Microstructure and performance of graphite/TZM alloy joints with different interfacial structures formed by vacuum diffusion bonding

Abstract Dissimilar joints of graphite and TZM alloys were obtained via vacuum diffusion bonding with a Zr interlayer. The influence of interfacial structure on the microstructure and mechanical properties of graphite/TZM alloy joints were investigated. The microstructure and compositions on the interface were observed and analyzed, and the tensile shear strength of the joints were evaluated. The interfacial morphologies showed good metallurgical combination with no apparent defects. A transition layer with a width of approximately 200 μm was formed. The interface products were squeezed into triangular grooves in the graphite, forming a serrated structure in the joint with a triangular groove structure. The microstructures in the transition layer were Mo2Zr, ZrC and solid solution. Some eutectic penetrated into the porous graphite pores of the adjacent graphite matrix, forming an island-like morphology. The welding mechanism was consistent with transient liquid phase bonding. The interfacial shear strength of the joint with a triangular groove structure could reach 38 MPa, which was higher than that of graphite. Fracture occurred partly in the graphite and partly in the transition layer. The serrated structure between the graphite and the transition layer effectively improved the bonding strength.