Vacuum brazing of TiAl based alloy with Ti-Mn-Fe-Ni-Co-V system filler metal

Regarding the metallurgical considerations and the melting points of Ti-Mn-Fe eutectic alloy and Ni-Co-V ternary alloy, a Ti-Mn-Fe-Ni-Co-V senary system filler metal was proposed for joining TiAl-based alloy. The senary filler alloy consisted of TiFe, TiMn and Ti-based solid solution phases. It exhibited the liquidus temperatures of 1110.8 ℃ and a contact angle of 37° on TiAl alloy after heating at 1110 ℃ for 10 min. The brazed joint was composed of B2, γ-TiAl and α₂-Ti₃Al as well as residual brazing filler reaction phase. With increasing brazing temperature or prolonging dwell time, joint thickness and γ-TiAl phase volume fraction increased. The brazing condition of 1180 ℃/45 min gave the γ-TiAl phase content of 21.6 vol. % within the joint and the joint thickness of 270 μm, and the maximum joint tensile strength reached 488 MPa at ambient temperature, with the joint strength coefficient of 82.7%. The joints offered tensile strength of 521 MPa at 700 ℃ and 498 MPa at 800 ℃, corresponding to the joint strength coefficient of 85.1% and 96.3%, respectively. In this case, the joint fractured at the brazing seam with a flexural morphology, leading to the improvement of joint strength. The typical composition within the joint was characterized by 0.47−2.09 at.% Fe, 1.15−2.11 at.% Mn, 0.08−0.59 at.% Ni, 0.03−0.25 at.% Co and 0.15−0.35 at.% V, and these alloying elements had a positive strengthening effect on the brazed joint.