【作者】 孙宁；

【导师】 陈茂爱；

【作者基本信息】 山东大学 ， 材料工程（专业学位）， 2021， 硕士

【摘要】 CMT电弧增材制造技术在复杂镍基合金零部件制造方面具有重要的应用前景。而电弧增材制造存在成形精度差、组织粗大且不均匀等问题。本文研究在CMT焊枪上施加超声振动,研究超声振动对增材制造件成形、组织及性能的影响。研究了工艺参数及超声振动对熔敷过程及单道熔敷层表面成形的影响规律,得到了熔敷层表面成形良好的工艺参数范围。结果表明,CMT周期并不随着送丝速度和行走速度的变化而变化,但施加超声将会使得CMT周期明显减小,熔滴过渡频率加快,最多可提升近43%。在本试验所采用的工艺条件下,过渡形式均为短路过渡。送丝速度一定时,随着行走速度的增大,熔敷层宽度、层高、基板熔深、熔宽及稀释率都变小;行走速度不变时,随着送丝速度的增加,熔敷层宽度、基板熔深、熔宽及稀释率都变大,层高先增大后减小。施加超声将会使熔宽减小进而降低稀释率,同时使真实送丝速度提高,继而提高熔覆层截面积。观察了不同工艺条件下熔敷层的显微组织。熔敷层组织从顶部至底部依次发生了等轴晶、树枝晶、胞状枝晶、胞状晶的转变,随着热输入的降低,各区域晶粒出现细化,枝晶间距减小,二次枝晶臂逐渐消失。施加超声后,柱状枝晶组织细化,较大尺寸的柱状晶被打散为小尺寸晶粒,等轴晶区域的高度增加。开展了不同工艺条件下增材制造试验,沉积方式选择逐层换向沉积及间隔沉积方式,对增材制造件的成形尺寸及成形精度进行分析。薄壁构件的宽度和高度与送丝速度呈正相关,而与行走速度呈负相关。沉积过程施加超声后,薄壁构件的宽度增加,而高度减小。薄壁构件的成形精度随着热输入增大,将会有所改善,施加超声使得成形精度有一定的提高。对增材制造件的横断面微观组织形态特征进行分析,对组织中的析出相进行判断,并对增材制造件的抗拉强度和耐蚀性能进行对比分析。结果如下:薄壁构件横截面经腐蚀后呈现明显的分层结构,层与层之间存在过渡区。薄壁构件层内组织由下部细小的胞状晶转变为上部胞状枝晶,过渡区组织为极细小的胞状晶,其晶粒生长方向由前一层决定,并决定着后一层枝晶生长方向。热输入的增大以及施加超声都将增大过渡区高度。在沉积过程中会在晶界处发生Nb元素偏析,生成Laves相及碳化物颗粒。随着热输入的增大,析出相的尺寸及数量均有明显的增大;施加超声有助于抑制析出相的生成。普通CMT电弧熔敷条件下,薄壁构件横向试样拉伸强度(700MPa)高于纵向试样拉伸强度(645MPa),纵向试样伸长率(50%)明显高于横向试样(42%)。行走速度对薄壁构件横向和纵向试样拉伸强度基本没有影响,但随着送丝速度的增大,横纵向试样拉伸强度平均提升8%左右,横纵向试样伸长率提升了 12%左右。施加超声条件下,相比于普通CMT电弧熔敷条件,横纵向试样拉伸强度及伸长率均有所提升。断口中可以观察到明显的韧窝形貌,断裂方式为韧性断裂,且超声条件下韧窝形貌尺寸更大且均匀。随着行走速度的增加,薄壁构件的耐蚀性逐渐增强,行走速度0.24m/min时的腐蚀电流密度明显高于行走速度为0.48m/min时的腐蚀电流密度。施加超声也会使得薄壁构件的耐蚀性增强,超声条件下的腐蚀电流密度是未施加超声条件下的1/4左右。更多还原

【Abstract】 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.更多还原