Diffusion bonding behaviour of β-γ TiAl alloys containing high niobium with Ti interlayer by spark plasma sintering

Abstract

High niobium β-γ TiAl alloy (HNBG) was diffusion bonded using spark plasma sintering with pure Ti as interlayer. The joint microstructural evolution, growth kinetics and mechanical properties were investigated. The joint included three diffusion zones. The β/B2 phase formed in the Zone I, α2 phase in the Zone II, and β-Ti and α-Ti phases in the Zone III. The thickness of β/B2 phase, the average grain size of α2 phase and the amount of β-Ti phase increased with the increase of bonding temperature or bonding time. The growth activation energies of β/B2 and α2 phases were 582 and 253 kJ/mol, respectively. The joint acquired at 1000 °C, 10 min and 10 MPa showed the maximum shear strength of 308 MPa. Fracture mainly occurred along the interfaces between Zone I and HNBG alloy, and between Zone I and Zone II. Fracture mechanism of the joint was characterized by brittleness rupture along the phase boundary.