Improving bonding strength and reliability of brazed titanium/copper dissimilar joint using vanadium interlayer

Abstract

Abstract Conventional practice of brazing titanium (Ti) to copper (Cu) using Ag-28Cu eutectic filler alloy is of limited success because of the generation of brittle Ti-Cu intermetallic compounds (IMCs). The bonding strength is unsatisfactory owing to embrittlement of IMCs, and it is difficult to reproduce the bonding strength as the joint microstructure is highly sensitive to brazing parameters. In the current study, it was demonstrated that the formation of such undesirable IMCs can be suppressed and strong Ti/Cu joint can be obtained by brazing at 850 °C using a refractory vanadium (V) interlayer 15 μm in thickness deposited on Ti substrate, in combination with an Ag-Cu-Ti active filler alloy. The V interlayer successfully blocked the interaction between Ti and filler alloy. Bonding mechanisms of the resultant joint can be deduced to be a synergy of active brazing in the V/Ag-Cu-Ti/Cu half and solid-state diffusion bonding at the Ti/V interface. The thus developed joint was comprised of continuous Ti-V solid solution, unconsumed V interlayer and remaining filler alloy. Attributed to elimination of brittle IMCs at joint interface, excellent bonding strength of ∼220 MPa which is comparable with strength of Cu base metal was achieved. Moreover, since the joint evolution was dominated by sluggish solid-state diffusion at the Ti/V interface and very limited erosion of V interlayer by the Ag-Cu-Ti filler, desirable IMC free joint can be obtained over a wide range of brazing time (2 ∼ 5 min), enabling outstanding reliability of the high bonding strength.