatment is also reported.