Pulse current diffusion bonding of high niobium β-γ TiAl alloy to IN718 superalloy by introducing pure Ni interlayer

Abstract

High niobium β-γ TiAl alloy (HNBG) was pulse current diffusion bonded to Ni-based superalloy (IN718) by introducing Ni foil as an interlayer using spark plasma sintering (SPS). Typical microstructure characteristics and mechanical properties of HNBG/Ni/IN718 joint were investigated in detail. The effects of bonding parameters and Ni interlayer on microstructure and mechanical properties were revealed, and the diffusion bonding mechanism of HNBG/Ni/IN718 joint was elaborated. The phase composition sequence from IN178 superalloy to HNBG alloy was IN718//γ-Ni//γ′-Ni3(Al, Ti)//τ4-Ni2AlTi//τ3-NiAl3Ti2//β/B2 + τ3-NiAl3Ti2//HNBG. The Kirkendall voids and interfaces gradually disappeared with increasing bonding temperature, time and pressure. The maximum shear strength of 346 MPa was achieved at 850°C × 20 min × 20 MPa. The introduction of Ni interlayer significantly improved the elemental distribution and microstructure, which enhanced shear strength of HNBG/Ni/IN718 joint by 34.6 % compared to that of the joint without any interlayers. Shear fracture mainly occurred in γ′ diffusion layer, and fracture mode was brittleness transcrystalline fracture when the bonding temperature was lower than 850 °C. As the temperature increased, fracture mainly occurred in τ3 diffusion layer, and the fracture mode was cleavage fracture.