Effect of Bonding Time, Composition of Interlayer, and Postbond Heat Treatment on Transient Liquid Phase Joints of Inconel 718 Superalloy

Abstract

The investigation aims to explore the relationship between the microstructure and mechanical properties of transient liquid phase‐bonded joints of Inconel 718 (IN718) nickel‐based superalloy, utilizing BNi‐1 and BNi‐2 interlayers with a thickness of 50 μm, produced at 1150 °C for varying durations. Microstructural analysis, facilitated by scanning electron microscopy, and phase analysis, utilizing energy‐dispersive spectrometer, reveal a diverse range of microstructures, including continuous eutectic intermetallic phases and eutectic‐free configurations under different bonding conditions. Additionally, the interfacial diffusion of IN718/BNi‐2 is simulated by molecular dynamics. Notably, higher mass fractions of Cr in the interlayer are found to prolong the time of isothermal solidification. The use of BNi‐2 interlayers, 50 μm in thickness, results in joints achieving isothermal solidification within a remarkably brief 10 min, a significantly shorter duration compared to previous studies. Mechanical tests, encompassing microhardness and uniaxial tensile experiments, are carried out on all samples. The microhardness of the isothermally solidified zone decreases with increasing bonding time. The tensile strength of bonded joints increases with extended bonding time before isothermal solidification completion, followed by a subsequent decline. The highest tensile strength (893.3 MPa) is observed in joints using BNi‐2 interlayer after applying postbond heat treatment, representing approximately 88.5% of the base metal tensile strength.