Microstructural Refinement of Tantalum for Superconductor Diffusion Barrier Applications

75778-Previous research has shown that the Ta diffusion barrier in composite Nb3Sn superconductors, such as those used in the superconducting magnets needed for fusion confinement systems, may develop a failure mode during wire drawing, due to the non-uniform deformation of the thin Ta layer. This non-uniform deformation can lead to breaches in the diffusion barrier and its premature fracture during wire drawing. In recent experiments with niobium (Nb), a process called Equal Channel Angular Extrusion (ECAE) was shown to be effective in refining the grain size in bulk material, homogenizing the microstructure, and substantially reducing the texture. This project will demonstrate that ECAE- processed Ta exhibits excellent mechanical characteristics for its use as a diffusion barrier in multi-filamentary composite Nb3Sn superconductors. Phase I will demonstrate: (1) the effectiveness of ECAE processing for grain refinement and microstructure homogenization of pure Ta; and (2) the superior mechanical characteristics of ECAE-processed Ta sheet, compared with commercially available Ta. Commercial Applications and Other Benefits as described by the awardee: The ECAE process should produce better and purer Ta for use as a Nb3Sn superconductor diffusion barrier material.