| Owing to its excellent mechanical properties,corrosion resistance,and thermal stability,Al2O3 ceramic is highly attractive for use in the aerospace,energy,optics,and automotive industries.TiAl alloy has successfully demonstrated its potential because of its high specific strength,good oxidation resistance,and excellent high-temperature mechanical properties.The development of reliable joining for Al2O3 ceramic and TiAl alloy is crucial to fabricate a nuclear reactor.However,there are difficulties in ceramic-metal joining due to the difference in physical and chemical compatibility between them and the wettability at Al2O3 surface.In this paper,the active brazing of TiAl alloy and Al2O3 ceramic using Ag-Cu-Ti filler metal was systemically studied.To further improve the joint property,low CTE TiB whiskers were synthesized in the brazing seam by adding B particles to the Ag-Cu-Ti brazing alloy to reduce residual stresses in the joint.The effects of brazing parameters and the the B and Ti content in brazing filler on the microstructure and mechanical properties of Al2O3/TiAl brazed joints were investigated.In addition,the formation mechanisms of brazing joint by using AgCuTi and AgCuTi+B filler alloy were discussed separately.The typical interface microstructure of the joints brazed using Ag-Cu-Ti brazing filler was Al2O3/Ti3（Cu,Al）3O/Ag（s.s）+Cu（s.s）+AlCu2Ti/AlCu2Ti+AlCuTi/TiAl.With the increase of brazing parameters,the dissolution of TiAl alloy was promoted,resulting in the thickening of Ti3（Cu,Al）3O reaction layer and the aggregation of AlCu2Ti phase.The shear strength first increased and then decreased with the brazing parameters and Ti content in filler alloy.The maximum shear strength was 102 MPa for the joints brazed with Ag-Cu eutectic+2wt.%TiH2 at 880°C for 10 min.When AgCuTi+B brazing filler was used in joining,Fine TiB whiskers were synthesized in the Ag matrix,acting as nucleation sites for the formation of fine Ti（Cu,Al）particles in the brazing seam.When the B content in the composite filler was increased,the microstructure of reinforced area became fine and homogeneous,but the the thickness of the Ti3（Cu,Al）3O reaction layer was reduced.The increase in brazing parameters promoted the dissolution of TiAl substrate,thus increasing both Ti and Al concentration in the liquid filler.However,TiAl dissolution was inhibited to a certain degree by the Ti content increase in brazing filler increase.The maximum shear strength of 148 MPa was realized for the joint brazed using Ag-Cu eutectic+2wt.%TiH2+0.5wt.%B composite filler at 900oC for 10 min.The optimal fracture path were initiated primarily in the Al2O3 substrate and partially propagated into the brazing seam. |
