Layer to layer molten pool thermal behavior in laser directed energy deposition influenced by ultrasonic vibration

Abstract Laser Directed Energy Deposition (LDED) is esteemed for its ability to fabricate intricate parts. However, it is prone to defects including lack of fusion, porosity, and microstructural inhomogeneity, which affects the performance. Ultrasonic vibration-assisted (UV-A) LDED was found useful in addressing these challenges, yet excessive heat accumulation can still degrade the microstructure and mechanical properties, necessitating precise thermal control. The earlier studies mainly emphasized single-track or single-layer observations, and quantitative layer to layer thermal evolution during deposition is still insufficient. The present study investigates the layer to layer thermal analysis of UV-A LDED using 17 − 4 PH stainless steel as the feedstock material and coaxial in-situ infrared thermography was utilized to capture molten pool images. The experiment was complemented by microhardness analysis and scanning electron microscopy (SEM) based microstructural characterizations with electron backscattered diffraction (EBSD) analysis. Results demonstrated that UV-A generated a more stable and uniform molten pool geometry, limiting layer to layer variation to only 3%. UV-A increased the peak center temperature by 21.2% and widened the temperature dispersion. UV-A maintained a narrower interlayer thermal gradient changes (5.7%) in comparison to without UV-A. A consistent cooling rate throughout the layers was attained with UV-A and a relative enhancement (6.3%) in microhardness was measured which was evident by a 7.3% reduction in grain size. Overall, UV-A mitigated uncontrolled interlayer heat accumulation and improved the thermal properties.