Internally oxidized Nb ₃ Sn wires with artificial pinning centers (APC) have been developed by manufacturing a multifilament PIT-style wire, each filament consisting of a Nb-Ta-Zr alloy tube filled with a mixture of Sn, Cu, and oxide powders. During heat treatment, the oxide decomposes, and the oxygen goes into solid solution in the Nb alloy. Upon Sn diffusion into the Nb alloy, ZrO ₂ nanoprecipitates form which serve both to inhibit grain coarsening and directly pin magnetic flux. The finer grain structure and high concentration of non-superconducting precipitates serve as flux pinning sites and enhance high-field J _c ; direct pinning by the precipitates also shifts the maximum pinning force to higher fields. To distinguish these two effects, an APC wire with a high heat treatment temperature (700 °C) was compared to a conventional PIT wire with very low heat treatment temperature (600 °C), resulting in similar grain size in both samples. The pinning force vs applied field ( F _p -B ) curve was deconvoluted into grain boundary and point pinning components. It was found that the grain boundary component of the APC wire was very close to the F _p - B curve for the PIT wire, demonstrating that the two pinning components in an APC wire are directly additive. It was then possible to show that, in the 15-20 T regime, direct pinning contributed 45-50% of the total pinning.

中文翻译：

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晶界细化和纳米沉淀在APC Nb ₃ Sn助熔剂固定中的作用

通过制造复丝PIT型焊丝，已经开发出具有人工钉扎中心（APC）的内部氧化Nb ₃ Sn焊丝，每根焊丝均由填充有Sn，Cu和氧化物粉末混合物的Nb-Ta-Zr合金管组成。在热处理过程中，氧化物分解，氧气进入固溶在Nb合金中。当Sn扩散到Nb合金中时，就会形成ZrO ₂纳米沉淀，这既可以抑制晶粒粗化，又可以直接钉扎磁通量。精细的晶粒结构和高浓度的非超导沉淀物可作为助焊剂固定位点并增强高磁场Ĵ _c ; 析出物的直接钉扎也会将最大钉扎力转移到较高的磁场。为了区分这两种效果，将具有较高热处理温度（700°C）的APC焊丝与具有非常低热处理温度（600°C）的常规PIT焊丝进行了比较，结果两个样品的晶粒尺寸相似。钉扎力与外加磁场（ F _p -B ）曲线反卷积为晶界和点钉扎分量。发现APC焊丝的晶界成分非常接近F _p - 乙PIT导线的曲线，表明APC导线中的两个钉扎组件是直接相加的。然后有可能表明，在15-20 T的工况下，直接钉扎贡献了总钉扎的45-50％。