Microstructural characterization of brazing turbine blade by Cu-Ti filler metal alloy

Brazing of polycrystalline IN-738LC Ni-base super alloy is executed using Cu-Ti filler alloys. The study is specifically concerned with the evaluation of the microstructure of the bonding zone and its mechanical properties. The joints were bonded by furnace brazing. In an Ar atmosphere with three Cu-Ti filler alloys contained (28, 44, and 50% Ti wt.%) at constant brazing time 10 min. Light optical and scanning electron microscopy (SEM) provided by the energy dispersive spectrometer (EDS) were used to study the joint microstructure, while the reaction phases were identified by X-ray diffraction (XRD). The mechanical properties were evaluated by micro-hardness and single-shear experiments. The brazed joints showed continuous bonding, indicating good wetting. The CuNiTi intermetallic phase contiguous to the substrate was developed by interaction between the IN-738LC and the filler alloy, as a result of the conjunction of Ni from the liquefied surface of the base metal and the filler metals. The residual liquid reactions produced Cu3Ti, Cu4Ti, and Cu3Ti2 intermetallic phases. CuNiTi was detected as a bonding phase which is responsible about the bonding mechanism with all samples were brazed with the mentioned filler alloys. The bonds with 50 wt.% had an incessant interfacial morphology showing (517 Hv) and (172 MPa), result of micro-hardness and shear strength, respectively. The bonds with 28 wt.% Ti revealed a discontinuous interfacial morphology with (457 Hv) and (220 MPa), micro-hardness and shear strength, respectively. The fracture behavior was clarified by using SEM image and correlated to the microstructure features, where the sample that brazed using 50 wt.% Ti showed a cleavage appearance.