NbTi/Cu多芯复合超导线多道次集束拉拔不均匀变形机理及其调控

With the development of controllable thermonuclear fusion, nuclear magnetic resonance imaging, magnetic levitation fields, etc. it is an urgent need for precision forming of multi-filamentary composite superconducting wire of NbTi/Cu with high performance and stability. However, how to effectively control uneven deformation of superconducting wire to eliminate uneven core wire, cross section distortion, broken cores and other defects in the bundling and drawing process, is a key scientific problem for precisely manufacturing NbTi/Cu multi-filamentary composite superconducting wire. In this project, taking multi-filamentary composite superconducting wires of NbTi/Cu formed by the multi-pass bundling and drawing process, with the characteristics of multi-pass, multi-scale, extremely large deformation, as the research object, NbTi/Cu wire deformation and damage behavior under different loading conditions will be studied using finite element simulation, combined with theory analysis and experiment method. The material constitutive and damage coupled model will be established, and the methods of characterization of uneven deformation and the uneven deformation rules and mechanism in the bundling and drawing process will be proposed and clarified. Then the relationship between uneven deformation and forming defects can be established. By studying the influences of the initial multi-filamentary assembly, die parameters and process conditions on uneven deformation and defects, the controlling methods of uneven deformation of NbTi/Cu multi-filamentary composite superconducting wire under the bundling and drawing process will be designed. Therefore, it is important and necessary for the development of precision forming theory and technology of high-performance multi-filamentary composite superconducting wire.

受控热核聚变、核磁共振成像、磁悬浮等技术领域的发展迫切需要高性能和高稳定性的NbTi/Cu多芯复合超导线的成形成性精确制造，而如何有效调控超导线集束拉拔过程中的不均匀变形以避免由此导致的芯径不均匀、截面畸变和断芯等缺陷是实现NbTi/Cu多芯复合超导线精确成形的关键科学问题。本项目以NbTi/Cu多芯复合超导线多道次集束拉拔成形为研究对象，针对其多道次、多尺度、极端大变形特点，采用有限元仿真、理论分析和实验相结合方法，研究NbTi/Cu在不同加载条件下的变形行为和损伤，建立材料本构和损伤耦合模型，提出不均匀变形表征方法并阐明集束拉拔不均匀变形规律和机理，揭示不均匀变形与成形缺陷间的关联关系，研究初始多芯组合体、模具参数及工艺条件对不均匀变形及成形缺陷的影响机制，以此提出NbTi/Cu多芯复合超导线集束拉拔过程不均匀变形调控方法，对发展高性能复合线材集束拉拔精确成形理论和技术具有重要意义。

受控热核聚变、磁悬浮等技术领域对高性能和高稳定的需求，亟待实现用于超导磁体的NbTi/Cu多芯复合超导线的成形成性精确制造，而揭示NbTi/Cu多芯复合超导线集束拉拔不均匀变形规律及机理，是实现多芯复合线材高质量制造迫切需要解决的关键科学问题。为此，本项目以NbTi/Cu多芯复合超导线多道次集束拉拔成形为研究对象，综合采用理论分析、实验研究和计算机仿真方法，研究阐明了NbTi合金在不同加载条件下的变形行为以及在变形、多级时效处理条件下的组织演变规律和机制，建立了能准确反映NbTi/Cu芯棒变形行为的本构模型和损伤模型。将模型引入显示有限元算法，并综合考虑“异质复合”材料特性和“多芯组合”结构特征，建立了NbTi/Cu多芯复合超导线多道次集束拉拔过程有限元数值仿真模型。提出了两种芯丝不均匀变形表征方法，探明了集束拉拔不均匀变形与多种成形缺陷的关联关系，揭示了NbTi/Cu多芯复合超导线集束拉拔过程不均匀变形、芯丝截面畸变和损伤规律，探明了拉拔模具结构参数和拉拔成形工艺参数对集束拉拔过程芯丝不均匀变形的影响规律，以及初始多芯组合体结构形式对集束拉拔过程芯丝不均匀变形和损伤的影响规律。考虑NbTi/Cu多芯复合超导线集束拉拔道次中间交替进行多级时效处理，探明了预变形和多级时效温度、时效级数对NbTi合金微观组织与性能的影响，确定了合理的多级时效处理制度和参数。以芯丝的均匀性和一致性为优化目标，对NbTi/Cu多芯复合超导线集束拉拔工艺参数和模具结构参数进行了优化，并实现了初始坯料多芯组合体结构形式的优化设计。获得了集束拉拔时施加振动辅助成形对集束拉拔不均匀变形的初步规律，提出了NbTi/Cu多芯复合超导线多道次集束不均匀变形调控和获得合理的微观组织的方法，以提高NbTi/Cu多芯复合超导线的成形质量和超导性能，这对于发展NbTi/Cu多芯复合线材多道次集束拉拔成形成性精确制造具有重要理论意义和应用价值。