Microstructure and mechanical properties of Al₂O₃ ceramic and Ti₂AlNb alloy joints brazed with Al₂O₃ particles reinforced Ag–Cu filler metal

This study focuses on the brazing of Al₂O₃ ceramic to Ti₂AlNb alloy using composite filler metal (AgCu28 modified with micron-scale Al₂O₃ particles). The effect of Al₂O₃ particles concentration on the microstructure and mechanical properties of Al₂O₃/Ti₂AlNb joint were investigated. Ti₃(Cu, Al)₃O has been identified as the main product of the reactions at the alumina–brazing alloy interface. The addition of Al₂O₃ particles significantly reduced the mismatch of coefficients of thermal expansion between Al₂O₃ ceramic and Ti₂AlNb alloy substrates, relieving the residual stresses of the joint. Nevertheless, a high concentration of Al₂O₃ particles led to excessive Ti₃Cu₃O phase exhibiting high elasticity modulus surrounded Al₂O₃ particles which impaired the plastic deformation ability of the brazing beam, thus, decreased the joint strength. The maximum shear strength of 110.49 MPa was achieved when the joint was brazed at 880 °C for 10 min using AgCu28 + 2 wt % Al₂O₃ particles filler metal. The fracture morphology revealed that the cracks initiated in the brazing seam, and mainly indicating the propagation of cracks occurred in the Al₂O₃ ceramic substrate.