In-process implication of inter-pass re-melting and ultrasonic vibration in direct energy deposition of Inconel 718...

Directed energy deposition (DED) of nickel-based super alloys, such as IN718, often faces challenges such as elemental segregation, grain inhomogeneity, presence of micro-pores, and lack of fusion. This study explores the real time implication of inter-pass laser re-melting (LR) and ultrasonic vibration (UV), during DED process, for producing refined and homogeneous grain structure, along with enhance mechanical and tribological performance. Hence, this study focuses on the fabrication of IN718 samples through DED with the individual and combined application of re-melting and ultrasonic vibration. Re-melting contributed to partial fragmentation of the columnar grains with partial dissolution of Laves phases along with a reduction in micro-pores. Whereas, the implication of ultrasonic vibration contributed to significant reduction in porosity along with complete grain fragmentation resulting in fine equiaxed microstructure. However, the individual techniques resulted in higher hardness, enhanced wear resistance and improved strength, the combined application of re-melting and vibration shows maximum reduction in deposition-related defects (∼99% pores-free) with markedly improved microstructural homogeneity, resulting in most significant enhancement in mechanical and tribological properties. The coefficient of friction and micro-hardness showed a reduction of ∼24-26%, and increase of ∼25%, respectively for the combined DED technique. Additionally, the wear rate has showed ∼48% reduction and the ultimate tensile strength improved by ∼23%. Hence, the synergistic effect of vibration and re-melting offers a robust approach for producing reliable, high-performance DED-fabricated IN718 components.