Grain refinement of Inconel 625 during wire-based directed energy deposition additive manufacturing by in-situ added TiB₂ particles: Process development, microstructure evolution and mechanical characterization

In this study, a novel method for enhancing the quality of components fabricated by wire and arc additive manufacturing (WAAM) was developed. This approach employs an innovative mechanism featuring an actuator that dispenses a solution containing refinement particles (TiB₂ inoculants), in conjunction with a soldering flux that vaporizes prior to reaching the electric arc. This leaves the particles to adhere to the welding wire or be carried by the shielding gas. By implementing this device, TiB₂ particles were successfully incorporated into the molten pool during the WAAM process of Inconel 625 at levels of 0.31 and 0.56 wt%. Microstructural analysis reveals a significant reduction in the size of interdendritic segregation regions when TiB₂ particles are introduced. Electron backscatter diffraction analysis further reveals the transformation of columnar grains into equiaxed grains. The average grain area decreased from 1823 μm² in the as-built sample to 583 μm² in the sample with a TiB₂ content of 0.56 wt%. In addition, an improvement in the Inconel 625 fabricated by WAAM mechanical strength was observed due to the use of TiB₂ inoculants, which was primarily attributed to the effect of the grain size refinement.