Microstructure and mechanical properties of TiAl/Ni-based superalloy joints vacuum brazed with Ti-Zr-Fe-Cu-Ni-Co-Mo filler metal

For the purpose of elevated temperature service and weight reduction in aerospace vehicle applications, a novel Ti-Zr-Fe-Cu-Ni-Co-Mo filler metal was employed to join TiAl to Ni-based superalloy (GH536). The effects of brazing temperature on interfacial microstructure and chemical composition of the joints were analyzed. The representative joint microstructure from TiAl substrate to GH536 substrate was primarily composed of four characteristic layers in order: B-2; Al3NiTi2; AlNi2Ti containing Cr-rich (Cr, Ni, Fe)(ss)(subscript ss represents solid solution), Ni-rich (Ni, Cr, Fe)(ss)and TiNi3; Cr-rich (Cr, Ni, Fe)(ss)containing AlNi2Ti, Ni-rich (Ni, Cr, Fe)(ss)and TiNi3. Layer IV has the majority of the brazing seam, while Layer II was the thinnest. And the thickness of Layer II was not affected by brazing temperature. With the increase in brazing temperature in the range of 1110-1170 degrees C, both the shear strength and the thickness of brazing seam firstly increased and then decreased. The joint performance was jointly controlled by the thickness of brazing seam, the amounts of microcracks and intermetallic compounds formed in brazing seam. The maximum shear strength of 183 MPa at room temperature was obtained together with a peak thickness when the joint was brazed at 1150 degrees C for 10 min and the shear fracture mainly occurred in the thinnest Layer II Al3NiTi2.