| Wire and Additive Manufacturing(WAAM)is widely used in aerospace,automotive,and rapid prototyping molds due to its high deposition efficiency,wide wire application type,unlimited size,and low cost of welding equipment.However,due to the multiple thermal cycles during the forming process,the material is prone to coarse columnar crystals,resulting in anisotropy,and inevitable deformation and residual stress in the Components,which seriously affects the properties of the Components.Ultrasonic impact technoque acts on the surface of the metal sample with its high frequency and high speed characteristics,causing obvious plastic deformation,resulting in increased dislocation density,reducing grain size,and refining microstructure.Moreover,due to the high frequency reciprocation of the impact head,the effect of Ultrasonic impact on the surface layer of the sample is superimposed and strengthened,the tensile stress of the sample is relaxed,and a favorable compressive stress is introduced,so that the surface of the material is strengthened,and the stress state of the material is effectively improved.In this thesis,HS321 wire was used as the raw material and 321 stainless steel plate was used as the substrate.The single-layer deposition was carried out by WAAM technoque.The influence of different process parameters on the forming was investigated and analyzed using the morphology and geometrical dimensions of the deposited layer as the index.The sedimentary layers under different process parameters were observed and measured.The effects of forming parameters on the microstructure and properties of the deposited layers were further explored.A well-formed set of sedimentary layers was selected for ultrasonic impact treatment of different powers,and the microstructure and performance analysis were carried out.The results show that:Arc fuse deposition formation has a large relationship with wire feed speed and running speed.When the wire feeding speed and the running speed are well matched,a deposited layer with good forming morphology can be obtained,which is parabolic;The deposited material is completely melted,and there is no crack,hole and other defects at the substrate,and there is excellent metallurgical bonding,and the composition is uniform,and no segregation of components is found;And with increasing wire feeding speed,the melting width increases remarkably,the melting height decreases,the aspect ratio increases significantly,the contact angle decreases,and the dilution rate increases,With increasing running speed,the width and the melting height decrease,the aspect ratio does not change evidentily,and the contact angle decreases,but the reduction is lower than the wire feeding speed,and the dilution rate decreases.Relative to the wire feeding speed,the running speed has little effect on the microstructure and properties of the deposited layer.With increasing wire feeding speed,the microstructure of the deposited layer becomes coarse,and its hardness decreases;The running speed has no obvious influence on the microstructure of the sediment layer,and its hardness is also lower.When the wire feeding speed is 4.5m/min,the hardness value is about 170HV.In order to study the influence of ultrasonic impact on the microstructure of the sedimentary layer,the ultrasonic impact technoque was used to perform ultrasonic impact treatment on the surface of the deposited layer with different powers(400W,800W,1000W).It is found that the ultrasonic impact is plastically deformed on the surface of the deposited layer,which increases the dislocation density and reduces the grain size.Through the observation of the tissue before and after ultrasonic impact,the top layer of the deposited layer without ultrasonic impact was a complete cell structure with a size of 45.5 ?m.The tissue after ultrasonic impact has certain plastic deformation,and there is obvious fragmentation and elongation observed,and the grain size is also significantly reduced.When the ultrasonic impact power is 400W,800W and 1000W,respectively,the cell grain size is about 28.7?m,25.3?m,18.7?m,which is reduced by 37%,44.4%,58.9%compared with the unimpacted cell structure.With the increase of the distance from the surface,the effect of ultrasonic impact on the refinement of th e structure.is gradually weakened;In addition to refining the microstructure,the ultrasonic impact induces martensite transformation at the surface of the sediment layer,and the ultrasonic impact power increases,and the degree of induced martensite is gradually increased.Ultrasonic impact treatment also has a certain effect on improving the performance of the deposited layer.In the surface layer of the sediment layer,with increasing ultrasonic impact power,the microhardness also increases gradually,and the depth of action also gradually increases.When the ultrasonic impact power is 1000W,the surface layer has the highest microhardness of 315.20HV,which is increased by 87.84%compared with the non-impacted layer,and its depth of action is up to 1600?m.Ultrasonic impact treatment introduces beneficial compressive stress on the surface of the deposited layer,which redistributes the stress of the deposited layer.When the deposited layer is not impacted,the tensile residual stress exsits in both the near surface and the back surface,which is balanced with the compressive residual stress of the core of the deposited layer.The X-direction tensile stress value of the surface of the non-impacted deposit layer is about 117 MPa,the tensile stress value in the Y direction is about 76 MPa,the compressive stress reaches the maximum at 770?m,the maximum stress in the X direction is around-59 MPa,and the maximum stress in the Y direction is-22 MPa.The deposited layer after ultrasonic impact conveted as compressive stress from tensile stress state,and with the increase of the distance from the surface layer,the compressive stress first increases and then decreases.And as the ultrasonic impact power increases,the depth of the region representing the compressive stress also increases. |
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