Microstructure and mechanical properties of the C/C composites and Nb joints brazed with CoCrFeNi HEAs

A robust brazing of C/C composites and Nb was achieved using CoCrFeNi high-entropy alloys (HEAs) with complete FCC structure. The effects of brazing temperature and holding time on microstructural evolution and mechanical properties of joints were evaluated. The filler infiltrated into the pores of the C/C composites and formed a mixture of FCC and carbides, expanding the bonding areas and interlocking the interface. Moreover, a lamellar eutectic structure composed of FCC and Laves formed in situ near Nb side, providing unique high-temperature performance. The optimal average shear strength of 29.1 MPa at room temperature and 23.6 MPa at 800 °C were obtained at 1260 °C for 10 min. The joining and fracture mechanism of brazed joints were also revealed.