Microstructure and mechanical properties of Al2O3/TiAl joints brazed with B powders reinforced Ag-Cu-Ti based composite fillers

Abstract In this manuscript, Al 2 O 3 ceramic and TiAl alloy were brazed with Ag-Cu-Ti based composite fillers containing B powder additive. The effects of B content, Ti content, and the brazing temperature on the microstructure and mechanical properties of the brazed joints were investigated. The typical interfacial microstructure of the brazed joint was: Al 2 O 3 /Ti 3 (Cu, Al) 3 O/Ag(s.s)+TiB+Ti(Cu, Al)+fine AlCu 2 Ti/blocky AlCu 2 Ti+AlCuTi/TiAl. TiB whiskers synthesized in situ by the reaction of the B additive with Ti, served as nucleation sites for the formation of fine Ti(Cu, Al) and AlCu 2 Ti grains and improved the bonding properties. With increasing B content, more fine-grains were formed in the brazing seam and the thickness of the Ti 3 (Cu, Al) 3 O reaction layer adjacent to the Al 2 O 3 ceramic decreased. Brazing parameters also influenced the joint microstructure. Growth of Ti 3 (Cu, Al) 3 O layer and AlCu 2 Ti formed with increase in brazing temperature. Moreover, the formation of dispersed fine-grains in the brazing seam depended largely on the initial Ti content in the composite filler. With increase in initial Ti content, the TiB-reinforced area was broadened while the blocky AlCu 2 Ti content decreased gradually. The maximum shear strength of Al 2 O 3 /TiAl joint brazed with B-reinforced composite filler was 148 MPa, which was 246% higher than that brazed without B addition. The joint shear strength was determined by the combined influences of the thermal expansion mismatch between the joined materials, the thickness of the Ti 3 (Cu, Al) 3 O layer, and the presence of defects in the joints.