The use of β titanium alloys in the aerospace industry

Beta titanium alloys have been available since the 1950s (Ti-13V-11Cr-3Mo or B120VCA), but significant applications of these alloys, beyond the SR-71 Blackbird, have been slow in coming. The next significant usage of a β alloy did not occur until the mid-1980s on the B-1B bomber. This aircraft used Ti-15V-3Cr-3Al-3Sn sheet due to its capability for strip rolling, improved formability, and higher strength than Ti-6Al-4V. The next major usage was on a commercial aircraft, the Boeing 777, which made extensive use of Ti-10V-2Fe-3Al high-strength forgings. Ti-15V-3Cr-3Al-3Sn environmental control system ducting, castings, and springs were also used, along with Ti-3Al-8V-6Cr-4Mo-4Zr (β-C) springs. Beta-21S was also introduced for high-temperature usage. More recent work at Boeing has focused on the development of Ti-5Al-5Mo-5V-3Cr, a high-strength alloy that can be used at higher strength than Ti-10V-2Fe-3Al and is much more robust; it has a much wider, or friendlier, processing window. This, along with additional studies at Boeing, and from within the aerospace industry in general will be discussed in detail, summarizing applications and the rationale for the selection of this alloy system for aerospace applications. This paper was presented at the Beta Titanium Alloys of the 00’s Symposium sponsored by the Titanium Committee of TMS, held during the 2005 TMS Annual Meeting & Exhibition, February 13–16, 2005 in San Francisco, CA.     

Aerospace applications of beta titanium alloys

Beta alloys are beginning to play a significant role in both military and commercial aircraft. Ti-10V-2Fe-3Al forgings, for example, play major roles in the McDonnell Douglas C-17 and the Boeing 777. The attractive properties of Beta-C are increasing the use of titanium, rather than steel, in aircraft springs. Ti-15V-3Cr-3Al-3Sn is subject to increasing usage primarily because of its strip producibility and formability. Beta-21S is gaining importance for high-temperature applications. New alloys such as β-CEZ, SP-700, and Timetal® LCB could become important because of advantageous costs, processing, and/or properties. In the past, the use of beta alloys has largely been driven by their superior properties and weight-savings potential. In the future, cost will become more important. As a result, a greater emphasis will be placed on lower cost alloys and/or taking advantage of the improved processing capabilities of these alloys to minimize final component costs.     

Recent developments in metastable β strip alloys

The strip producibility, good fabricability, and excellent mechanical properties of β alloys make them useful for a variety of fabricated sheet metal structures on aircraft. TIMETAL 15-3 is currently used for environmental control system ducting on the Boeing 777 and, more recently, has been used on the Airbus A380. For applications that require exposure to higher temperatures, such as the exhaust assemblies, TIMETAL 21S is now used on the Boeing 777, Airbus A340, and various other civil and military aircraft. This paper was presented at the Beta Titanium Alloys of the 00’s Symposium sponsored by the Titanium Committee of TMS, held during the 2005 TMS Annual Meeting & Exhibition, February 13–16, 2005 in San Francisco, CA.     

Innovations in the Superplastic Forming and Diffusion Bonded Process

The Superplastically Formed and Diffusion Bonded (SPF/DB) titanium structure in production today for Boeing products, not including engines, are all diffusion bonded using matched metal tooling and are all fabricated using the common 6Al-4V alloy. The matched metal tooling concept presents a challenge in obtaining high-quality bonds over large areas due to tolerance build-up in the tools and the titanium sheets. Boeing Commercial Airplanes (BCA) is currently advancing the state of the SPF/DB process in several ways. One of these advances is using stop-off between the sheets and diffusion bonding the pack first and then superplastically forming the stiffening features. This generates a component that is very well bonded in the required locations. However, this process also has its challenges. One of these involves how to apply the stop-off material in the proper location using the most cost effective process. Historically, silk screening has been used to define the required pattern for the stop-off material. This process requires several pieces of equipment including a wash booth since the screen needs to be cleaned after each part. A paper maskant and laser scribing process has been developed for defining the stop-off pattern. Also, because diffusion bonding is performed first, when the component is superplastically formed, there is a tendency to form creases on the surface of the part. Methods have been developed to eliminate these surface creases on the unformed surface. Another advance in the SPF/DB process is in the titanium alloys being used for products. A fine grain 6Al-4V material has been developed that bonds and forms at 775 °C. The use of this material will minimize wear on the tools and presses as well as significantly reducing the amount of alpha case on the part surface. This article was presented at the AeroMat Conference, International Symposium on Superplasticity and Superplastic Forming (SPF) held in Baltimore, MD, June 25-28, 2007.     

Advances in fabricating superplastically formed and diffusion bonded components for aerospace structures

Superplastic forming and diffusion bonding (SPF/DB) production hardware is being fabricated today for aerospace applications. Metal tooling is being used to bring the titanium sheets into contact so diffusion bonding can occur. However, due to material sheet and tooling tolerances, good bond quality is difficult to achieve over large areas. A better method for achieving DB is to use “stop-off” inside sealed sheets of titanium, which constitutes a pack, and then the pack is bonded using external gas pressure. A good method for heating the pack for this process is to use induction heating. Components using “stop-off” that were diffusion bonded first and then superplastically formed have shown much better bond quality than components that were produced using matched metal tooling. This type of tooling has been successful at bonding small areas as long as the exerted pressure is concentrated on the area where bonding is required. Finite element modeling is providing weight effect solutions for titanium SPF/DB aerospace structures. This paper was presented at the International Symposium on Superplasticity and Superplastic Forming, sponsored by the Manufacturing Critical Sector at the ASM International AeroMat 2004 Conference and Exposition, June 8–9, 2004, in Seattle, WA. The symposium was organized by Daniel G. Sanders, The Boeing Company.     

A Quantitative Study on the Effect of Heat Treatment on the Microstructure and Orientation of Titanium Hydride in Electrochemically Hydrogenated Pure Titanium

The electrochemical hydrogen charging of pure titanium and its alloys has been investigated previously, while how a subsequent annealing treatment affects the type of hydride and its orientation relationship with matrix is not clear. In the present study, a quantitative study on the microstructure and orientation of titanium hydrides during electrochemical hydrogen charging and subsequent annealing treatment was carried out using scanning electron microscopy, transmission electron microscopy and electron backscatter diffraction. The results show that δ-hydride is the main in both the electrochemically hydrogenated sample and the subsequent annealing treated sample. After electrochemical hydrogen charging for 48 h, the surface is mainly composed of dense δ-hydride with a thickness of approximately 42 μm, the orientation relationship between α-matrix and δ-hydride follows only the orientation relationship of OR2, {0001}_α//{1$\overline{1}$1}_δ, $\langle 1\overline{2}10\rangle_{\alpha }$//$\langle 110\rangle_{\delta }$ and an interface plane $\{ 10\overline{1}3\}_{\alpha }$//$\{ 1\overline{1}0\}_{\delta }$. Besides OR2, a part of hydrides show an orientation relationship of OR1 with the matrix after annealing, {0001}_α//{001}_δ, $\langle 1\overline{2}10\rangle_{\alpha }$//$\langle 110\rangle_{\delta }$ and an interface plane of $\{ 10\overline{1}0\}_{\alpha }$//$\{ 1\overline{1}0\}_{\delta }$. It is further found that the relative frequency of OR1and OR2 is closely related to annealing duration. Under an argon atmosphere at 450 °C, the frequencies of OR1 and OR2 are nearly balance with an annealing time of 12 h, while OR1 becomes to be the predominant one with a relative frequency of 96.5% after annealing for 96 h. The mechanism for the evolution of orientation relationship of hydrides with annealing time was discussed.     

Manufacturing advantages of superplastically formed fine-grain Ti-6Al-4V alloy

Superplastic forming (SPF) of Ti-6Al-4V has traditionally been performed at 900 °C. Although SPF equipment and dies have been developed to withstand this high temperature, their life is limited and maintenance is high. In addition, the formed sheets need chemical milling after processing to remove a significant layer of alpha case, and parts require hand polishing due to a rough die surface caused by high temperature oxidation. The recent development of a Ti-6Al-4V alloy with a grain size of around 1 μm has led to the possibility of superplastic forming at a much lower temperature than regular Ti-6Al-4V. In addition, the forming speed can be increased. This work looks at some of the SPF attributes of fine-grain titanium, in particular, the optimum forming temperature, the thinning characteristics, alpha case formation, and forming speeds. The authors also address manufacturing advantages, such as die life, equipment needs, and operator comfort. Some prototype and preproduction aircraft components on Boeing airplanes are presented. The results show that the new fine-grain material could significantly lower the cost of SPF Ti-6Al-4V part production for the aerospace industry. This paper was presented at the International Symposium on Superplasticity and Superplastic Forming, sponsored by the Manufacturing Critical Sector at the ASM International AeroMat 2004 Conference and Exposition, June 8–9, 2004, in Seattle, WA. The symposium was organized by Daniel G. Sanders, The Boeing Company.     

3D打印医用钛合金研究进展

钛合金拥有较高的比强度、较好的耐蚀性能与生物相容性,其在医用植入物的应用市场前景十分引人关注。但传统医用钛合金植入物常采取铸造的生产方式,产品种类单一,无法满足"精准医疗"的诊疗目标。3D打印技术以其丰富的加工方式在医用钛合金方面应用优势逐渐凸显。本文介绍多孔医用钛合金的发展历史及3D打印钛合金的制造现状,分析现有3D打印医用钛合金的技术壁垒,并为未来3D打印医用钛合金的发展方向提供建议。     

Postprocessing effect on the ductility and flexural behavior of three titanium alloys under simulated superplastic forming conditions

Ductility of three titanium alloys was evaluated after exposure to time and temperature conditions representative of superplastic forming (SPF). Following exposure, flexural specimens were postprocessed to remove the α-case by one of three methods: no material removed, the standard amount of material removed by chemical processing, or a reduced amount of material removed also by chemical processing. Results include the evaluation of the specimens per ASTM E 290-97a and AMS-T 9046, springback analysis, and prediction of minimum bend radius criteria for the three alloys from finite element method simulation. It was found that results varied based on alloy and exposure temperature and the reduced postprocessing of titanium SPF parts produced acceptable results under certain conditions. This paper was presented at the International Symposium on Superplasticity and Superplastic Forming, sponsored by the Manufacturing Critical Sector at the ASM International AeroMat 2004 Conference and Exposition, June 8–9, 2004, in Seattle, WA. The symposium was organized by Daniel G. Sanders, The Boeing Company.     

Numerical modeling of a wing skin peen forming process

For many years shot peering has been used to provide fatigue resistance and form to airplane wing skins at the Boeing Commercial Airplane Company. In this process, the peening intensities used to form a new wing skin have been obtained through the use of approximate geometric relationships, along with a considerable amount of trial and error testing. This paper describes a numerical model that has been applied to replicate the shot peening process used at Boeing. The model is used to predict peening intensities and the initial size of the skin (flat pattern) given an arbitrary aerodynamic contour requirement. Discussion focuses on the finite element method and special optimization techniques used in the approach.     

The GTAW of Ti-6Al-4V castings and its effect on microstructural and mechanical properties

The gas-tungsten arc welding of Ti-6Al-4V investment castings is an integral part of titanium casting processing due to the need to repair casting defects. It is speculated that the refined alpha/beta microstructure produced by faster solidification of the weld metal can affect the static and dynamic properties of the casting. This report examines the effects of weld repair on microstructure and mechanical properties. For more information, contact James Ault, PCC Structurals, 4600 SE Harney Drive, Portland, Oregon 97206-0898; (503) 788-5456; fax (503) 777-8857.     

Characterisation of anodic oxide films formed on titanium and two ternary titanium alloys in hydrochloric acid solutions

The purpose of this paper is to characterise the anodic oxide films formed on titanium and two ternary titanium alloys, Ti‐15Mo‐5Al and Ti‐10Mo‐10Al in 1%, 10% and 20% hydrochloric acid solutions at 25, 50, and 75°C. The anodic film on titanium in hydrochloric acid is stable between + 0.6 V (SCE) and + 2.0 V (SCE). For our new ternary titanium alloys, the passive film is formed at about + 0.6 V (SCE) and is stable to + 2.0 V (SCE). The anodic polarization curves for alloys differ from the base metal curve, presenting two peaks for the critical passivation current density in the active‐passive potential range. At the first current peak (the first critical passivation potential E_cr1) a porous titanium pentaoxide (Ti₃O₅) is formed. When the potential reaches the second current peak (the second critical passivation potential E_cr2) the compact and protective titanium dioxide (TiO₂) is formed. The impedance spectra exhibit the typical behaviour for a passive film i.e. a near capacitive response illustrated by a phase angle close to − 90 ° over a wide frequency range. The oxide film on titanium and its alloys in hydrochloric acid solutions exhibits a high resistance and a low capacitance (with the increase of the potential) attributed to the surface roughness decrease as the oxide layer thickens.     

Examination of superplastic forming combined with diffusion bonding for titanium: Perspective from experience

Superplastic forming (SPF) combined with diffusion bonding (DB) has been used successfully for the fabrication of titanium aerospace hardware. Many of these applications have been for military aircraft, whereby a complex built-up structure has been replaced with monolithic parts. Several methods for applying the two- and four-sheet titanium SPF/DB processes have been devised, including the welding of sheets prior to forming and the use of silk-screened stop-off (yttria) to prevent bonding where it is undesirable. Very little progress has been made in the past few years toward understanding and modeling the SPF/DB process using constitutive equations and data by laboratory testing. Concerns that engineers face in designing for fatigue life, acceptable design loads, and damage tolerance are currently being studied, but the database is very limited. This is a summary of past work found in the literature and forms the foundation for additional research. This paper was presented at the International Symposium on Superplasticity and Superplastic Forming sponsored by the Manufacturing Critical Sector at the ASM International AeroMat 2004 Conference and Exposition, June 8–9, 2004, in Seattle, WA. The symposium was organized by Daniel G. Sanders, The Boeing Company.     

Al-Ti 液固界面的组织结构演变

采用镶嵌式扩散偶技术制备 Al-Ti 扩散偶,在 Al 熔点以上,Ti 熔点以下进行扩散热处理,研究 Al-Ti液-固界面扩散反应层的组织结构演变及生长机制。实验结果表明,热处理后的扩散反应层为TiAl3颗粒和铝的混合组织,以TiAl3和液相铝的平衡化学位共存区逐层生长,生长界面朝铝基一侧移动;TiAl3相是热处理过程中最先出现也是唯一出现的新生相;钛相变前后,扩散反应层的生长机制发生了改变。相变前,由钛向液相铝中的溶解速度控制;相变后,转变为Al、Ti原子的化学反应速度控制,生长速度大幅度加快。     

Tribological properties of titanium aluminides coatings produced on pure Ti by laser surface alloying

Titanium aluminides coatings were in-situ synthesized on a pure Ti substrate with a preplaced Al powder layer by laser surface alloying. The friction and wear properties of the titanium aluminides coatings at different normal loads and sliding speeds were investigated. It was found that the hardness of the titanium aluminides coatings was in the following order: Ti₃Al coating > TiAl coating > TiAl₃ coating. Friction and wear tests revealed that, at a given sliding speed of 0.10 m/s, the wear volume of pure Ti and the titanium aluminum coatings all increased with increasing normal load. At a given normal load of 2 N, for pure Ti, its wear volume increased with increasing sliding speed; for the titanium aluminides coatings, the wear volume of Ti₃Al coating and TiAl coating first increased and then decreased, while the wear volume of TiAl₃ coating first decreased and then increased with increasing sliding speed. In addition, the friction coefficients of pure Ti and the titanium aluminides coating decreased drastically with increasing sliding speed. Under the same dry sliding test conditions, the wear resistance of the titanium aluminium coatings was in the following order: Ti₃Al coating > TiAl coating > TiAl₃ coating.     

Reactions between Ti and Ti_3SiC_2 in temperature range of 1 273-1573K

1Introduction Recently,the layered ternary carbide Ti3SiC2has attracted attention due to its unique properties such as high toughness,high fatigue-crack growth threshold and elastic modulus,plasticity at high temperature,excellent electrical and thermal c…     

航空用损伤容限型钛合金研究与应用

为了满足新型飞机的大尺寸、高减重、长寿命和低成本的设计与应用需求,采用损伤容限型钛合金材料及其应用技术是一条重要途径。国外发达国家已经在新型损伤容限型钛合金材料研制和在先进飞机上的应用方面走在了前列,特别是像中强度的Ti-6Al—4VELI和高强度的Ti一6—22—22S等,已经成功地应用在了美国F-22／F-35,C-17等新一代飞机中,大大地提高了飞机的使用寿命和战斗力。这几年我国先后自主创新发展了中强度损伤容限型钛合金TC4-DT和高强度损伤容限型钛合金TC21,建立了损伤容限型钛合金的口处理加工技术,为我国新型飞机的研制奠定了材料应用技术基础。通过分析国内外损伤容限型钛合金材料及其新型加工工艺技术的研究发展情况,结合我国新型损伤容限型钛合金材料研究进展,重点探讨了新型损伤容限型钛合金的材料特点、性能水平和应用前景。     

钛合金叶片盘近净热流变成形的数值模拟及其应用

研究了TC11钛合金叶片盘的近净热流变成形。采用几何造型软件UG NX3对TC11钛合金第二级叶片盘的坯料和模具进行实体造型,同时基于刚粘塑性不可压缩材料的变分原理,运用体积分析软件DEFORM 3D对3种不同应变速率下的叶片盘等温近净热流变成形过程进行数值模拟,研究了工件在成形过程中的速度场、温度场和等效应变场的分布情况,以及凸模和凹模的载荷-行程曲线,为优化工艺参数提供了理论依据。同时与传统的方法进行了比较,发现用此方法生产的产品,其力学性能及微结构都有明显的改进。结果分析表明,随着变形速率的减小,金属向凹模型腔内的流动越均匀,叶型更容易充满。     

Thermodynamic Interactions of Si and Ti in Liquid Cu

The activity coefficients of titanium in liquid Cu-Ti at 1623 and 1673 K were measured by equilibrating the liquids with Ti₃O₅ in a oxygen partial pressure controlled by C(s)/CO(g) equilibrium. Furthermore, the thermodynamic interaction parameter of silicon on titanium and the self-interaction parameter of titanium in liquid Cu-Ti-Si at 1773 K were determined by equilibrating the 58 mass% TiO₂-42 mass% CaF₂ slag with Cu-Si-Ti liquids. And the interaction parameters e_\textTi^\textTi e_{\text{Ti}}^{\text{Ti}} and e_\textTi^\textSi e_{\text{Ti}}^{\text{Si}} obtained using a multiple regression were as large as −69.32 and 15.44 respectively. Based on the above determined value of e_\textTi^\textTi e_{\text{Ti}}^{\text{Ti}} , the relationship between Henrian constant of titanium in liquid Cu-Ti melt, \upgamma_{\textTi(\texts)}⁰ \upgamma_{{{\text{Ti}}({\text{s}})}}^{0} , from 1473 to 1923 K was evaluated, and is expressed as:

Synthesis of titanium aluminide coatings on aluminum and titanium surfaces by mechanical alloying and subsequent annealing

Intermetallic Ti-Al-based coatings were synthesized by mechanical alloying in a vibratory ball mill and subsequent annealing. A titanium layer was deposited on aluminum specimens and an aluminum layer and aluminum-titanium mixture were deposited on titanium specimens. Under the effect of milling balls, powder particles deposit at the substrates, forming layers that have a very good cohesion with the substrate. During subsequent heating, diffusion layers on the basis of titanium-aluminum phases are synthesized as a result of the chemical interaction between titanium and aluminum. In the case of titanium layer deposited on aluminum, the temperature interval of transformations is 600–650°C; first, a Ti₃Al₅-based phase is formed; then, as diffusion saturation with Al increases, an Al₂Ti-based layer appears; and finally, the Al₃Ti compound is formed. The reaction rates depend on the temperature and the duration of annealing. On titanium with a (Ti + Al) layer deposited on its surface, the Al₃Ti, Al₂Ti, TiAl, and Ti₃Al compounds are formed in a temperature interval of 600–900°C. In the case of deposition a homogeneous aluminum layer on titanium, only Al₃Ti and Ti₃Al phases were observed after annealing.