Investigation on microstructural properties of transient liquid phase (TLP) bonded IN-738LC superalloy with AMS 4776 filler metal

In the present study, microstructural evolutions at the joint region of transient liquid phase bonded IN-738LC superalloy were examined. The experiments were carried out at 1100°C with different holding times using Ni-B-Si-Cr-Fe filler alloy, AMS 4776, with B and Si as the melting point depressant elements. It was found that insufficient isothermal solidification of liquated insert caused the formation of continuous centreline eutectic phases. The width of the eutectic decreased with the increase in holding time. Complete isothermal solidification, which precluded the formation of the centreline eutectic, occurred within 45 min of holding time. In addition to the centreline eutectic products, precipitation of boron rich particles was observed at the diffusion affected zone. Homogenisation of isothermally solidified joints at 1120°C for 300 min resulted in the elimination of intermetallic phases formed at the diffusion affected zone and formation of significant γ′ precipitates in the joint region.