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Study on Modification Mechanism of Rare Earth in ZA27 Cast Alloy with Electronic Theory and Molecular Dynamics Method

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Journal of Materials Science & technology 2004年第5期20卷 586-588页

作者： Guili LIU, Rongde LI and Zhenping ZHOUsch.ol of Materials Science and eng.neering, Shenyang University of technology, Shenyang 110023, China sch. of Mat. Sci. and eng. Shenyang Univ. of Technol. Shenyang 110023 China

A model of liquid ZA27 cast alloy is established according to molecular dynamics theory and an atomic structural model of co-existent a phase and liquid is also presented by means of computer programming. Recursion method is adopted to calculate the electronic structure of RE (rare earth) in grains and around phase boundaries respectively. The calculation shows that RE is more stable around phase boundaries than in grains, which explains the fact that the solution of RE in a phase is less, and RE mainly aggregates in front of phase boundary. The calculations of bonding order integrals also show that RE in front of phases hardly solidify onto the grain surfaces as active element so as to prevent grains growth and refine the grains. As a result, the modification mechanism of RE may be explained from the view of electronic structure.

关键词： Atomic structural model Recursion method Electronic structure Modification mechanism Rare easth

A Simple Method for Grain Refinement of Pure Aluminium

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Journal of Materials Science & technology 2003年第2期19卷 187-188页

作者： Dae-Heon Joo, Jeong-Keun Lee and Myung-Ho Kimsch.ol of Materials Science and eng.neering, Inha University, Inchon 402-751, Korea sch. of Mat. Sci. and eng. Inha Univ. Inchon 402-75 South Korea

In order to produce the fully equiaxed and fine grained pure Al, a simple casting process that used cooling slope was examined and compared with conventional casting process under same casting conditions. By using cooling slope, grains over the whole section of castings were suddenly refined and ability of grain refinement kept up at very high mold temperature up to 550癈 in examined casting conditions.

关键词： Equiaxed microstructure Heterogeneous nucleation Grain refinement

Kinetic Characteristic of Hydrogenation Zr-Ti-Cu-Ni-Be Bulk Amorphous Alloys

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Journal of Materials Science & technology 2004年第2期20卷 157-159页

作者： Delin Peng. Jun SHEN, Jianfei SUN and Yuyong CHENsch.ol of Materials Science and eng.neering, Harbin Institute of technology, Harbin 150001, China sch. of Mat. Sci. and eng. Harbin Inst. of Technol. Harbin 150001 China

The relationship between the hydrogen content and the microhardness and the charging period, the effect of hydrogen on the activation energy, the kinetics of glass transition and crystallization of Zr-Ti-Cu-Ni-Be bulk amorphous alloy were studied by differential scanning calorimetry (DSC) and the Kissinger equation. It shows that both of the hydrogen content and the microhardness are related to the charging period, and that the glass transition and crystallization behavior are associated with the heating rate, and possess the kinetic effect. Hydrogen increases the glass transition temperature and the crystallization temperature, decreasing the enthalpies in the different stages of crystallization. Hydrogen increases the activation energies of the glass transition and the crystallization and changes the kinetic effect. The dependent extent between the glass transition, the crystallization and heating rate decreases after hydrogen charging.

关键词： Bulk amorphous Hydrogenation Glass transition Crystallization Kinetic

Effect of Traveling Magnetic Field on Mould-Filling Leng.h of the A357 Melt during Casting Thin Walled Plate

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Journal of Materials Science & technology 2003年第1期19卷 43-46页

作者： Tiejun ZHANG, Jingjie GUO, Yanqing SU, Hongsheng.DING, Weisheng.BI, Jim JIA and Heng.hi FUsch.ol of Materials Science and eng.neering, Harbin Institute of technology, Harbin 150001, China sch. of Mat. Sci. and eng. Harbin Inst. of Technol. Harbin 150001 China

In order to improve the mould filling ability, the method for production of thin-walled castings in the travelingmagnetic field was applied. The relationship between magnetic field density and input voltage as well as distancewas investigated, and the mould filling leng.h of A357 melt has been studied. The electromagnetic forces appliedon the melt were also analyzed. The result shows that the mould-filling leng.h of the melt increase rapidly with theincrease of magnetic flux density. The mould filling leng.hs in gypsum upper mould and magnetic material uppermould were compared from the standpoint of application. It demonstrated that the steel upper mould is superior togypsum mould.

关键词： Mould filling Traveling magnetic field A357 melt

Effect of Triple Annealing Treatment on Stress Relaxation of Ti-6Al-4V Alloy

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Journal of Materials Science & technology 2004年第3期20卷 292-294页

作者： Yong LIU Jingchuan ZHU Zhongda YIN Mingwei LI sch.ol of Materials Science and eng.neering, Harbin Institute of technology Harbin 150001,China sch. of Mat. Sci. and eng. Harbin Inst. of Technol. Harbin 150001 China

The effect of triple annealing on stress relaxation of Ti-6Al-4V alloy as well as the microstructure after stress relaxation werestudied. The results showed that triple annealing treatment enhanced the resistance of stress relaxation performance, andwhen the temperature was rising, this effect became notable. The stress relaxation deformation mechanism is of dislocationcreep at 400℃ and recovery creep at 600℃.

关键词： Triple annealing Ti-6Al-4V alloy Stress relaxation

Gibbs Free Energy and Activation Energy of ZrTiAlNiCuSn Bulk Glass Forming Alloys

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Journal of Materials Science & technology 2004年第3期20卷 298-300页

作者： Jianfei SUN Jun SHEN Zhenye ZHU Gang WANG Dawei XING Yulai GAO Bide ZHOU sch.ol of Materials Science and eng.neering, Harbin Institute of technology, Harbin 150001,China sch. of Mat. Sci. and eng. Harbin Inst. of Technol. Harbin 150001 China

The Gibbs free energy differences between the supercooled liquid and the crystalline mixture for the (Zr_(52.5)Ti_5Al_(10)-Ni_(14.6)Cu_(17.9))_((100-x)/100)Sn_x (x=0, 1, 2, 3, 4 and 5) glass forming alloys are estimated by introducing the equationproposed by Thompson, Spaepen and Turnbull. It can be seen that the Gibbs free energy differences decrease firstas the increases of Sn addition smaller than 3, then followed by a decrease due to the successive addition of Snlarger than 3, indicating that the thermal stabilities of these glass forming alloys increase first and then followed by adecrease owing to the excessive addition of Sn. Furthermore, the activation energy of Zr_(52.5)Ti_5Al_(10)Ni_(14.6)Cu_(17.9) and(Zr_(52.5)Ti_5Al_(10)Ni_(14.6)Cu_(17.9))_(0.97)Sn_3 was evaluated by Kissinger equation. It is noted that the Sn addition increases theactivation energies for glass transition and crystallization, implying that the higher thermal stability can be obtainedby appropriate addition of Sn.

关键词： Bulk glass forming alloy Supercooled liquid Gibbs free energy Activation energy Kissinger equation

AC Complex Impedance Analysis of Doped Strontium Titanate Multifunctional Ceramics

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Journal of Materials Science & technology 2002年第5期18卷 479-480页

作者： QingXU WenCHEN DuanpingHUANG RunzhangYUAN sch. of Mat. Sci. and eng. Wuhan Univ. of Technol. Wuhan 430070 China

Doped SrTiO3 capacitor-varistor multifunctional ceramics were fabricated by a single sintering process. AC complex impedance analysis was performed to investigate electrical features of grains and grain boundaries for both as-reduced ceramic and reoxidized ceramics. The results showed that the as-reduced ceramic exhibited inductive response at high frequencies above 2 MHz, which is attributed to the contribution of electron behavior in semiconducting grains. The high frequency inductive response disappeared in impedance plots of reoxidized ceramics.

关键词： Strontium titanate Impedance Grain Capacitor

Assessment of the apparent activation energies for gas/solid reactions—carbonate decomposition

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Journal of University of Science and technology Beijing 2003年第2期10卷 25-29页

作者： Jianhua Liu and Jiayun ZhangMetallurgical eng.neering sch.ol, University of Science and technology Beijing, Beijing 100083, China Metall. eng. sch. Univ. of Sci. and Technol. Beijing Beijing 100083 China

The guidelines for assessing the apparent activation energies of gas/solidreactions have been proposed based on the experimental results from literatures. In CO_2 free inletgas flow, CaCO_3 decomposition between 950 and 1250 K with thin sample layer could be controlled bythe interfacial chem.cal reaction with apparent activation energy E = (215+-10) KJ/mol and E=(200+-10) kJ/mol at T = 813 to 1020 K, respectively. With relatively thick sample layer between 793and 1273 K, the CaCO_3 decomposition could be controlled by one or more steps involvingself-cooling, nucleation, intrinsic diffusion and heat transfer of gases, and E could vary between147 and 190 kJ/mol. In CO_2 containing inlet gas flow (5 percent-100 percent of CO_2), E wasdetermined to be varied from 949 to 2897 kJ/mol. For SrCO_3 and BaCO_3 decompositions controlled bythe interfacial chem.cal reaction, E was (213+-15) kJ/mol (1000-1350K) and (305+-15) kJ/mol(1260-1400 K), respectively

关键词： assessment activation energy decomposition carbonate

Effect of Preparation Atmosphere on the Structure and Properties of Vanadium Pentoxide Xerogel Films

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Journal of Materials Science & technology 2004年第3期20卷 365-367页

作者： Wen CHEN Manzhu KB Qing XU Quanyao ZHU Liqiang MAI Li LI sch.ol of Materials Science and eng.neering, Wuhan University of technology,Wuhan 430070, China sch. of Mat. Sci. and eng. Wuhan Univ. of Technol. Wuhan 430070 China

In this article, the vanadium pentoxide sols are synthesized by two different routes (melted and quenched in oxygenatmosphere or in air). The structure and properties of the vanadium pentoxide xerogel films are characterized byXRD, ESR, cyclic voltammograms curves and UV-visible transmittance analysis. The results show that the sampleprepared in oxygen has poorer crystallization. lower content of V^(4+) ions and higher Li^+ insertion capacity comparedwith that prepared in air.

关键词： Preparation atmosphere V_2O_5 Structure Properties