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Coarsening Kinetics of γ' Precipitates in Dendritic Regions of a Ni_3 Al base Alloy

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Journal of Materials Science & Technology 2012年第3期28卷 221-228页

作者： h.b.Motejadded M.Soltanieh S.Rastegari School of Metallurgy and Materials Engineering Iran University of Science and TechnologyTehranIran

Coarsening behavior of γ＇ precipitates in the dendritic regions of a Ni 3 Al base alloy containing chromium,molybdenum,zirconium and boron was *** treatment was performed up to 50 h at 900,1000 and 1100℃.The alloy was produced by vacuum-arc remelting *** show that coarsening of the γ＇ precipitates in this complex alloy containing high volume fractions of γ＇ phase follows Lifshitz-Slyozov-Wagner（LSW） *** activation energy of the γ＇ precipitates was evaluated to be about 253.5 ***-1 which shows that the growth phenomenon is controlled by volume diffusion of *** an innovative approach,diffusion coefficient of the solute element（s） and the interfacial energy between γ＇ precipitates and γ＇（matrix） were estimated at 900,1000 and 1100℃.Accordingly,the interfacial energies at 900,1000 and 1100℃ are 4.49±1.48,2.08±0.69 and 0.98±0.32 mJ.m-2,*** the diffusivities of solute element（s） at these temperatures are 3.41±1.08,30±9.5 and 145.15±45.85（10-15 m-2.s-1）,respectively.

关键词： Ni3 Al base intermetallic Coarsening kinetics Activation energy

Extending SSD Lifespan with Comprehensive Non-Volatile Memory-based Write buffers

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Journal of Computer Science & Technology 2019年第1期34卷 113-132页

作者： Ziqi Fan Dongchul park Department of Computer Science and Engineering University of Minnesota-Twin CitiesMinneapolisMN 55455U.S.A. Division of Computer and Electronic Systems Engineering Hankuk University of Foreign Studies Gyeonggi-do 17035South Korea

New non-volatile memory (NVM)technologies are expected to replace main memory DRAM (dynamic random access memory)in the near *** flash technological breakthroughs have enabled wide adoption of solid state drives (SSDs)in storage ***,flash-based SSDs,by nature,cannot avoid low endurance problems because each cell only allows a limited number of *** can give rise to critical SSD reliability *** many SSD write operations eventually cause many SSD erase operations,reducing SSD write traffic plays a crucial role in SSD reliability. This paper proposes two NVM-based buffer cache policies which can work together in different layers to maximally reduce SSD write traffic:a main memory buffer cache design named hierarchical Adaptive Replacement Cache (h-ARC)and an internal SSD write buffer design named Write Traffic Reduction buffer (WRb).h-ARC considers four factors (dirty,clean, recency,and frequency)to reduce write traffic and improve cache hit ratios in the *** reduces block erasures and write traffic further inside an SSD by effectively exploiting temporal and spatial *** two comprehensive schemes significantly reduce total SSD write traffic at each different layer (i.e.,host and SSD)by up to ***,they help extend SSD lifespan without system performance degradation.

关键词： buffer cache policy write buffer non-volatile memory solid state drive flash memory

CFD-DEM simulation of a pseudo-two-dimensional spouted bed comprising coarse particles

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Particuology 2019年第2期17卷 171-180页

作者： b. Mahmoodi S.h. hosseini G. Ahmadi llam Gas Treating Company llam Iran Department of Chemical Engineering llam University llam 69315-516 Iran Department of Mechanical and Aeronautical Engineering Clarkson University Potsdam NY 13699-5725 USA

In the present study, computational fluid dynamics (CFD) and the discrete element method (DEM) are used in conjunction with the Eulerian-Lagrangian method to simulate a pseudo-two-dimensional spouted bed comprising coarse 6-mm particles. The open-source OpenFOAM code is used to solve the governing equations. The predicted vertical particle velocity along the bed axis, particle velocity profiles in the radial directi on, power spectral den sity, time-averaged particle velocity vectors, bed pressure drop, and solid flow pattern are evaluated and compared with existing experimental data. Good agreement is found between the CFD-DEM results and the measured data. It is also shown that the present CFD-DEM model accurately predicts the particle flow pattern throughout the bed. It is found that the drag force, solid stresses, and gravity play important roles in the CFD-DEM simulation of a spouted bed comprising coarse particles.

关键词： CFD-DEM Pseudo-2D spouted bed hydrodynamics Coarse particles

Comment on “Evidence for Mesoproterozoic collision,deep burial and rapid exhumation of garbenschiefer in the Namaqua Front,South Africa” by Valby Van Schijndel,David ***,Robert Anczkiewicz,Anders Schersten,Geoscience Frontiers,Volume 11,Issue 2,Pag

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Geoscience Frontiers 2020年第5期11卷 1889-1894页

作者： Steffen h.buttner Department of Geology Rhodes University6139Makhanda(Grahamstown)South Africa

In their recent publication Van Schijndel et al.(2020) present new age data and P-T analysis from the eastern margin of the Namaqua Sector of the Namaqua Natal Metamorphic *** authors claim to provide evidence for the... 详细信息

关键词： Province. burial eastern

Exact solution and transient behavior for torsional vibration of functionally graded finite hollow cylinders

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Acta Mechanica Sinica 2009年第4期25卷 555-563页

作者： h. M. Wang C. b. Liu h. J. Ding Department of Mechanics Zhejiang University Department of Civil Engineering Zhejiang University

Exact solutions are obtained for transient torsio- nal responses of a finitely long, functionally graded hollow cylinder under three different end conditions, i.e. free-free, free-fixed and fixed-fixed. The cylinder with its external surface fixed is subjected to a dynamic shearing stress at the internal surface. The material properties are assumed to vary in the radial direction in a power law form, while keep invariant in the axial direction. With expansion in the axial direction in terms of trigonometric series, the governing equations for the unknown functions about the radial coordinate r and time t are deduced. by applying the variable substitution technique, the superposition method and the separation of variables consecutively, series-form solutions of the equations are obtained. Natural frequencies and the transient torsional responses are finally discussed for a functionally graded finite hollow cylinder.

关键词： Exact solution Functionally graded material Finite hollow cylinder Transient torsional vibration

Dynamical amplification of electric polarization through nonlinear phononics in 2D SnTe

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npj Computational Materials 2020年第1期6卷 155-162页

作者： Dongbin Shin Shunsuke A.Sato hannes hübener Umberto De Giovannini Noejung park Angel Rubio Max Planck Institute for the Structure and Dynamics of Matter and Center for Free-Electron Laser Science Luruper Chaussee 149Hamburg 22761Germany Center for Computational Sciences University of TsukubaTsukuba 305-8577Japan Nano-bio Spectroscopy Group Departamento de Fisica de MaterialesUniversidad del Pas VascoSan Sebastian 20018Spain Department of Physics Ulsan National Institute of Science and TechnologyUNIST-gil 50Ulsan 44919Korea Center for Computational Quantum Physics(CCQ) The Flatiron Institute162 Fifth AvenueNew YorkNY 10010USA

Ultrafast optical control of ferroelectricity using intense terahertz fields has attracted significant *** we show that the nonlinear interactions between two optical phonons in SnTe,a two-dimensional in-plane ferroelectric material,enables a dynamical amplification of the electric polarization within subpicoseconds time *** first-principles time-dependent simulations show that the infrared-active out-of-plane phonon mode,pumped to nonlinear regimes,spontaneously generates in-plane motions,leading to rectified oscillations in the in-plane electric *** suggest that this dynamical control of ferroelectric material,by nonlinear phonon excitation,can be utilized to achieve ultrafast control of the photovoltaic or other nonlinear optical responses.

关键词： nonlinear ferroelectric phonon

Phase Formation and Magnetic Properties of Nanocomposite Nd-Fe-b Adjusted by Small Amount of Dy and Co

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Journal of Rare Earths 2004年第Z2期22卷 89-94页

作者： T S Jang T W Lim h S Aum D h Lee M b Kim Division of Materials and Chemical Engineering Sun Moon UniversityKorea Division of Materials and Chemical EngineeringSun Moon UniversityKorea Division of Mechanical EngineeringSun Moon University 100 Kalsan LiTangjung MyonAsan CityChoongnam 336-708Korea Division of Materials and Chemical EngineeringSun Moon UniversityKorea Division of Materials and Chemical EngineeringSun Moon UniversityKorea

In order to improve and stabilize the magnetic properties of nanocomposite Nd2Fe14b/α-Fe magnetic alloys by a compositional adjustment, small amount of Dy and/or Co was added to Nd9Fe84b7 alloys. DTA analysis on the amorphous of the alloys took place as the soft magnetic phases were crystallized, and then the hard magnetic Nd2Fe14b was precipitated from them. While α-Fe and a metastable 1:7 (TbCu7-type) phase were formed simultaneously in Dy and Co-free alloys, they were crystallized separately at different temperatures after Dy or Co was added. This phase separation occurred more clearly in the Dy-treated alloys and the other soft magnetic phase Fe3b was also stabilized by Dy and/or Co. The 1: 7 phase that was stabilized by Dy and/or Co was not eliminated at 700 ℃, decreasing magnetic properties of the alloys. It was eventually disappeared above 725 ℃, but Fe3b was not eliminated even at 750 ℃ when Dy was added more than 0.5 at% or Co was added more than 2.0 at%. Amount of Nd2Fe14b in the alloys tended to increase as Dy addition increased,whereas Co addition did not lead to any appreciable change in the ratio of α-Fe and Nd2Fe14b. Moreover, Dy addition apparently increased coercivity of an alloy while Co addition had a beneficial effect on remanence. The grains in the Dytreated alloys were usually finer than those in the Co-treated alloys. The grain size of both α-Fe and Nd2Fe14b in the alloys exhibiting mr ≥ 0.72 was in the range of 20 ～ 40 nm or even larger 50 nm, which is larger than the theoretical optimum size ( ～ 10 nm). Typical magnetic properties obtained from a Nd7.5Dy1.5Fe82.5Co1.5b7 alloy annealed for 12 min at 725 ℃were ihc=4.85 kOe, br= 11.32 kG, (bh)max = 15.73 MGOe, and mr=0.73.

关键词： nanocomposite Nd-Fe-b magnetic properties remanence coercivity

A new thermodynamically stable Nb_(2)Ni intermetallic compound phase revealed by peritectoid transition within binary Nb-Ni alloy system

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Journal of Materials Science & Technology 2022年第5期100卷 246-253页

作者： J.F.Zhao h.P.Wang b.Wei School of Physical Science and Technology Northwestern Polytechnical UniversityXi’an 710072China

A new intermetallic compound of thermodynamically stable Nb_(2)Ni phase is discovered within Nb-Ni binary system,refreshing the current situation that there are only three stable intermediate phases of Nb_(7)Ni_(6),NbNi_(3) and NbNi_(8).The new stable phase is generated from the peritectoid transition:(Nb)+Nb_(7)Ni_(6)→Nb_(2)Ni,and the transformation temperature is 1533 *** refreshes the current equilibrium Nb-Ni binary phase *** is confirmed by transmission electron microscopy and the annealing experiments,which is determined to be the FCC structure(Pearson:cF96,space grope:Fd-3m O2,a=11.888A).Furthermore,the equilibrium properties of Nb_(2)Ni phase are produced by density functional theory,including the formation energy,cohesive energy,bulk modulus and lattice constant.

关键词： Intermetallic compound Peritectoid transition Transmission electron microscopy Density functional theory Nb alloy

A strategy for designing stable nanocrystalline alloys by thermo-kinetic synergy

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Journal of Materials Science & Technology 2020年第8期36卷 21-31页

作者： h.R.Peng b.S Liu F.Liu State Key Laboratory of Solidification Processing Northwestern Polytechnical UniversityXi’an710072China School of Materials and Chemical Engineering Xi’an Technological UniversityXi’an710021China Analytical and Testing Center Northwestern Polytechnical UniversityXi’an710072China

Aiming to design stable nanocrystalline(NC)materials,so far,it has been proposed to construct nanostructure stability maps in terms of thermodynamic parameters,while kinetic stabilization has seldom been considered,despite the synergy of thermodynamics and ***,the thermodynamically stabilized NC materials may be easily subjected to grain growth at high temperatures due to the weakly kinetic *** from the thermo-kinetic synergy,a stabilization criterion is proposed as a function of intrinsic solute parameters(*** activation energy for bulk diffusion and the segregation enthalpy),intrinsic solvent parameters(*** intrinsic activation energy for Gb migration and the Gb energy)and processing parameters(*** grain size,the temperature and the solute concentration).Using first-principles calculations for a series of combinations between fifty-one substitutional alloying atoms as solute atoms and Fe atom as fixed solvent atom,it is shown that the thermal stability neither simply increases with increasing the segregation enthalpy as expected by thermodynamic stabilization,nor monotonically increases with increasing the activation energy for bulk diffusion as described by kinetic *** combination of thermodynamic and kinetic contributions,the current stabilization criterion evaluates quantitatively the thermal stability,thus permitting convenient comparisons among NC materials involved by various combinations of the solute atoms,the solvent atoms,or the processing *** of this thermo-kinetic stabilization criterion has been tested by current experiment results of Fe-Y alloy and previously published data of Fe-Ni,Fe-Cr,Fe-Zr and Fe-Ag alloys,etc.,which opens a new window for designing NC materials with sufficiently high thermal stability and sufficiently small grain size.

关键词： Thermo-kinetic Synergy Criterion Thermal stability Nanocrystalline materials