Elucidation of the critical current enhancement mechanism due to the repeated bending treatment for high-strength Nb_3Sn wires

研究的主观目的是了解预反应NbaSn股在室温下施加重复弯曲应变而产生临界电流增强效应的基本机理，并找到使用预反应NbaSn股制造NbaSn股电缆工艺的重要指导原则。为了应用重复弯曲应变处理对NbaSn股的临界电流增强效应，用CuNb复合材料增强NbaSn股制备了试验油，并在施加大环向应力的试验线圈中验证了临界电流增强效应。对从重复弯曲处理样品中蚀刻出的NbaSn单链定向细丝进行了SEM观察。研究发现，重复弯曲处理在NbaSn丝芯中引入了微裂纹缺陷，并且对于NbaSn丝芯中含有的NbaSn丝芯，这种微裂纹缺陷直到容忍应变极限为0.8%时才增加。外部部分加筋。采用高分辨率、高强度粉末衍射仪中子衍射仪对预弯曲前后的NbaSn束进行了测量。预弯处理前后制备的NbaSn链的残余应变在横向上有明显的差异。我们成功地用中子衍射直接表明了重复弯曲NbaSn的残余应变减小。这意味着对Nb_3Sn链的临界电流增强选择有了重要的认识。利用临界电流增强效应，制备了由3股Nb_3Sn股和4股不锈钢股组成的3+4股（3+4）钢绞线，开发了新型NbaSn支架电缆。在实际钢绞线布线过程中，制备的3+4股钢绞线确实保持了这种增强效应。

Research subjective was to understand the basic mechanism for the critical current enhancement effect due to the applying repeated bending strain at room temperature fur pre-reacted NbaSn strands and to find the important guiding principle for the manufacturing process of NbaSn strand cables, employing pre-reacted NbaSn strands.To apply the critical current enhancement effect for NbaSn strands with the repeated bending strain treatment, a test oil was prepared by NbaSn strands reinforced with CuNb composite, and the critical current enhancement was confirmed in the test coil applied by a large hoop stress. The SEM observation was carried out for NbaSn strand-directional filaments etched out from the repeated-bending-treatment sample. It is found that the repeated bending treatment introduces micro-crack defects into NbaSn filament cores, and that such micro-crack defects do not increase until a tolerated strain limit of 0.8 %, in the case of NbaSn strands with. CuNb reinforcement in the outer portion. The NbaSn strands with and without the prebending treatment were measured by the neutron diffraction, which is a high resolution and high intensity powder diffractmeter at KEK in Tsukuba. The residual strains for the prepared NbaSn strands with and without the prebending treatment reveal the clear difference in the lateral direction between the two. We succeeded in indicating the residual strain reduction for the repeated bend NbaSn directly by the neutron diffraction. This means that the important understandings for the critical current enhancement elect of Nb_3Sn strands were obtained.The three + four (3+4) strand cable Consisting of three Nb_3Sn strands and four stainless steel strands were fabricated to develop new NbaSn stand cables applying the critical current enhancement effect It is found that the prepared 3+4 strand cable surely maintains such enhancement in the practical strand cabling process.