Brazing graphite to Hastelloy N superalloy using pure Au foil

Pure Au foil was used to braze graphite and Hastelloy N alloy at 1 333 K with different holding time (1~90 min), and the effect of holding time on the microstructure and mechanical propertithe of welding joints was researched. The results showed that the brazing seam basically consists of Au (s.s), Ni (s.s) and the Mo₂C particles scattered in brazing seam. Mo₂C and Mo6Ni6C particles were precipitated in the grains and at the grain boundary of Hastelloy N alloy near the brazing seam. With the holding time increasing to 60 min, the joint average shear strength changed little with the extension of holding time. When the holding time is 90 min, due to the precipitation of Mo₂C and Mo₆Ni₆C particles in the grains and at the grain boundaries in the Hastelloy N beside the brazing seam, the particles constituted the material which liked the metal matrix composite. It is the reason why joint strength reached maximum 34.1 MPa which similar to the strength of the graphite substrates. The thermal expansion coefficient gradient transition structure that formed in the joint after brazing resulted in low stress level in the joint and high quality joint was obtained. The performed investigation will provide necessary technical support for the construction of molten salt reactor.