Cu foil-assisted interface design in vacuum brazing of C/C composites and TZM alloy using CoCrFeNiCu high-entropy alloy: Microstructure, properties, and mechanism

High-entropy alloys (HEAs) show great potential for high-temperature brazing in nuclear energy applications due to their multi-principal-element design and thermal stability. However, conventional HEA fillers suffer from high melting temperatures and poor metallurgical compatibility with TZM and C/C composites. Here, a Cu foil-assisted interface design using a phase-separating CoCrFeNiCu HEA filler was proposed to achieve reliable joining between C/C composites and TZM alloys. The Cu foils significantly reduced the brazing temperature, increased the liquid-phase fraction, and improved wettability, thereby enhancing interfacial bonding. The optimized joint exhibited a TZM/ μ-M₇Mo₆/ FCC + Cu(s, s)/ M₇C₃/ C/C microstructure. Crack propagation strongly depended on the thickness of the M₇C₃ reaction layer. An optimal balance between interfacial reaction and residual stress was achieved at 1200 °C for 15 min, yielding a maximum shear strength of 36.5 MPa. This study provides a feasible strategy for designing high-reliability joints between C/C composites and TZM alloys using HEA-based fillers.