On the formation mechanism and microstructure-property relationships of diffusion-bonded joint of ZrC-SiC composite using Tix-Zr30-Tix sandwich interlayer

Constructing a nearly-homogeneous interface using Ti-Zr-Ti sandwich interlayer is a promising approach to enhance both the joint strength and reliability of ZrC-SiC composite, yet its formation mechanism remains unclear. Here, it is revealed that the interlayer rapidly transforms into a (Ti, Zr) solid solution, whose Ti/Zr ratio governs its reaction pathways with SiC, which can be predicted based on the Ti-Zr-Si and Ti-Zr-C phase diagrams. Increased Ti content promotes the formation of Ti₃Zr₃Si₃, thereby causing a high interfacial brittleness, and also aggravates the residual stress by increasing thermal expansion mismatch. However, Ti₃Zr₃Si₃ could react with the (Ti, Zr) phase and form Ti-Zr-Si liquid at ∼1350 °C, while the continuous extrusion of liquid at 1400 °C progressively extracted the dissolved Ti, enabling the (Ti, Zr) solid solution to transform into either a single ZrC_x layer (at 30.5 at.% and 56.9 at.% Ti) or a ZrC_x layer with dispersed (Ti, Zr)C_x stripes (at 72.5 at.% Ti). Through this transformation, residual stresses generated during joining are significantly alleviated, and controlling reaction-induced damage of the ZrC-SiC composite becomes crucial to joint performance. The joint efficiency is only ∼67% at a Ti content of 30.5 at.% or 72.5 at.% due to violent SiC decomposition, whereas it reaches 96% at 56.9 at.% Ti for the moderate reaction. These findings provide a theoretical foundation for the optimized design of nearly-homogeneous joints of ZrC-SiC composite, thereby broadening their application prospects in nuclear systems.