Tailoring an Al-Co-Cr-Fe-Ni-W High-Entropy Alloy for High-Temperature Ceramic Joining through Thermodynamic Design

High-Entropy Alloys (HEAs) are promising candidates for high-temperature joining processes, yet their behaviour in the molten state, i.e., wetting, remains poorly understood. In this work, a specific HEA composition (Al_0.15CoCrFeNiW_0.15, called HEA-6) previously designed via CALPHAD thermodynamic modelling, was tested as a brazing filler for the joining of C- and SiC-based materials. Sessile drop experiments at 1500°C showed good wetting on glassy carbon (GC), SiC, and C_f/SiC composites, but also revealed extensive dissolution and interfacial reactivity that compromise its applicability. Guided by thermodynamic predictions performed using the in-house-built GHEA database, a modified HEA containing 40 at. % Si (HEA-Si) was developed to suppress substrate dissolution. The HEA-Si alloy exhibited excellent wetting with minimal interfacial degradation, enabling successful fabrication of SiC–SiC and C_f/SiC–C_f/SiC joints. Shear testing revealed failure in the SiC substrate for SiC–SiC joints and in the brazed region with partial composite delamination for C_f/SiC–C_f/SiC joints. These findings demonstrate that CALPHAD calculations are an effective tool in tuning the composition of HEAs to produce effective brazing fillers for advanced ceramic systems.