Effect of transient liquid phase bonding time on the microstructure, isothermal solidification completion and the mechanical properties during bonding of Inconel 625 superalloy using Cr-Si-B-Ni filler metal

Abstract

The effect of bonding time on microstructure and mechanical properties of a transient liquid phase (TLP) bonded Inconel 625 superalloy, using a BNi-2 interlayer, was investigated. The superalloy was kept in a vacuum furnace at a pressure of 10−5 torr and a temperature of 1025 °C for 35, 65 and 95 min until TLP process occurred. Microstructure analyses were performed using optical microscopy (OM), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). Microhardness examinations and shear tests were performed to determine the effect of bonding time on the mechanical behavior of TLP bonded joints. By increasing the bonding time, the diffusion of melting point depressant (MPD) increased and the isothermal solidification zone (ISZ) was completed. Isothermal solidification was completed at 1025 °C by 95 min bonding time. Also, by increasing the bonding time to 95 min, that caused the reduction of the eutectic phase, the ISZ widened and the hardness increased. At the bonding time of 35 min the amount of shear strength was 208.7 MPa, while by increasing the bonding time to 95 min, this amount increased to 448.9 MPa. So, the stress concentration factors decreased by reduction of the eutectic phases, which caused an increase in the shear strength.