Research on the temperature rise mechanism of ultrasonic field-assisted laser cladding

In order to investigate the temperature rise mechanism of laser cladding assisted by ultrasonic energy field, the multi-field heat flow behavior of laser cladding with or without ultrasonic field assistance is studied.Based on the theoretical analysis of laser-powder interaction and thermal effect of ultrasonic energy field, the coupling equation of laser effective heat input and ultrasonic effective heat conversion is obtained.A numerical model of three-dimensional phase-change heat transfer in laser cladding assisted by ultrasonic energy field is established. The solid–liquid phase change and dynamic evolution of the cladding layer are treated by the apparent heat capacity method and the deformation geometry method respectively. The variations of transient heat and velocity with distance based on laser spot center with or without ultrasonic energy field are studied. The effect of ultrasonic energy field on multi-field coupling of heat flow in laser cladding layer is discussed.Then ultrasonic field-assisted laser cladding IN718 experiment is conducted. The surface temperature of the melt pool is tracked in real time. The evolution law of the microstructure of the cladding layer and the distribution of alloying elements are analyzed.The reliability of the model is verified by analyzing the experimental results.The results show that when the laser cladding time is 2 s, the peak temperature and velocity of the molten pool reach the maximum value, which are 2483 K and 0.316 m/s respectively.Under the action of ultrasonic field, when the cladding time is 1 s, 2 s, 3 s and 3.5 s, the peak temperature of the molten pool increases by 26 K, 38 K, 105 K and 121 K respectively. The velocity of the molten pool reaches the maximum when the ultrasonic field acts for 2 s, which reaches 0.319 m/s.With the continuous application of ultrasonic field, the temperature gradient(G) of the cladding layer decreases gradually, and the solidification rate(R) and cooling rate increase. The ratio of temperature gradient to solidification rate (G/R) decreased.In the test range, the temperature variation of the molten pool surface is basically consistent with the simulation results.Ultrasonic field can promote the transformation of microstructure of IN718 cladding layer from columnar dendrites to equiaxial dendrites. The average minimum grain size of the top, middle and bottom of the cladding layer is reduced by 53.70%, 21.8% and 40.82% respectively. The element distribution of the cladding layer is also more uniform.