Research On Microstructure And Properties Of Nickel-based Alloys By Ultrasonic-assisted CMT Additive Manufacturing

CMT arc additive manufacturing technology has important application prospects in the manufacture of complex nickel-based alloy parts.However,arc additive manufacturing has problems such as poor forming accuracy,coarse and uneven structure.This paper studies the application of ultrasonic vibration to the CMT welding gun,and studies the effect of ultrasonic vibration on the forming,structure and performance of additive manufacturing parts.The influence of process parameters and ultrasonic vibration on the deposition process and the surface formation of a single-pass cladding layer was studied,and the range of process parameters with good surface formation of the cladding layer was obtained.The results show that the CMT cycle does not change with the wire feeding speed and walking speed,but the application of ultrasound will significantly reduce the CMT cycle and accelerate the droplet transition frequency,which can increase by nearly 43%at most.The application of ultrasound will reduce the melting width and thus reduce the dilution rate,and at the same time increase the true wire feeding speed,and then increase the cross-sectional area of the cladding layer.The microstructure of the deposited layer under different process conditions was observed.The structure of the deposited layer has undergone the transformation of equiaxed crystals,dendrites,cellular dendrites,and cellular crystals from top to bottom.After ultrasound is applied,the columnar dendritic structure is refined,the larger-sized columnar crystals are broken up into small-sized crystal grains,and the height of the equiaxed crystal region increases.Experiments on additive manufacturing under different process conditions have been carried out.The width and height of thin-walled components are positively correlated with wire feeding speed,but negatively correlated with walking speed.After the application of ultrasound during the deposition process,the width of the thin-walled member increases while the height decreases.As the heat input increases,the forming accuracy of thin-walled components will improve,and the application of ultrasound will improve the forming accuracy to a certain extent.Analyze the morphological characteristics of the cross-sectional microstructure of the additive manufactured parts,judge the precipitated phases in the structure,and compare and analyze the tensile strength and corrosion resistance of the additive manufactured parts.The results are as follows:the cross-section of the thin-walled component shows an obvious layered structure after corrosion,and there is a transition zone between layers.The increase in heat input and the application of ultrasound will increase the height of the transition zone.During the deposition process,Nb element segregation occurs at the grain boundary,forming Laves phase and carbide particles.With the increase of heat input,the size and quantity of the precipitated phases have increased significantly;the application of ultrasound helps to suppress the formation of the precipitated phases.Under ordinary CMT arc welding conditions,the tensile strength of the transverse specimen of the thin-walled component(700MPa)is higher than the tensile strength of the longitudinal specimen(645MPa),and the elongation of the longitudinal specimen(50%)is significantly higher than that of the transverse specimen(42%).Under ultrasonic conditions,compared with ordinary CMT arc welding conditions,the tensile strength and elongation of the transverse and longitudinal specimens are improved.Obvious dimple morphology can be observed in the fracture,the fracture mode is ductile fracture,and the size of the dimple morphology is larger and uniform under ultrasonic conditions.As the walking speed increases,the corrosion resistance of thin-walled components gradually increases,and the application of ultrasound will also increase the corrosion resistance of thin-walled components.