Characterization of microstructure and mechanical properties of Al2O3/TiAl joints vacuum-brazed with Ag-Cu-Ti + W composite filler

Al2O3 ceramic was successfully joined to TiAl alloy by active brazing using an Ag-Cu-Ti + W composite filler. The effects of brazing temperature, holding time, and W content on the microstructure and mechanical properties of the brazed joints were investigated. The typical interfacial structure of joints brazed at 880 °C for 10 min was: Al2O3/Ti3(Cu, Al)3O/W + Ag(s.s) + TiCu + dispersed AlCu2Ti/blocky AlCu2Ti + Ag(s.s)/AlCu2Ti layer + AlCuTi layer/TiAl alloy. By increasing the brazing temperature and holding time, the thickness of the Ti3(Cu, Al)3O reaction layer increased, and the blocky AlCu2Ti amount in the middle of the brazing seam aggregated and grew gradually. W particles added in the brazing seam could decrease the mismatch of coefficients of thermal expansion between the Al2O3 ceramic and brazing seam, thus relieving the residual stresses yielded in the ceramic substrate and improving the joint strength. The maximum shear strength reached 148 MPa when the joints were brazed with Ag-Cu-Ti + 20 wt. % W composite filler at 880 °C for 10 min. However, excessive W particles resulted in defects such as microcracks and micropores in the joint, leading to a reduction in shear strength.