Tantalum sheet with improved copper-tantalum co-deformability
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Poor co-deformation behavior of commercial polycrystalline tantalum (Ta) sheet used for tin diffusion barriers in Nb3Sn composite superconductors leads to the use of more Ta than is necessary in these conductors, and to premature Ta layer fracture during wire drawing. These problems arise because the Ta layer deforms nonuniformly in the composite conductor as it is reduced in thickness. The origin of the problem resides in the microstructure of the Ta and the co-deformation mechanics of relatively strong BCC Ta with surrounding weaker and more ductile FCC Cu. In an attempt to remedy this problem, 25mm square bars of Ta were processed by multi-axis severe plastic deformation (SPD) via equal channel angular extrusion (ECAE), then rolled to sheet and annealed. The SPD processing refined the microstructure and reduced nonuniformities in grain size and texture. Measurements of grain size, microstructural uniformity, Ta layer thickness, and Cu-Ta interface roughness are reported. The Ta sheet incorporating an SPD processing step during its manufacture co-deforms more uniformly with pure Cu than does commercially available Ta sheet.
