Heat-resistant heterogeneous joints strengthened by cost-effective 3D network graphene

Using ductile Cu interlayers is a well-established strategy for stress relaxation in ceramic/metal dissimilar joining, enabling the fabrication of mechanically robust joints at room temperature. However, the mechanical performance of such joints with pure Cu interlayers degrades drastically at elevated temperatures. In this work, we fabricated a three-dimensional network graphene (3DNG)-reinforced Cu interlayer through a cost-effective route combining powder metallurgy and an induction-assisted method using solid sucrose as the carbon source. The obtained 3DNG was continuously distributed along Cu grain boundaries and formed atomic-scale bonding with the Cu matrix. More importantly, the 3DNG embedded in the Cu interlayer maintained its intact three-dimensional network structure after the brazing process. Consequently, the Ti₃SiC₂/Nb dissimilar joints brazed with the 3DNG-reinforced Cu interlayer achieved a shear strength of 157 MPa at 700 °C, which is nearly 70% higher than that of joints brazed with pure Cu interlayers. Electron backscatter diffraction (EBSD) characterization revealed that the sp²-hybridized structure of 3DNG served as an effective physical barrier, refining Cu grains from ∼36 μm to ∼1 μm during the thermal cycling inherent to the brazing process. The synergistic strengthening mechanisms underlying the performance enhancement of these dissimilar joints are systematically proposed and discussed. This work provides new insights into the high-temperature performance optimization of ceramic/metal dissimilar joints, and offers a facile and viable strategy for their reliable service in harsh thermal environments.