Brazing Process And Bondingmechanism For Brazing C_f/SiC Composite And Nb-1Zr Alloy

Cf/Si C composite material with its characteristics of high temperature resistance and low density has important application in the field of aerospace and astronautics. Nb-1Zr alloy with its good resistance to high temperature and the plastic processability become important candidate materials in the field of space. So the Cf/Si C composite material and Nb-1Zr alloy’s welding problem are in urgent need of solution. This paper adopts Ti Co Nb solder to achieve the connection of Cf/Si C composites and Nb-1Zr alloy. Then, the effect of the brazing parameters、composition and thickness of filler alloy on the microstructure and properties of joint were investigated. We also try to find the relationship between microstructure and mechanical properties and explore the design of composite solder. Futher more, thermo dynamics and reaction dynamics of the joint were discussed in the processing of soldering.A reliable joint can be obtained between the Cf/Si C composites and the Nb-1Zr alloy by using the Ti Co Nb solder. On the interface between Cf/Si C and Ti Co Nb solder generates a(Ti,Nb)C interfacial reaction layer. On the surface of interfacial reaction layer generates another(Ti,Nb)2Co and Ti Si layer. And the weld center area is filled by Nb(s,s)、Co(s,s) and Co Nb4 Si compounds. So the interface structure of joint is: Cf/Si C composites /(Ti,Nb)C/(Ti,Nb)2Co+Ti Si/Ti Co+Nb(s,s)+Co Nb4 Si /Nb-1Zr alloy.Study on the Ti Co Nb solder shows that: with the increase of the Nb component of solder, the silicon compounds in the solder increase, which lead to the joint strength gradually reduce; When solder layer ’s thickness increase, the total active elements in solder is increasing, so the interface reaction layer on the surface of composite is thickening, and the weld width also increases, so the joint strength showed a trend of decrease after the first increase. Study on brazing process parameters: With the increase of brazing temperature and holding time, the thickness of interfacial reaction layer increases too; Solder’s ability of caulking and liquidity is enhanced, the solder’s filling into the ceramic also enhanced, welding line become more thin; At the same time, the number of silicon compounds formed in the weld gradually increased; The Joint strength first increases then decreases.In this paper, the best parameters in brazing the Cf/Si C composites and Nb – 1Zr alloy by using the Ti Co Nb solder were:solder composition is Ti45Co45Nb10(at.%), solder layer thickness is 600μm, brazing temperature is 1280 ℃, holding time is 10 min. The maxmiun shear strength at room temperature up to 242.6 MPa, high temperature resistance of joint shear strength were also tested, the shear strength under 800℃ and 1000℃ were 201.7 MPa and 134.7 MPa.Carbon fiber composite solde which was made by Melting alloy way can realize the connection between Cf/Si C composites and Nb-1Zr alloys, But the carbon fiber and filler metals actice elements react with each other in the brazing process, so this affected the formation of the interface reaction layer between Cf/Si C composite and solder, The joint strength then decreased obviously, In the heat preservation time,, The maximum shear strength of the joint was 57.2 MPa at 1320 ℃ for 10 min.The connection mechanism between Cf/Si C composites and Nb-1Zr alloys by using Ti Co Nb solder is: Under the brazing temperature, solder begin to melt, Ti, Nb elements react with Cf/Si C and generate the Ti C and Nb C interface layer and release Si element at the same time, Then the Ti near the interfacial reaction layer react with Si element and generate Ti Si phase, at the same time the Ti, Nb and Co near the interface layer of formate(Ti,Nb)2Co, two kinds of reaction products both attach to the interface reaction layer and form a new reaction layer, the rest of Si element diffused into the center of weld area and reacted with part of the Co(s, s) and Nb(s, s) to form Co Nb4 Si compounds, the rest of Ti Co and Nb(s, s) together with the Co Nb4 Si compounds form the center area of the weld joint.