【作者】 秦优琼；

【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， 博士

【摘要】 近年来,随着新型材料的发展,C/C复合材料由于其密度低、导热性能好、抗热冲击和抗疲劳性能好,特别是其优异的高温强度,被认为是一种理想的航空航天领域高温结构材料,已经成功应用于飞机刹车盘、核反应堆以及火箭发动机喷嘴等部件。将C/C复合材料与TC4连接制成火箭喷管构件,可大大降低重量,提高火箭发动机效率。本文利用AgCuTi和TiZrNiCu（加缓冲层）两种钎料来连接C/C复合材料与TC4,揭示了界面反应机理,并对接头微观组织与力学性能关系进行了深入研究。采用AgCuTi钎料时,接头的界面结构为C/C复合材料/TiC/TiCu/Ag（s.s） +Ti₃Cu₄+TiCu/Ti₃Cu₄/TiCu/Ti₂Cu/Ti（s.s）+Ti₂Cu/TC4 ;当钎焊工艺参数改变时,接头界面产物的种类没有发生改变,但界面各反应层的厚度均发生了相应的变化。随着钎焊温度的升高或保温时间的延长,TiC/TiCu以及Ti₃Cu₄/ TiCu/Ti₂Cu/Ti（s.s）+Ti₂Cu反应层的厚度增加,焊缝中心的Ag（s.s）+Ti₃Cu₄+ TiCu反应层厚度变小,TiCu+Ti₃Cu₄黑块数量减少;当钎焊温度为1183K、保温时间为600s时,接头的抗剪强度最高,为25MPa,低于或高于此工艺参数时,接头的抗剪强度下降;断口分析表明,接头断裂的位置与被连接界面的碳纤维方向有关,当碳纤维轴平行于连接面时,断裂发生在复合材料中;当碳纤维轴垂直于焊接面时,在钎焊温度较低或适中的条件下,断裂主要发生TiC层中。在钎焊温度较高的条件下,断裂主要发生在TiC层以及TiCu/Ti₂Cu界面处。为降低接头残余应力、提高接头的高温性能,采用TiZrNiCu钎料、Cu/Mo复合中间层对C/C复合材料与TC4进行了连接,结果发现,在较低工艺参数下,Cu/C/C复合材料界面结构为Cu/Cu₅₁Zr₁₄/Ti₂（Cu,Ni）+Ti（Cu,Ni） +TiCu+Cu₂TiZr/TiC/C/C复合材料。随着工艺参数的提高,TiCu和Cu₂TiZr反应相逐渐消失,Ti（Cu,Ni）₂新相生成,此时的界面结构为Cu/Cu₅₁Zr₁₄/ Ti₂（Cu,Ni）+Ti（Cu,Ni）+Ti（Cu,Ni）₂/TiC/C/C复合材料。钎焊工艺参数较高时界面结构为Cu/Cu₅₁Zr₁₄/Cu（s.s）+Ti（Cu,Ni）₂/TiC/C/C复合材料。随着钎焊温度的增加以及保温时间的延长,界面反应层Cu₅₁Zr₁₄和TiC反应层厚度增加;通过剪切试验发现当钎焊温度为1173K、保温时间为300s时,接头的室温抗剪强度最大,为21MPa,在923K时高温抗剪强度可达到27MPa,可满足实际应用的需要;改变Cu箔厚度,接头的室温抗剪强度增加,但增加幅度不大,最高不超过23MPa;断裂部位分析结果表明,当碳纤维轴平行于连接面时,断裂发生在复合材料中;当碳纤维轴垂直于焊接面时,断裂主要发生在C/C复合材料与钎料界面处的TiC层中。利用有限元方法,模拟了C/C复合材料/TC4接头残余应力的分布特征。结合断口分析表明,接头力学性能与断裂部位主要与残余剪应力τ_xy有关。最大剪应力τ_xy分布在接头边缘的C/C复合材料/钎料界面处。采用AgCuTi钎料钎焊C/C复合材料与TC4时,在C/C复合材料/钎料界面应力集中区域的剪应力τ_xy低于采用TiZrNiCu直接连接C/C复合材料与TC4的应力;当采用TiZrNiCu钎焊C/C复合材料与TC4时,中间层的加入有利于缓和接头残余应力,其中Cu/Mo复合中间层的缓和效果优于单一中间层Cu和Mo;改变中间层的厚度对接头剪应力τ_xy的分布影响不大,但剪应力τ_xy值随着中间层厚度的增加有所降低,且降低幅度不大。综合利用反应自由能理论及扩散理论对C/C复合材料钎焊过程中界面处反应产物及反应层厚度进行了研究,建立了C/C复合材料/钎料/TC4（Cu）界面反应层成长动力学方程,确定了反应层成长的动力学参数,为预测连接接头的组织结构与机械性能提供理论依据。更多还原

【Abstract】 In the recent development of new materials, C/C composite has been considered to be an ideal high temperature material with potential application in aerospace field because of its low density, high thermal conductivity, high thermal shock and fatigue resistance, especially its high mechanical properties at high temperature. It has been successfully used as aircraft brakes materials, armour materials for the divertor and nozzle materials. The nozzle component made of C/C composite and TC4 can greatly decrease the weight and increase the efficient of rocket engine. In this paper, the interface reaction mechanism was analyzed, and the relationship between microstructures and mechanical properties was investigated when the C/C composite and TC4 were brazed with AgCuTi and TiZrNiCu （adding to interlayer） filler metals.The interface structure was C/C composite/TiC/TiCu/Ag（s.s）+Ti₃Cu₄+TiCu/ Ti₃Cu₄/TiCu/Ti₂Cu/Ti（s.s）+Ti₂Cu/TC4 with AgCuTi filler metal. The kinds of the reaction products were not changed but the thicknesses of the reaction layers were changed with different brazing parameters. With increased brazing temperature and bonding time, the thicknesses of the TiC/TiCu and Ti₃Cu₄/ TiCu/Ti₂Cu/Ti（s.s）+Ti₂Cu increased, while the Ag（s.s）+Ti₃Cu₄+TiCu in the middle of brazing seam decreased as well as the amount of TiCu+Ti₃Cu₄ decreased. When the brazing temperature was 1183K for 600s, the optimum shear strength was 25MPa. The shear strength decreased at other brazing parameters. The fracture surface analysis showed that the fracture location was related to the orientation of carbon fiber. When carbon fiber was parallel to the joined surface, the joints were fractured in the composites. When carbon fiber was vertical to the joined surface, the joints were fractured at TiC layer at low and middle brazing parameters and the joints were fractured at TiC layer or TiCu/Ti₂Cu interface at high brazing parameters.To release residual stress and increase the mechanical properties at high temperature, C/C composite and TC4 were brazed with TiZrNiCu filler metal and Cu/Mo composite interlayer. The interface structure was Cu/Cu+（51）Zr₁₄/Ti₂（Cu,Ni） +Ti（Cu,Ni）+TiCu+Cu₂TiZr/TiC/C/C composite at low brazing parameters. With the increased brazing parameter, TiCu and Cu₂TiZr disappeared, and Ti（Cu,Ni）2 appeared. The interface structure was Cu/Cu₅₁Zr₁₄/Ti₂（Cu,Ni）+Ti（Cu,Ni）+ Ti（Cu,Ni）2/TiC/C/C composite. At high brazing parameter, the interface structure was Cu/Cu₅₁Zr₁₄/Cu（s.s）+Ti（Cu,Ni）2/TiC/C/C composite. The thicknesses of Cu₅₁Zr₁₄ and TiC reaction layers increased with the increased brazing temperature and holding time. The maximum shear strength was 21MPa at room temperature and 27MPa at 923K when the brazing parameter was 1173K for 300s, which can meet the performance requirement. The shear strength gradually increased with the increased thickness of Cu, but the maximum shear strength was no more than 23MPa. The fracture surface analysis showed that the situation of fracture was related to the orientation of carbon fiber. When carbon fiber was parallel to the joined surface, the joints were fractured in the composites. When carbon fiber was vertical to the joined surface, the joints were fractured at TiC at low and middle brazing parameters and the joints were fractured at TiC and TiCu/Ti₂Cu interface at high brazing parameters.The distribution of residual stress of the C/C composite/TC4 brazed joint was simulated by FEM calculation. Combining the analyses of fracture, it was shown that the mechanical properties and fracture location were mainly related to the shear stressτ_xy. The shear stressτ_xy at the edge of the C/C composite/filler metal interface using AgCuTi filler metal was lower than that of TiZrNiCu filler metal. Using TiZrNiCu filler metal, the residual stress of the joint would be released with interlayers. The releasing the residual stress of Cu/Mo composite interlayer was better than that of Cu or Mo single interlayer. With the increased of thickness of interlayer, the distribution of shear stressτ_xy was not changed, but the shear stressτ_xy gradually decreased.Based on the Gibbs energies of formation and diffusion theory, the reaction phases and thickess of reaction layers were studied. The kinetic equations of C/C composite/filler metal/TC4 （or Cu） interface were set up. The kinetic equation parameters were achieved which can predict the microstructure and mechanical properties of the joint.更多还原