Microstructure And Property Regulation Of Inconel625 In Ultrasonic Assisted CMT Arc Additive Manufacturing

Arc additive manufacturing based on cold metal transition technology(CMT-AM)has the advantages of rapid prototyping,short cycle and high efficiency.It shows great potential in additive manufacturing of complex nickel base alloy parts,but there are some problems such as uneven microstructure and properties of additive parts.Ultrasonic vibration has complex effects such as cavitation effect,acoustic flow effect and mechanical effect in the propagation medium.The action of ultrasonic on the arc molten pool can accelerate the flow of liquid in the molten pool and obviously refine the grains of solidification structure in the molten pool,which can improve the performance of CMT arc additive manufacturing parts.Therefore,this paper mainly focuses on the regulation of microstructure and properties of nickel based Inconel625 parts manufactured by ultrasonic assisted CMT arc additive:Firstly,the effects of different CMT process parameters and ultrasonic vibration on the forming of Inconel625 parts made of additive materials are studied.The results show that the formability of the surfacing layer is affected by CMT process and ultrasonic vibration.When the heat input is in the range of 5.45～9.01 k J/cm,ultrasonic vibration can increase the fusion width,penetration,wetting angle and penetration ratio.Excessive heat input can weaken the ultrasonic effect and cause crater and splash defects;When the heat input is too small,ultrasound can accelerate the solidification of weld pool,which is not conducive to the formation of surfacing layer.The change of ultrasonic frequency has little effect on the forming of surfacing layer.In the additive manufacturing of multi-layer thin-walled specimens,ultrasonic vibration can promote the spread of molten pool more evenly,which is conducive to the good transition between layers,improve the forming accuracy and significantly reduce the weld beading between layers.Next the microstructure,element distribution and phase structure of the additive sample were analyzed.The results are as follows: under different welding current or welding speed,ultrasonic vibration has the effect of refining grain and breaking dendrite in the surfacing layer.Ultrasonic vibration can also disrupt the continuity of columnar dendrites in thin-walled samples and reduce the preferred orientation of thin-walled samples.Ultrasonic vibration promotes the diffusion of solute elements such as Mo and Nb and reduces the segregation degree of Nb in the precipitate.The higher the ultrasonic frequency is,the more significant the effect of Nb element segregation inhibition is.XRD analysis shows that applying ultrasonic vibration is beneficial to reduce the lattice distortion of microstructure.Finally,the effect of ultrasound on the properties of thin-walled specimens was studied.The results show that the hardness of conventional thin-walled samples is mainly distributed in 245～265HV.Ultrasonic vibration has the most obvious effect on the upper area of thin-walled samples,and the average hardness is increased by about11 HV.The higher the ultrasonic frequency is,the more beneficial it is to reduce the degree of hardness mutation in the transition zone of thin-walled specimens.The tensile property of the upper area of the thin-walled sample is the worst.The tensile strength of the conventional thin-walled sample is 413.83 MPa.Ultrasonic vibration can improve the tensile strength of the thin-walled sample in the welding direction,and the effect of improving the tensile strength of the upper area is the best.The tensile strength is increased to 488.22 MPa,and the increase rate is 17.98%.The effect of changing ultrasonic frequency on tensile strength is more complex.When ultrasonic frequency is 20 k Hz,the tensile strength of tensile specimen in additive direction is increased by 6.23%,and that of transverse tensile specimen is increased by 6.27% when ultrasonic frequency is 28 k Hz.40 k Hz ultrasound is beneficial to promote the isotropy of thin-walled specimens.The effect of ultrasonic vibration on the elongation in the welding direction is 1～5%,and the closer it is to the base metal,the more obvious the effect is.The change of ultrasonic frequency has little effect on the elongation.The elongation difference between tensile specimens under different frequencies is less than 3%.The fracture analysis shows that the fracture mechanism is ductile fracture,and there are a large number of dimples at the fracture section.The size of dimples is larger and uniform under the action of ultrasound.