A modified Johnson-Cook model for NC warm bending of large diameter thin-walled Ti-6Al-4V tube in wide ranges of strain rates and temperatures

Numerical control（NC） warm bending is a proven strategy to form the large diameter thin-walled（LDTW） Ti-6 Al-4 V tubes, which are typical light-weight and high-performance structural components urgently required in many industries. In virtue of unveiling the thermo-mechanical coupled deformation behaviors, uniaxial tensile tests were conducted on Ti-6 Al-4 V tube within wide ranges of temperatures（25-600 ℃） and strain rates（0.00067-0.1 s～（-1））. Moreover, a modified Johnson-Cook（JC） model is proposed with a consideration of nonlinear strain rate hardening and the interaction between strain hardening and thermal softening. Resultantly, the present model gives more accurate predictions for flow stress over the entire deformation ranges and the maximum error decreases by about 90%. By employing proposed model to NC warm bending, preferable precision is obtained in predicting forming defects including fracture, wrinkling and over thinning. The present work lays foundation for the forming limit prediction and process optimization in NC warm bending of LDTW Ti-6 Al-4 V tubes.

Formation, microstructure and mechanical properties of double-sided laser beam welded Ti-6Al-4V T-joint

The T-joints of Ti?6Al?4V alloy were manufactured by double-sided synchronized laser beam welding with the homologous filler wire. The formation, microstructure and mechanical properties of welded joints as well as the correlations of each other were investigated. The results indicate that the quality of weld seams is good without defects such as discontinuity, beading, visible cracks or porosity, which is linked to the steady molten pool behavior and droplet transition. The morphologies of the heat affected zone (HAZ) located on the skin and stringer are disparate. The microstructure of the HAZ and fusion zone (FZ) is mainly comprised of acicular martensiticα′ phases. The microhardness of the HAZ and FZ is higher than that of the base metal (BM) and reaches a maximum value at the HAZ near FZ on the stringer. The tensile specimens along the skin and stringer fractured at the BM with ductile fracture surfaces.

激光选区熔化Ti-6Al-4V合金的微纳压痕尺寸效应

目的研究不同状态激光选区熔化Ti-6Al-4V合金的纳米压痕尺寸效应。方法对原始态合金分别进行600、700、800、900℃退火处理,利用扫描电子显微镜观察原始态和4种退火态合金的显微组织。基于纳米压痕技术测量原始态及4种退火态合金的纳米硬度和弹性模量。基于比例试样阻力模型、Nix-Gao模型和Meyer定律对纳米硬度进行函数拟合。结果随着退火温度的升高,原始态组织从魏氏体逐渐演变为网篮组织。5种形态的Ti-6Al-4V合金的硬度和弹性模量均出现随压入深度的增加而减小的现象,表现出典型的压痕尺寸效应,基于试验测得的原始态及4种退火态合金的纳米硬度分别为3.66、4.36、3.96、3.88、4.77 GPa,弹性模量分别为113.1、125.2、102.1、100.3、108.7 GPa;基于比例试样阻力模型计算的纳米硬度分别为3.53、4.34、3.92、3.52、4.04 GPa;基于Nix-Gao模型计算的纳米硬度分别为3.68、3.94、4.07、3.85、4.47 GPa;基于Meyer定律拟合出的迈耶指数分别为1.75、1.86、1.82、1.80、1.81,均小于2,均表现为正压痕尺寸效应。结论激光选区熔化Ti-6Al-4V合金的硬度及弹性模量均有典型的压痕尺寸效应;3种模型均能较好地描述原始态和退火态合金的压痕尺寸效应,Nix-Gao模型直接建立了纳米硬度和压痕深度的关系,其拟合结果更接近于试验结果,计算的硬度值也最为准确。

Ti-6Al-4V六槽深浅腔动静压轴承刚度数值分析

针对传统材料制造的动静压轴承刚度较差的问题,提出一种基于Ti-6Al-4V材料制造六槽深浅腔交错分布的动静压轴承。利用ANSYS有限元软件建立六槽深浅腔动静压轴承流固耦合模型,研究轴径间隙、转速以及偏心率对QSn4-3轴承和Ti-6Al-4V轴承刚度的影响规律。结果表明:钛合金材料制成的轴承刚度优于传统锡基合金材料制造的轴承,各工况参数中,轴径间隙对轴承刚度的影响最为显著,其次是偏心率。该研究可为钛合金滑动轴承的数值模拟和设计提供参考。

选区激光熔化Ti-6Al-4V合金在模拟乏燃料后处理环境中的腐蚀行为

研究选区激光熔化(SLM)制备的Ti-6Al-4V合金在乏燃料后处理环境中的腐蚀行为。借助光学显微镜、X射线衍射、扫描电子显微镜、电子背散射衍射以及电化学测试等手段研究SLMTi-6Al-4V合金的显微组织及耐蚀性。结果表明,相较于铸造合金,SLM Ti-6Al-4V合金在含氧化性离子的6 mol/L热硝酸溶液中的耐腐蚀性更好。进一步分析表明,SLMTi-6Al-4V合金具有α'+β的微观结构,β-Ti相含量较高且分布均匀,同时其晶粒尺寸较小、晶界密度较高,这种微观结构可提高其在含氧化性离子的硝酸中的钝化能力以及耐腐蚀性。SLM Ti-6Al-4V合金有望在乏燃料后处理过程中得到广泛应用。

电子束熔丝增材制造Ti-6Al-4V钛合金研究进展

电子束熔丝增材制造技术因其电子束能量密度高、所处真空环境等优势,逐渐成为金属增材制造领域的研究热点之一。回顾了电子束熔丝增材制造技术的发展历程及现状,介绍了一种新型电子束熔丝增材制造技术——同轴送丝电子束熔丝增材制造。结合作者课题组近几年的研究工作,针对Ti-6Al-4V钛合金的成形缺陷、显微组织及力学性能,对传统电子束熔丝增材制造技术和同轴送丝电子束熔丝增材制造技术进行了对比论述,其中同轴送丝电子束熔丝增材制造有望沉积β晶粒更细、更等轴的钛合金构件。最后结合当前研究存在的不足,对电子束熔丝增材制造的发展给出了建议。

基于NaCl溶液的射流电解微铣削加工Ti-6Al-4V试验研究

钛合金在航空航天、生物医疗、精密仪器等领域的微小构件制造中的应用前景广阔。基于电化学阳极溶解原理去除材料的射流电解微铣削加工技术在钛合金微细加工方面具有原理优势。然而,在电化学作用下,钛合金表面极易生成致密的钝化膜,导致材料溶解过程难以持续稳定进行。对此,试验测试了Ti-6Al-4V在不同组分和不同浓度电解液中的极化曲线,发现质量分数10%NaCl溶液对钝化膜的破除能力强,且钝化-溶解过程相对稳定。在此基础上,探究了金属喷嘴内径、加工电压、扫描速度对射流电解微铣削加工微槽深宽比和杂散腐蚀范围的影响规律。最后,采用金属喷嘴内径300μm、加工电压35 V、扫描速度75μm/s的优选工艺参数,在Ti-6Al-4V表面加工出平均槽宽为823.1μm(标准差为10.42μm),平均槽深为157.26μm(标准差为5.89μm),表面粗糙度为2.006μm(标准差为0.088μm)的方形螺旋微结构。

双级退火对Ti-6Al-4V合金组织及力学性能的影响

对Ti-6Al-4V合金进行了双级退火处理,采用扫描电镜和Gleeble-3500热模拟试验机研究了不同退火温度对合金的微观组织演化和力学性能的影响。结果表明:随着首次退火温度的升高,合金的显微组织中初生α相含量减少,次生α相含量增加,合金的抗拉强度和剪切强度均升高,伸长率和断面收缩率逐渐下降,在1000℃时出现大幅下降。随再次退火温度的升高,组织中等轴α相含量增加,同时片层次生α相发生粗化现象,合金的抗拉强度和剪切强度降低,伸长率和断面收缩率增加。当首次退火温度为950℃时,随着再次退火温度由550℃升高到650℃,合金的伸长率由8.9%增加到12.8%,断面收缩率由26.2%提升到39.5%,随着再次退火温度由650℃升高到700℃,合金的伸长率和断面收缩率无明显提升,抗拉强度和剪切强度下降幅度较大,抗拉强度由1184.6 MPa下降到1089.2 MPa,剪切强度由708.6 MPa下降到678.4 MPa。综合分析可知,经950℃×1 h/WC+650℃×2 h/AC的双级工艺退火后,合金的综合性能最佳。

激光选区熔化生物医用Ti-6Al-4V合金的弯曲疲劳行为

分析了SLM Ti-6Al-4V合金的弯曲疲劳行为及相应的微观组织和断口形貌,设置与SLM试样化学成分相同的轧制态Ti-6Al-4V合金进行对比研究.采用X射线衍射(XRD)、结合电子背散射衍射(EBSD)的扫描电子显微镜(SEM)对合金的微观组织进行分析.结果表明,三点弯曲疲劳裂纹起始于准解理断裂表面附近的应力集中,随后向内扩展.SLM成形Ti-6Al-4V合金的弯曲疲劳寿命高于轧制成形Ti-6Al-4V合金,SLM Ti-6Al-4V合金内部孔洞缺陷导致表面附近应力集中,促进疲劳裂纹形核;而SLM Ti-6Al-4V合金中随机取向的α+β晶粒、二次裂纹和孔洞延缓了裂纹扩展,提高了疲劳寿命.对于轧制态Ti-6Al-4V合金,由大量近似取向α晶粒组成的宏观区引起应力集中,形成微裂纹,导致疲劳裂纹形核,而且宏观区对裂纹扩展的阻碍作用较小,不利于材料的疲劳寿命.

Heat-treated microstructure and mechanical properties of laser solid forming Ti-6Al-4V alloy

The effects of heat treatment on the microstructure and mechanical properties of laser solid forming （LSF） Ti-6Al-4V alloy were investigated The influences of the temperature and time of solution treatment and aging treatment were analyzed. The results show that the microstructure of LSFed samples consists of Widmanstatten α laths and a little acicular in columnar prior β grains with an average grain width of 300 μm, which grow epitaxiaUy from the substrate along the deposition direction （27）. Solution treatment had an important effect on the width, aspect ratio, and volmne fraction of primary and secondary a laths, and aging treatment mainly affects the aspect ratio and volume fraction of primary α laths and the width and volume fraction of secondary a laths. Globular a phase was first observed in LSFed samples when the samples were heat treated with solution treatment （950℃, 8 h/air cooling （AC）） or with solution treatment （950℃, 1 h/AC） and aging treatment （550℃, above 8 h/AC）, respectively. The coarsening and globularization mechanisms of a phase in LSFed Ti-6Al-4V alloy during heat treatment were presented. To obtain good integrated mechanical properties for LSFed Ti-6Al-4V alloys, an optimized heat treatment regimen was suggested.

Tensile behavior of Ti-6Al-4V alloy fabricated by selective laser melting: effects of microstructures and as-built surface quality

Selective laser melting （SLM） is a powerful additive manufacturing （AM） technology, of which the most prominent advantage is the ability to produce components with a complex geometry. The service performances of the SLM-processed components depend on the microstructure and surface quality. In this work, the microstructures, mechanical properties, and fracture behaviors of SLM-processed Ti-6AI-4V alloy under machined and as-built surfaces after annealing treatments and hot isostatic pressing （HIP） were investigated. The microstructures were analyzed by optical microscope （OM）, scanning electron microscope （SEM） and transmission electron microscopy （TEM）. The mechanical properties were measured by tensile testing at room temperature. The results indicate that the as-deposited microstructures are characterized by columnar grains and fine brittle martensite and the as- deposited properties present high strength, low ductility and obvious anisotropy. After annealing at 800-900~C for 2-4 h and HIP at 920~C/100MPa for 2 h, the brittle martensite could be transformed into ductile lamellar （a＋~） microstructure and the static tensile properties of SLM-processed Ti-6AI-4V alloys in the machined condition could be comparable to that of wrought materials. Even after HIP treatment, the as-built surfaces could decrease the ductility and reduction of area of SLM-processed fi-6AI-4V alloys to 9.2% and 20%, respectively. The crack initiation could occur at the columnar grain boundaries or at the as-built surfaces. The lamellar （a＋13） microstructures and columnar grains could hinder or distort the crack propagation path during tensile tests.

Variation effect of strain rate on microstructure in isothermal compression of Ti-6Al-4V alloy

Isothermal compression of the Ti-6Al-4V alloy at the deformation temperatures of 950 and 980℃,height reductions of 30% and 60%,and strain rates of 0.001,0.010,0.100 and 1.000 s-1 was conducted,wherein the variations of microstructure with strain rate were investigated.The experimental results showed that the variation of the microstructure with the strain rate under one condition was significantly different from that under another condition,which meaned that the interaction between the processing parameters was great.The optimization of the strain rate under one condition was not suitable for another condition.Therefore,selecting the forging equipment and optimizing the strain rate should be based on simultaneously considering the deformation temperature and height reduction.

Thermal cycle and its influence on the microstructure of laser welded butt joint of 8 mm thick Ti-6Al-4V alloy

Ti-6Al-4V alloy is extensively used in the manufacture of components in aviation.In the current study,the laser welding process is adopted to joint the Ti-6Al-4V alloy plate which has the thick of 8 mm.A three-dimensional finite element model is established to simulate the temperature distribution of laser welding process.The thermal cycle curves are produced on the strength of the simulation results.Meanwhile,the microstructure characteristics of the welded joint are investigated combined with simulation results.The results show that weld zone,heat affected zone and based metal experience similar thermal cycles process and the cooling rate has an important influence on the formation of microstructure.Moreover,the simulation results are well matched with experiment results.

Influence of multiple laser shock peening treatments on the microstructure and mechanical properties of Ti-6Al-4V alloy fabricated by electron beam melting

Laser shock peening(LSP)is an attractive post-processing method to tailor surface microstructure and enhance mechanical performances of additive manufactured(AM)components.The effects of multiple LSP treatments on the microstructure and mechanical properties of Ti-6Al-4V part produced by electron beam melting(EBM),as a mature AM process,were studied in this work.Microstructure,surface topography,residual stress,and tensile performance of EBM-manufactured Ti-6Al-4V specimens were systematically analyzed subjected to different LSP treatments.The distribution of porosities in EBM sample was assessed via X-ray computed tomography.The results showed that EBM samples with two LSP treatments possessed a lower porosity value of 0.05%compared to the value of 0.08%for the untreated samples.The strength of EBM samples with two LSP treatments was remarkably raised by 12%as compared with the as-built samples.The grains ofαphase were refined in near-surface layer,and a dramatic increase in the depth and magnitude of compressive residual stress(CRS)was achieved in EBM sample with multiple LSP treatments.The grain refinement ofαphase and CRS with larger depth were responsible for the strength enhancement of EBM samples with two LSP treatments.

Electrochemical Hydrogen Charging on Corrosion Behavior of Ti-6Al-4V Alloy in Artificial Seawater

This study employs advanced electrochemical and surface characterization techniques to investigate the impact of electrochemical hydrogen charging on the corrosion behavior and surface film of the Ti-6Al-4V alloy.The findings revealed the formation ofγ-TiH andδ-TiH_(2) hydrides in the alloy after hydrogen charging.Prolonging hydrogen charging resulted in more significant degradation of the alloy microstructure,leading to deteriorated protectiveness of the surface film.This trend was further confirmed by the electrochemical measurements,which showed that the corrosion resistance of the alloy progressively worsened as the hydrogen charging time was increased.Consequently,this work provides valuable insights into the mechanisms underlying the corrosion of Ti-6Al-4V alloy under hydrogen charging conditions.

激光增材制备Ti-6Al-4V/TiC金属陶瓷熔覆层组织与性能强化

Ti-6Al-4V合金因具有良好的强度、塑性、韧性、耐蚀性以及可焊性,在航空航天以及化工装备制造领域具有广泛应用,但其硬度以及耐磨性不高等性能短板,一定程度上限制了其摩擦磨损工况下的服役寿命。本研究基于激光熔覆优化工艺方法,增材制备具有TiC添加相的Ti-6Al-4V合金同质金属陶瓷熔覆层,表征并验证TiC增强相对熔覆层组织以及基本力学性能的强化作用。结果表明:熔覆层主要物相包括α-Ti,β-Ti以及TiC,其中TiC在熔覆层内过饱和析出,且受熔覆层不同位置过冷度差异影响,析出的TiC在熔覆层顶部以细小的颗粒状为主,而在熔覆层中部则主要呈树枝及花瓣状析出,熔覆层底部新增了麦穗状的析出形状,而稀释区则未见明显TiC析出。熔覆层平均显微硬度为530HV0.5,较基体提升了61%;在35 N载荷下,熔覆层平均摩擦因数为0.3583,较基体降低了11%,体积磨损率约为基材的87%,磨损形式为黏着磨损和磨粒磨损。

Influence of spark plasma sintering on microstructure and wear behaviour of Ti-6Al-4V reinforced with nanosized TiN

Ti-6Al-4V/TiN composites were successfully consolidated by spark plasma sintering(SPS).TiN addition to Ti-6Al-4V was varied from1%to5%(volume fraction).The effect of TiN addition on the densification,microstructure,microhardness and wear behaviour of Ti-6Al-4V was studied.Experimental results showed reduction in sintered density of the compacts from99%to97%with increase in TiN content.However,an increase in microhardness value was recorded from HV0.1389to HV0.1488.X-ray diffraction(XRD)analysis showed that the intensity of diffraction peaks of TiN phase in the composites increased also with formation of small amount of secondary Ti2N phase.SEM analysis of SPS sintered nanocomposites possessed a refinement ofα/βphase microstructure in Ti-6Al-4V with the presence of uniformly dispersed TiN particles.The worn surface of the composite showed improved abrasive wear resistance with non-continuous grooves as compared to the sintered Ti-6Al-4V without TiN addition.

Composition and structure of coatings on Ti-6Al-4V alloy by micro-plasma oxidation in NaAlO2 solution

Compound ceramic coatings on Ti-6Al-4V alloy were prepared for different time by pulsed bi-polar micro-plasma oxidation (MPO) in NaAlO2 solution. The phase composition was studied by XRD. And the electrochemical impedance spectra (EIS) of the coatings were measured to study the structure of the coatings, combined with the surface morphology. Using the proper EIS interpreting software, the "equivalent circuit" of the coatings was established, and meanwhile fitting values of equivalent element were obtained. The results show that the coating is composed of Al2 TiO5, α-Al2O3 and rutile TiO2, of which Al2 TiO5 is the main crystalline. Increasing the MPO time, the contents of Al2TiO5, rutile TiO2 and α-Al2O3 in the surface of the coating increase. And the EIS analysis and the surface morphology of the coatings illustrates the double-layer structure of the coatings, and the outer layer is loosen and the inner layer is compact. With the increase of the oxidizing time, the surface coarse degree of the coatings and the porosity of the outer layer of the coating are increased while the compactness of the inner layer of the coating is improved.

微量Ti-6Al-4V掺杂对SLM打印纯钛机械性能与显微结构的影响

目的:探究选区激光熔化(selective laser melting,SLM)打印制造的添加微量Ti-6Al-4V粉末的纯钛材料,在两种不同热处理温度(650℃,2 h和700℃,2 h)及不同扫描速度(1000 mm/s和500 mm/s)下的机械性能。方法:制备SLM打印的试样,测试材料的机械性能,观察拉伸试样的断口形貌及显微结构。结果:SLM打印的纯钛试样的极限拉伸强度在1000 mm/s扫描速度时高于500 mm/s扫描速度时的25%;在650℃及700℃不同热处理条件下,650℃,2 h在两种扫描速度下都表现出更加优异的机械性能,但延伸率在700℃,2 h在低扫描速度组更高。结论:添加微量Ti-6Al-4V粉末后打印的纯钛材料相较于Ti-6Al-4V合金更能满足口腔修复体的要求。

选区激光熔化成形Ti-6Al-4V钛合金的研究进展

Ti-6Al-4V钛合金具备良好的生物相容性、较小的密度以及较高的比强度而常用于航空领域和生物医学领域。选区激光熔化技术作为一种增材制造技术能够制备复杂的零件而被大量用于成形钛合金。选区激光熔化成形的钛合金相比于传统工艺有着更加优异的强度,但是塑性较差。如何制备出成型质量好、力学性能优异的钛合金依然是选区激光熔化技术面临的挑战。基于此,本文结合国内外研究现状,综述了选区激光熔化成形钛合金的进展,包括工艺参数和能量密度以及制备过程中所产生的缺陷对合金性能的影响,探讨了缺陷产生的原因;并总结了后处理对成形试样的拉伸性能和疲劳性能的影响;最后对增材制造钛合金的进一步研究方向进行了展望。