Microstructure and flux pinning in commercial Nb‐25% Zr superconducting wires

摘要

A detailed structural examination was carried out on commerical Nb‐25% Zr conductors which had been heavily cold worked and annealed in the temperature range 600–700 °C for times ranging from 1/4 to 10 h. The magnetization of some of these wires had previously been measured (Mathur et al.) as a function of applied magnetic field at temperatures ranging from 4.2 °K to the transition temperature and the results were interpreted in terms of a flux‐pinning model proposed by Kramer. Additional magnetization measurments on larger‐diameter wires were made to aid in the interpretation of the flux‐pinning mechanisms. Transmission electron microscopy, x‐ray analysis, and hardness measurements revealed that the predominant structural change in the annealed wires was recovery of dislocation structure. No βZr or αZr precipitates were detected. It is concluded that the optimum flux‐pinning properties in Nb‐25% Zr conductors for the processing schedules studied are associated with a highly recovered and small dislocation cell structure.