Size and Shape Characterization of Gamma Prime Phases within the FAST-Bonded Ni-Based Superalloy Interphases

Field Assisted Sintering Technology (FAST) is a promising method of joining materials because its high-temperature ramp rate minimizes unwanted changes in the original micro-structure unlike friction or diffusion bonding. Currently, a knowledge gap exists about the relationship between the FAST process and microstructure change, especially about the effect of electromigration. In this paper, the gamma prime phase growth was quantitatively characterized during FAST joining between Ni-based superalloy PWA1429 and PWA1480. FIJI/ImageJ software and the Weka Segmentation machine learning plugin were used to segment the scanning electron microscopy (SEM) images of FAST-joined sample cross-sections and to assign phases. The assigned gamma prime phases were characterized by their area, orientation, and non-dimensional shape factor. As a result, directional grain growth, while its degree is small, was observed only within the interphase, and not within the parent materials, indicating that the electromigration effect is small and enhanced only with lattice mismatch and defect inclusion. In the future, more FAST-joined samples prepared with varying FAST conditions (temperature, pressure, and electric current) and varying sample preparation conditions (lattice mismatch and sample roughness) can be characterized to further advance the process-structure relationship study.