【作者】 刘玉章；

【导师】 冯吉才；

【作者基本信息】 哈尔滨工业大学 ， 材料加工工程， 2007， 硕士

【摘要】 C/SiC复合材料是一种新型超高温结构材料,在航空航天、武器装备等领域具有广阔的应用前景。本文分别以60wt.%Ni+40wt.%TiH₂混和粉末、4层100μmTi+80μmNi叠层箔片和6层10μmNi+80μmTi+10μmNi叠层箔片为钎料,实现了C/SiC与Nb的真空钎焊。通过分析工艺参数对钎焊接头界面结构及强度的影响,初步揭示了Ti-Ni钎焊C/SiC与Nb的机理。试验中发现钎焊过程中Nb向液态钎料溶解、液态钎料在毛细作用下填充C/SiC母材的孔洞并与其发生界面反应。Nb向钎料的溶解可以提高钎缝的塑性,钎料向母材孔洞的填充可以起到钉轧母材的作用。但Nb的溶解量过大,则母材溶蚀严重;溶解量过小,则钎料脆性大,填充孔洞的钎料对母材拘束太强,接头残余应力大。焊前热处理可以对C/SiC起到活化的作用,相同工艺下在界面处生成的TiC+NbC反应层更厚,界面结合强度更高。采用Ni+TiH₂粉末钎焊时,Nb向钎料中的溶解量可以通过改变钎焊温度或者升温过程来控制。升温到1000℃长时间保温,可以使钎料大部分转化为TiNi,减少钎焊温度下液态钎料的量,控制Nb向钎料的溶解。采用4层Ti/Ni箔片钎焊时,升温过程中接触C/SiC的Ni与SiC反应形成Ni-Si液相。钎焊温度低于Ti-Ni系高Ni共晶点1118℃时,Ni-Si液相可以起到降低连接温度的作用;钎焊温度高于1118℃时,Ni-Si液相可以增加液态钎料的存在时间,增大Nb向钎料的溶解量,改善接头的力学性能。采用6层Ni/Ti/Ni箔片钎焊时,由于Ti的流失比Ni严重,焊后接头主要由（Nb,Ti）和TiNi组成,未发现熔点较低的Ti2Ni,使较低温度下的钎焊接头可以具有较高的使用温度。C/SiC与Nb的钎焊强度由接头相组成、接头致密性、钎料与C/SiC结合情况、钎料对母材钉轧的强弱四种因素决定。采用4层箔片在1180℃,10min钎焊时,接头中富Nb相的比例较高,接头中没有孔洞,钎料与母材的结合良好,剪切时C/SiC母材的C纤维被剪断,钉轧母材的钎料具有一定的塑性,属准解理断裂,接头强度最高。未处理C/SiC与Nb的接头室温抗剪强度为67MPa,热处理C/SiC与Nb的接头强度达到128MPa。更多还原

【Abstract】 C/SiC composite is a type of promising ultra-high temperature structural materials in the aerospace and weaponry fields. In this study, C/SiC and Nb was brazed with 60wt.%Ni+40wt.%TiH₂ powder mixture, four layers of 100μmTi + 80μmNi and six layers of 10μmNi+80μmTi+10μmTi in a vacuum furnace. By analyzing the influence of brazing parameters on the microstructure and the strength of the joint, the brazing mechanism of C/SiC and Nb with Ti-Ni is revealed basically.Nb dissolves into the brazing alloy during brazing. The brazing alloy fills in the hole of C/SiC under the capillary force and reacts with the C/SiC at the interface. The plasticity of filler metal is improved by the solution of Nb to the filler metal. The filler metal that fills in the C/SiC hole can anchor the composite. The solution of Nb to the filler metal must be controlled, when it is too much the base metal is corroded. However, when it is too little, the filler metal is brittle. The constrained force of the filler metal that fills in the C/SiC hole on the composite is too high, and a large residual stress is generated in the joint. Preheating can activate the C/SiC, which thickens the TiC+NbC interfacial reaction layer between C/SiC and the filler metal and strengthens the bond of the interface.When brazing with the powder mixture, the solution of Nb to the filler metal can be controlled by changing the brazing temperature or the heating profile. If holding at 1000℃for a long time during the heating period, the powder mixture can be translated into TiNi mostly, which can decrease the quantity of liquid phase at the brazing temperature. Therefore, the content of Nb in the filler metal can be controlled.When brazing with the four layered Ti/Ni interlayers, the Ni foil adjacent to the C/SiC reacts with it during the heating period, and results in a Ni-Si partial liquid phase. If the brazing temperature is lower than the Ti-Ni eutectic point of 1118℃, the Ni-Si liquid phase leads to the decrease of the brazing temperature. If the brazing temperature is higher than 1118℃, the effect of the Ni-Si liquid phase is increasing the present time of the liquid filler metal and the solution quantity of Nb to the interlayer. Thus, the mechanical property of the brazing joint is improved.When brazing with the six layered Ni/Ti/Ni interlayers, Ti runs off more seriously than Ni, the joint is mainly composed of （Nb, Ti） and TiNi. Ti2Ni with a low melting point does not appear in the joint. The joint that achieved at a low brazing temperature can be applied in a high temperature condition.The strength of the brazing joint between C/SiCand Nb is determined by the phase composition of joint, the density of joint, the bond between filler metal and the C/SiC and the anchor of the filler metal on the composite. Brazing with the four interlayers under a parameter of 1180℃and 10min, the joint has a high percentage of Nb rich phase and no brazing defect is observed. During shearing, the carbon fibers of the composite are shorn due to good connection between filler metal and composite. Good plasticity of filler metal that fills in the composite hole is found and the fracture in the filler metal presents a quasi-cleavage characteristic. The maximum shear strength at room temperature of the original C/SiC and Nb joint is 67MPa and the heat treated C/SiC and Nb joint reachs 128MPa.更多还原