Effect of Bonding Parameters on Microstructure of Transient Liquid Phase Bonded IN738/MBF-15/IN738

In this research, the effect of bonding time and gap size on the microstructure of transient liquid phase(TLP) bonded IN738 superalloy was investigated. The bonding process was carried out at 1130 °C for 5-60 min using MBF-15 amorphous brazing foil with thickness of 35-140 μm. Microstructures of TLPbonded samples were characterized by optical microscope, scanning electron microscope and energydispersive spectroscopy. The results indicated that three different regions including isothermal solidifiedzone, athermally solidified zone and diffusion affected zone are formed in the bonding zone. Based onSEM/EDS analysis results, eutectic phases formed in the athermally solidified zone of the joints withincomplete isothermal solidification were characterized as nickel-rich and chromium-rich borides. Theblocky and acicular Cr-rich boride and carboboride precipitates were observed at diffusion affected zone.It was found that isothermal solidification was completed by performing TLP process at 1130 °C for 30min with foil thickness of 35 μm. TLP bonding process was described by parabolic model based onFick’s second law. The findings indicated that the experimental results are well correlated withthe calculated results. In addition, by increasing the gap size, centerline eutectic constituents wereformed along the joint layer and continuously increased from view point of width and density.

Effect of Bonding Parameters on Microstructure of Transient Liquid Phase Bonded IN738/MBF-15/IN738 Keywords:

Transient liquid phase bonding , IN738 superalloy , Isothermal solidification , Amorphous brazing foil