Effect of two-step heating transient liquid phase bonding on microstructure and mechanical behaviour of IN-738LC gas turbine components

The long isothermal solidification and homogenization time is the major concern in repairing turbine parts by the conventional transient liquid phase method. In this study, microstructure and morphology of the proposed two-step heating transient liquid phase joints were compared to results of the conventional ones conducted at the same temperature. After the isothermal solidification, deleterious precipitates such as Ni3Si, Ni3B and CrB were removed. The application of the two-step technique increased the shear strength of the joints up to 28% (516-674 MPa) due to collision of two non-planar interfaces and formation of the longer bonding line. The shear fracture surfaces of all bonds with the complete isothermal solidification stage represent a dimple pattern that is characterized by ductile fracture. The stress-rupture life of the joint at 982 degrees C was about 85% of the superalloy service life at this temperature.