Pj. Lee et Dc. Larbalestier, Compositional and microstructural profiles across Nb3Sn filaments producedby different fabrication methods, IEEE APPL S, 11(1), 2001, pp. 3671-3674
The next generation of high field magnets for fusion and accelerator applic
ations requires the development of Nb3Sn strand with significantly higher c
ritical current densities Our recent work has shown that when the specific
pinning force is normalized to the grain boundary density (the primary pinn
ing site in this material), a strong increase in pinning force is observed
for high Sn content strand, suggesting a strong compositional dependency fo
r pinning in this material, In this study we use advanced FESEM techniques
to quantify the compositional and microstructural variations to a sub-100 n
m level A stepped compositional and microstructural variation was observed
across a bronze-processed Nb3Sn filaments with sharp interfaces for both Ca
(Sn)-Nb3Sn and Nb3Sn-Nb. Microstructural variation was observed on the scal
e of the original filaments in high Sn, MJR but not across the coalesced fi
lament mass, A very high microstructural uniformity was observed in a PIT m
onofilament. Thus a major influence of Sn appears to be exerted through its
influence on the composition gradient.