The effect of brass interlayer applied as foil and thermal spray coat on microstructure and mechanical properties of transient liquid phase bonding of Al alloy to Ti alloy

Thermal spraying is economical and rapid coating process that creates a rough and clean surface. As a result it can be used for applying the interlayer in transient liquid phase bonding. In the present study, transient liquid phase bonding Al 2024 to Ti-6Al-4V was investigated using brass interlayer, where the interlayer was Cu-Zn foil Cu-Zn thermal spray coat on Al substrate, respectively. The results show that by using thermal spray coat as interlayer, because of the formation of different defects that can be considered as diffusion channels, diffusion potential of Ti and Al becomes higher at the interface. It is concluded that the mechanism of bonding formation involves the diffusion of Cu into Al and Ti base materials and formation of TiAl، TiAl، Cu2 Al and AlCuMg phases and also diffusion of Cu through Al grain boundaries and formation of eutectic phases across the grain boundaries. The formation of these intermetallic phases was confirmed by energy dispersive spectroscopy and X-ray diffraction. Dissolution of the base metals in the joint area and the isothermal solidification process of the thermal sprayed interlayer is more and faster than the foil interlayer. The joint with thermal spray brass coat as interlayer, gives higher shear strength of 25 MPa in comparison with the case of using brass foil as interlayer (14.6 MPa). The decrease in bond strength can be attributed to aggregation and growth of the brittle intermetallics near the joint interface due to lower diffusion potential of Ti and Al in the joint zone.