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

Abstract

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.