材料期刊网

Numerical Simulation of Macro-Segregation in Steel Ingot During Solidification

C.W. Ma , H.F. Shen , T.Y. Huang , B.C. Liu

金属学报(英文版)

A mathematical model coupling the momentum, energy and species conservation equa- tions was proposed to calculate the macro-segregation of Fe-C alloy ingot during solidification. The corresponding simulation software which concurrently solves the macro- scopic mass, momentum, energy and species conservation equations has been developed by applying the SIMPLE algorithm. The thermo-solutal convection in a NH4Cl-H2O ingot is verified and the result shows good agreement with that reported. Then macro-segregation in a steel ingot is simu- lated by using the developed program. The steel ingot is in a rectangular mold with a riser. The fluid flow is mainly induced by the temperature field and the solid fraction. The macro-segregation pattern is mainly affected by the thermo-induced convection in the mushy zone. The negative segregation forms along the walls of the casting. The positive segregation forms at the top center of the casting into the riser. The species concentration reaches the peak in the center of the ingot where solidi¯cation ends lastly.

关键词: macro-segregation , null , null , null

Decomposition of B4C and magnetic properties of Nd-Fe-(B,C) alloys synthesized by mechanical alloying

Journal of Alloys and Compounds

Nd-Fe-(B.C) alloys have been synthesized by mechanical alloying and subsequent heat-treatment, with B4C as one of the starting materials. It is found that when the pure B4C is milled alone, it proves difficult to decompose. When the B4C compound is milled with Nd and Fe, the complete decomposition of B4C and the formation of Nd2Fe14(B,C) phase is observed. Furthermore, the competition between B and C atoms for entering the Nd2Fe14B lattice. the effects of the B4C content on the structure and the magnetic properties of Nd2Fe14(B,C)-based alloys are investigated. A coercivity as high as 18.3 kOe and the maximum energy product of 10.4 MGOe have been achieved for the Nd-Fe-(B,C) alloys. (c) 2005 Elsevier B.V. All rights reserved.

关键词: permanent magnets;mechanical alloying;fe-c alloys;permanent-magnets;r2fe14c;nd

液硅渗透法制备Si—B—C改性C／C—SiC复合材料

刘建功 , 殷小玮 , 成来飞 , 张立同 , 王琴

复合材料学报

为了降低液硅渗透法制备C／C—SiC复合材料中残留Si的含量，采用浆料浸渗结合液硅渗透工艺制备B12（C，Si，B）3改性C／C—SiC复合材料。通过分析不同比例B4C—Si体系在不同温度的反应产物，确定了B12（C，Si，B）3的生成条件。结果表明：B4C和Si在1300℃开始反应，生成少量B12（C，Si，B）3和SiC，且B12（C，Si，B）3的生成量随反应温度的升高而增加；当B4C和Si的摩尔比为3：1、反应温度为1500℃时，产物为B12（C，Si，B）3和SiC液硅渗透法制备的C／C—SiC复合材料相组成为非晶态C、β-SiC和B12（C，Si，B）3，未见残留Si。

关键词: 复合材料 , C , C—SiC , B12(C，Si，B)3 , 浆料浸渗 , 液硅渗透

B-C-N材料的合成

李阿丹

物理测试 doi:10.3969/j.issn.1001-0777.2006.02.006

本文介绍了六方及立方B-C-N合成的理论基础和近年来人工合成B-C-N新材料的方法、合成产物的结构及其物理化学特性,介绍了笔者采用化学法合成B-C-N化合物的方法,提出了今后的发展方向.

关键词: B-C-N , 六方结构 , 性质

Thermodynamic Properties of FeCN and FeCBN Melts

CHEN Erbao , WANG Shijun , DONG Yuanchi , WU Baoguo , ZHOU Yun

钢铁研究学报(英文版)

The saturated solubility of carbon and nitrogen in FeCN and FeCBN melts was measured experimentally at 1 485 ℃ to obtain the activity interaction coefficients between components in these melts. A new method was used to treat experimental results. Using thermodynamic derivation and calculation, some important interaction coefficients between components in these melts were obtained.

关键词: FeCN melt;FeCBN melt;FeCB melt;interaction coefficient;thermodynamic property

Mean-field theory on mixed ferro-ferrimagnetic compounds with (A(a)B(b)C(c))(y)D

Physics Letters A

The magnetic properties of the mixed ferro-ferrimagnetic compounds with (A(a)B(b)C(c))(y)D, in which A, B, C and D are four different magnetic ions and form four different sublattices, are studied by using the Ising model. And the Ising model was dealt with standard mean-field approximation. The regions of concentration in which two compensation points or one compensation point exit are given in c-a, b-c and a-b planes. The phase diagrams of the transition temperature T-c and compensation temperature T-comp are obtained. The temperature dependences of the magnetization are also investigated. Some of the result can be used to explain the experimental work of the molecule-based ferro-ferrimagnet ((NiaMnbFecII)-Mn-II-Fe-II)(1.5) [Cr-III (CN)6] - zH(2)O. (C) 2003 Elsevier B.V. All rights reserved.

关键词: mixed ferro-ferrimagnet;Ising model;four sublattices;phase diagram;transition temperature;compensation temperature;magnetic-properties;prussian blue;alloy

Diffusion mobilities for the B2-b.c.c. phase in the Ni-Al binary system

Journal of Alloys and Compounds

A model for diffusion is applied to the Ni-Al system to optimize the mobility parameters for the 132-b.c.c. phase by fitting the experimentally obtained diffusivities. In the model, the activation energy for diffusion is expressed as a function of the degree of ordering which is evaluated from thermodynamic data. The diffusivities, from the model are used to simulate diffusion experiments. The results are compared with experimental data and it is concluded that the model can yield satisfactory prediction. (C) 2007 Elsevier B.V. All rights reserved.

关键词: intermetallics;diffusion;thermodynamic modeling;alloys;fe;interdiffusion;model

(a-AB-b+b-C-b)型线型缩聚体系的分子量分布

闫福安

高分子材料科学与工程

用统计理论得到了(a-AB-b+b-C-b)型线型缩聚体系的分子量分布函数;而且双官能度单体可以控制均缩聚的平均聚合度,所得聚合物的分子量分布远比Flory分布窄.

关键词: (a-AB-b+b-C-b)型线型缩聚 , 分子量分布 , 统计理论

B4C晶体的结构与C原子占位研究

刘立强 , 陈蕴博

功能材料

设计了多种B4C结构模型,并对模型进行了结构优化,计算了各模型结构的单点能.结果表明,B4C的稳定结构为CBC(B11C),即它由C-B-C三原子链和B11C二十面体组成,B11C中C原子为极地占位.由于双极地占位的B10C2+B12结构能量与B11C结构相差较小,在通常材料制备条件下,B4C晶体中有少量B10C2+B12结构的存在是可能的.计算结果表明,B11C中极地C原子占位分布为有序化时能量较低,当B4C晶体在能量最低的平衡态时C原子在B11C二十面体中的占位应有一定的有序性.

关键词: B4C , 晶体结构 , 原子占位 , 单点能 , 稳定性

B,C,Al对热压SiC烧结的影响

苏国跃 , 夏非 , 闻立时

金属学报

<正> SiC～Al_C_5-BC三元系在1800℃下除了生成Al_4SiC_4和Al_4Si_2C_5以外,还析出新的B-C-Al化合物,即Al_8B_4C_7相. 本文研究了Al_8B_4C_7相的存在范围,及其在不同温度和压力下对热压SiC烧结的影响. 实验采用工业SiC粉.试样在高于1800℃热

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