Microstructure and brazing mechanism of TiAl/Ni-based superalloy joints using Ti-Zr-Cu-Ni-Co-Mo-B filler metal with different cooling rates

Abstract

For the purpose of elevated temperature service and weight reduction in aerospace vehicle applications, a novel Ti-Zr-Cu-Ni-Co-Mo-B filler metal was employed to join TiAl to Ni-based superalloy (GH536). The effect of cooling rate on interfacial microstructure of the joints were analysed by scanning electron microscope and energy dispersive X-ray spectrometer. The representative joint microstructure was primarily composed of six characteristic layers, including TiAl substrate / B2 / τ3 (Al3NiTi2) / τ4 (AlNi2Ti) / Cr-rich (Cr, Ni, Fe)ss, τ4 (AlNi2Ti), Ni-rich (Cr, Ni, Fe)ss and TiNi3) / GH536 substrate. With the decrease of cooling rate in the range of furnace cooling-5 °C/min, the joint shear strength firstly increased and then decreased. The joint brazed at 1170 °C for 10 min and cooling to 870 °C with 10 °C/min obtained the maximum shear strength of 252 MPa and the shear fracture mainly occurred in τ3 phase area.