Multi-rate Superplastic Forming of Fine Grain Ti-6Al-4V Titanium Alloy

Most parts made by superplastic forming (SPF) have been formed at an optimum strain rate. The rate is selected to give the best SPF properties of the material. However, it has been proposed that multi-rate forming, where an initial high strain rate is successively reduced as the part is strained, can be used to make high strain parts in a much shorter time than traditional SPF forming. This paper examines the performance of fine grain Ti-6Al-4V alloy at very high initial strain rates, from 10–30 times faster than usual, with step reductions at prescribed levels of strain that still enables a total strain of over 2.1 (800%) to be achieved without degradation of the material. The paper also shows that the forming time to 100% deformation can be reduced from 55 min to 9 min. This technique can be used by industry to enable faster flow times and lower production costs of SPF parts. This article was presented at the AeroMat Conference, International Symposium on Superplasticity and Superplastic Forming (SPF) held in Seattle, WA, June 6–9, 2005.     

激光快速成形Ti-6Al-4V合金力学性能

采用实验研究的方法，对激光快速成形Ti-6Al-4V合金的力学性能进行了探讨。结果发现：和锻造件相比，激光快速成形沉积态Ti-6Al-4V合金的拉伸性能具有高强低塑特点和更显著的各向异性；成形试样的组织、氧含量和冶金缺陷都将影响到拉伸性能，其中组织的影响最显著，其次为氧含量和熔合不良缺陷：对于氧含量符合GJBGJB2921-1997标准的激光快速成形Ti-6Al-4V合金，经固溶时效热处理后所获得的网篮组织综合性能最好，不论是强度指标还是塑性指标都高于锻件标准。     

Supersonic Plasma Spray Deposition of CoNiCrAlY Coatings on Ti-6Al-4V Alloy

Plasma spray is a versatile technology used for production of environmental and thermal barrier coatings, mainly in the aerospace, gas turbine, and automotive industries, with potential application in the renewable energy industry. New plasma spray technologies have been developed recently to produce high-quality coatings as an alternative to the costly low-pressure plasma-spray process. In this work, we studied the properties of as-sprayed CoNiCrAlY coatings deposited on Ti-6Al-4V substrate with smooth surface (R _a = 0.8 μm) by means of a plasma torch operating in supersonic regime at atmospheric pressure. The CoNiCrAlY coatings were evaluated in terms of their surface roughness, microstructure, instrumented indentation, and phase content. Static and dynamic depositions were investigated to examine their effect on coating characteristics. Results show that the substrate surface velocity has a major influence on the coating properties. The sprayed CoNiCrAlY coatings exhibit low roughness (R _a of 5.7 μm), low porosity (0.8%), excellent mechanical properties (H _it = 6.1 GPa, E _it = 155 GPa), and elevated interface toughness (2.4 MPa m^1/2).     

高功率激光立体成形Ti-6Al-4V合金组织研究

针对高功率条件下激光立体成形Ti-6Al-4V合金组织特征展开研究,揭示高功率条件下组织形成机理,并对比分析了高功率与中/低功率条件下组织形成的差异及原因。结果表明:由于高功率条件下具有更低的温度梯度和更高的凝固速度,激光立体成形Ti-6Al-4V合金的宏观组织由粗大的柱状晶、竹节状的小柱状晶和等轴晶三部分组成,并且沉积层之间存在层带;而中/低功率条件下只有贯穿多个沉积层呈外延生长的粗大的柱状晶。高功率条件下层带内典型微观组织是由大量的魏氏α集束组成,而层带间为α板条编织成的网篮状组织,并且部分α相球化成等轴状。与中低功率条件下典型组织相比,高功率条件下α板条长宽比明显减小,不存在针状α。     

Ti-6Al-4V合金双半球结构脉冲电流辅助超塑成形

针对Ti-6Al-4V合金板材超塑成形能耗高、效率低的问题,提出了一种脉冲电流辅助超塑成形工艺。该工艺将成形坯料直接串联到脉冲电流回路,利用脉冲电流迅速将坯料加热至超塑成形温度。通过脉冲电流加热实验,分析了平均脉冲电流密度对坯料温度及升温速率的影响。结果表明,采用该加热方式可将坯料加热时间从数十分钟缩短至几十秒,能量消耗降至传统工艺的20%左右,极大地提高了加热效率、降低了能耗,实现了节能环保的绿色超塑成形技术。利用该工艺成形了Ti-6Al-4V合金双半球结构,并分析了在脉冲电流辅助工艺条件下细晶态Ti-6Al-4V合金的超塑变形机制。     

非球形Ti-6Al-4V粉末粒度对激光快速成形的影响

为了找到适合激光快速成形技术的非球形Ti-6Al-4V粉末粒度范围,采用高速摄影的方法研究了不同粒度粉末的输送情况,并通过不同粒度粉末的激光快速成形实验,研究了粉末粒度对粉末利用率、成形件表面精度和成形件内部气孔缺陷的影响.结果表明,在64～122 μm粒度范围内,随粉末平均粒度的变细,粉末利用率先增大后降低,成形件表面精度先提高后降低,成形件内部气孔先减小后增多,适合激光快速成形的粉末粒度应在86～98 μm之间.     

Dehydrogenation of Hydrogenated Ti-6Al-4V Alloy

对未置氢及置氢Ti-6Al-4V合金进行了TG/DSC试验,研究了置氢钛合金的除氢行为。结果表明,当温度超过600℃时,置氢钛合金的失重规律与未置氢钛合金具有较大的差别。当加热温度在600~900℃之间时,置氢钛合金的失重随着氢含量的增加而增加。这是由于置氢合金中的亚稳相发生了分解。不考虑合金氧化的影响,置氢钛合金的最大失重与合金中的氢含量一致。置氢钛合金的最佳除氢温度为750℃。对于不同氢含量的置氢钛合金,其除氢工艺是相同的。     

Ti-6Al-4V合金的疲劳性能

简要综述了Ti-6Al-4V合金的显微组织和织构对其疲劳性能的影响及其机理.     

Numerical Simulation and Superplastic Forming of Ti-6Al-4V Alloy for a Dental Prosthesis

This article investigates superplastic forming (SPF) technique in conjunction with finite element (FE) simulation applied to dental repair. The superplasticity of Ti-6Al-4V alloys has been studied using a uniquely designed five-hole test with the aim of obtaining the modeled grain size and the flow stress parameters. The data from the five-hole test are subsequently put into the FE program for the simulation of a partial upper denture dental prosthesis (PUD4). The FE simulation of the PUD4 is carried out to set up appropriate input parameters for pressing due to the SPF process being fully automatic controlled. A variety of strain rates ranging from 2.4 × 10⁻⁵ to 1 × 10⁻³ s⁻¹ are selected for the characterization of superplastic properties of the alloy. The Superflag FE program is used to generate an appropriate pressure-time profile and provide information on thickness, grain size, and grain growth rate distribution. Both membrane elements and solid elements have been adopted in the simulation and the results from both types of elements are compared. An evaluation of predicted parameters for the SPF of the prosthesis is presented.     

Stress relaxation behavior of Ti-6Al-4V alloy

1　INTRODUCTIONTi 6Al 4VisoneofthemostimportantTial loys[1,2 ] .Butthisalloyhasbadformabilityforitshighelasticresilience .Therefore ,hotsizingisimpor tant[36 ] .Asthebaseofhotsizing ,thestudyofstressrelaxationhasimportanttheoreticalvalueandpracticalsignificance .Ontheotherhand ,Ti 6Al 4Visusedasfastenermaterialssometimes .Whenthefastenersworkatthetemperaturehigherthanroomtemperature ,stressrelaxationmayresultsinacci dents .Sohowtopreventthestressrelaxationisveryimportant[7] .Uptonow ,…     

Ti及Ti-6Al-4V的水基凝胶注模成形研究

将凝胶注模工艺应用于金属Ti及Ti-6Al-4v合金粉末的坯体成形，研究了高固相含量的Ti粉和Ti-6Al-4V合金粉末的料浆的制备。结果表明，用凝胶注模工艺制备出了固相含量为54φ%的钛合金粉末料浆和形状复杂的坯体；粉末的颗粒形状是影响料浆固相含量的重要因素，球形粉末配制成的浆料固相含量最高，近球形次之，片状最低；分散剂柠檬酸铵也可以显著提高浆料的固相含量。     

Ti-6Al-4V钛合金的等离子W-Mo共渗

采用双层辉光等离子表面合金化技术对Ti-6Al-4V钛合金进行W-Mo共渗,研究了880～1000 ℃ W-Mo共渗时基体温度对渗层厚度的影响,采用SEM和XRD观察、检测渗层组织结构和相组成.结果显示,Ti-6Al-4V合金的W-Mo渗层组织良好.纳米压痕试验结果表明,合金渗层硬度高于基体.     

The laser additive manufacture of Ti-6Al-4V

Laser additive manufacturing (LAM) is a manufacturing technique with cost-reduction potential for titanium aerospace components. The mechanical properties of LAM Ti-6Al-4V have been investigated extensively, but little work on microstructure evolution has been performed to date. The results presented here provide a first look at the relationships between LAM processing parameters and microstructure in as-deposited Ti-6Al-4V. For more information, contact P.A. Kobryn, U.S. Air Force Research Laboratory, Materials and Manufacturing Directorate, AFRL/MLLMP, Wright-Patterson AFB, OH 45433 USA; (937) 255-1313; fax (937) 255-3007; e-mail Pamela.Kobryn@afrl.af.mil.     

Hydrogen-induced hot workability in Ti-6Al-4V alloy

The effect of hydrogen on hot deformability of Ti-6Al-4V alloy was investigated by isothermal hot compression test with temperature of 800 ℃ and velocity of 0.1 mm/s. By optical microscopy （OM） and transmission electron microscopy （TEM）, the influence of hydrogen on the microstructural features was systematically examined including the morphology of a grain, volume fraction of a phase and dynamic recrystallization （DRX）. The flow stress shows an initial decrease but a later increase with the increase of hydrogen content. The minimum of peak compression flow stress is obtained when 0.2% hydrogen is added into the alloy. The hydrogen-induced softening of Ti-6Al-4V alloy may be that hydrogen induces the increase of proportion of soft β phase, the increase of DRX and the increase of extent of twins.     

Thermoelectric non-destructive texture characterization in Ti-6Al-4V

Due to the manufacturing process Ti-6Al-4V alloy exhibited a very strong anisotropic texture caused by the existence of a preferred crystallographic orientation in the polycrystalline microstructure. This crystallographic alignment can result in anisotropic behavior of the material so that the material properties are different depending on whether they are measured in perpendicular or parallel direction. In addition to this morphological anisotropy, due to the dominantly hexagonal grain structure, the Ti-6Al-4V alloy also exhibited a substantial thermoelectric anisotropy. This study was conducted to investigate the effect of thermoelectric anisotropy on the thermoelectric power measurements in a highly textured Ti-6Al-4V specimen using a completely non-destructive technique based on the Seebeck effect. The result shows the thermoelectric power dependence associated with texturing and the macroscopic grain structure in a rolled Ti-6Al-4V specimen which was annealed at 710 °C for 2 h and slowly cooled. The measurements clearly demonstrate that the intrinsic sensitivity of the thermoelectric contact technique is a very useful tool that could be exploited for QND material characterization.     

Ti-6Al-4V钛合金热成形极限图及其应用

在650℃、700℃和750℃温度条件下进行Ti-6Al-4V钛合金成形极限试验,建立其热态成形极限,在此基础上,利用ABAQUS有限元分析软件进行数值模拟,对Ti-6Al-4V钛合金热态成形的破裂缺陷进行预测,并通过试验对其结果进行验证。研究结果显示,随着温度的升高,Ti-6Al-4V钛合金的热成形极限增加,有限元分析结果与试验结果相吻合,表明该文所建立的韧性断裂预测模型具有工程参考价值。     

Ti-6Al-4V钛合金搅拌摩擦焊缝的织构(英文)

采用W-Re合金搅拌头对α+β双相Ti-6Al-4V钛合金进行搅拌摩擦焊并在合适的工艺参数下获得无缺陷焊缝,利用取向成像显微镜对Ti-6Al-4V钛合金搅拌摩擦焊缝的织构进行研究。Ti-6Al-4V钛合金母材为轧制退火态,组织由变形的初生α相和转变β组织构成,具有典型的轧制织构。焊核区组织与母材明显不同,由大量的等轴动态再结晶晶粒组成,并在搅拌摩擦焊过程中形成{φ1=30°,φ=62°,φ2=30°}取向的织构。     

Mold wear during permanent-mold casting of Ti-6Al-4V

Mold wear during the casting of Ti-6Al-4V in a permanent (steel) mold was investigated using a combination of macro- and micro-scale observations and measurements. For this purpose, a steel mold with interchangeable inserts of three candidate mold steels (H13, P20, and 1040) was used. Inserts were removed at regular intervals during casting under prototype-production conditions and inspected to assess mold wear. Two major mold wear types were identified: soldering and “wrinkling.” Soldering was concluded to be a result of local over-heating of the mold, and wrinkling a result of cyclic stresses caused by a combination of solid-state phase transformations and large temperature gradients. The 1040 inserts performed the best; soldering was less severe and wrinkling did not occur. The better performance of the 1040 inserts was attributed to lower mold temperatures and thermal gradients due to the higher thermal conductivity of 1040 relative to H13 or P20.     

Superplastic bulging capability of Ti-6Al-4V buttcover plate

The investigation on the superplastic bugling capability of 1.5 mm mill annealed Ti-6A1-4V buttcover plate by means of manual gas tungsten arc welding (M-GTAW) and fusion type plasma arc welding (F-PAW) have been evaluated respectivdy. The result shows that untreated Ti-6A1-4V buttcover plate by M-GTAW exhibits no superplasticity,while the same untreated plate by F-PAW, shows good superplastic ability because of extremely fine acicular martensite microstructure of weld metal. To the buttcover plate by M-GTAW, the microstructure of weld metal changed into streaky α structure which exhibits good superplasticity from the original//structure under the condition of the constant temperature of 940℃ with the deformation degree of 45 %, and changed into the fine equiaxed grain which possesses excellent superplastic ahilitv under the condition of the constant temperature of 800℃ with the deformation degree of 40 %.