Tantalum Sheet for Superconductor Diffusion Barrier Applications

This report presents preliminary results of a project with the aim to fabricate fine‐grained tantalum sheet having a uniform microstructure that co‐deforms well with pure copper for superconductor diffusion barrier applications. Multi‐pass equal channel angular extrusion (ECAE) was used to refine the microstructure of 25 mm square cross‐section bars of Ta; rolling was used to convert the bars to 0.38 mm thick sheet. Cu‐Ta co‐deformation characteristics were evaluated by assembling and drawing experimental Cu‐Ta composite wires, containing the ECAE processed sheets, to 0.83 mm diameter and metallographically examining the thinned 2–4 micron Ta layer. The ECAE processed Ta sheet co‐deformed well with Cu, and was found to have a smaller recrystallized grain size, a narrower grain size distribution and a slightly higher hardness compared to commercial diffusion barrier grade Ta sheet. The favorable results encourage further work.