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

摘要

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 B_2, α_2-Ti_3Al, α-Ti and γ-(Ti, Zr)_2(Cu, Ni). With the increase of brazing temperature, Al concentration in 7 matrix phase increased, and the 7 matrix phase was gradually transformed into t_3 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 218 MPa was obtained when the joints brazed with Ti-Zr-Ni-Cu filler metal at 980 ℃ for 20 min; while it reached 250 MPa with the addition of 6 wt.% 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.