The effect of substrate's heat treatment on microstructural and mechanical evolution of transient liquid phase bonded IN-738 LC

Transient liquid phase (TLP) bonding of Inconel-738 LC superalloy was investigated using AMS 4777 filler alloy. The bonding was performed at 40 and 80 mu m gap sizes at sufficient time in order to achieve complete isothermal solidification. Solution treatment (1120 degrees C/2 h) was carried out in two different sequences, one before and the other after TLP bonding of the base metal accompanying subsequent aging treatment (845 degrees C/24 h) which are called HT-A and HT-B, respectively. In both cases, no morphological changes in diffusion affected zone (DAZ) precipitates were observed. However, line scan analysis indicates enrichment of base metal alloying elements (Ti, Al) at isothermal solidification zone (ISZ) of heat treated samples, particularly HT-A joints resulted in increased hardness of the centerline. In addition, improved shear strength was seen in heat treated joints conforming to the ductile fracture surfaces. The maximum hardness of 759 Hv and the highest shear strength of 565 MPa in the joint area, were found in HT-A condition with 40 gap size. Enhanced mechanical properties were mainly controlled by solid solution strengthening mechanism. (C) 2015 Elsevier Ltd. All rights reserved.