Metallurgical variables and their influence on the superconductivity of niobium-40% zirconium

Abstract Superconducting transition temperatures and zero-field critical current densities (computed from low-field magnetization measurements) for Nb-40% Zr are reported as a function of heat treatment. The variation of these properties is correlated with the microstructure which has been studied in the same set of specimens using both optical and electron microscopy. The transition temperatures show that the proximity effect of a precipitate phase on a matrix has been observed directly. The critical current densities are discussed in comparison with directly measured values for wires of Nb-25% Zr. It is concluded that the achievement of the highest value of critical current correlates with the appearance of a suitable dispersion of the pinning constituent and is independent of the type of pinning constituent.