Effect of Molten Pool Behavior Under Ultrasonic Vibration on the Elimination of Pores in Directed Energy Deposition

Abstract

Pore defect plays an important factor on leading to a decrease in the strength performance and reliability of deposition layers manufactured by directed energy deposition. The ultrasonic energy field assistant method usually improves the structure of materials, now is induced to reduce porosity by acoustic streaming driven effect in directed energy deposition process. In this work, 1Cr12Ni3MoVN powder (29% hollow particles) was used to controllable generate bubbles in the molten pool to induce the imperfect deposition conditions in the experiments. The distribution of pores with different laser processing parameters under ultrasonic vibration (UV) was investigated, and the principle that ultrasonic vibration drives the bubble motion under the complex physical environment was also analyzed by numerical simulation. The results show that acoustic streaming lead by UV effect, in competition with other flows (Marangoni flow and non-isothermal flow), makes the small bubbles to escape or large bubbles to move toward the edge of the molten pool. Based on this mechanism of pores elimination, a new UV-assistant hybrid additive manufacturing system was designed to improve the forming reliability, especially under the imperfect deposition conditions. Mechanical performance testing and microstructure observation have demonstrated the dominance and reliability of UV effect in improving material performance by eliminating pore defects.

Keywords: Ultrasonic vibration, Directed energy deposition, Porosity, Bubble evolution, Hybrid additive manufacturing