Vacuum brazing of TiAl to 42CrMo steel with Ag-Cu-Ti filler metal

Vacuum brazing of TiAl to 42CrMo steel was carried out at 860 - 1 000 degrees C for 5 min using Ag-33Cu-4.5Ti (mass fraction, %) filler metal. Formation phases and microstructures of the joints were investigated by SEM and EPMA. The strength of the joints were evaluated by means of tensile tests. The results show that five interfacial formation phases occur in the brazing seam: AlCuTi and AlCu2Ti compounds, Ag solid solution, Ag-Cu eutectic phase and the reaction layer of TiC adjacent to the steel. The tensile strength of the brazed joints changes with the chang of brazing temperature. When the brazing temperature is 900 V, the tensile strength of the joint is 347 MPa. TiAl turbine and 42CrMo steel shaft was brazed and the strength of TiAl/42CrMo turbine rotor was evaluated by means of tensile test, when the tensile load reached 100 kN the joint of the rotor kept well.