Reaction control over wettability: Achieving robust joining of reaction‐bonded silicon carbide with a moderate‐temperature borosilicate glass

Abstract This study develops a moderate‐temperature (<1100°C) glass filler in the Al 2 O 3 ‐B 2 O 3 ‐SiO 2 system, modified with K 2 O/Li 2 O, for joining reaction‐bonded silicon carbide (RB‐SiC). The optimized composition (2.5 wt% Al 2 O 3 , B/Si = 1:2) achieves a coefficient of thermal expansion (CTE) of 3.25×10 −6 /K, closely matching that of RB‐SiC (ΔCTE < 0.05×10 −6 /K), and yields a superior shear strength of 44 MPa when joined at 900°C. Contrary to conventional wisdom, maximum joint strength was achieved not under conditions of optimal wettability (which occurred at higher temperatures) but where interfacial reactions were optimally controlled to prevent defect formation. Comprehensive characterization reveals the bonding mechanism: the in‐situ formation of a nanoscale interfacial layer comprising a silica‐rich region and alkali carbonates, facilitating strong covalent bonding between the glass and the substrate. This work demonstrates that controlling interfacial chemistry, rather than solely pursuing optimal wettability, is the key to developing robust glass‐to‐ceramic joints, offering a promising joining solution for high‐performance RB‐SiC components.