Microstructual Refinement of Ta For Superconductor Diffusion Barrier Applications

75778B 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, 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 demonstrated: (1) the effectiveness of ECAE processing for grain refinement and microstructure homogenization of pure Ta and Cu, and, (2) the superior mechanical characteristics of ECAE processed Ta sheet, compared with commercially available Ta, for a diffusion barrier in Nb3Sn multi-filamentary superconductors. Phase II will demonstrate that ECAE-processed Ta sheet is superior to commercially available Ta sheet for multifilamentary Nb3Sn uperconductor diffusion barrier applications. Superiority will be demonstrated by forming a thinner and more regular Ta layer in experimental fusion magnet conductors. Commercial Applications And Other Benefits as described by the awardee: The technology should be applicable a to the production of Ta sheet for use as Nb3Sn superconductor diffusion barrier material, with favorable economics.