Microstructure and mechanical properties of TiAl alloy joints vacuum brazed with Ti–Zr–Ni–Cu brazing powder without and with Mo additive

Abstract

Ti–43Al–9V–0.3Y (at.%) alloy was successfully vacuum brazed with Ti37.5–Zr37.5–Ni15–Cu10 (wt.%) brazing powders without and with Mo additive. The effects of brazing temperature and Mo content on the interfacial microstructure and mechanical properties of the TiAl brazed joints were investigated. The typical joint microstructure was primarily composed of three characteristic zones, and the reaction phases in the brazed joint were B2, α2-Ti3Al, α-Ti and γ-(Ti, Zr)2(Cu, Ni). With the increase of brazing temperature, Al concentration in γ matrix phase increased, and the γ matrix phase was gradually transformed into τ3 compound with an atom site substitution mechanism of Ti/Al exchange. The eutectoid transformation of β-Ti was inhibited because of the addition of Mo particles, which is beneficial to improve the bonding properties. The maximum shear strength of 218MPa was obtained when the joints brazed with Ti–Zr–Ni–Cu filler metal at 980°C for 20min; while it reached 250MPa with the addition of 6wt.% Mo. The elastic modulus (E) and hardness (H) of the reaction products were first determined by nano-indentations to reveal the correlations between the microstructure and shear strength of the brazed joints.