On mechanical properties of the superconducting niobium

The overall mechanical properties of the high purity niobium (RRR) sheets, which are used in fabrication of the superconducting accelerator cavities, were investigated in this study. High purity niobium has a microstructure that leads to a rough surface on the free surfaces after plastic deformation. High purity niobium is a rate sensitive material and its strength and ductility increases with increasing strain rate. Due to the presence of an unstable texture, the r values in high purity niobium sheets decrease with plastic deformation. From tensile tests in different in-plane directions and bi-axial bulge tests, a new mathematical model was developed to describe the evolving yield function that predicts the variation of the r values with respect to the effective strain and angle to the rolling direction. From this analysis, suggestions for optimal microstructure and texture for fabricating cavities from high purity niobium are proposed.