Solid-state diffusion bonding for INCONEl 617 superalloy using field-assisted sintering technology (FAST) guided by CALPHAD approach

Abstract

This study investigates solid-state diffusion bonding between two INCONEl 617 alloy samples using field-assisted sintering technology (FAST). The study focuses on analyzing the faying surface validating the theoretical alloy design modeling done by the CALculation of PHAse Diagrams (CALPHAD) approach followed by experimental validation. Varying kinetics’ limitations enabled phase stability and phase control governed by the CALPHAD approach alloy design. The alloy design contains a pseudo-binary phase diagram assisted with thermal mapping of a property phase diagram to obtain the optimum temperature of solid-state diffusion bonding while understanding phase fields and their evolution through Mo-increasing content and temperature increase. The FAST parameters recommended by CALPHAD were 800 °C under 10 MPa pressure with a holding time of 30 minutes. The investigation observations were promising where the faying surface contains γ only, while the further region on the alloy contains γ and γ`. It is worth mentioning that FAST advantage resulted in fine faying surface thickness of around 10 µm and a controlled heat affected zone (HAZ) leading to extreme reduction in recrystallization zone yielding an average grain size of 60-100 µm before and after diffusion bonding. Furthermore, two modes of metal carbide (MC) have been found, MC formed under the faying surface and micro-MC pools formed around the faying surface.