涂层导体用Ni-9W合金自生复合基带微观组织与立方织构演变机制

The second-generation high-temperature YBCO coated superconductors have wide perspective in electric power and high strong magnet applications owing to their excellent electric performance. The realization of YBCO-based coated conductors in the rolling assisted biaxial textured substrate (RABiTS) approach is based on the use of a cube-textured substrate, in which the desired crystallographic orientation is transferred to both the buffer layer and the YBCO films through epitaxy. The essential requirement for the substrate employed in coated superconductors is to develop a sharp cubic texture in materials having high strength and low magnetism. Hence many attempts have been made to develop textured Ni-W alloy substrates, such as Ni-5at% W and Ni-9at%W. Although Ni-5W substrate with highly cubic texture has been produced, there remains the challenge of improving the mechanical and magnetic properties of the substrates through increasing the tungsten content in the Ni-W alloy. Unfortunately, the sharp cube recrystallization texture is not easily formed when W volume is more than 7at% in Ni-W alloy because of its lower stacking fault energy (SFE). The main aim of the present project will be emphasized on the gradient distribution of W element along corss-section of Ni-9W ingot fabracated by centrifugal casting process and the cube texture developed by cold rolling and subsequent recrystalization annealing. During centrifugal casting processing, W atoms in melt Ni-9W alloy will be directionally moved form inner layer to out layer, impelled by relative centrifugal force (RCF), which results in the formation of in-situ composite of Ni-9W alloy ingot with gradient distribution of W element. Therefore, it is expected that the highly sharp cube texture will be contributed to the inner-layer with low volume fraction of W element, and the high strength and low magnetism will be contribute to the outer-layer with high volume fraction of W element in the Ni-9W composite substrate processed by heavy cold rolling and subsequent recrystallization annealing. The present project is focus to reveal to gradient distribution behavior of W element in the centrifugal casting processed Ni-9W ingot, and the evolution and formation mechanism of microstruture and cube texture induced by gradient distribution of W element during cold rolling and subsequent recrystallization annealing. The technological route involed centrifugal castinng, cold rolling and recrystallization annealing will be established based on the experimental results and theoretic analysis, which could offer the essential groundwork in order to produce the high performance Ni-W alloys substrate with sharp cube textured and high strength and low magnetism based on low cost and large scale manufacturing for coated superconductor application.

YBCO涂层导体以其卓越载流能力，在电力和强磁体领域具有广泛应用前景。在以轧制辅助双轴织构基带制备涂层导体技术路线中，金属基带的高立方织构、高强度和低磁性是决定超导性能的关键。目前现有低钨和高钨含量的镍钨合金基带均无法同时满足上述要求。针对这一关键问题，本项目提出基于"离心铸锭法"制备高性能镍钨合金基带的新构想：即利用离心铸造过程中高比重钨元素易偏析属性，旨在获得外层为高钨、内层为低钨且钨含量呈连续梯度分布的复合铸锭。依据低钨层易获得高立方织构，高钨层具有高强度和低磁性特性，通过冷轧-再结晶工艺调控，以期获得集高立方织构、高强度和低磁性于一体的镍钨合金基带。本项目着重阐明钨元素在离心凝固过程中的偏析行为；揭示具有连续成分梯度的镍钨合金在冷轧-再结晶过程中微观组织与织构演变规律及机制；建立基于离心铸造-冷轧-再结晶工艺路线制备高性能镍钨合金基带的技术原型；为涂层导体制备提供关键基带材料。

YBCO涂层导体以其卓越载流能力，在电力和强磁体领域具有广泛应用前景。在以轧制辅助 双轴织构基带制备涂层导体技术路线中，金属基带的高立方织构、高强度和低磁性是决定 超导性能的关键。目前现有低钨和高钨含量的镍钨合金基带均无法同时满足上述要求。针 对这一关键问题，本项目提出基于"离心铸锭法"制备高性能镍钨合金基带的新构想：即利 用离心铸造过程中高比重钨元素易偏析属性，旨在获得外层为高钨、内层为低钨且钨含量 呈连续梯度分布的复合铸锭。依据低钨层易获得高立方织构，高钨层具有高强度和低磁性 特性，通过冷轧-再结晶工艺调控，以期获得集高立方织构、高强度和低磁性于一体的镍钨合金基带。本项目（1）明确了钨元素在离心凝固过程中的偏析行为；（2）着重揭示了具有连续成分梯度的镍钨合金在冷轧-再结晶过程中微观组织与织构演变规律及机制；利用有限元辅助模拟方法研究了不同异步轧制路径对变形行为的影响机制，为合理采用异步轧制方法调控冷变形织构提供了理论指导；（3）特别针对Ni基合金中杂质元素（特别是有害气体元素如O，N及非金属元素如S、P等）对再结晶立方织构形成的不利影响，利用电子束熔炼方法对Ni基合金进行了超纯净化处理，以期显著降低合金中有害杂质元素的含量，为后续的再结晶立方织构调控提供有益的原始材料基础，利用magniga效应对合金元素及杂质净化行为进行了理论分析和实验研究，建立了有害杂质元素的迁移及除去机制，为高质量的基带材料的制备提供了可靠的制备途径和技术方法，在此基础上，建立了电子束精炼-异步冷轧-再结晶工艺路线制备高性能镍钨合金基带的技术原型，可为涂层导体得制备提供可靠的基带材料。