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Microstructural evolution of a PM TiAl alloy during heat treatment in α+γ phase field

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Rare Metals 2012年第5期31卷 424-429页

作者： SU Meike zheng lijing LANG Zebao YAN Jie ZHANG Hu School of Materials Science and Engineering Beijing University of Aeronautics and Astronautics Beijing 100191 China

In this study, the effect of temperatures and cooling rates of heat treatment on the microstructure of a powder metallurgy (PM) Ti-46Al-2Cr-2Nb-(B,W) (at.%) alloy was studied. Depending on the cooling rate and temperature, the different structures were obtained from the initial near-γ (NG) microstructures by heat treatment in the α+γ field. The results show that the microstructures of samples after furnace cooling (FC) consist primarily of equiaxed γ and α 2 grains, with a few grains containing lamellae. Duplex microstructures consist mainly of γ grains and lamellar colonies were obtained in the quenching into another furnace at 900°C (QFC) samples. However, further increasing of the cooling rate to air cooling (AC) induces the transformation of α→α_2 and results in a microstructure with equiaxed γ and α_2 grains, and no lamellar colonies are found.

关键词： γ-TiAl-based alloys powder metallurgy heat treatment duplex structure phase volume fractions

Permutation polynomials x~(2k+1+3)+ax2k+2+bx over F_(22k) and their differential uniformity

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Science China(Information Sciences) 2020年第10期63卷 255-257页

作者： Jie PENG lijing zheng Chunsheng WU Haibin KAN Mathematics and Science College Shanghai Normal University School of Mathematics and Physics University of South China Department of Mathematics Lianyungang Normal University Shanghai Key Laboratory of Intelligent Information Processing School of Computer ScienceFudan University Fudan-Zhongan Joint Laboratory of Blockchain and Information Security Shanghai Blockchain Engineering Research Center Shanghai Institute for Advanced Communication and Data Science Shanghai Institute of Intelligent Electronics & Systems

Dear editor,A polynomial f（x）∈Fq[x] is called a permutation polynomial （PP） over the finite field Fq if the associated mapping f:c （?） f（c） from Fq to itself is bijective.A PP f is called a complete permutation polynomial if f（x）+x is a *** over finite fields of even characteristic have wide applications,including cryptography,coding theory,and communication *** many block ciphers with substitution-permutation network structure,the substitution box is usually a PP over F_(22k)for some positive integer *** resist the differential attacks,the differential uniformity of this

关键词： Finite fields Permutation polynomial Binomial Trinomial Differential uniformity

Formation Mechanisms of Rudstones and Their Effects on Reservoir Quality in the Shulu Sag, Bohai Bay Basin, Eastern China

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Journal of Earth Science 2017年第6期28卷 1095-1108页

作者： Xufeng Liu lijing zheng Zaixing Jiang Xiangxin Kong School of Energy Resources China University of Geosciences Key Laboratory of Petroleum Resources Research Institute of Geology and Geophysics Chinese Academy of Sciences

Based on observations made on cores and cuttings from several wells in the lowermost part of the third member of the Shahejie Formation, several rock types, specifically clast-supported rudstone, matrix-supported rudstone, mixed-source rudstone, calcisiltite/calcarenite, massive calci- lutite and laminated calcilutite, have been identified in the Shulu sag. According to the sedimentary structures and distribution characteristics of these rocks, the carbonate breccias fall into two cate- gories, based on their origins： one formed by fan-delta channel sedimentation, whereas the other formed by earthquake-induced slump fan deposition. Clast-supported rudstone and matrix- supported rudstone are the main lithologies deposited by braided rivers in the fan delta plain and front, of which the pore space is mainly dissolution pores within gravels and tectonic fissures. Clast- supported rudstone, matrix-supported rudstone and mixed-source rudstone are the main lithologies of the earthquake-induced slump fans. These carbonate breccias developed along with soft-sediment deformation structures, which are interpreted as seismites and are widely distributed in the sag, in which intercrystalline pores, intergranular pores and fissures created from diagenetic shrinkage are developed. The two kinds of rudstones have different reservoir characteristics and oil/gas testing re- suits. The rudstones generated in the fan delta have higher porosity and permeability, as well as bet- ter oil/gas testing results. Thus, they are key targets for petroleum exploration.

关键词： rock type formation mechanism depositional model reservoir quality Shulu sag

Corrosion resistance of carbon ion-implanted M50NiL aerospace bearing steel

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Progress in Natural Science:Materials International 2017年第5期27卷 615-621页

作者： Fangfang Wang Chungen Zhou lijing zheng Hu Zhang School of Materials Science and Engineering Beihang University

The effect of carbon implantation on the corrosion behavior of M50NiL aerospace bearing steel through surface modification was investigated. X-ray photoelectron spectroscopy, Auger electron spectroscopy and X-ray diffraction were used to analyze the composition and structure of the carbon-implanted layer. The corrosion properties of the untreated and carbon ion-implanted samples were evaluated by potentiodynamic curves and electrochemical impedance spectroscopy, which were carried out in 3.5% NaCl solution. Ion implantation of carbon in the M50NiL bearing steel yielded a distinct decrease of the corrosion current densities and an obvious increase of the polarization resistance. The experimental results indicated that the content of chromium oxide in the passive film increased with carbon implantation and that the intergranular corrosion was suppressed in the carbon-implanted sample. Better corrosion protection was observed in the carbon ion implantation sample.

关键词： Aerospace bearing steel Ion implantation Electrochemical test Corrosion resistance

Microstructure, Mechanical Properties and Oxidation Resistance of Nb-22Ti-14Si-2Hf-2Al-xCr Alloys

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Chinese Journal of Aeronautics 2012年第2期25卷 292-296页

作者： WANG Ligang JIA Lina CUI Renjie zheng lijing ZHANG Hu School of Materials Science and Engineering Beihang UniversityBeijing 100191China

Nb-22Ti-14Si-2Hf-2Al-xCr （x=2, 6, 10, 14, 17 at%） alloys are prepared by arc-melting under argon atmosphere. Microstructural characteristics, mechanical properties and oxidation resistance of the arc-melted alloys are investigated. At 2 at% Cr content, the microstructure is composed of Nbss, Nb3Si and a small quantity of Nb5Si3, when the Cr contents increase, Nb3Si disappears. For the high Cr content （x ≥ 10 at%） alloys, besides the Nbss and Nb5Si3, Cr2Nb is also detected. With the increase of Cr content, the volume fractions of Cr2Nb and Nb5Si3 increase, while that of Nbss increases firstly and then begins to degrade when the Cr content is higher than 6 at%. For the alloy with 2 at% Cr, the room temperature fracture toughness is about 14.5 MPa·m1/2, but badly decreases to about 8.5 MPa·m1/2, when the Cr contents increase. Vickers hardness of Nbss tends to increase linearly from about 400 to 500, while that of silicides is not sensitive to Cr contents, about 950. The appearance of Cr2Nb phase significantly improves the high temperature oxidation resistance of the alloys with high Cr contents. The isothermal oxidation tests show that the oxidation kinetics of the alloys with various Cr contents follows parabolic oxidation kinetics.

关键词： arc-melted alloys Nb-Si alloys microstructure mechanical properties oxidation resistance

Primary Solidification Phase and Lamellar Orientation in Directionally Solidified Ti-45Al-7Nb Alloy

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Chinese Journal of Aeronautics 2012年第3期25卷 489-492页

作者： YAN Jie zheng lijing XIAO Zhixia YANG Lili ZHANG Hu Key Laboratory of Aerospace Advanced Materials and Performance of Ministry of Education School of Material Science and Engineering Beihang UniversityBeijing 100191China

Primary solidification phase and lamellar orientation are investigated in Ti-45Al-7Nb alloy at very high ratio of temperature gradient to growth rate （G/v） by a liquid-metal-cooled directionally solidified method. It shows that Ti-45Al-7Nb alloy solidifies with primary ct phase. Longitudinal （parallel to growth direction） microstructure shows that a dendrites in solid-liquid mushy zone are discontinuous and transverse mierostructure of a dendrites is worm-like feature. Growth direction of a phase is about 80° away from （0001）,a direction, and close to （1120） a direction. The corresponding lamellar orientation is aligned at the angle of about 10° to growth direction, which is consistent with a-dendrite growth direction according to Blackburn orientation relationship. Therefore, due to the altered growth direction of a phase, the lamellar orientation in Ti-45Al-7Nb alloy is controlled at the G/v ratio of 5 × 10^9 ***^-2.

关键词： metallic material titanium aluminides directional solidification crystal growth lamellar orientation

High temperature tensile properties of directionally solidified Ni-43Ti-4Al-2Nb-2Hf alloy

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Rare Metals 2012年第4期31卷 328-331页

作者： Jiang, Dongwen zheng, lijing Zhou, Lei Pan, Liwen Tang, Xiaoxia Zhang, Hu School of Materials Science and Engineering Beijing University of Aeronautics and AstronauticsBeijing 100191China

By liquid metal cooling(LMC) process,the Ni-43Ti-4Al-2Nb-2Hf(%,atomic fraction) alloy was directionally solidified(DS).The microstructure and tensile properties at room and elevated temperature were *** was found that the DS process significantly improves the room temperature tensile strength,increasing by 70% compared with the as-cast *** appropriate heat treatment(HT),the average tensile strength reaches above 1900 MPa,nearly twice of the as-cast *** 800 and 900 ℃,the tensile strengths are about 308 and 169 MPa,respectively.

关键词： NiTi-Al based alloy directional solidification heat treatment tensile prosperity

Effect of Alloying on the Microstructure and Fracture Toughness of Nb-Mo-Si Alloys

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稀有金属材料与工程 2009年第A3期38卷 58-61页

作者： Wei Qiang Li Yang zheng lijing Ma Chaoli Li Huanxi Beijing University of Aeronautics and Astronautics Beijing 100083 China

It was found that typical Nbss /Nb5Si3 eutectic lamellar structure formed in the Nb-Mo-Si alloy. The interface between Nbss and Nb5Si3 phases was so strong that the alloy fractured mainly in the cleavage mode. In this paper, the fourth element was added with the aim of modifying interface structure. The microstructural characterization and the fracture toughness of Nb-17Si-10Mo ternary alloy doped with Ga, In, Zn and V, respectively, were investigated. It was revealed that the lamellar structure maintained with the addition of Ga and In, whereas it changed slightly with Zn and V additions. Moreover, a little increase in fracture toughness of Nb-17Si-10Mo ternary alloy was obtained through the addition of Ga and Zn.

关键词：共晶层状结构铌钼硅合金物理性能结构分析

Microstructure and mechanical properties of cast Ti-47Al-2Cr-2Nb alloy melted in various crucibles

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China Foundry 2012年第1期9卷 48-52页

作者： Wang Ligang zheng lijing Cui Renjie Yang Lili Zhang Hu School of Materials Science and Engineering Beihang UniversityBeijing 100191China

The main factors limiting the mass production of TiAI-based components are the high reactivity of TiAl- based alloys with the crucible or mould at high temperature. In this work, various crucibles （e.g. CaO, Y203 ceramic crucibles and water-cooled copper crucible） were used to fabricate the Ti-47Al-2Cr-2Nb alloy in a vacuum induction furnace. The effects of crucible materials and melting parameters on the microstructure and mechanical properties of the alloy were analyzed by means of microstructure observation, chemical analysis, tensile test and fracture surface observation. The possibilities of melting TiAI alloys in crucibles made of CaO and Y2O3 refractory materials were also discussed.

关键词： Ti-47Al-2Cr-2Nb alloy ceramic crucibles mechanical properties microstructure