Deformation and recrystallization behavior of super high-purity niobium for SRF cavity

Abstract

Deformation and recyrstallization behavior of pure niobium was investigated in order to clarify the origin of its low hydro-formability despite of its high ductility comparable with pure iron. It was found that pure niobium exhibits lower strain hardening in cold rolling compared with pure iron. Furthermore, in post-deformation annealing, the hardness of niobium decreased monotonously with an increase of temperature, and the typical sharp drop by recrystallization was not evident. This softening behavior was contrasted with the high-purity iron. It is suggested that niobium exhibit the so-called in-situ recrystallization possibly because of low elastic modulus and low accumulative plastic strain energy in spite of high melting temperature. The low hydro-formability of pure niobium sheets or tubes is caused by its low strain hardening and its unique plastic anisotropy which is associated with this recovered residual rolled texture.