Interfacial reaction-enabled strengthening of Al 2 O 3f /Al 2 O 3 composite joints brazed via TiO 2 -modified Ag-Nb 2 O 5 fillers

Abstract Alumina fiber-reinforced alumina ceramic matrix composites (Al2O3f/Al2O3 CMCs) are strategic for extreme-environment applications, motivating the development of compatible joining methods. In this work, the reactive air brazing (RAB) of Al2O3f/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 with the TiO2 content increasing, while the Ag interlayer gradually becomes discontinuous. When brazed with Ag-4Nb2O5-2TiO2, the CMC/Al2O3 butt joint exhibits 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. 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 GH3536 alloy.