Influence of Hf Addition on the Superconducting Properties of Nb3Sn

Nb
₃
Sn strands are widely used to make magnets above 10 T. At present, one major effort to further broaden their application is enhancing the non-Cu critical current density
J
_c,non-Cu
to meet the requirements of large scientific devices such as nuclear fusion and accelerator engineering. Element doping is an effective way to improve the properties of Nb
₃
Sn. In this work, Nb-1at.%Hf alloy along with pure Nb were utilized to manufacture monofilament Tube-type sub-elements to study the influence of Hf addition on the superconducting properties of Nb
₃
Sn. Hf addition was found to refine the Nb
₃
Sn average grain size from 135 nm to 100 nm. Generally, ternary additives could enhance the upper critical field
B
_c2
of Nb
₃
Sn by introducing disorders in the Nb
₃
Sn lattice. However, no promotion effect on
B
_c2
was found for Hf addition. Flux pinning behavior obtained from the magnetization measurements indicates that grain boundary pinning dominates. This suggests that no second-phase particles that provide point pinning were generated during the heat treatment. In addition, it was found that Hf addition has a weak impact on the superconducting critical temperature of Nb
₃
Sn.