Electric Current-Assisted TLP: Bonding of Ultrathin-Walled Inconel 718 Capillaries Temperature Field Simulation and Microstructural Analysis

This study achieved the effective bonding of Inconel 718 ultra-thin-walled capillaries by employing a self-designed apparatus and a novel approach involving current-assisted transient liquid phase (TLP) bonding using BNI-2 brazing material in a vacuum environment. During the bonding process, rapid heating and a subsequent period of maintenance were achieved using Joule heating, followed by rapid cooling in the furnace. Compared to the traditional furnace-based TLP bonding, this method significantly improved the bonding efficiency, reduced energy consumption, and minimized the thermal impact on the base material. A temperature field simulation of the ultra-thin-walled capillary bonding was conducted using COMSOL multiphysics simulation software, allowing for the visualization of temperature distribution through temperature contour plots. Microstructural observations of specimens under various process parameters revealed the existence of the Diffusion Affected Zone (DAZ) and Isothermally Solidified Zone (ISZ) in the vertical brazed area of the capillary. Inadequate control of process parameters can lead to defects such as weld seam voids and channel blockage. Given the limited heat resistance of the thin-walled capillaries, excessive current and prolonged bonding time can result in elevated temperatures, which, in turn, may compromise the mechanical properties of the thin-walled capillary.