At present, Nb3Sn superconductors are becoming more popular in high magnetic fields. The growth law of Nb3Sn phase in a planar CuSn/Nb diffusion couple has been studied, whereas the formation mechanism of Nb3Sn phase in a cylindrical CuSn/Nb diffusion couple is still controversial. The purpose of this work is to investigate the growth exponent of Nb3Sn phase at the initial stage of annealing by use of scanning electron microscopy (SEM) through which the thickness of Nb3Sn layer can be obtained. In this study, bronze-processed Nb3Sn multifilamentary wires with different annealing time were investigated. The Nb3Sn phase was formed during isothermal annealing at 670 °C by solid-state diffusion, which was accomplished by the movement of Sn atoms from the CuSn/Nb3Sn interface to Nb3Sn/Nb interface. However, the formation mechanism of Nb3Sn phase at the initial stage of annealing is still not well understood. Microstructural evolution of Nb3Sn phase during isothermal annealing was studied by SEM. The mean thickness of the Nb3Sn layer (ΔxNb3Sn\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\Delta x_{{{\text{Nb}}_{ 3} {\text{Sn}}}}$$\end{document}) is expressed as a power function of the annealing time (t) by the equation ΔxNb3Sn2=k(t/t0)n\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\Delta x_{{{\text{Nb}}_{ 3} {\text{Sn}}}}^{2} = k(t/t_{0} )^{n}$$\end{document}, where t0 is the unit time, k is the reaction rate constant and n is the growth exponent. The growth exponent has the average value of 0.82, which means that the formation of the Nb3Sn phase is both governed by the interface reaction and the grain boundary diffusion.

中文翻译：

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通过电子显微镜研究 Nb-青铜基复合线中 Nb3Sn 相形成的初始阶段

目前，Nb3Sn超导体在高磁场中越来越受欢迎。平面CuSn/Nb扩散对中Nb3Sn相的生长规律已得到研究，而圆柱形CuSn/Nb扩散对中Nb3Sn相的形成机制仍有争议。这项工作的目的是通过使用扫描电子显微镜 (SEM) 来研究退火初始阶段 Nb3Sn 相的生长指数，通过扫描电子显微镜 (SEM) 可以获得 Nb3Sn 层的厚度。在这项研究中，研究了不同退火时间的青铜处理的 Nb3Sn 复丝。Nb3Sn 相是在 670°C 等温退火过程中通过固态扩散形成的，这是通过 Sn 原子从 CuSn/Nb3Sn 界面移动到 Nb3Sn/Nb 界面来实现的。然而，Nb3Sn 相在退火初始阶段的形成机制尚不清楚。通过扫描电镜研究了等温退火过程中 Nb3Sn 相的显微组织演变。