TC4钛合金电弧增材制造叠层组织特征

采用CMT电弧增材制造技术制造了TC4钛合金薄壁墙构件，并对其组织特征进行了研究. 结果表明，在电弧增材制造过程中，受其热输入、多次热循环及冷却速度的影响，在其构件中产生了从高温保留下来的贯穿数个堆积层的原始β柱状晶晶界、水平层带条纹、马氏体组织和网篮组织等. 显微硬度显示，中下部区域硬度相对较高，平均硬度为336HV 0.1，上部显微硬度有明显降低，平均硬度为323.3HV 0.1.     

Mitigation of thermal distortion in wire arc additively manufactured Ti6Al4V part using active interpass cooling

ABSTRACT

In this study, active interpass cooling using compressed CO₂ was innovatively employed in the wire arc additively manufactured Ti6Al4V process with the aim of mitigating part distortion. A comparative analysis between simulation and experimental results was performed to explore the effects of active interpass cooling on the thermal behaviours, geometric features and distortion levels of deposit. The results show that active interpass cooling with CO₂ gas is an effective means of reducing Wire arc additive manufacturing (WAAM)-part distortion by increasing heat dissipation and reducing heat accumulation within the deposition. It can contribute to a maximum reduction of 81% in longitudinal distortion and 69% in transverse distortion for the wall structures produced in this study. Compared to the cooling gas flow rate, cooling time alternation is more effective in mitigating WAAM-part distortion due to more effective heat dissipation per unit time. The findings reveal that using active interpass cooling in WAAM can offer significant cost and build-time savings, as well as providing conditions for the improvement of WAAM-part quality.     

Fine equiaxed β grains and superior tensile property in Ti-6Al-4V alloy deposited by coaxial electron beam wire feeding additive manufacturing

Coarse columnar β grains result in anisotropic mechanical properties in Ti alloys deposited by additive manufacturing. This study reports that Ti-6Al-4V alloy fabricated by coaxial electron beam wire feeding additive manufacturing presents a weak anisotropy, high strength and ductility. The superior tensile property arises from a microstructure with fine equiaxed β grains (EGβ), discontinuous grain boundary α phase and short intragranular α lamellae. A large region of fine EGβ arises from a special combination of the temperature gradient and solidification rate, and attractive α morphology is caused by solid phase transformations during interpass thermal cycling and post heat treatments.     

Simulations in multipass welds using low transformation temperature filler material

Transient thermal and residual stress fields in flux-cored arc welds were examined using a finite element (FE) model. Experimental multipass welds were produced using both conventional and low transformation temperature (LTT) filler metals. Temperature-dependent material properties and both convective and radiant heat loss boundary condition have been considered in the FE model. The effects of the transformation temperature and interpass intervals on residual stresses were examined. It was found that compressive longitudinal residual stresses were developed at the weld centreline in the LTT filler metal. A short-time interpass interval causes the weld fusion zone to be above the martensite start temperature allowing the optimal use of the phase transformation effect. The FE model is sensitive to alteration in welding parameters and can satisfactorily predict the residual stress distribution in welded parts.     

基于焦耳热的滑压式增材制造方法温度场数值模拟与实验

提出了一种针对小型金属零部件的低成本、高精度的焦耳热金属熔丝增材制造技术。在此过程中,系统温度场和热历史对于实验分析具有重要意义。本研究主要利用有限元仿真软件建立三维焦耳热金属熔丝增材制造的热-电-结构耦合有限元模型,分析了制造过程中温度场变化规律以及丝材内部和基板的温度分布和等温面形状。结果表明：焦耳热在丝材与滚轮之间产生,丝材内部在0.1 s内升温至2700 ℃,滚轮移动后,最大温度位置随着滚轮的移动而移动,丝材内部温度梯度呈拱形,基板温度梯度呈半椭球形。模拟结果的截面熔核区域与实验截面熔核区域吻合较好。因此,所建立的有限元模型能够较准确地模拟焦耳热熔丝增材制造过程温度场,对实验机理的研究和后期的进一步加工有着重要指导意义。     

航空压气机叶片增材修复最优热输入分析

建立了压气机叶片MPAW增材修复传热模型，首先通过分析合金的热物性，计算出叶片MPAW增材修复的热输入范围，得到了不同热输入下熔池的温度分布. 之后创建了增材高度与送丝速度的数学模型，求解出不同送丝速度下的增材高度，并通过对焊缝截面温度分布的数值分析，进一步缩小热输入范围，得到试验参数. 最后通过数值分析及试验对比，揭示了合金修复区组织形貌与热输入率的演化规律，得到了最优的热输入和匹配的焊接参数.结果表明，试验结果与理论模型吻合度较好，验证了理论方法的有效性. 对于1 mm厚度的超薄压气机叶片的增材修复，采用研究得到的焊接参数，可达到最优热输入率，实现较好的增材形貌和增材修复效果.     

CMT+P过程及后热处理对TC4钛合金增材构件组织和性能影响

采用CMT+P程序进行TC4钛合金焊丝电弧增材制造,针对增材过程中热积累造成的组织性能不均匀性,采用两种不同热处理工艺以期改善这种不均匀性,并提高增材构件性能. 结果表明,采用CMT+P进行增材制造可以获得成形良好的沉积零件,当送丝速度为6 m/min,焊枪行走速度为0.3 m/min时,其热输入为313 J/mm, 沉积零件显微组织从上至下不断粗大. 热处理后试样不同部位晶粒大小变得均匀,抵抗塑性变形的能力增强. 拉伸试验表明,在600℃,4 h热处理条件下,构件的抗拉强度最高,为1 124 MPa. 断口分析表明, 所有试样断裂方式均为韧性断裂.     

Process-Structure-Property Relationships for 316L Stainless Steel Fabricated by Additive Manufacturing and Its Implication for Component Engineering

We investigate the process-structure-property relationships for 316L stainless steel prototyping utilizing 3-D laser engineered net shaping (LENS), a commercial direct energy deposition additive manufacturing process. The study concluded that the resultant physical metallurgy of 3-D LENS 316L prototypes is dictated by the interactive metallurgical reactions, during instantaneous powder feeding/melting, molten metal flow and liquid metal solidification. The study also showed 3-D LENS manufacturing is capable of building high strength and ductile 316L prototypes due to its fine cellular spacing from fast solidification cooling, and the well-fused epitaxial interfaces at metal flow trails and interpass boundaries. However, without further LENS process control and optimization, the deposits are vulnerable to localized hardness variation attributed to heterogeneous microstructure, i.e., the interpass heat-affected zone (HAZ) from repetitive thermal heating during successive layer depositions. Most significantly, the current deposits exhibit anisotropic tensile behavior, i.e., lower strain and/or premature interpass delamination parallel to build direction (axial). This anisotropic behavior is attributed to the presence of interpass HAZ, which coexists with flying feedstock inclusions and porosity from incomplete molten metal fusion. The current observations and findings contribute to the scientific basis for future process control and optimization necessary for material property control and defect mitigation.     

热输入对1OCrMo91O钢焊缝金属根焊层热循环的影响

利用焊接热循环测试系统,分别在不同热输入条件下,实时采集了10CrMo910耐热钢焊缝金属根焊层的温度参数.通过对不同热输入下焊接热循环曹线和参数的对比,并结合金相组织观察、硬度测试,研究了焊接热输入对10CrMo910耐热钢焊缝金属根焊层焊接热循环的影响.结果表明,热输入对10CrMo910耐热钢焊接热循环影响较大,...     

复杂零件等离子熔积无模成形的温度场模拟

提出高斯-双椭球复合热源和辐射-对流综合边界模型以考虑等离子热源及热边界.为提高计算效率、再现等离子熔积"增材制造"全过程,采用了动态网格自适应技术和"生死单元".基于ANSYS开发了复杂零件参数化设计和优化成形的APDL高效计算程序,实现了高能束三维瞬态温度场的模拟,并用试验进行了验证.计算和试验结果表明,采取对称跳跃扫描路径及适当的热输入和冷却工艺,能有效改善零件的温度场和增强焊道的自由伸缩能力,从而有利于降低拉应力和热裂倾向.