Induction Brazing of γ-TiAl to Alloy Steel AISI 4140 Using Filler Metal of Eutectic Ag-Cu Alloy Coated with Ti Film

Abstract

The induction brazing of TiAl to alloy steel AISI 4140 was carried out using a filler metal of eutectic Ag-Cu alloy coated with Ti film. The brazement was comprised of Ag-rich, Ti-rich, CuTi and CuTi2 phases at a brazing temperature of 1073 K. Two reaction layers, AlCuTi and AlCu2Ti phases, were observed between the filler metal and TiAl. The consumption of Cu to form these intermetallic compounds during brazing resulted in the increasing amount of Ag-rich and Ti-rich phases in the brazement with increasing the brazing temperature and time. The maximum tensile strength of the joints, 294 MPa, was achieved at 1073 K for 60 s, which was 71% of that of the TiAl base metal. The mechanical strength of the joint decreased with increasing the brazing temperature and time due to the growth of brittle reaction products at the interface. The fracture mode of the specimen brazed at 1073 K for 60 s was a mixed mode, consisting of 16% TiAl base metal fracture and 84% interface fracture through the AlCu2Ti and AlCuTi phases. However, the fracture location shifted toward the interfacial reaction layers with increasing the bonding temperature and time.