三维网络石墨烯强化复合中间层及其钎焊C/C复合材料与Nb的机理研究

Considering that brazing C/C composite material with Nb often have problems of low strength and high stress, this project proposes a method that graphene with three-dimensional network structure (3D-graphene) are used as a reinforced composite interlayer to improve the properties of C/C composite material and Nb joints. Graphene with three-dimensional network structure (3D-graphene) are synthesized using Ni foam as the skeleton and catalyst. The composite interlayer consists of TiNi/3D-graphene/TiNi. With the advantage of the network structure, problems such as misdistribution and segregation caused by large amounts of graphene added in the brazing seam can be solved effectively, which gives full play to an enhanced role of graphene and realizes a gradient transition to relieve joint stress and improve the properties of joints. This project focuses on the immersive behavior of brazing alloy in the internal of 3D-graphene and elucidates a wetting mechanism of brazing alloy on the surface of 3D-graphene. Based on the analysis on the evolution mechanism of interface structure, this project reveals the mechanism of the effect of graphene on the interfacial structure of joints. According to the theoretical analysis method of composite materials, we build a mathematical model of CTE and elastic modulus of composite interlayer. Moreover, with the stress analysis of joints, we reveal the effect mechanism of graphene on reducing residual stress of joints. Here, we elucidate a strengthening mechanism and a brazing mechanism of 3D-graphene on the properties of joints to ensure a high quality joints between C/C composite material and Nb. The objective of this project is to promote the applications of nanomaterials and network structure materials in the field of joining, and enhance the development of brazing composite materials with metals.

本项目针对C/C复合材料与Nb接头的强度低、应力高问题，提出了一种三维网络石墨烯强化复合中间层提高C/C复合材料与Nb连接质量的方法。采用泡沫镍为骨架及催化剂制备三维网络石墨烯，以TiNi/网络石墨烯/TiNi作为复合中间层，借助网络结构优势解决钎缝中大量石墨烯添加引起的分散不均、偏聚等难题，发挥石墨烯增强作用，实现接头性质的梯度过渡缓解接头应力，提高连接质量。重点研究网络石墨烯内钎料的浸入行为，阐明钎料在网络石墨烯表面的润湿机理。基于界面组织的演化机理分析，揭示网络石墨烯对接头界面结构的影响机制。借助复合材料理论分析方法，建立复合中间层热胀系数及弹性模量的数学模型，结合接头应力分析揭示网络石墨烯对接头残余应力的缓解机制，阐明网络石墨烯对接头性能的强化机制及钎焊机理，保证C/C复合材料与Nb的高质量连接。本项目旨在推广纳米及网络结构材料在连接领域的应用，促进复合材料与金属连接技术的发展。

本项目针对C/C复合材料与Nb焊后接头的高残余应力问题，提出并验证了三维网络石墨烯强化复合中间层辅助钎焊复合材料与金属的新方法。利用CVD方法在泡沫金属上原位生长石墨烯实现了三维网络石墨烯复合中间层的制备，借助网络结构优势解决了钎缝中大量石墨烯添加引起的分散不均、偏聚等难题，揭示了网络石墨烯的生长机制。研究发现，活性钎料在网络石墨烯表面具有良好的润湿性，并且本征石墨烯与Ti原子的相互作用力相对较弱，能够有效阻隔活性钎料与泡沫金属之间的相互反应及扩散溶解，保证了钎缝中网络结构骨架的完整性。采用COMSOL软件，结合有限元方法模拟计算了网络石墨烯厚度及孔隙率对接头应力分布状态的影响规律，得到了网络石墨烯最佳孔隙率为90%，接头钎缝的最佳厚度为0.15mm。网络石墨烯复合中间层发挥了石墨烯与泡沫金属的协同强化作用，有效提高了接头的塑性，通过转移应力、位错强化以及细晶强化等多方面共同作用提高接头的强度，接头的剪切强度由~19MPa提高至~43MPa。此外，我们又设计了一种碳层包覆网络结构复合中间层，发挥钎料中活性元素Ti的作用，在焊缝中形成均匀分布的片状TiC增强相，降低了钎缝整体的热胀系数，实现了接头性质的梯度过渡缓解了接头残余应力，并对焊缝组织起到了细晶强化作用，显著提高了接头的力学性能，接头的剪切强度提高至~53MPa。研究工作得到国内外同行的广泛关注，多次受邀在国内外学术会议上做特邀报告。发表学术论文33篇，其中SCI论文31篇，申请国家发明专利13项，已获授权9项，成果转化2项，技术应用2项。荣获中国机械工程学会科技奖-优秀论文奖，中国腐蚀与防护学会科技术奖一等奖。研究成果已应用在地质钻探装备核心部件PDC复合片钻头、陶瓷异质结构电气贯穿件、微小力传感器、战斗机发动机报警器膜盒以及核电电子元件等关键部件的焊接制造中。本项目研究成果为高性能复合钎料设计及复合材料与金属的连接提供了新的思路，促进了纳米及网络结构材料在连接领域的应用。