Vacuum-furnace brazing of C103 and Ti–6Al–4V with Ti–15Cu–15Ni filler-metal

Abstract

C103 and Ti–6Al–4V alloys joined by vacuum-furnace brazing using Ti–15Cu–15Ni (wt.%) commercial filler-metal was investigated. This study examines how brazing conditions affect the microstructural evolution and shear strength of the C103/TiCuNi/Ti–6Al–4V joint. According to the microstructural observations, all the characteristic structures of the joint interface can be classified into seven categories, based on their morphology and chemical composition. The microstructural morphology of each characteristic zone depends on the brazing time and the brazing temperature. Excessive increasing the brazing time and the brazing temperature form the coarse acicular Widmanstätten structure in front of Ti–6Al–4V parent-metal and cause grain growth of Ti–6Al–4V alloy. However, if the brazing time is too short or the brazing temperature is too low, the continuous intermetallic-layer consisting of intermetallic compounds, such as Ti2(Cu, Ni) and Ti2(Ni, Cu), will remain in the brazed joints after brazing. Additionally, during brazing, the diffusion of molten liquid filler-metal and the dilution of parent-metals cause the composition of the filler-metal to deviate from the Ti–Cu–Ni eutectic into the hypoeutectic or hypereutectoid. Therefore, the joint interface is anticipated to be comprised mostly of eutectic and/or eutectoid structures. The fine hypoeutectic and hypereutectoid structures consisting of α-Ti, Ti2(Ni, Cu) and Ti2(Cu, Ni) are observed in the joint interface brazed at 960°C for 15min. The maximum shear strength reaches 354MPa under this brazing condition. Further increasing the brazing time and/or raising the brazing temperature cause excessive growth of the Widmanstätten structure and the grain of Ti–6Al–4V alloy, which significantly deteriorate the shear strength of joint. The high temperature shear strength of the C103/TiCuNi/Ti–6Al–4V joint was investigated to evaluate its limit service temperature. Moreover, the overlap-length and the joint clearance investigations are also conducted to realize the relations between different brazing conditions and the joint performance.