Effect of in-situ ultrasonic impact treatment on flow and solidification behavior of laser metal deposition: By finite element simulation

Due to the special thermal history of laser metal deposition (LMD), the microstructure of deposition layer is mainly columnar crystal which has a negative effect on the mechanical properties of the additive manufactured parts. In-situ ultrasonic impact treatment is an assistive technology, which can refine grain size, reduce residual stress and improve fatigue strength effectively. Finite element simulation is an important method to study the heat and mass transfer phenomenon in molten pool, which can save time and materials. However, few scholars have studied the influence of ultrasonic impact treatment on molten pool by finite element simulation. The effect of acoustic streaming in the molten pool caused by ultrasonic impact treatment on the flow behavior, heat transfer behavior and solidification conditions at the solidification boundary of the molten pool have been studied by finite element simulation in this paper. The results show that ultrasonic impact treatment can promote the maximum velocity in the molten pool, reduce the temperature of the molten pool and change the shape of the molten pool from round to oval. Besides during the solidification process, the temperature gradient decreases first and then increases, and the solidification rate increases first and then decreases with increasing ultrasonic power. Ultrasonic impact treatment can improve the microstructure of the deposition layer during solidification process by increasing cooling rate. This finite element simulation research can provide guidance for process development, structure control and property improvement for in-situ ultrasonic impact treatment assisted laser metal deposition.