Effect of diffusion annealing regimes on the structure of Nb3Sn layers in ITER-type bronze-processed wires

• Published in: Journal of physics. Conference series Vol. 969; no. 1
• Main Authors: Valova-Zaharevskaya, E G, Popova, E N, Deryagina, I L, Abdyukhanov, I M, Tsapleva, A S
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 01.03.2018
• Subjects: Annealing; Bronzes; Copper; Diffusion annealing; Diffusion effects; Diffusion layers; Equiaxed structure; Low temperature; Niobium; Physics; Superconductivity
• ISSN: 1742-6588; 1742-6596
• DOI: 10.1088/1742-6596/969/1/012055

The goal of the present study is to characterize the growth kinetics and structural parameters of the Nb3Sn layers formed under various regimes of the diffusion annealing of bronze-processed Nb/Cu-Sn composites. The structure of the superconducting layers is characterized by their thickness, average size of equiaxed grains and by the ratio of fractions of columnar and equiaxed grains. It was found that at higher diffusion annealing temperatures (above 650°C) thicker superconducting layers are obtained, but the average sizes of equiaxed Nb3Sn grains even under short exposures (10 h) are much larger than after the long low-temperature annealing. At the low-temperature (575 °C) annealing the relative fraction of columnar grains increases with increasing annealing time. Based on the data obtained, optimal regimes of the diffusion annealing can be chosen, which would on the one hand ensure complete transformation of Nb into Nb3Sn of close to the stoichiometric composition, and on the other hand prevent the formation of coarse and columnar grains.