Mechanical properties of TiAl fabricated by electron beam melting—A review

As a typical intermetallic material, TiAl is inevitably difficult to process by conventional methods. Additive manufacturing (AM) has recently become a new option for making net-shape TiAl components. Among all AM methods, electron beam melting (EBM) shows the potential to make TiAl components with good mechanical properties and is used for low pressure turbine blades. The mechanical properties, including tensile and compression properties, fracture toughness, fatigue and creep properties of EBM TiAl are reviewed and compared to the conventionally fabricated alloys. Results show that the tensile strength of EBM alloys is higher than cast alloys, and other properties are comparable to the cast/forged alloys. The sensitivity of mechanical properties and microstructure to EBM processing parameters is presented. Issues including layered microstructure, anisotropy in mechanical properties, and fatigue failure from defects are also reviewed. Finally, some opportunities and challenges of EBM TiAl are identified.     

TiAl基合金熔模精密铸造技术的发展现状

TiAl基合金作为一种新型轻质高温结构材料,以其密度低、比强度和比模晕高,具有较好的抗氧化和蠕变性能以及优异的抗疲劳性能,在航空航天和汽车等领域具有广阔的应用前景.本文主要介绍了TiAl基合金的熔炼技术、熔模精密铸造技术及应用研究,并提出了TiAl基合金熔模精密铸造技术的不足与展望.     

The significance of acoustic emission during stressing of TiAl-based alloys. Part II: Influence of cracks induced by pre-stressing on the fatigue life

Fully lamellar samples of Ti44Al8Nb1B have been tested in tension–tension fatigue, after being pre-stressed, in order to investigate the effect on fatigue life of the cracks which are introduced by pre-stressing. It has been found that pre-stressing samples at 0.95 of the 0.2% proof stress leads to early failure when they are fatigue-tested at stress levels of about 0.65 of the 0.2% proof stress. Samples tested in fatigue at this same stress level, but which have not been pre-stressed, can show significantly longer fatigue lives, although the fatigue lives show a very large scatter. Tinting experiments, carried out after pre-stressing, have shown conclusively that the cracks initiated by pre-stressing act as failure initiation sites during the subsequent fatigue tests. Even in the absence of pre-stressing, samples of Ti44Al8Nb1B fail in fatigue at stress levels of about 0.65 of the 0.2% proof stress in contrast to the fatigue limit of low strength TiAl alloys of about 0.9 of their 0.2% proof stress. The significance of these observations on the use of grain-refined higher strength TiAl alloys under fatigue conditions is discussed.     

TiAl金属间化合物制备技术的研究进展

TiAl金属间化合物以其低的密度、高的比强度和比模量,具有较好的抗氧化性能以及优异的抗疲劳性能成为一种新型轻质高温结构材料,在航空航天工业和汽车等民用工业领域引起了广泛的关注。本研究着重介绍了TiAl金属间化合物的几种制备方法及其应用,并展望了TiAl金属间化合物的发展前景。     

DEFORMATION AND FRACTURE OF TiAl PST CRYSTALS UNDER MONOTONIC AND CYCLIC LOADING

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TiAl金属间化合物及其连接技术的研究进展

近年来 ,TiAl金属间化合物由于其密度小、硬度大、耐高温、具有优良的抗氧化能力等独特的性能 ,因此越来越引起广泛的关注并得到了迅猛的发展。根据目前TiAl金属间化合物被认为是在航空、航天飞行器等军事和民用两者都具有广泛应用前景的高温结构材料 ,文中介绍了世界范围内TiAl金属间化合物研究发展现状。TiAl金属间化合物有效的运用必须要有可靠的连接技术 ,因此TiAl金属间化合物的连接问题是其实用化所要面临的问题之一。固态焊接是实现TiAl金属间化合物连接十分有效的方法。文中介绍了TiAl金属间化合物连接技术的发展现状 ,重点评述了TiAl金属间化合物固态焊接的研究状况 ,指出了需要深入研究的问题     

TiAl金属间化合物及其连接技术的研究进展

近年来 ,TiAl金属间化合物由于其密度小、硬度大、耐高温、具有优良的抗氧化能力等独特的性能 ,因此越来越引起广泛的关注并得到了迅猛的发展。根据目前TiAl金属间化合物被认为是在航空、航天飞行器等军事和民用两者都具有广泛应用前景的高温结构材料 ,文中介绍了世界范围内TiAl金属间化合物研究发展现状。TiAl金属间化合物有效的运用必须要有可靠的连接技术 ,因此TiAl金属间化合物的连接问题是其实用化所要面临的问题之一。固态焊接是实现TiAl金属间化合物连接十分有效的方法。文中介绍了TiAl金属间化合物连接技术的发展现状 ,重点评述了TiAl金属间化合物固态焊接的研究状况 ,指出了需要深入研究的问题     

Assessment of Titanium Aluminide Alloys for High-Temperature Nuclear Structural Applications

Titanium aluminide (TiAl) alloys exhibit high specific strength, low density, good oxidation, corrosion, and creep resistance at elevated temperatures, making them good candidate materials for aerospace and automotive applications. TiAl alloys also show excellent radiation resistance and low neutron activation, and they can be developed to have various microstructures, allowing different combinations of properties for various extreme environments. Hence, TiAl alloys may be used in advanced nuclear systems as high-temperature structural materials. Moreover, TiAl alloys are good materials to be used for fundamental studies on microstructural effects on irradiation behavior of advanced nuclear structural materials. This article reviews the microstructure, creep, radiation, and oxidation properties of TiAl alloys in comparison with other nuclear structural materials to assess the potential of TiAl alloys as candidate structural materials for future nuclear applications.     

Y, Nb对快速凝固TiAl合金组织和性能的影响

研究了元素Y和Nb对用熔体快淬法制备的TiAl基快速凝固合金组织及性能的影响。发现添加Y的快速凝固TiAl合金主要为等轴晶,主要组成相为α2和少量的γ相。随着Y含量的增加,γ相的含量增加,快速凝固TiAl合金的组织逐渐细化。不同Nb含量的快速凝固TiAl合金的组织为块状结构和层片状结构,主要由γ和α2两相组成,层片间距显著细化,为15～17nm。快速凝固TiAl合金的硬度比其铸态合金显著提高。     

The fatigue resistance of TiAl-based alloys

TiAl-based alloys are a class of intermetallic alloys that show potential as a high-temperature structural material. Many applications considered for TiAl-based alloys require certain damage-tolerance characteristics. In this article, the fatigue resistance of two-phase TiAl alloys is reviewed to assess the current understanding of the fatiguedamage processes in this class of emerging materials. Salient features of fatigue-crack growth and stress-life curves are summarized to identify the challenges these fatigue characteristics present in the life assessment of TiAl components.     

Microstructure and mechanical properties of TiAl castings produced by zirconia ceramic mould

Owing to their low density and attractive high-temperature properties, gamma titanium aluminide alloys (TiAl alloys, hereafter) have significant potential application in the aerospace and automobile industries, in which these materials may replace the heavier nickel-based superalloys at service temperatures of 600-900℃. Investment casting of TiAl alloys has become the most promising cost-effective technique for the manufacturing of TiAl components. Ceramic moulds are fundamental to fabricating the TiAl casting components. In the present work, ceramic mould with a zirconia primary coat was designed and fabricated successfully. Investment casting of TiAl blades and tensile test of specimens was carried out to verify the correctness and feasibility of the proposed method. The tensile test results indicate that, at room temperature, the tensile strength and the elongation are about 450 MPa and 0.8%, respectively. At 700℃, the tensile strength decreases to about 410 MPa and the elongation increases to 2.7%. Microstructure and mechanical properties of investment cast TiAl alloy are discussed.     

快速凝固TiAl化合物的研究进展

TiAl合金是一种很有希望的航空、航天及汽车用高温结构材料,但是其较低的室温塑性限制了它的应用.快速凝固技术有望使其性能得到改善.综述了近年来快速凝固TiAl合金的研究进展,包括快速凝固工艺、合金的发展以及合金的组织演变及其特征、力学性能及添加合金化元素的作用,亚稳相的产生及稳定性以及快速凝固薄带或粉末的固结等.     

无包套近等温锻造TiAl合金的显微组织和拉伸性能(英文)

以真空自耗电弧熔炼技术熔炼名义成分为Ti-47Al-2Nb-2Cr-0.4(W,Mo)(摩尔百分数)的TiAl合金铸锭,并以该熔炼铸锭进行无包套的近等温锻造实验,研究该TiAl合金铸锭的高温可锻性、显微组织及拉伸性能。结果表明:在无包套的近等温锻造工艺中,该熔炼铸锭显示出较好的高温可锻性,经涂覆玻璃粉浆保护,铸锭在经过60%锻造变形后其锻饼表面无明显裂纹。TiAl合金的铸造组织由细小、均匀的层片状晶团(α2+γ)和少量存在于片层团界的等轴γ晶粒构成;经近等温锻造后,锻饼组织则主要由平均晶粒尺寸为20μm的等轴γ晶粒和一些破碎的片层组织构成,在一些难变形区域,依然存在弯曲变形的片层组织。室温拉伸性能检测表明,由于晶粒细化效应,锻饼的平均抗拉强度由铸锭的433MPa提高到573MPa。     

磁过滤对多弧离子镀(TiAl)N薄膜的影响

介绍了利用过滤电弧离子镀沉积(TiAl)N薄膜初步的研究结果.在电弧靶材前沿的磁场作用下,有效减小了薄膜的宏观颗粒尺寸,并极大地降低了颗粒密度.同时,过滤电弧的作用,使偏压对膜成分的影响减弱,薄膜的硬度随膜中铝含量的增加而提高,(TiAl)N的抗氧化能力明显提高.     

Plasma Alloying of TiAl with Niobium and Its Wear Resistance

将双层辉光离子渗铌技术应用于TiAl合金从而改善其耐磨性能。对TiAl渗铌合金层组织,室温和600℃高温摩擦学性能进行了研究。结果表明,TiAl经离子渗铌后表面形成厚度约12μm的铌合金层,渗层组织致密均匀,其组成物主要包括AlNb2、AlNb3、Ti2AlNb和Nb。铌合金层在600℃的耐磨性明显提高,并且室温耐磨和减摩性能均优于TiAl基材。     

Microstructure and properties of a beta-solidifying TiAl-based alloy with different refiners

This study systematically compared the influences of yttrium(Y),boron(B),and carbon(C) on the microstructural refinement and properties of a Ti-43Al-5Nb alloy.The microstructural refinement effect in the TiAl alloy closely depends on the refiner used.The refinement effects of the three elements on colony size and lamellar thickness can be arranged as B Y C and Y C B,respectively.Moreover,a microstructure with a small grain size and ultra-fine lamellar spacing can be obtained by adding B and Y or B and C.The mechanical properties of TiAl alloy are also influenced by the refiners.TiAl alloys with proper B and Y contents exhibit favorable hot workability,tensile properties,and fracture toughness,whereas the C-containing alloy displays poor tensile properties and low fracture toughness.These results indicate that Y and B are more suitable microstructure refiners than C.This study may serve as a reference for practical alloying design.     

Research progress on refractory composition and deformability of shell molds for TiAl alloy castings

At present, most TiAl components are produced by an investment casting process. Environmental and economic pressures have, however, resulted in a need for the industry to improve the current casting quality, reduce manufacturing costs and explore new markets for the process. Currently, the main problems for investment casting of TiAl alloys are cracks, porosities, and surface defects. To solve these problems, many studies have been conducted around the world, and it is found that casting defects can be reduced by improving composition and properties of the shell molds. It is important to make a summary for the related research progress for quality improvement of TiAl castings. So, the development on refractory composition of shell molds for TiAl alloy investment castings was reviewed, and research progress on deformability of shell mold for TiAl alloy castings both at home and abroad in recent years was introduced. The existing methods for deformability characterization and methods for improving the deformability of shell molds were summarized and discussed. The updated advancement in numerical simulation of TiAl alloy investment casting was presented, showing the necessity for considering the deformability of shell mold during simulation. Finally, possible research points for future studies on deformability of shell mold for TiAl alloy investment casting were proposed.     

TiAl合金与异种材料的摩擦焊接

TiAl合金与42CrMo直接摩擦焊接性较差,为此分别引入高温合金GH3039、K418、N80A和纯镍N6作为中间材料,对TiAl-GH3039/K418/N80A/N6-42CrMo异种材料的摩擦焊接工艺进行了研究。采用硬度计、扫描电镜和电子万能试验机对焊后接头区域的硬度、组织和焊合区成分变化以及接头力学性能进行了分析。研究表明,TiAl合金与异种材料焊后接头中形成了复杂的多层状金属间化合物;TiAl合金与GH3039、N80A的摩擦焊接性较好,与K418、N6的摩擦焊接性较差;根据不同材料线膨胀系数随温度的变化规律、与TiAl合金摩擦焊接后接头的性能及其与42CrMo的摩擦焊接性,最终选择GH3039作为中间材料。通过引入中间材料,摩擦焊制备了TiAl合金涡轮-42CrMo转轴的异种材料整体转子,使得TiAl合金在涡轮增压器领域的应用成为可能。     

TiAl基合金与钢连接技术研究进展

TiAl灿基合金具有质轻耐高温的特点，有可能代替Ni基高温合金在发动机中应用，这必然要求解决TiAI基合金与结构钢的连接技术问题。本文综述了以此为应用背景的TiAl基合金与钢连接技术的研究状况，主要涉及摩擦焊、扩散连接以及钎焊等方法，指出了这些方法的特点、最新进展及适用性。     

表面喷涂Mo和WC对TiAl基合金耐磨性的影响

针对TiAl基合金排气门在 483Q柴油发动机台架试验后杆部产生局部磨损的情况 ,进行了TiAl基合金表面喷涂Mo和WC的摩擦磨损试验研究。结果表明 :TiAl基合金表面与Mo和WC涂层间的结合方式为机械咬合 ;TiAl基合金表面喷涂Mo能显著提高其耐磨性 ,磨损量减少 50 % ;喷涂WC使硬度提高 30 % ,但耐磨性下降 ,磨损量上升 30 %。