Standard heat treatment effects on TLP bonded IN-738LC superalloy using BNi-9 filler: An approach to make an ideal joint
(Department of Materials Science and Engineering, Engineering Faculty, Ferdowsi University of Mashhad, Mashhad, Iran)
Abstract: 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 reveal that bonding at 1120 °C for 5 min 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 min leads 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 results in the complete elimination of the boride phases in the diffusion-affected zone and also the formation of γ′ precipitates in the isothermally solidified zone. However, discontinuously re-solidified products are observed in joint district in the non-isothermally solidified sample. The highest shear strength (～801 MPa) is achieved for isothermally solidified specimen after standard heat treatment; this strength is approximately 99% that of the substrate material.
Key words: IN738LC; standard heat treatment; diffusion brazing; isothermal solidification; γ'' precipitates; mechanical properties