Study On Technology And Mechanism Of Brazing C/SiC Composite To Niobium

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.