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Observations on the Formation of Ultrafine Ferrite Grain Size in Steels by Physical Simulation Routes

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Journal of Materials Science & Technology 2003年第Z1期19卷 112-114页

作者： l.x. Pan l.P. Karjalainen M. C. Somani University of Oulu Department of Mechanical Engineering P.O. Box 4200 FIN-90014 Oulu Finland University of Oulu Department of Mechanical Engineering P.O. Box 4200 FIN-90014 Oulu Finland University of Oulu Department of Mechanical Engineering P.O. Box 4200 FIN-90014 Oulu Finland

Some observations are reported on the simulation of two thermomechanical routes to produce ultrafine ferrite grainsize in steels. One C-Mn grade and Nb, Nb-Ti and Nb-high Ti bearing steels were used in the tests performed ona Gleeble simulator and a laboratory rolling mill. The routes included severe hot deformation of prior grain-refinedaustenite at the temperature close to Ar3 (DIF) and static recrystallization of fine-grained cold-rolled martensite(SRM). It was observed that the hot deformation induces the formation of ferrite above the Ar3 temperature of thesteel, but severe reductions are required for the complete transformation. Strain of 1.2 can result in about 70% offerrite with the grain size of about 1.4～2μm in all the studied steels. Similarly, in short annealing of cold-workedmartensite, the static recrystallization can also lead to a grain size of about 1.5 μm. The distribution of carbonvaries in the microstructures, carbon being in the second phase in the DIF route and in carbide particles in the SRMroute, which may have a significant influence on the mechanical properties and the thermal stability of ultrafine grainstructure.

关键词： Ultrafine grain size, Steels, Physical simulation, Strain-induced ferrite, Cold rolling and annealing

Context-free Grammars for Triangular Arrays

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Acta Mathematica Sinica,English Series 2015年第3期31卷 445-455页

作者： Robert x.J.HAO larry x.W.WANG Harold R.l.YANG Center for Combinatorics LPMC-TJKLC Nankai University

We consider context-free grammars of the form G = {f → f^b1＋b2＋1g^a1＋a2, g → f^b1 g^a1＋1},where ai and bi are integers sub ject to certain positivity conditions. Such a grammar G gives rise to triangular arrays {T（n, k）}0≤k≤n satisfying a three-term recurrence relation. Many combinatorial sequences can be generated in this way. let Tn （x） =∑k=0^n T（n, k）x^k. Based on the differential operator with respect to G, we define a sequence of linear operators Pn such that Tn＋1（x） = Pn（Tn（x））. Applying the characterization of real stability preserving linear operators on the multivariate polynomials due to Borcea and Br？ndén, we obtain a necessary and sufficient condition for the operator Pn to be real stability preserving for any n. As a consequence, we are led to a sufficient condition for the real-rootedness of the polynomials defined by certain triangular arrays, obtained by Wang and ***, as special cases we obtain grammars that lead to identities involving the Whitney numbers and the Bessel numbers.

关键词： Context-free grammar stable polynomials real-rootedness Bessel numbers Whitneynumbers

Phase Selection in Solidi?cation of Undercooled Co–B Alloys

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Journal of Materials Science & Technology 2017年第4期33卷 352-358页

作者： x.x.Wei W.xu J.l.Kang M.Ferry J.F.li State Key laboratory of Metal Matrix Composites School of Materials Science and EngineeringShanghai Jiao Tong UniversityShanghai 200240.China Australian Research Council Centre of Excellence for Design in light Metals School of Materials Science and EngineeringThe University of New South WalesSydneyNSW 2052Australia

A series Co-（18.5–20.7） at.% B melts encompassing the eutectic composition（Co81.5B18.5） were solidified at different degrees of undercooling. It is found that the metastable Co23B6 phase solidifies as a substitute for the stable Co3 B phase in the alloy melts undercooled above a critical undercooling value of -60 *** Co23B6 and α-Co phases make up a metastable eutectic. The corresponding eutectic composition and temperature are Co80.4B19.6 and 1343 K, respectively. On exposure of the metastable Co23B6 phase at a given temperature above 1208 K, it does not decompose even after several hours. But it transforms by a eutectoid reaction to α-Co ＋ Co3 B at lower temperature.

关键词： Undercooling Rapid solidi?cation Metastable phase diagram Structure evolution

Stress-Induced Martensitic Transformation of Zr_(50)Cu_(25)Ni_(10)Co_(15) Nanocrystals Embedded in an Amorphous Matrix

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Journal of Materials Science & Technology 2017年第3期33卷 276-280页

作者： W.H.Gao x.Y.Yi x.l.Meng G.Song W.Cai l.C.Zhao School of Materials Science and Engineering Harbin Institute of Technology Department of Mechanical Engineering University of Houston

The stress induced martensitic phase transformation of spherical ZrCu nanocrystals embedded in an amorphous matrix was studied in this paper. Microstructural observations revealed that the martensitic transformation of the nanocrystal was hindered by the surrounding amorphous coating. The existence of two-step transformation from the austenite phase（B2） to the base structure martensite（B19＇） and finally to the most stable superstructure martensite（Cm） was also demonstrated. The Cm martensite with（021） type I twinning symmetrically accommodation was surrounded by the B19＇ martensite with dislocation morphologies.

关键词： Nanocrystals ZrCu Martensitic phase transformation Shape memory Transmission electron microscopy

Simulation and characteristics analysis of a wavefield in a thermoelastic medium adopting the rotated staggered-grid pseudospectral method and l-S theory

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Science China Earth Sciences 2021年第8期64卷 1390-1408页

作者： Yuanxie lI Cai lIU Zhiqi GUO Yang lIU xuan FENG you TIAN Qi lU College of Geo-exploration Science and Technology Jilin UniversityChangchun 130026China

The simulation of wave propagation in high-temperature media requires thermoelastic *** this paper,we apply the rotated-staggered-grid pseudo-spectral method(RSG-PSM)to solving thermoelastic governing equations based on l-S theory.A time splitting method is used to solve the stiffness problem of the equations,and we introduce the rotated staggered pseudo-spectral operator and centered pseudo-spectral operator to compute the first-order spatial derivatives and second-order spatial derivatives,*** the case of the heterogeneous-medium model,the Crank-Nicolson explicit method is used instead of the pseudo-spectral method to compute the *** properties and propagation of the thermal coupled wavefield are discussed,and we compare the simulation results obtained using the pseudo-spectral method,staggered-grid pseudo-spectral method,and *** the case of an isotropic homogeneous medium,we obtain stable and highly accurate results using the time splitting method combined with the ***,the algorithm cannot be applied with a large time step when the thermal conductivity changes dramatically,and the algorithm is unstable when the reference temperature has a gradient *** optimal combined application of the mesh generation mode and numerical algorithm is explored,laying a foundation for the extension of these methods to thermoporoelasticity,thermoviscoelasticity,and anisotropy.

关键词： Thermoelastic wave l-S theory Rotated-staggered-grid pseudo-spectral method Seismic wavefield simulation Time splitting method

Seasonal dependency of controlling factors on the phytoplankton production in Taihu lake, China

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Journal of Environmental Sciences 2019年第2期31卷 278-288页

作者： Qiaohua Zhao Jing Wang Jianjian Wang Julian x.l.Wang College of Hydrometeorology Nanjing University of Information Science and Technology Air Resources laboratory National Oceanic and Atmospheric AdministrationCollege Park

In this study, 44 profiles of gross primary productivity(GPP) and sunlight, along with water temperature, Chlorophyll-a(Chla) and nutrients, were observed in Meiliang Bay of Taihu lake, China, in the spring, summer, and fall seasons. Effects of water temperature, light,and nutrient concentration were examined in relation to the GPP-unit-Chla(GPP of algae per Chla). The results showed that the optimum temperature for the GPP of phytoplankton was 27.9°C, the optimal PNA-unit-Chla(photon number absorbed by phytoplankton per Chla) was 0.25(mol), and the HSCN-unit-Chla and HSCP-unit-Chla(half-saturation constants of nitrogen and phosphorus of algae per Chla) were 0.005(mg/l) and 0.0004(mg/l), respectively. The seasonal dependency of the effect of different factors on the GPP was analyzed. Compared with temperature and nutrients, light was found to be the most important factor affecting the GPP during the three seasons. The effect of temperature and nutrients on the GPP of phytoplankton has obvious seasonal change. In spring, temperature was the secondary factor affecting the GPP of phytoplankton, and the effect of nutrients may be negligible in the eutrophic lake on account of temperature limit, which showed that the GPP of algae was only affected by the physical process. In summer and fall, temperature didn't affect the GPP of algae, and the presence of nutrients was the secondary factor affecting the GPP of phytoplankton. From summer to fall, effect of phosphorus was weakened and effect of nitrogen was enhanced.

关键词： Temperature limited effect Gross primary productivity Eutrophication light limit Optimum temperature Half-saturation constants

Effects of Electric Field on the Electronic Structures in Electroluminescent Polymers

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Journal of Materials Science & Technology 1999年第4期15卷 354-356页

作者： Fu, Rl Chu, JH Fu, RT li, l Sun, x Chinese Acad Sci Shanghai Inst Tech Phys Natl Lab Infrared Phys Shanghai 200083 Peoples R China Fudan Univ Dept Phys Shanghai 200433 Peoples R China

The effects of the electric field on the electronic structures in electroluminescent polymers were studied with the tight-binding model including electron-phonon interactions plus an applied electric field. It is found that the applied electric field changes both the energy levels and the electronic wavefunctions in electroluminescent polymers: applied field induces two localized electronic states near the midgap, and also polarizes these localized electronic states, so the polarization occurs at weak or moderate fields. In addition, the strong field will dissociate a bipolaron exciton and lead to photoluminescence quenching.

关键词： Polymers

Accelerating bainite transformation by concurrent pearlite formation in a medium Mn steel:Experiments and modelling

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Journal of Materials Science & Technology 2024年第9期176卷 211-223页

作者： l.K.Huang F.liu M.x.Huang Department of Mechanical Engineering The University of Hong KongPokfulam RoadHong KongChina State Key laboratory of Solidification Processing Northwestern Polytechnical UniversityXi’anShaanxi710072China

Bainite transformation has yet to be utilized and even thoroughly studied in medium Mn ***,we investigate the isothermal bainite transformation in a 10Mn steel at 450°C experimentally and theoretically,focusing on the effect of dislocations introduced by warm *** show that the bainite transformation in the studied medium Mn steel exhibits extremely sluggish kinetics(on a time scale of days),concurrent with the pearlite *** introduced dislocations can significantly accelerate bainite transformation kinetics while also facilitating the pearlite *** is likely the first report on the simultaneous occurrence of these two solid-state reactions in medium Mn *** respect to the roles of dislocations in the acceleration of bainite transformation observed in this work,we propose a new‘carbon depletion mechanism’,in which dislocations-stimulated pearlite formation makes a twofold contribution:facilitating the formation of bainitic ferrite sub-units to further enhance the autocatalytic effect and preventing the carbon enrichment in the remaining *** this basis,a physical model is developed to quantitatively understand the bainite transformation kinetics considering the effect of concurrent pearlite formation,revealing good agreements between model descriptions and experiment *** findings,herein,offer fundamental insights into the bainite transformation in medium Mn steels and uncover a previously unidentified role played by introduced dislocations in influencing the kinetics of bainite formation,which may guide its future application in manipulating microstructure for the development of advanced high-strength steels.

关键词： Medium Mn steels Bainite Thermodynamics Kinetics Phase transformation

Revisiting anisotropy in the tensile and fracture behavior of cold-rolled316l stainless steel with heterogeneous nano-lamellar structures

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Nano Materials Science 2020年第1期2卷 72-79页

作者： Zesheng you Huangliu Fu Shoudao Qu Weikang Bao lei lu Herbert Gleiter Institute of Nanoscience Nanjing University of Science and TechnologyNajing210094China Shenyang National laboratory for Materials Science Institute of Metal ResearchChinese Academy of SciencesSheryang110016China

We produced a 316 l stainless steel with heterogeneous nanometer-thick lamellar structures by severe cold-rolling at room temperature,and conducted micro-scale tensile tests in different orientations to evaluate both the inplane(parallel to the nano-lamellae)and out-of-plane(normal and 45inclined to the nano-lamellae)mechanical *** parallel orientation demonstrates the greatest tensile strength while the inclined orientation exhibits the least *** tensile tests in normal and inclined directions also indicate significant transient elastic-plastic response due to the strain path *** examination demonstrates that the specimen fails in the normal direction by premature micro-void nucleation and growth,which restricts its tensile strength;however,we identified zig-zag cracking associated with lamellar shear cracking in the inclined direction.

关键词： Heterogeneous nano-lamellar structure Mechanical anisotropy Fracture behavior Specimen size effect Strain path effect