Microstructure and mechanical properties of C/C composites/Ni superalloy dissimilar brazed joint for high-temperature applications

In this paper, the brazing of high-reliability C/C composite-metal joints for high-temperature application was studied. The surface of C/C composites was modified by the Cr metallization process and then brazed to Ni-based superalloy by AgPd braze. Alumina block was used as interlayer, and a zig-zag interfacial structure was constructed at the composites/braze interface. The results show that, after the metallization process, a strong adhesion reaction layer consisting of Cr carbides was coated on the C/C surface which in turn obviously improved the wettability of braze. The molted braze filled completely into the laser-machined holes in the C/C substrate and well-bonded interfaces and a homogeneous Ag(Pd) solution microstructure were obtained in the joint. The strength of the joint with C/C metalized at 1100 degree celsius is higher than that of the joint with 1300 degree celsius. The joints exhibit very high bending strength of up to 82 MPa and shear strength of up to 54 MPa, respectively. The braze spikes increase the connection area and provide a strong pinning effect.