Interfacial microstructure and shear performance of TiAl to Nb-Si alloy diffusion bonded with pure Ti interlayer

Diffusion bonding of high niobium beta-gamma TiAl (HNBG) to Nb-Si alloy was carried out using Ti foil as interlayer. The interfacial microstructural evolution, growth kinetics and mechanical properties of HNBG/Ti/Nb-Si joint were investigated in detail. The microstructure observations indicate that the interfacial microstructure of the joint was composed of beta-(Nb, Ti)5Si3, (Nb,Ti)ss//alpha-Ti, beta-Ti//alpha 2//beta/B2 from zone I to zone IV. The beta-Ti phase and alpha-Ti phase in zone II obey the orientation relationship, {110}beta || {0002}alpha and < 111 >beta|| < 11-20 >alpha. The gamma phase in HNBG alloy and beta/B2 phase in zone IV obey the orientation relationship, {111}gamma || {110}beta/B2 and < 110 >gamma || < 111 >beta/B2. The growth activation energies of beta-(Nb, Ti)5Si3 and beta/B2 phases were 166 kJ/mol and 507 kJ/mol respectively. The content of beta phase in zone II and the average grain size of alpha 2 phase in zone III increased with bonding temperature or bonding time. The shear test results showed that the ultimate shear strength was 385 MPa at 1000 degrees C-10 min-10 MPa. Fracture mainly occurred beween the interface of zone III and IV, and between the interface of zone IV and HNBG alloy. The fracture mode was mainly characterized by brittleness rupture along the phase boundaries of alpha 2 and beta/B2, beta/B2 and HNBG alloy with slight amount of cleavage fracture in zone IV.