Regulating microstructure and mechanical properties of additively manufactured Inconel 718 alloy via dual-dimensional ultrasonic vibration strategies

Non-uniform microstructure, coarse grain size, and defects hinder the performance of Laser Directed Energy Deposition (LDED) Inconel 718 alloy parts. To overcome these limitations, this study introduces dualdimensional ultrasonic vibration strategies during the LDED process, specifically BD + TD (building direction + tangential overlapping direction) and BD + SD (building direction + scanning direction). Both strategies significantly improve dynamic flow characteristics, macroscopic morphology, densification, and microstructural evolution. The BD + TD strategy enhances molten pool area, molten pool expandability, flow homogeneity, and pool shape, minimizing trailing tails and improving surface quality despite increased sticky powder. It also reduces porosity and pore diameter. The BD + SD strategy refines grain size by 50.8 %, promotes a columnar-toequiaxed grain transition, transforms the Laves phase into fine spherical particles, and enhances microhardness. Dual-dimensional ultrasonic vibration strategies achieve tensile strengths exceeding 910 MPa while balancing strength and ductility. BD + SD strategy attains >935 MPa tensile strengths while maintaining elongations >90 % compared to non-ultrasonic vibration LDED parts, primarily due to grain refinement, Laves phase spheroidization, defect reduction and dislocation homogenization. Additionally, ultrasonic vibration strategies minimize mechanical property anisotropy in Inconel 718. Overall, dual-dimensional ultrasonic vibration-assisted additive manufacturing offers a promising approach for producing high-quality, high-performance metal parts with comprehensive mechanical property enhancements.