碳/碳和钛合金钎缝吸能复合结构的材料本构及多维界面动态冶金行为研究

The brazing technology of C/C and titanium alloy has a bright prospect in the field of supersonic and hypersonic aircraft. The residual stress relieving is a main difficulty during brazing with large bonding area. In this project, based on the functional and structural properties of metal foam, C/C and titanium alloy is brazed with metal foam as an energy absorbing interlayer. Combining mechanical response of the absorbing composite structure and the constitutive theories of materials, the constitutive relation of the absorbing composite structure will be studied. The stress evolution of the joint in the brazing process is simulated, and the optimal design and selection principles of the energy absorption interlayer are proposed. High speed photographical observation, microscopic analysis, thermodynamic calculation, diffusion and metallurgical reaction deduction are used to study the macro-meso, multi-dimension, dynamic metallurgical reaction inside the foam cell and the interfaces, consequently, the interfacial microstructure evolution mechanism of the joint will be proposed. The damage electrometric method with microscopic observation is adopted to study the quantitative relationship between fatigue load- crack initiation and propagation-resistance strain and conclude the damage mechanism of the joint. Large area, high performance C/C and titanium alloy brazing technology will promote and support the application of C/C in the aerospace industry.

C/C与钛合金钎焊技术在超音速和高超音速飞行器中有远大前景，减缓高残余热应力是大面积接头制备的技术瓶颈。本项目基于泡沫金属结构功能一体化特性，采用其作为吸能中间层钎焊C/C和钛合金。测试钎缝吸能复合结构的力学响应，结合材料本构理论，探索其材料本构关系；在此基础上，采用数值仿真技术模拟接头钎焊过程中的应力演变，并提出吸能中间层设计原则和优选准则。采用高分辨高速摄影观测、显微分析与热力学、扩散和冶金反应推导相结合，探索接头各反应界面和泡沫金属胞孔内部宏-细观、多维度、动态冶金反应过程和界面组织演变；损伤电测法和显微观测相结合，探索高低温热循环或疲劳载荷-裂纹萌生扩展-电阻应变的量化关系，研究接头在疲劳载荷下的损伤机理。发展大面积、高性能C/C与钛合金的钎焊技术，为推动C/C在航空航天产业中应用提供技术支持。

C/C复合材料是航空航天领域最有前途的新一代耐高温结构材料，拥有远大的应用前景，C/C复合材料与钛合金钎焊技术存在重大需求。本项目针对C/C复合材料与钛合金钎焊接头高残余应力导致接头性能下降问题开展基础研究，基于泡沫金属结构功能一体化特性和吸能原理，提出添加泡沫金属吸能中间层缓释C/C和钛合金钎焊接头残余热应力的新思路。首次采用实测方法表征了添加泡沫中间层复合结构的线膨胀系数、密度、弹性模量、应力-应变特性等热物理性能，建立了钎焊接头复合结构的物理模型和本构关系。在材料本构的基础上，采用数值模拟技术探索添加泡沫金属吸能中间层C/C和钛合金钎焊接头应力演变规律、影响因素及控制原则；在开展添加泡沫纯金属（泡沫铜、镍）的基础上，针对泡沫金属在钎焊过程中参与冶金反应导致的泡沫结构局部塌陷问题，创造性的提出了石墨烯增强泡沫金属中间层的新思路，利用石墨烯膜包裹并调控泡沫金属参与钎焊接头冶金反应，从而大幅度提高了钎焊接头的力学性能,即：直接钎焊接头剪切强度约为26MPa，添加泡沫铜中间层钎焊接头的剪切强度约为31MPa，添加石墨烯增强泡沫铜中间层钎焊接头抗剪强度提高至50MPa。详细分析了添加不同泡沫金属中间层钎焊接头成形过程和成形机理，并对添加泡沫金属吸能中间层C/C和钛合金钎焊工艺参数进行了优化。在上述研究的基础上，实现大尺寸、高性能C/C与钛合金的钎焊连接技术，实现了本项目的研究目标。同时，项目组将添加吸能中间层缓释C/C与钛合金钎焊接头残余热应力技术推广到Si3N4陶瓷和Invar合金钎焊、C/C复材与Ti3Al 的钎焊连接，并取得了很好的效果。另外，在本项目研究成果基础上，成功获批军委科技委领域基金项目1项，并在航天多功能结构散热系统上推广应用。

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