Joining PIP-SiC_f/SiC composite to Co-base superalloy using a compositionally tuned Cu-Ni-Ti filler for balanced reactivity and high-temperature reliability

In advanced nuclear energy systems, structural materials must withstand extreme temperatures and irradiation environments. SiC_f/SiC composites are promising candidates for critical components such as heat exchangers owing to their low density, high thermal conductivity, and excellent radiation resistance. However, joining them with Co-base superalloys is a major challenge, as it often leads to interfacial reactions, thermal stresses, and degradation of their intrinsic thermal and radiation properties. To address these challenges, a compositionally tuned Cu-xNi-10Ti filler was designed, in which Ni content served as a key variable to balance interfacial reactivity and high-temperature reliability. The effects of Ni content on non-equilibrium solidification, microstructural evolution, and joint performance were systematically investigated. It was found that increasing Ni content suppressed the elemental interdiffusion, while excessive Ni enrichment promoted SiC_f/SiC decomposition and brittle silicide formation. The reaction layer at the SiC_f/SiC-seam interface consisted of a TiC_0.5+Ni-Ti-Si reaction layer and an adjacent infiltration zone, which was the weakest region. In essence, the joint strength was governed by both the copper content in the seam and the thickness of the infiltration region. Consequently, the optimized joint exhibited a room-temperature shear strength of 88 MPa and a high-temperature shear strength of 50 MPa, while maintaining good heat-transfer performance. This work provides a foundation for joining ceramic composites to superalloys in nuclear systems by controlling reactions through filler composition.