Development of Ti-6Al-4V and Ti-1Al-8V-5Fe Alloys Using Low-Cost TiH2 Powder Feedstock

Thermo-mechanical processing was performed on two titanium alloy billets, a beta-titanium alloy (Ti1Al8V5Fe) and an alpha-beta titanium alloy (Ti6Al4V), which had been produced using a novel low-cost powder metallurgy process that relies on the use of TiH₂ powder as a feedstock material. The thermomechanical processing was performed in the beta region of the respective alloys to form 16-mm diameter bars. The hot working followed by the heat treatment processes not only eliminated the porosity within the materials but also developed the preferred microstructures. Tensile testing and rotating beam fatigue tests were conducted on the as-rolled and heat-treated materials to evaluate their mechanical properties. The mechanical properties of these alloys matched well with those produced by the conventional ingot processing route.     

Producing High-Quality Titanium Alloy by a Cost-Effective Route Combining Fast Heating and Hot Processing

Powder metallurgy is a very attractive method for producing titanium alloys, which can be near-net-shape formed and have freedom in composition selection. However, applications are still limited due to product affordability. In this paper, we will discuss a possible cost-effective route, combining fast heating and hot processing, to produce titanium alloys with similar or even better mechanical properties than that of ingot metallurgy titanium alloys. Two titanium alloys, Ti-5Al-5V-5Mo-3Cr (Ti-5553) and Ti-5Fe, were successfully produced from HDH titanium powder and other master alloy powders using the proposed processing route. The effect of the processing route on microstructural variation and mechanical properties have been discussed.     

Preparing damage-tolerant titanium-matrix composites

In-situ TiB-reinforced titanium alloy composites have been produced by both rapid solidification and ingot metallurgy techniques. The reinforcements have been shown to result in strength and modulus improvements, improved fracture toughness, increased fatigue endurance limit, and better fatigue crack growth and creep resistance than conventional monolithic titanium alloys. In addition to improved mechanical properties, in-situ composite structures and components with complex shapes can be fabricated using conventional ingot metallurgy, near-net shape forming techniques.     

Rolling of Plates and Sheets from As-Cast Ti-6Al-4V-0.1B

Trace boron addition (~0.1 wt.%) to conventional titanium alloys reduces the as-cast prior-beta grain size by an order of magnitude to about 200 μm, a grain size typically observed after ingot breakdown. In this study, the feasibility of producing plate and sheet by hot rolling of as-cast Ti-6Al-4V-0.1B (wt.%) was evaluated. Starting from an initial thickness of 25 mm, as-cast Ti-6Al-4V-0.1B was successfully rolled to 2 mm sheet in a multistep rolling process. As-cast Ti-6Al-4V (without boron addition) rolled under similar conditions exhibited severe cracking. Tensile properties of the sheets and plates made from the boron-containing alloy met or exceeded AMS 4911 specifications for Ti-6Al-4V plates and sheets produced by conventional processing route. The process of making plate and sheet stock from cast titanium alloy ingots, without recourse to expensive ingot breakdown, can significantly reduce the number of expensive and time-consuming processing steps for making titanium alloy components, thereby enhancing the affordability and expanding the range of titanium applications.     

诺威力复合锭铸造法的原理和工艺及应用

采用DC法商业化铸造复合铝合金锭是铝业界工程师几十年来追求的目标之一,2005年底美国诺威力公司奥斯威戈轧制厂在瓦格斯塔夫公司专家的协助下,终于成功地实现了复合锭的工业化规模铸造,到2006年3月份已成功地铸出50多种不同合金的复合锭。用此种锭轧制的1200／2124合金薄板及4147／3003合金钎焊带箔已发往用户。奥斯威戈轧制厂已形成70kt／a复合锭的生产能力,诺威力公司将在韩国蔚山轧制厂与瑞士谢尔轧制厂各建一条铸造复合锭的生产线。复合锭的商业化生产将大大扩大复合铝板带箔的应用范围,在DC法发展历程中具有里程碑意义。     

Selective laser melting of a beta-solidifying TNM-B1 titanium aluminide alloy

The interest for a wider range of useable materials for the technology of selective laser melting is growing. In this work we describe a new way to optimize the process parameters for selective laser melting of a beta solidifying titanium aluminide. This kind of material has so far not been processed successfully by this method. The new approach is easy to conduct and well transferable to other materials. It is based on the fact that the parts generated from selective laser melting can be described by an addition of multiple single tracks. Multiple types of single track experiments are performed and in combination with knowledge from laser welding tests optimized parameter combinations are derived. Compact samples are built with the optimized process parameters and characterized in terms of microstructure, phase composition and mechanical properties. With this technique the generation of a TNMB1 titanium aluminide alloy sample with a density greater than 99% could be achieved. The mechanical properties are comparable with material produced by conventional techniques.     

离心喷射沉积距离对TiAl基合金组织的影响

研究了γＴｉＡｌ基合金经离心喷射沉积成形时不同喷射距离对合金组织的影响。合金经等离子弧熔炼并重熔后，在真空条件下进行离心喷射沉积成形，喷射沉积距离分别为２００、３００、４００和５００ｍｍ。结果表明，经离心喷射沉积后的合金仍存在着孔隙，且随喷射距离的增加，孔隙率增加，孔隙越细密。成形后的组织结构为层片状组织，其形貌、层片大小也随成形距离的不同而变化     

Evaluation of microstructure and phase relations in a powder processed Ti-44AI-12Nb alloy

Titanium aluminides based on the ordered face-centered tetragonal γTiAI phase possess attractive properties, such as low density, high melting point, good elevated temperature strength, modulus retention, and oxidation resistance, making these alloys potential high-temperature structural materials. These alloys can be processed by both ingot metallurgy and powder metallurgy routes. In the present study, three variations of the powder metallurgy route were studied to process a Ti-44Al-12Nb (at. %) alloy: (a) cold pressing followed by reaction sintering (CPprocess); (b) cold pressing, vacuum hot pressing, and then sintering (HP process); and (c) arc melting, hydride-dehydride process to make the alloy powder, cold isostatic pressing, and then sintering (AM process). Microstructural and phase relations were studied by x-ray diffraction (XRD) analysis, optical microscopy, scanning electron microscopy with an energy-dispersive spectrometer (SEM-EDS), and electron probe microanalysis (EPMA). The phases identified were Ti₃AI and TiAl; an additional Nb₂AI phase was observed in the HPsample. The microstructures of CPand HP processed samples are porous and chemically inhomogeneous whereas the AM processed sample revealed fine equiaxed microstructure. This refinement of the microstructure is attributed to the fine, homogeneous powder produced by the hydride-dehydride process and the high compaction pressures.     

大规格钛合金真空自耗铸锭热封顶技术探讨

针对真空自耗熔炼大规格(?≥760mm)钛合金铸锭易出现头部缩孔较深、切头量大的问题,分析了缩孔产生的原因,论述了热封顶工艺制定的原则和方法,并据此制定了适合实际生产的热封顶工艺制度。试生产发现,该工艺可显著减小缩孔深度,提高铸锭的成品率。     

Rapidly solidified Al-Ti alloys via advanced melt spinning

Rapidly solidified Al-Ti based binary and ternary alloys containing 3 to 12 wt.% titanium and additions of cerium or vanadium have been produced by melt spinning continuous ribbons, pulverization into powders and consolidation by hot-extrusion into round bars. The mechanical property data show that significantly improved elevated-temperature strengths can be obtained by suitable alloy design and processing. The rapidly solidified Al-Ti base alloys have improved general corrosion and pitting corrosion resistance in comparison to ingot metallurgy Al 7075-T73 alloys and higher resistance to pitting corrosion than rapidly solidified Al-8Fe-2Mo.     

Allotropic phase transformation and high-temperature tensile deformation behaviour of powder metallurgy Ti-5553 alloy

Ti-5Al-5V-5Mo-3Cr metastable beta titanium alloy was prepared by rapid thermomechanical powder consolidation approach from blended elemental powder mixture. Allotropic phase transformation and high-temperature tensile behaviour of the consolidated powder metallurgy Ti-5553 alloy were investigated in this work. The studied alloy has a high β phase transformation temperature of 975 °C±5 °C, which is higher than other conventional ingot metallurgy Ti-5553 alloys. The β grains in the microstructure of the alloy are coarsened significantly with increasing the heating temperature from 890 °C to 1050 °C, however, the grain coarsening tendency is mitigated when the heat treatment temperature reach to the range of 1080 °C–1100 °C. The high-temperature tensile mechanical properties of the alloy are sensitive to both the deformation temperature and strain rate, and superplastic deformation of the alloy was achieved at the condition of 850 °C/0.001 s⁻¹ with the tensile elongation of 103.5%. The microstructural evolution characteristics and the fracture mechanisms of the alloy are varied with changing the deformation variables, which are revealed by the microstructure observation of the fractured specimens from different sampling positions.     

A study on the preparation of iron aluminium based intermetallic alloy by aluminothermic smelting technique

Iron aluminium based intermetallic alloys or iron aluminide alloys are usually made by conventional melting and powder processing routes. Melting is carried out either in vacuum induction melting or arc melting furnaces. However,the use of high vacuum and high temperature expensive furnaces, high cost associated with the procurement of pure individual metal components, operational problems during melting stages are some of the most deterrent factors in making these alloys by melting route. Powder processing route utilises atomised, carbonyl or rapidly solidified pre alloyed powders as starting materials and alloying is carried out either by mechanical alloying or reaction synthesis or by consolidation through hot isostatic pressing. This process also involves many processing steps and considerable expense. In the present investigation, it has been found possible to eliminate the above problems by adopting a simple aluminothermic reduction (thermit) smelting technique for the preparation of iron aluminide alloy of targetted composition Fe–16Al–5.46Cr–0.5V–0.05C (wt %) by the direct co-reduction of oxides of iron,chromium and vanadium in presence of carbon and excess aluminium. Incorporation of slag fluidizer CaO amounting to 10 wt % of total charge, aluminium, 10 wt % excess over stoichiometric requirement and carbon, double the theoretical amount have been found to be adequate to form the above alloy with maximum overall yield of 99.4 wt %. The compositional variation of alloying components like iron, chromium,vanadium, aluminium and carbon in the aluminothermically produced iron aluminide alloy from the target composition have been minimized under optimum experimental conditions. The reactions have been found to be well controlled, rapid and self-sustaining and are conducted in an off-furnace manner using a simple experimental set-up.Studies on composition and microstructure characterization, hot rolling behaviour and oxidation resistance of the said alloy points towards its suitability for use.     

采用数值模拟方法分析影响VAR熔炼钛合金铸锭表面质量的因素

采用数值模拟方法分析影响铸锭表面质量的因素,借此达到提高铸锭成品率的目的。通过Melt Flow软件对VAR熔炼过程的温度场进行分析,将高温液相与坩埚接触长度与表面质量建立联系。分析得出,从工艺角度考虑,熔炼电流、稳弧电流以及稳弧周期这3个因素对铸锭表面质量有影响,结合实验验证表明,采用较大的熔炼电流、大稳弧电流以及短稳弧周期有利于铸锭表面质量提高,提高成品率。     

一种新型低成本阻燃钛合金的微观组织与力学性能

研究了一种名义成分为Ti-25V-15Cr-5Mo-0.25Si-0.08C的新型低成本阻燃钛合金TF-X,通过三次真空自耗熔炼制备了φ120mm铸锭,经包套挤压得到φ25mm棒材,观察了铸锭和挤压棒材的微观组织,测试并分析了挤压棒材的室温和高温拉伸性能、热稳定性能、高温蠕变性能。结果表明：TF-X合金具有与TF550合金大致相同的微观组织;TF-X合金室温及高温拉伸强度高于TF550合金,并且具有很好的塑性;试验条件下,TF-X合金的热稳定性能低于TF550合金,熔炼过程中应该严格控制氧含量;TF-X合金在540℃/250MPa/100h条件下蠕变性能与TF550合金相当,显著高于Ti40合金。     

Ti—47Al—2Mn—2Nb—0.8TiB2合金韧脆转变温度及其应变速率敏感性

采用拉伸试验,研究了不同应变速率（１０＾－５－１０＾－１ｓ＾－１）下温度对含体积分数为０．８％的ＴｉＢ、具体近全片层组织的Ｔｉ－４７Ａｌ－２Ｍｎ－２Ｎｂ金属间化合物的屈服强度和延伸率的影响,得到合金韧脆转变温度随应变速率升高而升高的变化关系,确定这种ＴｉＢ２的ＴｉＡｌ合金的韧脆转变激活能为２５６ｋＪ／ｍｏｌ。这一数值低于无ＴｉＢ２的ＴｉＡｌ合金韧脆转变过程可能受位错攀移机制控制。     

Modeling corrosion behavior of gas tungsten arc welded titanium alloy

The pitting corrosion characteristics of pulse TIG welded Ti-6Al-4V titanium alloy in marine environment were explained. Besides the rapid advance of titanium metallurgy, this is also due to the successful solution of problems associated with the development of titanium alloy welding. The preferred welding process of titanium alloy is frequently gas tungsten arc（GTA） welding due to its comparatively easier applicability and better economy. In the case of single pass GTA welding of thinner section of this alloy, the pulsed current has been found beneficial due to its advantages over the conventional continuous current process. The benefit of the process is utilized to obtain better quality titanium weldments. Four factors, five levels, central composite, rotatable design matrix are used to optimize the required number of experiments. The mathematical models have been developed by response surface method（RSM）. The results reveal that the titanium alloy can form a protective scale in marine environment and is resistant to pitting corrosion. Experimental results are provided to illustrate the proposed approach.     

Temperature induced porosity in hot isostatically pressed gamma titanium aluminide alloy powders

In this study the occurrence of temperature induced porosity (TIP) in hot isostatically pressed (HIP) compacts of different gamma Titanium aluminide alloys was investigated. Two gamma Titanium aluminide alloys Ti-48.9at.%Al and an advanced Niobium containing alloy Ti-46at.%Al-9at.%Nb have been atomized by gas atomization and by centrifugal atomization in an inert gas atmosphere. The alloy powders were studied regarding porosity and the content of inert gas entrapped in the powder particles. Selected powder batches were hot isostatically pressed at 1280 °C and were investigated with respect to TIP evolution after a high temperature exposure to 1390 °C for short and long time periods. It was found that gas atomized Titanium aluminide alloy powders contain a certain amount of atomization gas, the concentration of which increases with the powder particle size. The amount of inert gas entrapped in centrifugally atomized powders is higher as compared to powders produced by gas atomization. The occurrence of TIP after high temperature annealing of the HIP’ ed compacts depends on the grain size, the processing medium (Argon or Helium), the amount of entrapped inert gas and the annealing time. Guidelines are presented for minimizing or prevention of TIP in γ-TiAl alloys processed by powder metallurgy.     

Microstructure and mechanical properties of a forged β-solidifying γ TiAl alloy in different heat treatment conditions

In the cast condition γ titanium aluminide alloys that solidify completely through the β phase are characterized by fine and homogeneous microstructures, weak textures and low segregation. For these reasons such alloys have a relatively good workability and can be closed-die forged without preceding ingot breakdown even if the alloys contain no large fractions of the β phase at the working temperature. The present work was devoted to a combined study of the constitution and microstructural morphologies that develop in various two-step heat treatments of a single-step forged β solidifying alloy. The study included high-energy X-ray diffraction for in situ investigations of the constitution at the heat treatment temperature. It was observed that the phase transformations are quite sluggish in the material which results in fine microstructures and some conditions that significantly deviate from thermodynamic equilibrium. Further, tensile and creep testing was carried out on the different material conditions in order to identify the range in which the properties can be varied. It is found that this easily forgeable material exhibits comparable strength, ductility and creep strength as more conventional peritectically solidifying alloys.     

Interfacial reactions in titanium-matrix composites

A study of the interfacial reaction characteristics of SiC fiber-reinforced titanium aluminide and disordered titanium alloy composites has determined that the matrix alloy compositions affect the microstructure and the distribution of the reaction products, as well as the growth kinetics of the reaction zones. The interfacial reaction products in the ordered titanium aluminide composite are more complicated than those in the disordered titanium-alloy composite. The activation energy of the interfacial reaction in the ordered titanium aluminide composite is also higher than that in the disordered titanium alloy composite. Designing an optimum interface is necessary to enhance the reliability and service life at elevated temperatures.     

Wrought processing of γ—TiAl alloys

1　ＩＮＴＲＯＤＵＣＴＩＯＮＩｎｔｅｒｍｅｔａｌｌｉｃｔｉｔａｎｉｕｍａｌｕｍｉｎｉｄｅａｌｌｏｙｓａｒｅａｎｅ ｍｅｒｇｉｎｇｃｌａｓｓｏｆｍａｔｅｒｉａｌｓｔｈａｔｅｘｈｉｂｉｔａｔｔｒａｃｔｉｖｅｔｈｅｒ ｍｏｐｈｙｓｉｃａｌｐｒｏｐｅｒｔｉｅｓａｎｄ