In-situ transition zone supported bonding mechanisms and micromechanical assessment of IN718 LDED on C/SiC
Description
C/SiC ceramic matrix composites offer low density and excellent high-temperature stability, but reliable joining and repair remain challenging. In this study, powder-fed laser directed energy deposition (LDED) was used to fabricate a load-bearing IN718 layer directly on C/SiC, and the interfacial formation and load-transfer mechanisms were investigated. The deposition process showed a threshold-like start-up behavior: the first layer mainly induced preferential substrate ablation with limited metal attachment, while repeated remelting and resolidification enabled stable, continuous build-up. A continuous transition zone (TZ) formed between IN718 and C/SiC. Atomic-scale TEM revealed a mixed interfacial architecture, including metallurgically continuous metal–metal bonding and metal–carbon coupled interfaces on the IN718/TZ side, as well as metal–carbon coupling on the C/SiC/TZ side. Interfacial dislocations helped accommodate mismatch strain. Nanoindentation mapping showed a gradual transition in hardness and elastic modulus from IN718 to TZ to C/SiC, with strong fluctuations within the multiphase TZ. In situ micro-cantilever bending revealed different failure modes: abrupt rupture at the IN718/TZ interface and cohesive failure within the TZ near the C/SiC side. Overall, bonding arises from mechanical interlocking, reaction-assisted chemical bonding, and remelting-enhanced fusion bonding.