C / C Composite Active Brazing Joint Interface Structure And Connection Mechanism Study

Carbon-carbon (C/C) composites has been widely used in aerospace, aviation, chemical and other fields for its excellent performance such as high specific modulus and strength, good friction and wear properties. The widely use of C/C composite in high-tech filed inevitable requires the joining of carbon/carbon which is one of the key technologies in the engineering application of carbon/carbon.In this study,86wt.%Al+14wt.% Ti powder mixture was Used to braze C/C an TiZrNiCu was Used to braze C/C with Ti.By SEM,EDS, and XRD,the interfacial microstructure and the growing process of brazing joint were discussed.The wet abilites of Al-based with different content of Ti were tested in a specific contact area method.It revealed that the wettability of the sample came to the best when the content of Ti reached 14%。While the brazing filler metal was Al-14Ti foil,the microstructure of the joints was C/C composite/(Al4C3+TiC)/Al-Ti solid solution+TiAl3/(Al4C3+TiC)/C/C composite when brazing temperature was under1223 k. And when the temperature was or above 1323k, Al4C3 disappeared.With increasing of brazing temperature and soak time, the thickness of TiC increase.the join effect of the sample brazed at 1100℃for 10min was good,The strength got the level of practical applications up to 14.7 MPa.The thermodynamics and the kinetic of forming TiC and Al4C3 in C/C composite/Al-14Ti interface have been studied. The experiment shows that Al4C3 reaction layerswere formed after TiC layers.The whole joining process can be divided into two parts:the reaction layers forming and the formation of TiAl3 and Al-Ti solid solution.The SiC coating for C/C composite was produced by pack cementation technique,The SiC coating has favorable wettability with TiZrNiCu filler which helps the adherence of C/C composite to Ti.Microstructure study and XRD phase analysis indicate that the joints was C/C-SiC/(TiC+ZrC) /[Ti,Zr)2CuNi+CuZr+Ti-Zr solid solution]/a-Ti+Ti2(Cu, Ni)/Ti When the brazing temperature was 1150K for 5 min. And when the holding time was or above 20min,the reaction layers was content of TiC+Ti5Si3, the thickness of Ti2Cu+(Ti, Zr) Cu+β-Ti layer increase.The shear stress was tested to evaluate the mechanical property of the joints.The results showed the join effect of the sample brazed at 1150k×5min was good,The strength got the level of practical applications up to 15.3 MPa.And at this time,the fracture took place in the SiC coating adjacent to C/C composites.The whole joining process can be divided into 3 steps:(1) partial melting of filler metal; (2) whole melting of filler metal, atoms diffusion and the formation of reaction layers and reaction phase; (3) Freezing of reaction layers and reaction phase, the formation of solid solution.