Ultrasonic-induced nucleation kinetics in directed energy deposition

The nucleation kinetics activated by ultrasonic vibrations in ultrasonics assisted directed energy deposition (UADED) remains unknown and poses a challenge. The ultrasonic volume force and heat enhancement terms are incorporated to the ultrasonic-induced heat-flow-microstructure coupling model to establish the new nucleation kinetics model for better controlling of microstructures in UADED. Mechanism on the nucleation and grain evolutions is proposed to clarify the nucleation kinetics between the ultrasonic features and the microstructural evolutions in UADED. The heat input is increased by 27.3 W/m³ caused by ultrasonic vibrations induced heat enhancement term, and the flow velocity is increased by 43.3% caused by ultrasonic vibrations induced kinetic energy density in UADED. The comprehensive role of the combination of ultrasonic-induced heat input and flow behaviors can lead to an increase in the thermal undercooling by 40.7 K. The nucleation rate is then increased by 68.6% in comparison with the traditional DED, leading to the decrease of the average grain size from 220 μm to 130 μm. The proposed NKT and designed experimental platform are meaningful for the microstructure control in AM.