扩散型高钨含量镍钨合金复合基带再结晶织构演变和强立方织构形成机理的研究

In recent years, the novel Ni-W alloy composite substrates with high content of W element (the content of W in outer layer of the composite substrate is more than 7 at.%) are considered to be the most promising substrate material for the second generation of high-temperature superconducting tapes with high performance, because they are characterized by higher mechanical strength, no-ferromagnetism and sharper cube texture than that of the more commonly used Ni-based substrates. However，how to develop sharp cube texture and to understand the mechanism of recrystallization texture evolution in these substrates are still the challengable missions so far, and these difficulties are also the major factors in restricting their industrial applications. In this project, a novel model of solute diffusion has been proposed for the first time. Through a precise design of the appropriate material structure and elemental component, the diffusion typed Ni-8at.%W/Ni-12at.%W/Ni-8at.%W alloy composite substrates with high content of W, high strength, no-ferromagnetism as well as sharp cube texture will be fabricated using this processing model. The evolution of deformation texture and microstructure during cold rolling process will be investigated, and the recovery process of the highly deformed samples will be characterized, which are used to well understand the mechanism of the deformation and recovery processes for these novel composite substrates. The nucleation and grain growth of the recrystallization process will be studied via analysis of the texture and microstructure transition as well as the migration of the grain boundaries during annealing. In addition, the effect of the substrate thickness, interbedded ration as well as the elemental diffiusion on the shear structure in the different depth of the cross section will be invesigated in order to understand the relevant relationship between the cube texture formation and the diffusion in the outer and inner layers of the composite substrate. Furthermore, the theoretical model of texture evolution and elemental diffusion will be established. Consequently, the mechanism of recrystallization texture evolution and cube texture formation in diffusion typed-composite substrates with high W content will be systematically elaborated and proposed.

近年来，为了获得高性能第二代高温超导带材，制备高强度、无磁性、强织构的新型高钨含量（外层钨含量大于7at.%）镍钨合金复合基带成为人们研究的热点之一。目前如何在这种镍钨合金复合基带表面获得强立方织构和理解再结晶织构演变的规律仍是一项极具挑战的任务，也是制约其产业化的主要瓶颈。本课题将首次引入溶质原子扩散思路，通过对材料结构和成分的精确设计，提出并制备外层具有强立方织构、整体实现无磁性和高强度的扩散型高钨含量Ni-8at.%W/Ni-12at.%W/Ni-8at.%W合金复合基带；拟通过研究复合基带形变与低温回复组织的演变机制，分析基带再结晶形核和晶粒长大动力学及再结晶过程中晶界迁移和变化规律；通过研究复合基带内外层间比和厚度对截面各区域剪切组织形成的影响，建立内外层元素扩散模型和构建轧制与立方取向的关系，最终系统阐述和归纳扩散型高钨含量镍钨复合基带再结晶织构演变和强立方织构形成的机制。

近年来，镍基高钨合金基带由于其高机械强度以及低（无）磁性，受到人们的广泛研究，但其立方织构的形成是制约其产业化应用的一个主要瓶颈。为了研究高钨合金基带的制备及立方织构形成机理，本项目首先采用粉末冶金技术路线，设计了一种元素扩散型具有“三明治”结构的Ni8W/Ni12W/Ni8W合金复合基带。结合该制备思路，通过轧制中间回复热处理和两步再结晶热处理工艺，显著提高了复合基带中再结晶立方取向的百分比，发现层间比为1:2:1的复合基带表面立方织构含量为96.8%（<10°），同时合金基带表面的W含量达到了9.12at.%。基于以上实验首次提出了通过扩散型复合基带制备镍基高钨含量合金基带的新方案。同时研究了不同层间比（1:1:1、1:2:1和1:3:1）对复合基带冷轧织构、磁性能、力学性能以及立方织构形成的影响。研究发现了层间比为1:2:1的复合基带立方织构含量最高，屈服强度达到了339Mpa，77K时的饱和磁化强度仅为0.39emu/g，同时原位拉伸实验表明其表面立方织构在一定的应力应变条件下具有良好的稳定性。首次阐明了轧制中间回复热处理在采用粉末冶金制备的高钨含量Ni8W/Ni12W/Ni8W复合基带立方织构形成中的作用机制。通过XRD和EBSD数据显示了不同形变量下复合基带Ni8W外层冷轧织构和组织形态，结合轧制中间回复热处理前后的硬度变化，可以确定回复热处理主要是通过冷轧组织的回复，使得冷轧过程中组织均匀形变，从而减少剪切带的出现。另外揭示了复合基带外层再结晶过程中立方织构的形成和层间元素互扩散之间的关系，建立了内外层元素互扩散与再结晶晶粒长大模型。研究发现由于W含量的不同导致内外层再结晶晶粒长大的速率不同，外层晶粒W含量较低，晶粒长大速率快，随着热处理温度的升高和保温时间的延长，外层晶粒吞并内层晶粒完成长大，同时促进了内层的W元素向外层扩散。项目期间已发表SCI论文21篇，EI论文1篇，核心论文2篇；获得授权中国发明专利15项，授权美国发明专利2项，目前有10项国家发明专利在申请中。参加国际国内学术会议6次，做国际会议学术报告2次，国内会议学术报告4次，两人获得国内学术研讨会优秀墙报奖。已促成青年教师，博士生等赴不同国家的大学或研究机构联合培养学习和深造5人次，共培养毕业与该项目相关的博士研究生2人，毕业硕士研究生9人，其中7名获得北京工业大学优秀毕业学位论文奖。