The present research is focused on the effects of standard heat treatment on the microstructure and mechanical properties of diffusion brazed IN-738LC superalloy. Three distinct heat treatment cycles of full solution annealing, partial solution annealing, and aging treatment were applied to the bonded specimens, sequentially. The results revealed that bonding at 1120°C for 5 minutes leads to incomplete isothermal solidification and formation of eutectic phases including Ni- and Cr-rich borides in the joint centerline. Increasing the holding time to 45 minutes led to the full isothermal solidification and formation of a nickel proeutectic solid-solution phase (γ) in the joints. The standard heat treatment of isothermally solidified and non-isothermally solidified specimens resulted in the complete elimination of the boride phases in the diffusion-affected zone and also formation of γˊ precipitates in the isothermally solidified zone. However, discontinuously re-solidified products were observed in joint district in the non-isothermally solidified specimen. The highest shear strength (∼801 MPa) was achieved for isothermally solidified specimen after standard heat treatment; this strength was approximately 99% of the shear strength of the substrate material.

Keywords