Interfacial reaction-enabled strengthening of Al₂O_3f/Al₂O₃ composite joints brazed via TiO₂-modified Ag–Nb₂O₅ fillers

Alumina fiber-reinforced alumina ceramic matrix composites (Al₂O_3f/Al₂O₃ CMCs) are strategic for extreme-environment applications, motivating the development of compatible joining methods. In this work, reactive air brazing (RAB) of Al₂O_3f/Al₂O₃ CMC using Ag–4Nb₂O₅–xTiO₂ (0 ≤ x ≤ 4, in mol%) fillers was performed, and the microstructure evolution, interfacial behavior, and mechanical properties of brazed joints were systematically investigated. The main interfacial reaction product evolves from AgNbO₃ to AlNbO₄ as the TiO₂ content increases, while the Ag interlayer gradually becomes discontinuous. When brazed with Ag–4Nb₂O₅−2TiO₂, the CMC/Al₂O₃ butt joint exhibits a higher average shear strength (45.3 MPa) among the joints tested, outperforming the CMC/CMC butt joint, CMC/CMC flat joint, and CMC/GH3536 butt joint, with shear strengths of 38.1, 7.6, and 27.7 MPa, respectively. The fracture behavior of these joints is governed by multiple factors, namely interfacial features (the AlNbO₄ reaction layer, interlocking structure, and pores) and elemental diffusion from the GH3536 alloy.