Microstructure and mechanical properties of ZrB2-SiC/Nb joints brazed with CoFeNiCrCuTix high-entropy alloy filler

ZrB₂-SiC ceramics and Nb alloy were brazed at 1160°C for 60 min with CoFeNiCrCuTi_x high-entropy alloy filler. The influence of Ti content on the interface structure and mechanical properties of ZrB₂-SiC/Nb joint was systematically studied. It is found that the rich-Ti Laves phase was formed due to the addition of large atomic size Ti fill into the filler alloy or brazing joint, and its content increases with Ti content. The joint brazed by high-entropy alloys filler without Ti can be divided into a tooth-shaped Cr₂B reaction layer and a central area composed of a eutectic mixed structure of FCC phase and rich-Nb lamellar Laves phase. Ti and Nb are mutual solid solution elements. The increase of Ti content in the joint makes the FCC phase and the rich-Nb lamellar Laves phase to transform into a big bulk Ti-rich Laves phase and the quadrilateral (Ti, Nb)B phase. The tooth-shaped Cr₂B was disappeared. The residual stress generated in the joint during the brazing process tends to cause defects such as holes and microcracks in the bulk Ti-rich brittle Laves phase. Therefore, with the addition of Ti, the normal temperature performance of the joint decreases from 216 MPa to 52 MPa. However, with the increase of Ti, the high-temperature mechanical properties of the joint first decrease, and then increase. It was mainly due to the formation of rich-Ti Laves phase and quadrilateral (Ti, Nb)B with excellent high-temperature mechanical properties. When brazing with CoFeNiCrCuTi_1.5 filler, the high-temperature performance of the joint reached 92% of its room temperature performance.