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Hot Deformation Behavior and Microstructural Characteristics of Ti–46Al–8Nb Alloy

Acta Metallurgica Sinica(English Letters) 2018年第9期31卷 933-944页

作者： Tian-Rui Li Guo-Huai liu Mang Xu Tian-Liang fu Yong Tian Ra-Ja Devesh Kumar Misra Zhao-DongWang State Key Laboratory of Rolling and Automation Northeastern UniversityShenyang 110819China Laboratory for Excellence in Advanced Steel Research Department of MetallurgicalMaterials and BiomedicalEngineeringUniversity of Texas at E1 PasoE1 PasoTX 79968-0521USA

Hot deformation behavior, microstructural evolution and flow softening mechanism were investigated in Ti-46A1-8Nb alloy via isothermal compression approach. The true stress-strain curves exhibited typical work hardening and flow softening, in which the dependence of the peak stress on temperature and strain rate was obtained by hyperbolic sine equation with Zener-Hollomon （Z） parameter, and the activation energy was calculated to be 446.9 kJ/mol. The microstructural analysis shows that the alternate dark and light deformed ribbons of Al-rich and Nb-rich regions appeared and were associated with local flow involving solute segregation. The Al segregation promoted flow softening mainly arising from the recrystaUization of V phase with low stacking fault energy. The coarse recrystallized 7 and several massive phase were observed at grain boundaries. While in the case of Nb segregation, t/B2 phase harmonized bending of lamellae, combined with the growth of recrystallized γ grains and α ＋ β ＋ γ→α＋ γ transition under conditions of temperature and stress, leading to the breakdown of α2/γ lamellar colony. During the hot compression process, gliding and dissociation of dislocations occurred in γ phase that acted as the main softening mechanism, leading to extensive γ twins and cross twins in α/γ lamellae and at grain boundaries. In general, homogeneous microstructure during the hot defor- mation process can be obtained in TiAl alloy with high Nb addition and low Al segregation. The deformation substructures intrinsically promote the formability of Ti--46Al-8Nb alloy.

关键词： Titanium aluminides Deformation behavior Activation energy Dynamic recrystallization Local flow softening

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Precipitation and decomposition behaviors of carbides in AISI M2 high-speed steel with nitrogen and mischmetal

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Journal of Central South University 2017年第4期24卷 782-788页

作者： liu Bao-long Lü Zhi-qing FENG Wei-wei REN Ting-zhi fu Wan-tang College of Mechanical Engineering Yanshan University China First Heavy Industries State Key Laboratory of Metastable Material Science and Technology Yanshan University

The behaviors of the precipitation and decomposition of carbides in AISI M2 high-speed steel modified by nitrogen and mischmetal were investigated using DSC, XRD, SEM and TEM. The as-cast microstructure of the experimental steel consists of dendrites of iron matrix, networks of eutectic carbides and secondary carbides. The average distance between networks is about 34 μm. The carbides mainly include M_2C, M(C,N) and M_6C, and their relative contents are 58.5%, 30.3% and 11.2%, respectively. The average spacing between the M_2C fibers is 1.5 μm. The decomposition of M_2C occurs from 897.2 to 1221.5 ℃(heating rate of 200 ℃/h). Some precipitated carbide particles occur in the M_2C matrix after holding for 15 min at 1100 ℃. With increasing holding time, the carbide fibers neck down more and more obviously until they are broken down. The spectral peaks of M_2C almost disappear after holding for 60 min. The spectral peaks of M_6C gradually strengthen with the holding time, and the relative content of M_6C increases to 79.8% after holding for 60 min. After holding for 180 min, the carbide fibers disappear, and the decomposition products consist of fine carbide particles(about 300 nm) and short rod-like carbides(about 3.5 μm).

关键词： high-speed steel metastable carbides decomposition phase transformation refinement

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Human umbilical cord-derived mesenchymal stem cells promote repair of neonatal brain injury caused by hypoxia/ischemia in rats

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Neural Regeneration Research 2022年第11期17卷 2518-2525页

作者： Yang Jiao Yue-Tong Sun nai-Fei Chen Li-Na Zhou Xin Guan Jia-Yi Wang Wen-Juan Wei Chao Han Xiao-Lei Jiang Ya-Chen Wang Wei Zou Jing liu Stem Cell Clinical Research Center National Joint Engineering LaboratoryRegenerative Medicine CenterThe First Affiliated Hospital of Dalian Medical UniversityDalianLiaoning ProvinceChina Dalian Innovation Institute of Stem Cells and Precision Medicine DalianLiaoning ProvinceChina Department of Neurology The First Affiliated Hospital of Dalian Medical UniversityDalianLiaoning ProvinceChina College of Life Science Liaoning Normal UniversityDalianLiaoning ProvinceChina

Administration of human umbilical cord-derived mesenchymal stem cells(hUC-MSCs)is believed to be an effective method for treating neurodevelopmental disorde *** this study,we investigated the possibility of hUC-MSCs treatment of neonatal hypoxic/ischemic brain injury associated with maternal immune activation and the underlying *** established neonatal rat models of hypoxic/ischemic brain injury by exposing pregnant rats to lipopolysaccharide on day 16 or 17 of *** offspring were intranasally administe red hUC-MSCs on postnatal day *** found that polypyrimidine tract-binding protein-1(PTBP-1)participated in the regulation of lipopolysaccharide-induced maternal immune activation,which led to neonatal hypoxic/ischemic brain *** delive ry of hUC-MSCs inhibited PTBP-1 expression,alleviated neonatal brain injury-related inflammation,and regulated the number and function of glial fibrillary acidic protein-positive astrocytes,there by promoting plastic regeneration of neurons and im p roving brain *** findings suggest that hUC-MSCs can effectively promote the repair of neonatal hypoxic/ischemic brain injury related to maternal immune activation through inhibition of PTBP-1 expression and astrocyte activation.

关键词： developmental brain disease model disease-associated astrocytes intranasal administration lipopolysaccharide maternal immune activation neonatal brain injury neuroplasticity repair polypyrimidine tract-binding protein-1 stem cell therapy umbilical cord-derived mesenchymal stem cells

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Muon anomalous Muon anomalous Muon anomalous magnetic dipole moment in theμνSSM

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Chinese Physics C 2022年第9期46卷 103-114页

作者： Hai-Bin Zhang Chang-Xin liu Jin-Lei Yang Tai-fu Feng Department of Physics Hebei UniversityBaoding 071002China Key Laboratory of High-precision Computation and Application of Quantum Field Theory of Hebei Province Baoding 071002China CAS Key Laboratory of Theoretical Physics Institute of Theoretical PhysicsChinese Academy of SciencesBeijing 100190China School of Physical Sciences University of Chinese Academy of SciencesBeijing 100049China College of Physics Chongqing UniversityChongqing 400044China Department of Physics Guangxi UniversityNanning530004China

Recently,the Muon g-2 experiment at Fermilab measured the muon anomalous magnetic dipole moment(MDM),aμ=(gμ-2)/2,and reported that the new experimental average increases the difference between the experiment and the standard model(SM)prediction to 4.2σ.In this work,we reanalyze the muon anomalous MDM at the two-loop level in theμfrom theνSupersymmetric Standard Model(μνSSM)combined with the updated experimental ***μνSSM can explain the current difference between the experimental measurement and the SM theoretical prediction for the muon anomalous MDM,constrained by the 125 GeV Higgs boson mass and decays,the rare decayˉB→Xsγ,and so *** also investigate the anomalous MDM of the electron and tau lepton,ae=(ge-2)/2 and aτ=(gτ-2)/2,at the two-loop level in theμν*** addition,the decaying of the 125 GeV Higgs boson into a pair of charged leptons in theμνSSM is analyzed.

关键词： supersymmetry magnetic dipole moment Higgs boson decays

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Supercondcuting properties in MgB2/Fe wires prepared by PIT method

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Chinese Science Bulletin 2003年第13期48卷 1331-1333页

作者： YAN Guo FENG Yong fu Baoquan liu Chunfang JI Ping ZHANG Pingxiang ZHOU Lian School of Materials and Metallurgy Northeastern UniversityShenyang110004China Supercondluscting Materials Research Center Northwest Institute for Nonferrous Metal Reseanch Xi'an 710016 China

The MgB2 formation was analyzed physically and chemically and the MgB2/Fe wires were fabricated by powder in tube (PIT) technology. The microstructure of MgB2 in wires was studied by the scanning electrical microscope (SEM), which shows a good connection of grains and the size of MgB2 grain is 13 mm. The results of Jc measured by the standard four probes method show that Jc value reaches 6.1?04 A/cm2 at 20 K in self field.

关键词：超导体 MgB2/Fe电线电流密度微观结构扫描电子显微镜

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Realizing n-Type Ge Te through Suppressing the Formation of Cation Vacancies and Bi-Doping

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Chinese Physics Letters 2021年第12期38卷 50-56页

作者： Min Zhang Chaoliang Hu Qi Zhang Feng liu Shen Han Chenguang fu Tiejun Zhu School of Materials Science and Engineering and State Key Laboratory of Silicon MaterialsZhejiang UniversityZhejiang 310027China

It is known that p-type GeTe-based materials show excellent thermoelectric performance due to the favorable electronic band ***,n-type doping in GeTe is of challenge owing to the native Ge vacancies and high hole concentration of about 10^(21)cm^(-3).In the present work,the formation energy of cation vacancies of GeTe is increased through alloying PbSe,and further Bi-doping enables the change of carrier conduction from p-type to *** a result,the n-type thermoelectric performance is obtained in GeTe-based materials.A peak zT of 0.34 at 525 K is obtained for(Ge_(0.6)Pb_(0.4))_(0.88)Bi_(0.12)Te_(0.6)Se_(0.4).These results highlight the realization of n-type doping in GeTe and pave the way for further optimization of the thermoelectric performance of n-type GeTe.

关键词： doping realization performance

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Porosity of crushed rock layer and its impact on thermal regime of Qinghai-Tibet Railway embankment

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Journal of Central South University 2017年第4期24卷 977-987页

作者： liu Ming-hao LI Guo-yu NIU fu-jun LIN Zhan-ju LIN Zhan-ju State Key Laboratory of Frozen Soil Engineering Cold and Arid Regions Environmental and Engineering Research InstituteChinese Academy of Sciences School of Resources and Environment University of Chinese Academy of Sciences

It has been proven that crushed rock layers used in roadbed construction in permafrost regions have a cooling effect. The main reason is the existence of large porosity of the rock layers. However, due to the strong winds, cold and high radiation conditions on the Qinghai-Tibet Plateau(QTP), both wind-blown sand and/or weathered rock debris blockage might reduce the porosity of the rock layers, resulting in weakening the cooling effect of the crushed rock layer(CRL) in the crushed rock embankment(CRE) of the Qinghai-Tibet Railway(QTR) in the permafrost regions. Such a process might warm the underlying permafrost, and further lead to potential threat to the QTR's integrity and stability. The different porosities corresponding to the different equivalent rock diameters were measured in the laboratory using water saturation method, and an empirical exponential equation between porosity and equivalent rock diameter was proposed based on the measured experimental data and an important finding is observed in our and other experiments that the larger size crushed rock tends to lead to the larger porosity when arbitrarily packing. Numerical tests were carried out to study impacts of porosity on permafrost degradation and differential thaw depths between the sunny and shady shoulders. The results show that the decrease in porosity due to wind-blown sand or weathered rock debris clogging can worsen the permafrost degradation and lead to the asymmetric thermal regime. In the traditional embankment(without the CRL within it), the largest differential thaw depth can reach up to 3.1 m. The optimized porosity appears in a range from 34% to 42% corresponding to equivalent rock diameter from 10 to 20.5 cm. The CRE with the optimized porosities can make underlying permafrost stable and 0 ℃ isotherms symmetric in the coming 50 years, even under the condition that the climate warming can lead to permafrost degradation under the CRE and the traditional embankment. Some practical implica

关键词： Qinghai-Tibet Railway crushed rock embankment porosity wind-blown sand permafrost degradation

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Suppression of ice nucleation in supercooled water under temperature gradients

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Chinese Physics B 2021年第6期30卷 657-666页

作者： Li-Ping Wang Wei-Liang Kong Pei-Xiang Bian fu-Xin Wang Hong liu School of Aeronautics and Astronautics Shanghai Jiao Tong UniversityShanghai 200240China

Understanding the behaviours of ice nucleation in non-isothermal conditions is of great importance for the preparation and retention of supercooled water. Here ice nucleation in supercooled water under temperature gradients is analyzed thermodynamically based on classical nucleation theory(CNT). Given that the free energy barrier for nucleation is dependent on temperature, different from a uniform temperature usually used in CNT, an assumption of linear temperature distribution in the ice nucleus was made and taken into consideration in analysis. The critical radius of the ice nucleus for nucleation and the corresponding nucleation model in the presence of a temperature gradient were obtained. It is observed that the critical radius is determined not only by the degree of supercooling, the only dependence in CNT, but also by the temperature gradient and even the Young's contact angle. Effects of temperature gradient on the change in free energy, critical radius,nucleation barrier and nucleation rate with different contact angles and degrees of supercooling are illustrated *** results show that a temperature gradient will increase the nucleation barrier and decrease the nucleation rate, particularly in the cases of large contact angle and low degree of supercooling. In addition, there is a critical temperature gradient for a given degree of supercooling and contact angle, at the higher of which the nucleation can be suppressed completely.

关键词： supercooled water ice nucleation temperature gradient thermodynamic analysis classical nucleation theory

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Adsorption of methane onto mudstones under supercritical conditions: Mechanisms, physical properties and thermodynamic parameters

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Petroleum Science 2023年第1期20卷 34-47页

作者： Yang Wang Hong-Fei Cheng Qin-Hong Hu Lang-Bo Jia Xi-Meng Wang Sha-Sha Gao Luo-fu liu School of Earth Science and Resources Chang'an UniversityXi'anShaanxi710054China Key Laboratory of West Mineral Resources and Geological Engineering of Ministry of Education Chang'an UniversityXi'anShaanxi710054China Department of Earth and Environmental Sciences The University of Texas at ArlingtonArlingtonTX76019USA Exploration and Development Research Institute Changqing Oil FieldPetroChinaXi'anShaanxi710000China Department of Geology and Geophysics Texas A&M UniversityCollege StationTX77843USA State Key Laboratory of Petroleum Resources and Prospecting China University of Petroleum(Beijing)Beijing102249China

Since the mechanisms of methane-mudstone interactions are important for estimating shale gas reserves,methane adsorption under supercritical conditions of 30 MPa pressure and 303.15,333.15,363.15 K temperatures was studied to measure the excess methane adsorption in two mudstone samples from Yanchang Formation,Ordos *** adsorption features inflection points where the amount of adsorbed gas changes from increasing to decreasing *** methods(fixed,slope,and freely fitted density)were applied to calculate the adsorbed-phase density(rad),which was then used to fit the measured excess *** criteria,the goodness-of-fit and whether the fitting can obtain reasonable absolute adsorption,were applied to determine the most accurate *** indicated that the supercritical Dubinin-Radushkevich(SDR)model with freely fitted rad was the most reasonable *** volume of adsorbed methane at 363.15 K is close to the micropore(d<2 nm)volume of the corresponding *** the actual geological conditions,the adsorbed gas should be predominantly stored in *** parameters reveal that the methane adsorption on mudstone is a physisorption process that is jointly controlled by the heterogeneity of,and interaction forces between the methane molecule and,the rock surface.

关键词： Supercritical methane adsorption Excess adsorption Adsorbed-phase density Adsorption model Thermodynamic feature

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Effect of cooling rate on microstructure and inclusion in non-quenched and tempered steel during horizontal directional solidification

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Journal of Iron and Steel Research International 2019年第9期26卷 973-982页

作者： Hui liu Zong-ze Huang Da-jiang Yu De-lin Hu Hong-gang Zhong Qi-jie Zhai Jian-xun fu State Key Laboratory of Advanced Special Steel School of Materials Science and EngineeringShanghai UniversityShanghai 200072China State Key Laboratory of Development and Application Technology of Automotive Steels (Baosteel Group) Shanghai 201900China

In order to investigate the relationship between microstructure and MnS inclusion in non-quenched and tempered steel, and cooling rate during horizontal directional solidification, 49MnVS steel was used to conduct the experiments with a selfdesigned device. The mathematical effect of cooling rate on dendritic arm spacing and mean diameter of MnS particles (dMnS) were determined by using linear regression method. The results show that the length of dendrite from solid–liquid interface to end-solidification decreased with increasing the withdrawal velocity (#). dMnS has a similar value in the area of the steady directional solidification;the value of dMnS was 4.1, 3.6, 3.3, 2.8 and 2.3 lm at withdrawal velocity of 50, 75, 100, 150 and 200 lm/s, respectively. dMnS increased with reducing # or RC (interface cooling rate). MnS precipitated in the gaps between dendrites and was influenced by secondary dendritic arm spacing. Besides, a new concept of the ‘Precipitation Unit Space’(PUS) was proposed and the relationships between dMnS, VPUS (volume of PUS) and RC were obtained.

关键词： Horizontal directional solidification Dendrite MnS Inclusion Cooling rate

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