Ultrasonic vibration-assisted laser directed energy deposition: effects on material movement in vertical and horizontal direction

Abstract

Laser directed energy deposition (LDED) is widely used in manufacturing but defects such as lack of fusion, porosity, and inhomogeneous microstructures are reducing the mechanical strength. To solve these issues, ultrasonic vibration-assisted (UV-A) LDED has been introduced. Studies show that ultrasonic vibration enhances the strength of the fabricated workpiece by reducing these defects. To control the mechanical properties and defect formation in LDED, it is essential to analyze the material flow inside the fabricated part. Despite many advances, understanding the material trajectories inside the fabricated part is still insufficient. This research aimed to investigate the material movement along the vertical and across the horizontal deposition direction. Experiments were designed utilizing an ultrasonic vibrator to examine the effects of ultrasonic vibration on material movement. Fe–Cr stainless steel powder was used for fabrication with an alternative powder (pure cobalt, Co) to trace the elemental movement during the process. The result demonstrated that utilizing ultrasonic vibration resulted in a homogenous distribution of Co in the vertical direction, exhibiting around 40% more concentration in the molten pool and around 54% higher in the upper layer. UV-A LDED affected Co distribution across adjacent tracks rising from around 1.1% at Location 1 to approximately 1.3–1.6% at Locations 2–4, in contrast to the inconsistent presence of 1.1–1.7% observed solely at Locations 2 and 3 without UV-A. Lastly, the influence of material distribution due to ultrasonic vibration on microhardness of the deposited tracks was also tested and it demonstrated positive enhancement in both vertical and horizontal direction.