Interfacial microstructure and mechanical property of TC4 titanium alloy/316L stainless steel joint brazed with Ti-Zr-Cu-Ni-V amorphous filler metal

Abstract

Vacuum brazing of TC4 titanium alloy and 316 L stainless steel (SS) was conducted using Ti-Zr-Cu-Ni-V amorphous filler metal. The effect of brazing temperature and brazing time on the interfacial microstructure and mechanical property was investigated. The cross section of brazed joint could be divided into four distinctive reaction zones. The typical interfacial microstructure of the joint brazed at 930 °C/15 min was TC4 substrate/Widmanstätten/β-Ti + Ti2Cu/(Ti, Zr)2(Cu, Ni)/Ti(Cu, Ni)2 + TiFe/TiFe2 (high Cr)/α-(Fe, Cr) + τ/γ-(Fe, Ni) + σ/316 L SS matrix. Residual filler metal disappeared at 960 °C due to complete mutual diffusion between molten filler metal and base metal. The diffusion of Cu atoms from residual filler metal region into β-Ti region dominated the precipitation of Ti2Cu phase. A transition zone formed adjacent to 316 L SS matrix, which consisted of three reaction layers, i.e., TiFe2/α-(Fe, Cr) + τ/γ-(Fe, Ni) + σ. With the increase of brazing temperature and brazing time, the shear strength of brazed joints first increased and then decreased. The maximum shear strength of 70 MPa was obtained at 960 °C/25 min. Fracture analysis indicated that cracks initiated at the interface of (Ti(Cu, Ni)2 + TiFe)/TiFe2, and then propagated along the zone of TiFe2 and α-(Fe, Cr) + τ with cleavage and intergranular fracture pattern. The sectionalized morphology of fracture surface was resulted from the joint distortion and uneven load distribution within the joint clearance.