Diffusion between Nb and Ti related to superconductor wire processing

Abstract

Quantitative data on the diffusion between Nb and Ti are important for the processing of Nb–Ti superconductor wires through the ‘artificial pinning centre–diffusion process’. In the literature, most of the Nb–Ti diffusion studies are focused on the 1173–1973 K temperature range which is inappropriate for this application. The objective of this study was to evaluate the diffusion between Nb and Ti at 1023 K and 1073 K, from a Nb–Ti cylindrical composite that has been mechanically deformed by swaging. It has been found that at both temperatures most of the diffusion layer is formed through the diffusion of Nb into Ti. A plot of diffusion layer thickness versus t1/2 (t is the time) showed a linear behaviour for both temperatures with angular coefficients of 0.0867 μm s−1/2 (1023 K) and 0.253 μm s−1/2 (1073 K). Longer heat treatment and higher temperature leads to a Ti-rich diffusion layer, which is not interesting in terms of superconducting properties. After heat treatment at 1023 K for 150 h, the monofilament wire (0.610 mm) presented a critical temperature of 10 K and an upper critical field close to 6 T.