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Effects of heat treatments on microstructures of tial alloys

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International Journal of Minerals,Metallurgy and Materials 2022年第6期29卷 1225-1230页

作者： Wen Yu Jianxin Zhou Yajun Yin Zhixin Tu Xin Feng Hai Nan Junpin Lin Xianfei Ding State Key Laboratory of Materials Processing and Die and Mould Technology Huazhong University of Science and TechnologyWuhan 430074China Cast Titanium Alloy R&D Center Beijing Institute of Aeronautical MaterialsBeijing 100095China Beijing Engineering Research Center of Advanced Titanium Alloy Precision Forming Technology Beijing 100095China Beijing Institute of Aeronautical Materials Co. Ltd.Beijing 100094China State Key Laboratory for Advanced Metals and Materials University of Science and Technology BeijingBeijing 100083China

This study aims to investigate the effects of heat treatments on the microstructure ofγ-tial alloys.Two Ti-47Al-2Cr-2Nb alloy ingots were manufactured by casting method and then heat-treated in two types of heat treatments.Their microstructures were studied by both optical and scanning electron microscopies.The chemical compositions of two ingots were determined as well.The ingot with lower Al content only obtains lamellar structures while the one higher in Al content obtains nearly lamellar and duplex structures after heat treatment within1270 to 1185℃.A small amount of B2 phase is found to be precipitated in both as-cast and heat-treated microstructures.They are distributed at grain boundaries when holding at a higher temperature,such as 1260℃.However,B2 phase is precipitated at grain boundaries and in colony interiors simultaneously after heat treatments happened at 1185℃.Furthermore,the effects of heat treatments on grain refinement and other microstructural parameters are discussed.

关键词： tial alloys microstructure heat treatment casting

Chemical, microstructure, and mechanical property of tial alloys produced by high-power direct laser deposition

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Journal of Materials Science & Technology 2022年第22期117卷 99-108页

作者： Xinyu Zhang Chuanwei Li Mengyao Zheng Xudong Yang Zhenhua Ye Jianfeng Gu Institute of Materials Modification and Modeling School of Materials Science and EngineeringShanghai Jiao Tong UniversityShanghai 200240China Materials Genome Initiative Center Shanghai Jiao Tong UniversityShanghai 200240China Shanghai Key Laboratory of Materials Laser Processing and Modification Shanghai Jiao Tong UniversityShanghai 200240China

Additive manufactured metals sometimes exhibit extraordinary microstructures and mechanical properties due to the particular processes. In this paper, we focus on a novel gradient tial alloys fabricated byhigh-power direct laser deposition, whose chemical composition, microstructure, and mechanical property vary along the building direction. The results indicate that Al concentration dramatically decreasesfrom 39.5 at.% to 30.1 at.% as the height increases from the bottom to the top. Meanwhile, microstructural characterization indicates that the specimen appears basket-weave microstructure at the bottom,then the α_(2) and γ phase gradually decrease, and eventually it transforms into acicular martensite microstructure in the top region. The indentation analysis shows that the associated hardness increases asthe height increases, while the plasticity reaches a minimum value in the middle region. The increasingamount of β_(o)(ω) is considered to be responsible for the increasing hardness because of the strong precipitation strengthening effect. The high plasticity in the bottom and top regions results from the strongdeformation behaviors of the γ and β_(o) phases.

关键词： Direct laser deposition tial alloys Inhomogeneity Microstructure Mechanical properties

Effect of trace tungsten on the microstructure of tial alloys containing Nb and B

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Rare Metals 2007年第4期26卷 323-329页

作者： LIU Bin LIU Yong HUANG Lan HUANG Jinsong ZHANG Yonghong HUANG Boyun State Key Laboratory of Powder Metallurgy Central South University Changsha 410083 China

New tial alloys, containing 45 at.% A1, 7 at.% Nb, x at.% W, and 0.15 at.% B （x = 0, 0.2, 0.4, and 0.7） were prepared by arc melting and drop casting consequently. Using optical microscopy, scanning electron microscopy （SEM）, and electron superprobe technologies, the effects of tungsten on the microstructural evolution of the TiA1 alloys, including the colony size and lamellar spacing, were analyzed. It was found that cellular structures and dendrites were formed in the as-cast TiA1 alloys, and heavy metals, such as niobium and tungsten, tend to segregate strongly at the interface of the cellular structures and dendrites. Trace tungsten can effectively impede the grain growth and narrow the interlamellar spacing. 0.4 at.% tungsten is more effective in refuting the microstructure of the TiAI alloys.

关键词： tial alloys tungsten grain size β（B2）phase microstructure

Changes of Oxygen Content in Molten tial alloys as a Function of Superheat during Vacuum Induction Melting

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Journal of Materials Science & Technology 2010年第10期26卷 900-903页

作者： Bo Chen,Yingche Ma,Ming Gao and Kui Liu Institute of Metal Research,Chinese Academy of sciences,Shenyang 110016,China Institute of Metal Research Chinese Academy of sciences Shenyang 110016 China

Experimental studies on the melting process of titanium aluminum alloy have been pursued from the viewpoint of contamination.tial alloys were prepared with vacuum induction melting （VIM） in calcia crucibles at 1873 K and 1923 K in order to determine the behavior of the oxygen content as a function of temperature,time and frequency of power.The experiment results showed that alloys were uncontaminated except for the increasing of oxygen content which was introduced from the reaction CaO（s）=Ca（in tial）＋O（in tial）,and the standard Gibbs energy of the reaction was determined to be △G0 =274000 102.8T（J/mol）.Oxygen content increased slowly with the melting time by about 50×10-6 wt pct/min,and decreased with induction melting frequency.Lower superheat and higher melting frequency can be used to reduce oxygen content increasing rate.

关键词： tial alloys Induction melting Calcia crucible Oxygen content

Strain rate sensitivity of tensile properties in high Nb containing tial alloys

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Journal of University of Science and Technology Beijing 2005年第6期12卷 535-539页

作者： Jianfeng Gao Xiangjun Xu Junpin Lin Xiping Song Yanli Wang Guoliang Chen State Key Laboratory for Advanced Metals and Materials University of Science and Technology Beijing Beijing 100083 China

The effect of strain rate on the yield strength of high Nb containing tial alloy was studied. The results show that the strain rate sensitivity varies with the test temperature, and the yield strength is not sensitive to the strain rate at room temperature but significantly sensitive to the strain rate at high temperature. An increase of the strain rate or a decrease of the temperature results in an obvious change of fracture mode. It is found that the strain rate sensitivity of this alloy varying with temperature is due to the dislocation climb generated at high temperature.

关键词： tial alloys strain rate tensile properties thermal activation

Chemical composition analysis on industrial scale ingots and castings of tial alloys

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China Foundry 2020年第6期17卷 441-446页

作者： Xian-fei Ding Yi-qun Zhao Jia-bin Zuo Xin Feng Hai Nan Yong-feng Liang Yan-qing Su Cast Titanium Alloy R&D Center Beijing Institute of Aeronautical MaterialsBeijing 100095China Beijing Engineering Research Center of Advanced Titanium Alloy Precision Forming Technology Beijing 100095China BAIMTEC Material Co. Ltd.Beijing 100094China State Key Laboratory for Advanced Metals and Materials University of Science and Technology BeijingBeijing 100083China National Key Laboratory for Precision Hot Processing of Metals Harbin Institute of Technology HarbinHarbin150001China

The chemical composition variation of the tial-4722 alloys was examined in a batch of the industrial scale master ingots,and in the corresponding castings prepared by conventional vacuum arc remelting(VAR)combined with induction skull melting(ISM)and investment casting processes.The content changes of major elements and interstitial elements were evaluated based on the chemical analysis at the top and bottom of the ingots and castings.Results show that the contents of C,N,H,Fe and Si have almost no change in the ingots and castings,suggesting that the chemical analysis on these elements can be based on the batch analysis.The O content keeps almost the same in different ingots,but exhibits relatively large differences in castings,which was probably influenced by the reaction between the shell mold and the molten alloy,and the spalling of face coat of the shell mold during casting.For the major elements of Al,Nb and Cr,the composition difference between the top and the bottom of the ingots is less than that of the castings.But for the O element,the trend is different,especially for the castings,suggesting that the investment casting is a homogenization process for Cr and Nb,but a differentiation process for O.The contents of major elements in castings fluctuate mainly in the same range as that in the ingots,indicating that the contents of the major elements are controllable during investment casting.

关键词： tial alloys melting casting chemical composition casting ingot

Microstructures and phase transformation in directionally solidified tial-Nb alloys

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China Foundry 2020年第6期17卷 402-408页

作者： Fu-qiang Zhang Xian-fei Ding Hai Nan Ru-yue You Qiang Wang Jian-ping He Yan-qing Su Yong-feng Liang Jun-pin Lin State Key Laboratory for Advanced Metals and Materials University of Science and Technology BeijingBeijing 100083China Cast Titanium Alloy R&D Center Beijing Institute of Aeronautical MaterialsBeijing 100095China AECC Hunan Aviation Powerplant Research Institute Harbin 150001China National Key Laboratory for Precision Hot Processing of Metals Harbin Institute of TechnologyZhuzhou 412002China

Intermetallic Ti-45Al-8Nb-(W,B,Y)(at.%)and Ti-46Al-5Nb alloys are directionally solidified at a constant growth rate of 30μm·s-1 using a Bridgman type apparatus.The quenched microstructures and lengths of different phase regions were observed and measured after various growing times of 0-30 min.Results show that the phase transformations in different phase regions are mainly depending on the high temperature microstructure and the supercooling degree during quenching process.After isothermal holding,the primary phase grows into the liquid phase,the dendrites change from equiaxed to columnar grains,and the length of the L+βphase region,L+β+αphase region and mushy zone varies,indicating that the entire directional solidification process can be described by a static equilibrium-nonequilibrium-dynamic equilibrium evolution process.In addition,the gap between the original growth interface and front interface shows that the actual crystal growth rate is not equal to the drawing velocity during directional solidification.

关键词： tial alloys directional solidification quenched microstructure phase transformation

Microstructure evolution and diffusion mechanism of Nb/tial alloy diffusion-bonded joints

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Rare Metals 2023年第5期42卷 1686-1694页

作者： Kun Huang Hong-Liang Sun Ze-Wen Huang Mo-Yu Liao Yang Li School of Materials Science and Engineering Southwest Jiaotong UniversityChengdu610031China Key Laboratory of Advanced Technologies of Materials Ministry of EducationChengdu610031China

The interdiffusion behavior in Nb/tial alloy diffusion couples was studied.The process was carried out in the temperature range of 950-1400℃for 8 h in the vacuum hot-pressure sintering furnace.The microstructural evolution was observed by optical microscopy(OM),electron backscattered diffraction(EBSD),X-ray diffraction(XRD)technique and transmission electron microscopy(TEM).The element concentration distribution at the bonded interface was obtained by scanning electron microscopy with an energy-dispersive X-ray spectroscopy(EDS)apparatus.The thickness of reaction interface increases with bonding temperature increasing.The formed phases in diffusion interface are found to be O-Ti_(2)AlNb,σ-Nb_(2)Al,δ-Nb_(3)Al and Nb solid solution(Nbss)at 1350℃.The average interdiffusion coefficient of the interface elements was calculated by the theory of Dayananda.The results indicate that Al diffuses faster than Nb and Nb diffuses faster than Ti in the Ti-Al-Nb system.Meanwhile,it is found that Ti promotes the diffusion of Al and Nb and Nb inhibits the diffusion of Ti and Al in the process of diffusion.

关键词： Diffusion bonding tial alloys Nb Interface microstructure Interdiffusion coefficient

In-situ synchrotron high energy X-ray diffraction study on the internal strain evolution of D019-α2 phase during high-temperature compression and subsequent annealing in a tial alloy

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Journal of Materials Science & Technology 2023年第32期163卷 212-222页

作者： X.Liu L.Song A.Stark F.Pyczak T.B.Zhang State Key Laboratory of Solidification Processing Northwestern Polytechnical UniversityXi’an 710072China Innovation Center NPU Chongqing Northwestern Polytechnical UniversityChongqing 400000China Institute of Materials Physics Helmholtz-Zentrum HereonMax Planck-Str.1Geesthacht 21502Germany

The residual stress in the D019-α2 phase is known to be significantly higher than that in the L10-γphase in tial alloys after deformation due to the poor plasticity and strong mechanical anisotropy of theα2 phase.However,the internal stress accumulation and relaxation in theα2 phase during high-temperature deformation and annealing are scarcely investigated.In this study,for the first time,the internal strain evolution and load partitioning between theα2 andγphases at high temperatures are characterized by in-situ synchrotron high energy X-ray diffraction(HEXRD)technique.The plastic deformation is at least initiated at a stress of roughly 200 MPa in theγphase and 775 MPa in theα2 phase.The intergranular strains in theα2 phase are generated by the onset of dislocation glide in theγphase,and accentuated with the accumulated dislocations and the ensuing twinning activity.After unloading,great intergranular strains are preserved in theα2 phase constrained by the heavily plastically deformedγphase.During subsequent heating from 400 to 1000℃,the internal strains in theα2 phase are almost fully relaxed by substantial dislocation annihilation and rearrangement in theγphase.During annealing at 800℃,the internal strain relaxation is rapid in the initial 10 min,whereas considerably retarded subsequently.The extent of relaxation after holding at 800℃for 1 h is equivalent to that of heating in an effective temperature range of 680-880℃for 10 min.The in-situ lattice strain measurements with various thermal relaxation schemes provide guidance for the stress relief annealing of tial components.

关键词： tial alloys Synchrotron radiation Intergranular strain Stress relaxation