A Combined Approach of Melt Pool Ultrasonic Vibration and Interpass Laser Remelting for Achieving Superior Mechanical Properties by Controlling Microstructure and Phases in L-DED of Inconel 625

Laser direct energy deposition (DED) is an additive manufacturing technique used in aerospace, automotive, and nuclear industries. However, challenges such as porosity, cracks, microstructural inhomogeneity, and elemental segregation usually affect the mechanical properties of fabricated components. This study proposes the synergistic application of ultrasonic vibration and interpass laser remelting in DED of Inconel 625 to effectively address these issues. Ultrasonic vibration to the melt pool results in equiaxed structures and reduces micropores by inducing acoustic streaming and cavitation effects, whereas interpass laser remelting selectively melts the previously deposited layers and reduces porosity. Both techniques influence the formation and distribution of intermetallic within the deposition. A synergistic application of these methods led to minimal porosity and equiaxed grains with thinner grain boundaries. Phase analysis revealed the significant presence of similar intermetallic compounds in as-deposited and vibration-assisted samples, with (γ′) phase appearing specifically in remelted and combined techniques. Further, intermetallic compounds, which were randomly distributed in as-deposited and remelted conditions, were found predominantly near the grain boundaries when vibration was applied alone or with remelting, resulting in better mechanical properties. The synergistic effect led to ∼20% increase in microhardness, ∼75% reduction in wear-rate, ∼32% higher ultimate tensile strength, and ∼25% increase in strain, and it also significantly enhanced corrosion resistance compared to as-deposited samples. This study underscores the potential of using ultrasonic vibration and interpass remelting synergistically to enhance the overall performance of DED-fabricated Inconel 625 components, outperforming their individual effects.