Microstructure evolution and mechanical properties of transient liquid phase (TLP) bonded joints of TiAl intermetallics

TiAl intermetallics were joined by transient liquid phase (TLP) bonding technique using Ti/Ni filler metal. The effects of bonding parameters and composition of filler metal on isothermal solidification and interfacial microstructure of the joints were studied. It was found that a continuous α2 layer was formed at the joint interface when the bonding temperature was below 1125 °C. This α2 layer hindered the atom interdiffusion between the TiAl substrate and liquid filler metal, which resulted in a long holding time required for complete isothermal solidification. When the bonding temperature was 1150 °C, no continuous α2 layer was formed in the joint and the isothermal solidification rate was enhanced. Furthermore, with decreasing of Ni content in the filler metal, the isothermal solidification rate was reduced due to the decrease in dissolution of TiAl substrate into the liquid filler metal. The shear testing results showed that the highest shear strength at ambient temperature (281 MPa) and at high temperature (800 °C) (243 MPa) were achieved, when the joint was bonded at 1150 °C for 5 min.

► A high quality joint with uniform microstructure and high strength was obtained.
► Effect of bonding parameters on joint isothermal solidification was investigated.
► Effect of Ni content in filler metal on joint isothermal solidification was studied.
► The ambient temperature/high temperature shear strength of the joint was evaluated.