Microstructural refinement of tantalum for Nb/sub 3/Sn 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/spl times/25/spl times/150 mm billets at room temperature in 90/spl deg/ 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 /spl sim/8 /spl mu/m) free of banding is obtained after four extrusions via route E multipass processing and a 1000/spl deg/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.