陶瓷表层结构梯度化缓解SiO2f/SiO2复合陶瓷/金属钎焊接头残余热应力的方法研究

The mismatch in the thermal expansion coefficient between SiO2f/SiO2 ceramic matrix composite and metal is extremely great, that is, for the former it is only 0.33×10-6 K-1, in general, the latter is high up to 4.6~15.5×10-6 K-1 . And this makes it very difficult to join them together due to the induced great residual thermal stresses existed within the joints. Therefore it is of great importance to take measures to effectively decrease the residual thermal stresses and to achieve a stable joining interface between the two dissimilar materials..In this project a method of decreasing residual thermal stresses within the joint between SiO2f/SiO2 ceramic matrix composite and metal is newly proposed. That is, firstly, a series of grooves are machined mechanically at the surface of SiO2f/SiO2 composite to be jointed, and then they are filled with brazing fillers or metal pieces through brazing. This means that a graded structure is formed at the surface of the SiO2f/SiO2 composite, and thus the thermal expansion coefficient shows a gradient form its inner part to the surface layer. Subsequently, besides the graded structure in the surface layers, the traditional interlayer method for decreasing residual thermal stresses will also be applied in the joining of SiO2f/SiO2 composite to metal. It is believed that our new method will be effective in decreasing residual thermal stresses within the joint between SiO2f/SiO2 ceramic matrix composite and metals. .The research will cover the design of the graded structure at the surface of the SiO2f/SiO2 composite to be joined, micro-analysis of the interface between the composite and the metals in the joint, the joint strength test, and numerical simulation of the residual thermal stresses within the joint by applying the method of finite element analysis, as well as the influence of the graded structure at the surface on the improvement in the distribution of residual thermal stresses throughout the joint. Finally, the brazing experiment for joining of SiO2f/SiO2 composite to metal with a large size will be carried out for verification of the newly proposed method..The present project will provide a potential solution to solve the technical difficulty in the joining of SiO2f/SiO2 composite to metal. It will not only be useful in putting the SiO2f/SiO2 ceramic matrix composite into engineering application in the fields of high temperature material, wave-transparent material, etc., but also be theoretically valuable in joining those dissimilar materials in a wider range in future.

对于热膨胀系数相差十几倍、几十倍的SiO2f/SiO2复合陶瓷材料与金属的组合连接，如何采取有效的技术措施大大降低连接接头残余热应力，从而获得残余应力分布相对均匀、界面冶金结合稳定的接头，是一个有很大技术难度、值得研究的科学问题。.项目提出通过在陶瓷表面加工沟槽、再向沟槽中填入钎料或金属块的方法，在被焊陶瓷表层构造出梯度过渡层，然后再结合中间缓冲层，缓解陶瓷/金属接头的残余热应力。将开展陶瓷表层梯度结构的设计、陶瓷与金属界面微观分析与强度研究、焊后残余应力的数值模拟计算，揭示梯度化结构改善残余应力分布的规律，实现较大尺寸SiO2f/SiO2与金属的钎焊实验验证。.解决有巨大热膨胀系数差的陶瓷与金属连接技术难点，对于促进SiO2f/SiO2在高温结构材料、透波材料等领域应用具有实用意义，而且将在陶瓷/金属连接领域形成有效缓解接头残余应力的新途径，对于更广阔范围内的异种材料连接具有科学价值。

对于热膨胀系数相差十几倍、几十倍的SiO2f/SiO2复合陶瓷材料与金属的组合连接，如何采取有效的技术措施大大降低连接接头残余热应力，从而获得残余应力分布相对均匀、界面冶金结合稳定的接头，是一个有很大技术难度、值得研究的科学问题。.项目首先开展了SiO2f/SiO2复合陶瓷与不同金属材料（不锈钢、铜、钼、铌、钛合金、Ti3Al）、SiO2f/SiO2复合陶瓷与C/C复合材料、Al2O3陶瓷材料组合接头的钎焊实验，界面微观分析与接头强度研究。进一步，提出了通过在陶瓷表面加工沟槽、再向沟槽中填入钎料或金属块的方法，在被焊陶瓷表层构造出梯度过渡层，然后再结合中间缓冲层，缓解陶瓷/金属接头的残余热应力。开展了被焊陶瓷表层梯度结构的设计、缓冲层材料与SiO2f/SiO2复合陶瓷样品的钎焊实验以及陶瓷与金属接头强度研究、不同梯度结构及连接区域的焊后残余应力分布的数值模拟计算，揭示了梯度化结构改善残余应力分布的规律，最终实现了直径190mm的SiO2f/SiO2与金属环形件完整钎焊的实验验证。.得到的主要研究结果：（1）采用AgCu-Ti钎料在880℃/10min规范下，实现了SiO2f/SiO2与金属Nb、Mo和Al2O3陶瓷的良好连接，接头平均抗剪强度分别为26.4MPa、29.9MPa和38.6MPa；（2）新设计了AgCuIn-(4.1~6.9)Ti钎料，相对于传统的AgCu-Ti钎料降低了熔化温度，在800℃/10 min条件下获得SiO2f/SiO2复合陶瓷与金属Nb的剪切强度值高达31.0MPa，高于AgCu-Ti获得的钎焊强度（26.4MPa），钎焊接头典型的界面产物结构依次为SiO2f/SiO2→SiO2+Cu3Ti3O→SiO2+TiO+T5Si4→Ag(s, s)+(Cu-Ti)→Nb;（3）陶瓷/金属环-环接头焊后残余热应力数值模拟计算表明，靠近焊缝处的复合陶瓷存在应力集中，陶瓷表面开槽处理可以大大降低该处的残余热应力，其中σy从200 MPa降至81 MPa, τyx从230 MPa降至53 MPa。.初预定研究内容外，项目还补充了对Al2O3、Si3N4、AlN等陶瓷的高温钎焊研究。.本项目为解决有巨大热膨胀系数差的陶瓷与金属连接技术难点提供了理论研究依据和实验研究基础，对于促进SiO2f/SiO2在高温结构材料、透波材料等领域应用具有实用意义