固溶与固溶时效热处理对Ti-6Al-4V合金微观组织及力学性能的影响

通过对Ti-6A1-4V钛合金螺栓紧固件的热处理实验,比较分析了固溶及固溶时效热处理对Ti-6A1-4V紧固件的微观组织分布的影响,并通过显微硬度计得到了螺栓紧固件各个位置的显微硬度分布。实验结果表明:Ti-6A1-4V螺栓经过固溶处理后,初生α组织的数量与尺寸减少而针状α组织的数量增多,并且初生α组织出现了即将溶解的状态。经过固溶时效热处理后,等轴状的初生α相组织变成了大晶粒β相的片层组织,组织分布较为均匀。固溶时效件试样的硬度分布更为均匀,固溶时效可以有效地提高螺栓的硬度,从而达到材料的使用要求。

Ti-6A1-4V微铣削表面完整性研究

为研究高强金属材料Ti-6A1-4V微铣削加工的表面完整性,利用直径为1mm的四刃微铣刀,分别对Ti-6A1-4V表面进行微沟槽铣削三因素四水平的正交试验和微小平面铣削的单因素试验。通过极差分析得出主轴转速、进给速度、切削深度对表面粗糙度值与残余应力值影响的变化规律及主次顺序,获得了理想的铣削参数组合。结果表明,在高转速、中低进给速度和切削深度的加工条件下表面粗糙度值和残余应力值可以达到比较理想状态。通过单因素试验得出了各个因素对于表面粗糙度值、压痕硬度值以及残余应力值的影响规律。试验结果对于提高高强金属材料Ti-6A1-4V的微铣削表面完整性具有一定的参考意义。

激光快速修复Ti-6Al-4V合金的显微组织与力学性能

针对Ti-6Al-4V合金在加工和服役过程中的损伤特点,对Ti-6Al-4V合金锻件的3种典型误加工缺陷——槽缺陷、面缺陷和体缺陷进行了激光快速修复研究。激光修复区与锻件基体形成致密冶金结合,Al、V合金元素由锻件基体到激光修复区均匀分布,无宏观偏析。激光修复区组织为粗大原始β晶粒内分布细长的α针及编织细密的α+β板条组织,呈现典型的魏氏结构,热影响区组织从锻件的等轴α+转变β组织逐步过渡到魏氏(α+β)组织。对预制有3种类型缺陷的激光修复试样进行室温静载拉伸试验和硬度测试,结果表明修复试样的拉伸性能达到锻件标准(HB5224-1982)。激光修复试样的硬度和强度高于锻件基体,而塑性则低于锻件基体。因此,激光修复区和锻件基体可看作是一种“强+弱”的组合,这与二者的显微组织是相对应的。

溅射参量对SiC涂层Ti-6Al-4V显微组织的影响

利用磁控溅射法在SiC纤维上沉积Ti-6Al-4V涂层制备成先驱丝.在功率密度一定时,沉积速率和工作气压有关.环境温度对涂层表面形貌及涂层与纤维结合的影响较大.涂层成分接近Ti-6Al-4V,沿涂层厚度方向成分分布均匀.涂层中柱晶晶粒尺寸为20-50 nm,为α-Ti固溶体.

Ti-6Al-4V钛合金板与304L不锈钢网的扩散焊

分别在800℃、825℃、850℃焊接温度、30 m in保温时间,3 MPa焊接压力下,进行Ti-6A l-4V钛合金板与304L不锈钢网的真空扩散焊接。对接头组织结构与化学元素扩散进行了扫描电镜与能谱分析,并测试了接头的剪切强度。结果表明:不添加中间过渡层金属,可以成功地实现钛合金板与不锈钢网的扩散焊接,并使接头的剪切强度达到90 MPa以上。不锈钢网中的Fe、N、iCr扩散并固溶到钛合金中,稳定了β相,使钛合金在一定深度上,其组织由原来的α+β双相结构转变为单相的β相。不锈钢中的Cr,由于钛合金中Ti的扩散进入,而在界面发生了上坡扩散现象。这种Cr在不锈钢一定深度内的富集,形成窄长的富Cr区域,冷却后转变为硬脆的σ相。但在焊接接头中没有发现明显其它的金属间化合物或氧化物相的生成,使得接头的机械性能得到了很好的保证。

Ti-6Al-4V ELI合金板材的显微组织与力学性能研究

研究了Ti-6Al-4V ELI合金板材的显微组织与力学性能。结果表明:双态组织,强度、塑性都比较高;而对于片层组织,随着片层的粗化,强度降低,延伸率先升高后降低,面缩呈下降趋势。片层粗化,抵抗裂纹穿越、迫使裂纹拐弯能力增大,提高了断裂韧性。

热处理对Ti-6Al-4V棒材固溶时效性能的影响

概述了对飞机转动件叶片用Ti-6Al-4V(TC4)钛合金棒材通过采用不同固溶时效热处理制度的实验,以研究TC4用钛合金棒材不同热处理制度与组织、固溶时效性能之间的关系,通过对比试验得出工业化生产满足宇航结构件和转动部件用TC4棒材制定合理的固溶时效热处理制度。

Ti-6Al-4V腐蚀疲劳的频率效应

一前言钛合金特别是Ti-6Al-4V,已得到广泛的应用。由于钛合金具有强度高、重量轻、耐腐蚀等特色,因此,特别适用于宇航、化工、海洋和生物工程。关于钛合金的力学性质,尤其是它在腐蚀介质环境中的疲劳特性,受到了工程技术界的高度重视,进行了大量的研究。关于钛合金在盐水中的疲劳裂纹扩展行为,已有不少学者进行了研究。Meyn研究了在3.5%NaCl溶液中频率对Ti-8Al-1Mo-1V合金的裂纹扩展速率da/dN的影响。他的试验结果是:当K1≥K1scc时,da/dN随频率的升高而降低,当K1<K1scc时,da/dN与频率无关。Wanhill研究了在3.5%Nacl溶液中,频率对Ti-2.5Cu（IMI230）和Ti-6Al-4V合金的裂纹扩展速率的影响,作者发现,不管K1是否高于K1scc,当频率从50Hz降到5Hz时,da/dN增加。

Ti-6Al-4V钛合金精铸件裂纹缺陷焊后荧光渗透检测一次合格率影响因素研究

以Ti-6Al-4V钛合金精铸件为研究对象,通过分析铸件缺陷补焊生产过程,运用二进制逻辑回归分析等方法进行数据分析,确定了影响铸件裂纹缺陷焊后荧光渗透检测一次合格率的关键因素,研究了裂纹缺陷的形成机理。结果表明:焊前打磨宽度比是关键因素。焊前打磨宽度比在0~3.0范围内,随着焊前打磨宽度比的增大,焊后荧光渗透检测一次合格率不断升高。规定焊前打磨宽度比在2.0~3.0范围时,较规定前,焊后荧光渗透检测的一次合格率由71.7%提高至90.5%。

电子束选区熔化成形Ti-6Al-4V合金不同沉积高度上的组织与性能

采用电子束选区熔化技术制备了厚度10 mm的Ti-6A1-4V合金板,研究了沿沉积方向合金的显微组织、拉伸性能和显微硬度的变化。结果表明:合金组织以α集束和α片层交织的网篮组织为主,底部由于经历多次热循环作用,α片层较顶部的略粗大,初生β晶的宽度随沉积高度增加而略有增大;合金底部、中部和顶部的屈服强度和抗拉强度呈逐渐升高趋势,但差异不大;不同沉积高度处的拉伸试样均表现为韧性断裂,断口处存在孔洞和未熔化的球形粉末;合金顶部的平均硬度(约315 HV)略高于底部(约295 HV),拉伸后由于应变硬化效应硬度略有提高。

Influence of Sc on high temperature strengthening behavior of Ti-6Al-4V alloy

Vacuum arc melting technique was used to prepare Ti-6Al-4V alloy containing Sc (0.3% and 0.5%, mass fraction). The ingots were melted twice by vacuum self-consumable electrode arc furnace. Forging of ingots was started in β-phase region and finished in high (α+β)-phase region. Annealing after forging was performed in low (α+β)-phase region for 30 min. Isothermal high temperature compression tests were conducted using thermal simulation machine under Ar atmosphere at 850 ℃ and 1 000 ℃, and the strain rate were 0.001, 0.01, 0.1 and 1.0 s-1. Optical microscope(OM), scanning electron microscopy(SEM), energy dispersive spectrum(EDS) and transmission electron microscope(TEM) were used to study the microstructure evolution during high temperature deformation. The results show that, the peak stress value of alloys increases with increasing Sc content after deformation at 850 ℃, however, there is no obvious strengthening of Sc when the alloys are deformed at 1000 ℃. Sc exists as Sc2O3 forms by internal oxidation during forging procedure, only minor Sc solutes in matrix. At 850 ℃, the interaction between dislocation and participated particles and twinning mechanism controls the deformation procedure accompanied recrystallization. At 1000 ℃, the deformation of alloys containing Sc is mainly controlled by twinning, while the deformation of alloy without Sc is not only controlled by twinning, but also the interaction between dislocation and precipitated particles inside the twinning lamellar.

Thermomechanical Behavior of Ti-6Al-4V Alloy

Ti-6AI-4V, among the Ti alloys, is the most widely used. In the present work, the behavior of Ti-6AI-4V alloy has been investigated by the uniaxial hot isothermal compression tests and a series of dilatometric experiments were also carried out to determine the transformation temperatures at different cooling rates. Specimens for hot compression tests were homogenized at 1050℃ for 10 min and then quickly cooled to different straining temperatures from 1050 to 850℃. Cooling rates were chosen fast enough to prevent high temperature transformation during cooling. Compression tests were conducted at temperatures from 1050 to 850℃ in steps of 50℃ at constant true strain rates of 10-3 or 10-2 s-1. The apparent activation energy for compression in two-phase region was calculated 420 kJ·mol-1. Partial globularization of a phase was observed in the specimen deformed at low strain rates and at temperatures near the transformation zone and annealed after deformation.

Evaluation of Microstructure and Wear Properties of Ti-6Al-4V Alloy Plasma Carbonized at Different Temperatures

Ti-6A1-4V （TC4） alloys were plasma carbonized at different temperatures （900, 950, and 1 000 ℃） for duration of 3 h. Graphite rod was employed as carbon supplier to avoid the hydrogen brittleness which is ubiquitous in traditional gas carbonizing process. Two distinguished structures including a thin compound layer （carbides layer） and a thick layer with the mixed microstructure of TiC and the a-Ti in carburing layer were formed during carburizing. Furthermore, it was found that the microstructure and the properties of TC4 alloy were significantly related to the carbonizing temperature. The specimen plasma carbonized at 950 ~2 obtained maximum value both in the hardness and wear resistance.

Superplastic Forming and Diffusion Bonding for Sandwich Structure of Ti-6Al-4V Alloy

Superplastic forming and diffusion bonding (SPF/DB) is a well-established process for the manufacture of components almost exclusively from Ti-6AI-4V sheet material. The sandwich structure of Ti-6AI-4V alloy is investigated. The effects of the microstructure on the SPF/DB process were discussed. The microstructure at the interfaces and the distribution of thickness were researched.

Investigation on the factors influencing the thickness distribution of superplastic-formed components

In the superplastic sheet forming process, the uniformity of the sheet's final thickness distribution is vital for ensuring the good mechanical quality of the formed components. The influences of the component shape and the contact friction on the final thickness distribution were investigated in this work by using finite element method on a series of axisymmetric models. It was concluded that shape optimization and friction elimination are required to get uniform thickness distribution, and eventually to improve the mechanical quality of the formed components. The constitutive equation of the Ti-6A1-4V superplastic material was also determined on the basis of experimental data.

轧制工艺对Ti-6Al-4V无缝管力学性能的影响

采用不同变形量开坯方式,分别经两道次和三道次轧制将管坯轧制成总变形量为70%的管材。在道次间进行800℃×1 h真空退火,冷却方法为炉冷至500℃后空冷至室温,观察其组织性能变化。结果表明,大变形量轧制时材料的流动呈条带状,小变形量轧制时材料的流动呈束状。总变形量相同的情况下,小变形量轧制方式能得到更好的外观质量,轧制道次越多,所得管材综合性能越好。

Multi-response optimization of Ti-6A1-4V turning operations using Taguchi-based grey relational analysis coupled with kernel principal component analysis

Ti-6A1-4V has a wide range of applications, especially in the aerospace field;however, it is a difficultto- cut material. In order to achieve sustainable machining of Ti?6A1-4V, multiple objectives considering not only economic and technical requirements but also the environmental requirement need to be optimized simultaneously. In this work, the optimization design of process parameters such as type of inserts, feed rate, and depth of cut for Ti-6A1-4V turning under dry condition was investigated experimentally. The major performance indexes chosen to evaluate this sustainable process were radial thrust, cutting power, and coefficient of friction at the toolchip interface. Considering the nonlinearity between the various objectives, grey relational analysis (GRA) was first performed to transform these indexes into the corresponding grey relational coefficients, and then kernel principal component analysis (KPCA) was applied to extract the kernel principal components and determine the corresponding weights which showed their relative importance. Eventually, kernel grey relational grade (KGRG) was proposed as the optimization criterion to identify the optimal combination of process parameters. The results of the range analysis show that the depth of cut has the most significant effect, followed by the feed rate and type of inserts. Confirmation tests clearly show that the modified method combining GRA with KPCA outperforms the traditional GRA method with equal weights and the hybrid method based on GRA and PCA.

A NOVEL APPROACH TO TESTING THE DYNAMIC SHEAR RESPONSE OF Ti-6Al-4V

Modifications were made on the traditional split Hopkinson pressure bar （SHPB） system to conduct dynamic shear tests. The shear response of Ti-6A1-4V was acquired at a shear strain rate of 104 s-1 by using this modified apparatus. The geometry as well as the clamping mode of the double-notch specimen was optimized by commercial FEM software ABAQUS, and the feasibility of the experiment set-up was validated. A shear stress calibration coeff^cient of γT = 1.03 and a shear strain calibration coefficient of γT- = 0.50 were obtained.We have employed high- speed photography to record the deformation process, especially the initiation and propagation of adiabatic shear band （ASB）, during the dynamic shear test. The frames show that the time duration from ASB initiation to its completion is less than 2 μs, from which we can estimate that the propagation speed of ASB within Ti-6A1-4V is more than 1250 m/s under such loading conditions. The temperature rise within ASB is also estimated to be △T2 ≈ 1460 ℃ based on energy balance. Such high temperature has led to softening of the material within the ASBs, and has intensified the shear localization and finally resulted in fracture of the material.

TC4钛合金盒形件超塑成形工艺

采用气压胀形方法对TC4钛合金某一特殊盒形结构件进行了超塑成形(SPF)。实验结果表明,在有限元模拟的基础上,成形温度为850℃,最大进气压力为1.5MPa时,成形时间为40min。超塑成形后的最佳取件温度为500℃。零件厚度分布率与有限元模拟结果大致相符合,减薄率最大处达53.7%。该工艺条件下成形的零件,其微观组织变化不大。