Collision and spreading behavior of rapid tin droplets on stainless-steel substrate surfaces under ultrasonic vibration

Applying ultrasonic vibration in a novel droplet-based additive manufacturing method holds significant promise. This is attributed to the ability of ultrasonic vibration to alter the dynamic dynamics of droplets spreading on the underlying substrate, enhancing wetting. Our study focuses on the dynamic properties and wettability of tin droplets on a stainless-steel surface under ultrasonic vibration. We investigate changes in spreading diameter, wetting angles, and post-solidification macroscopic morphology. Findings demonstrate that ultrasonic vibration considerably promotes droplet spreading, reducing retraction, especially at higher material temperatures. During expansion, dynamic wetting angle oscillations occur. Post-solidification, the tin droplet surface exhibits a more consistent ripple pattern. At lower temperatures, ultrasonic wave-induced wettability enhancement is minimal, but at higher temperatures, it significantly boosts substrate wetting by tin droplets. This enhancement is attributed to ultrasonic vibration’s influence on droplet kinetic, surface, and adhesion energy, notably above the tin droplets’ melting point. Ultrasonic vibration, providing up to 60% of the initial energy, significantly aids droplet wetting and spreading. Our study elucidates the importance of ultrasonic waves in high-speed droplet processes, offering theoretical guidance for ultrasound-assisted droplet deposition methods.