扫描路径对激光立体成形TC4构件热-力场的影响

为减缓激光立体成形过程中由于大的热梯度导致的残余应力和变形,首先采用原位测量监测成形过程中基板的温度及变形演化,并以此校验有限元模型,然后利用校准模型研究不同扫描路径对激光立体成形TC4钛合金构件热-力场演化行为的影响。结果表明:模拟结果与实验吻合良好。最大热梯度和最大拉应力均出现在第一层扫描过程中,温度梯度随沉积层数增加而逐渐减小。长边单向扫描方式下基板的变形量最大,而采用短边往复扫描方式下残余应力和变形最小;采用棋盘格扫描方式能有效减小基板的变形,但不能减小构件的残余应力。另外,基板的横向弯曲变形能有效抑制基板的纵向弯曲,而相变诱导的应力释放对激光立体成形构件的残余应力和变形具有显著的影响。     

TC4钛合金激光焊接应力变形有限元分析

基于ANSYS有限元分析软件,采用三维移动热源,对TC4钛合金激光焊接残余应力和变形进行了数值模拟和实验研究.结果表明:钛合金激光焊接产生很大的纵向残余应力,而横向残余应力较小.激光焊接线能量增加时,纵向残余应力拉伸区域变宽,峰值应力降低;而横向残余应力随线能量的增加而升高.在临界焊透规范以上焊接时,随焊接线能量的增大,角变形随之而减小,而横向收缩变形增大.焊件被完全穿透时,线能量对角变形的影响作用降低.钛合金激光焊接变形和残余应力实验结果与数值计算结果吻合性较好.通过焊缝金相实验分析了焊接残余应力和变形与线能量的内在关系.     

激光增材制造高温合金原位增强钛合金复合材料的组织与力学性能

采用激光选区熔化成形（selective laser melting,SLM）技术制备TCGH(TC4+GH4169)复合材料,探究TCGH钛合金复合材料的最佳成形工艺参数,并研究沉积态试样和热处理试样的显微组织与力学性能。结果表明：TCGH钛合金复合材料的最佳工艺参数为扫描速率900 mm/s、激光功率150 W,致密度达到99.5%以上。GH4169粉末的添加改变了TC4钛合金材料的固态相变行为,沉积态组织呈现明显高温凝固特征,使得逐行扫描搭接和逐层扫描堆积成形特征变得明显,沿打印方向原始粗大柱状β晶粒尺寸明显减小,复合材料抗拉强度提升。与沉积态试样相比,950℃热处理后,试样显微组织转变为近等轴组织,同时随着热处理温度上升,第二相的回溶导致复合材料的固溶强化作用占主导地位,使得复合材料抗拉强度和塑性均得到提升。     

不同基板预热温度对激光金属沉积成形过程温度场的影响

为降低成形过程的热应力,抑制成形过程裂缝的产生,减小成形过程试样和基板的翘曲变形,激光金属沉积成形往往需要进行基板预热,因此研究不同基板预热温度对激光金属沉积成形过程温度场的影响具有非常重要的意义．根据有限元分析中的“单元生死”技术,利用APDL编程建立了基板预热对激光金属沉积成形过程温度场影响的三维多道多层数值模拟模型,详细分析了基板未预热和分别预热到200,300,400,500,600 ℃时对沉积成形过程温度场和温度梯度的影响．通过中国科学院沈阳自动化研究所自行研制的激光金属沉积成形系统和基板预热系统,在与模拟过程相同的参数下,利用镍基合金粉末在基板未预热和分别预热到300,400,500,560 ℃时进行了成形试验,试验结果跟数值模拟结果吻合较好．     

TC4钛合金的激光快速成形特性及熔凝组织

在惰性保护气氛中对TC4钛合金的激光快速成形特性进行了试验研究.结果表明,虽然影响TC4钛合金激光快速成形的工艺参数较多,但其作用是通过对激光沉积特性的影响来体现的.显著影响成形过程沉积特性工艺参数主要包括单层熔覆厚度、单道熔覆宽度、Z轴的单层行程△Z和多道间搭接率,必须对其进行严格控制.成形件的熔凝组织由细小的针状马氏体α'和原始β晶界组成,各层之间为致密的冶金结合.和锻造TC4钛合金相比,激光快速成形过程的快热快冷使α-Ti固溶体的固溶度增大.     

TC4钛合金激光焊接/超塑成形组合工艺研究

本文将超塑成形(SPF)和激光焊接技术(LW)相结合,开发激光焊接/超塑成形组合工艺(LW/SPF),研究TC4钛合金激光叠焊接头的超塑性变形行为,并对超塑性变形前后的显微组织进行分析.结果表明,TC4钛合金激光叠焊接头能够承受焊板的变形,试样在母材断裂,并通过四层板的模拟件研制验证了超塑成形/激光焊组合工艺工业应用的可行性.     

激光相变热处理对TC４电子束焊缝残余应力的影响

利用CO２激光相变热处理技术对TC４钛合金电子束焊缝进行了处理,研究了激光功率、光斑直径、 辅助气体等激光工艺参数对电子束焊缝残余应力分布的影响。实验结果表明,激光相变热处理改善了焊缝残余 应力的分布,使焊缝表面残余应力由拉应力转变为压应力,其压应力值随着激光功率的增加而增大,随着激光 光斑直径的减小而增加;辅助气体为O２时残余压应力值比辅助气体为N２大３０～４０MPa,激光相变热处理显著 提高了TC４钛合金电子束焊缝的残余压应力及其使用寿命。     

成形气氛中氧含量对TC4钛合金激光快速成形工艺的影响

在惰性保护气氛中对TC4钛合金的激光快速成形进行了实验研究.研究结果表明,成形气氛中的氧含量,对成形工艺包括激光沉积工艺、成形表面质量、粉末利用率、熔覆层是否开裂等具有显著影响.氧含量严格控制在0.02%以下时,获得表面平整光洁、无裂纹等缺陷的TC4薄壁试样,粉末利用率达53%.     

激光选区熔化与铸造成形TC4钛合金的力学性能分析

借助有限元模拟、光学显微镜(OM)、扫描电镜(SEM)、能谱分析(EDS)和维氏硬度仪研究了激光选区熔化和铸造成形TC4钛合金的微观组织演变及力学性能,进一步分析了不同成形条件下液态金属凝固冷却对其微观组织和力学性能的影响。结果表明:激光选区熔化与铸造成形的TC4钛合金分别为针状马氏体α'相的网篮组织、α+β相的魏氏组织。与铸造相比,激光选区熔化成形TC4钛合金具有极快的冷却速率(1.78×107℃·s~(-1))和较高的温度梯度,元素类型相同,晶体取向明显。同时,利用激光选区熔化(SLM)技术成形的TC4试样的抗拉强度、屈服强度、伸长率和硬度分别为1 120.83 MPa、916.31 MPa、9.5%和123.04HV,而铸造试样的抗拉强度、屈服强度、伸长率和硬度分别为917.67 MPa、786.23 MPa、8.0%和77.876HV。与铸造成形相比,SLM成形的TC4试样的抗拉强度、屈服强度、伸长率和硬度增大,分别提升了22.14%、16.54%、18.75%和58%,因此激光选区熔化成形的TC4试样具有较好的力学性能。     

基板预热温度对激光金属沉积成形零件微观组织的影响

基板预热可以显著降低激光金属沉积成形（laser metal deposition shaping, LMDS）过程的热应力,从而抑制成形过程裂缝的产生,但基板预热温度的高低对成形零件的微观组织有着重要的影响,因此研究不同基板预热温度下激光金属沉积成形零件的微观组织变化规律对基板预热温度的选择具有非常重要的意义.利用中国科学院沈阳自动化研究所自行研制的激光金属沉积成形系统和基板预热系统,采用Ni60A金属粉末在基板未预热和预热到200,300,400,500和600 ℃时分别进行成形试验.然后利用扫描电子显微镜和能量散射谱仪对成形试件的微观组织进行深入的研究,得到不同基板预热温度对激光金属沉积成形零件微观组织的影响规律,为基板预热温度的优化选择提供了重要参考.     

TC4零件激光快速修复加工参数带的选择

通过研究激光加工参数,包括激光功率、光束扫描速度以及送粉率对热输入效率η和熔覆层形状系数ζ的影响规律,并结合激光快速修复过程对热输入效率和熔覆层形状系数的要求,建立了TC4激光快速修复的加工参数带。采用文章所确定的加工参数带中的参数,有利于减小激光快速修复件的变形,得到的修复件无熔合不良缺陷。     

Material characterization and corrosion behavior of hybrid coating Ti−Al−Si−Cu/Ti−6Al-4V composite

Titanium alloy grade 5 is a grade of the titanium material that is in-demand in the marine, aerospace, biomedical and turbo machinery industries. It offers great properties such as being light weight, good corrosion performance and great strength. However, some of the other properties, namely: its low hardness and poor tribological performance, has limited its various industrial application. Developments have focused on the enhancement of the surface properties without altering the bulk of the material. This has led to the laser metal deposition technique categorized under the additive manufacturing processes. It is a feasible technique that operates on layer-by-layer additive processing to manufactures whole parts or repair local damages in components. This study aims to ascertain the optimum processing conditions of the process by varying the laser intensity and scanning speed between 0.9 kW–1 kW and 1.0 m/min–1.2 m/min, respectively, while maintaining all the other process parameters. The specimens were produced by utilizing the ytterbium laser system to conduct laser surface alloying of Ti−Al−Si−Cu/Ti-6Al-4 V. Metallographic preparations, characterizations to conduct laser metal deposition (LMD), microhardness and corrosion test were conducted. It was deduced that Ti-9Si-3Cu alloy had the best optimum performance at 1 kW and 1.0 m/min. The hardness and corrosion were optimum improved at reduced scan speeds and increased laser power.     

基于Logistic回归模型的TC4零件激光熔化沉积工艺参数分析（英文）

In this paper, laser melting deposition(LMD), a new advanced manufacture technology. While manufacturing a metal part by LMD process, if we could control the energy distribution in internal different areas such as cladding layer or that between cladding layer and the substrate with optimal process parameters, the probability of internal defects of parts can be reduced, and the mechanical properties of parts will be greatly improved. To address the problem that whether the part made by LMD has internal defects, in this paper we designed the orthogonal rotation experiments through selecting different process parameters. Then a Logistic Regression model was built based on the experiments data. The calculation result of the regression model was in good agreement with the result of authentication test. Therefore, this Logistic Regression model has important reference for selecting LMD process parameters.     

低温对TC4脉冲激光焊接接头组织和性能的影响

在-120~25℃温度范围内对TC4钛合金薄板脉冲激光焊接接头进行了拉伸试验,并对拉伸断裂后的显微组织进行了观察,研究了低温对TC4钛合金脉冲激光焊接接头组织和力学性能的影响。试验结果表明:随着温度的降低,TC4钛合金脉冲激光焊接接头的显微组织并未出现明显变化,拉伸强度升高而延伸率下降,呈延性断裂模式。在低温拉伸过程中,TC4钛合金脉冲激光焊接接头母材区域的α相中有滑移带形成,预示变形机制仍然是位错滑移机制。     

粉末钛合金3D打印技术研究进展

粉末钛合金3D打印技术以低成本、易成形、柔性化制备、零件性能优异等优势,近年来成为钛合金近净成形制造领域的研究热点。总结了国内外粉末钛合金3D打印技术的研究进展,包括激光熔化沉积成形技术(LMD)、激光选区熔化成形技术(SLM)、电子束选区熔化成形技术(SEBM)。比较研究了3种成形技术制备的钛合金的组织特点及力学性能,并讨论了粉末钛合金3D打印技术的市场化现状与未来发展趋势。     

医用钴合金表面改性技术的研究进展

钴合金具有优异的生物力学特性、耐磨损性能和耐腐蚀性能,在医学植入领域有着广阔的应用前景,其表面改性技术已成为医用金属材料的研究热点和重点。本文简述了钴合金材料表面改性技术的优势,包括钴合金材料的生物力学特性、耐磨性能、耐腐蚀性能等。同时归纳了钴合金材料因人体体液腐蚀和摩擦磨损会释放出Co、Cr等金属离子而导致生物致敏等问题。在上述基础上,重点综述了近年来钴合金表面改性技术的研究进展,包括离子注入技术、选区激光熔化技术、真空沉积技术。其中,离子注入技术主要包括氮离子注入、钇离子注入、镧离子注入和钛镍离子注入等;选区激光熔化技术主要包括粉层厚度、激光功率、组分含量、扫描方式和扫描速度等;真空沉积技术主要包括物理气相沉积和化学气相沉积。针对不同钴合金表面改性技术,分别从钴合金材料的生物力学特性、耐磨性、耐腐蚀性和生物相容性等方面进行了归纳分析。最后分析了钴合金表面改性的发展趋势,认为钴合金表面改性技术应朝着高生物相容性、无金属离子释放、生物功能化、高耐腐蚀性和高耐磨性的方向发展。     

The relationship between thermo-mechanical history,microstructure and mechanical properties in additively manufactured CoCrFeMnNi high entropy alloy

Here,a single-track CoCrFeMnNi high entropy alloy(HEA)was successfully fabricated by laser melting deposition(LMD).Combining the experimental observations and numerical simulation,the microstruc-ture and mechanical properties of the as-deposited parts were systematically studied from the perspective of thermo-mechanical history experienced during the LMD process.The strengthening mech-anisms of the LMDed CoCrFeMnNi HEA parts were clarified.The frictional stress strengthening,grain boundary strengthening and dislocation strengthening contributed the whole yield strength of the parts.Dislocation strengthening dominated the strengthening mechanism.It was expected that the establish-ment of the relationship between thermo-mechanical history,microstructure and mechanical properties of the LMDed CoCrFeMnNi HEA could shed more insights into achieving HEA parts with the desired microstructure and high performance.     

Influence of process strategy on distortion and residual stresses for the powder based laser metal deposition process

Laser metal deposition (LMD) induces a complex 3‐axis residual stress state, which superimposes the external service stresses and can cause unpredicted in‐service failures. To optimize the process it is important to know the mechanisms and the opportunities to influence the occurrence of residual stresses. From the mathematical point of view, laser metal deposition represents a free boundary value problem. The track geometry is part of the solution. Previously the authors developed a thermal model that is used to calculate the time‐ and space resolved temperature distribution and the track geometry. The thermal model encompasses the powder stream, its interaction with the laser radiation, the shadowing of the laser radiation by the particles, the heating of the particles and the melt pool computation. In this publication, the evolution of residual stresses for overlapping tracks for single and multilayer processing for different powder mass rates is described.     

Effect of isothermal deformation on microstructure and properties of electron beam welded joint of Ti2AlNb/TC11

Abstract

The present paper reports the influence of hot work (isothermal deformation accompanied with heat treatment) on microstructure and properties of electron beam welded dissimilar joint. Ti₂AlNb alloy and TC11 alloy were used to fabricate the joints. Isothermal deformation and heat treatment were performed under certain conditions. The structures were analysed using optical microscopy, X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The results show that the as welded metal of Ti₂AlNb/TC11 joint is mainly composed of α₂ and β phases. The metastable β phase transformed into α+β phases during deformation and heat treatment processes. There are no big differences in tensile strength of joints under different conditions. However, the impact toughness of the weld has improved 72% after hot work.     

TC4钛合金电子束沉积修复工艺研究

目的 研究TC4钛合金电子束沉积修复工艺对修复试样成形形貌的影响。方法 主要对电子束流、送丝速度和成形速度3种工艺参数进行研究,观察其宏观形貌,从而归纳出工艺参数对电子束沉积修复钛合金TC4的影响规律。结果 在一定范围内,电子束流较小时,母材与修复区熔合不良,产生“V”型孔洞缺陷;随着电子束流增大,热影响区也随之增大。送丝速度主要影响试样的外观成形,较快或较慢的送丝速度都会使修复试样表面成形不良。成形速度较小时,成形表面有密集的鱼鳞纹,修复试样余高较低;成形速度增大时,热影响区随之减小,同时会产生孔洞缺陷。结论 不同的电子束流、送丝速度、成形速度都会对TC4钛合金电子束沉积修复形貌产生重要影响,需要合理的控制工艺参数。