Microstructure and mechanical properties of high niobium β-γ TiAl and IN718 alloy joints diffusion bonded by spark plasma sintering

Abstract

High niobium β-γ TiAl alloy(HNBG) was diffusion bonded with Ni-based superalloy (IN718) from 800 to 900 °C for 20 min under the pressure of 10 MPa by spark plasma sintering. The joint phase composition, growth kinetics and shear mechanical properties were investigated detailedly. The phase sequence was HNBG//β/B2, τ3-NiAl3Ti2//τ3-NiAl3Ti2//τ4-Ni2AlTi, σ-FeCr//Cr/Fe/Nb rich η-Ni3Ti, α-Cr, Cr rich γ-Ni/γ′-Ni3(Al, Ti)//IN718 in the joint. The growth activation energies of diffusion zones on the IN718 side were lower than that on the HNBG side. The molecular dynamics result showed that the dislocation density increased with bonding temperature on the IN718 side. The nano-indentation test results showed that the phases in the diffusion zones II and IV had relatively high hardness. The ultimate shear strength of 257 MPa was achieved at 850 °C. Fracture mainly occurred along the interface between diffusion zones III and IV with bonding temperature lower than 900 °C, while mainly occurred in the diffusion zone II at 900 °C. The shear failure mechanism of the joint was brittleness fracture along the phase interface and brittleness transcrystalline fracture. Finally, the formation mechanism of HNBG/IN718 joint was analysed.