Microstructural refinement of tantalum for Nb3Sn superconductor diffusion barriers

Cast pure Ta was deformation processed via equal channel angular extrusion and then recrystallized to produce a uniform, fine-grained bulk material. Extrusions were performed on 25×25×150 mm billets at room temperature in 90° tooling to strains of 9.3. The Vickers microhardness reaches near maximum levels after four extrusions. As-worked microstructures are composed of nonuniform submicron grains with apparent banding. A homogeneous and fine grained recrystallized microstructure (average grain size ∼8 μm) free of banding is obtained after four extrusions via route E multipass processing and a 1000°C heat treatment. The high microstructural homogeneity of such a material may exhibit better co-reduction characteristics with surrounding Cu over conventionally processed Ta for superconductor diffusion barrier applications.