材料期刊网

DEFORMATION AND FRACTURE MECHANISMS OF TWO-PHASE TiAl-BASED ALLOYS WITH FULLY LAMELLAR MICROSTRUCTURE

Y. G .Zhang , C. Q. Chen (Beijing University of Aeronautics and Astronautics , Beijing 100083 , China)Q. Xu (Beijing Laboratory of Electron Microscopy , Chinese Academy of Sciences. Beijing , China)M. C. Chaturvedi (The University of Manitoba , Winnipeg , Manitoba , Canada R3T 2N2)

金属学报(英文版)

A two-phase TiAl-based alloy with fully lamellar structure has been deformed al room temperature and the deformed microstructures have been examined in dtails by optical microscopy(OM), scanning electron microscopy(SEM) and transmission electron microscopy(TEM) . Deformation mechanisms in the γ-TiAl phase has been defined and the role of grain boundaries in the deformation and fracture has been assessed Some of the mechanisms of interactions between twinning or gliding dislocations and three types of γ γ domain boundaries or γ α_2 interface in a lamellar grain have been identified and resistance of the various domain boundaries or the interface to the propagation of twinning has been evaluated

关键词: :TiAl , null , null , null

CORRELATION BETWEEN STRESS COMPONENTS AND STRESS CORROSION CRACKS IN BRASS Lecturer,Department of Materials Physics,University of Science and Technology Beijing,Beijing 100083,China

QIAO Lijie LIU Rui XIAO Jimei University of Science and Technology Beijing , Beijing , China

金属学报(英文版)

The effects of stress components on nucleation sites and propagation directions of stress cor- rosion cracks in brass were investigated with specimens under mode Ⅱ and mode Ⅲ loadings. The results indicated that under mode Ⅱ loading,stress corrosion cracks nucleated on the site with maximum normal stress component and propagated along the plane perpendieular to the maximum normal stress,under mode Ⅲ loading,the stress corrosion crack was not evident on the 45°plane due to the general corrosion in aqueous solution with high NH_4OH concentra- tion,while stress corroded in aqueous solution with low NH_4OH concentration, numerous cracks with spacings of 10—150μm were found on the 45°plane with maximum normal stress and no stress corrosion cracks was observed on the plane with maximum shear stress.

关键词: stress corrosion cracking , null , null , null

Relationship between degeneration of M7C3 and precipitation of M23C6 in a cobalt base superalloy

Materials Science and Technology

The relationship between degeneration of the primary M7C3 carbide and precipitation of the secondary M23C6 carbide has been investigated in a cobalt base superalloy after 100 h aging at 850 degrees C. The results indicated that the primary M7C3 carbide could not transform in situ into the secondary M23C6 carbide. The M23C6 formed by a direct reaction between chromium and carbon atoms. The dissolution of M7C3 provided the precipitation of M23C6 with essential carbon, which acted as a carbon reservoir. Near M7C3, the chromium content is a controlling factor of M23C6 precipitation while away from it, the carbon content dominated the reaction. The precipitate free zone around M7C3 is attributed to chromium depletion which is inherited from the as cast condition. MST/4174

关键词:

Modeling of Nucleation and Growth of M₂₃C₆ Carbide in Multi-component Fe-based Alloy

Naqiong Zhu

材料科学技术（英文）

Three-dimensional atom probe (3DAP) technique has been used to study the nucleation and growth of  M₂₃C₆ carbide in a supersaturated multi-component Fe-based alloy aged at 800°C. 3D images indicate that the radius of  M₂₃C₆  carbide after ageing for 10 min is about 9 nm. Concentration profiles of alloy elements in the carbide are also obtained. Combined with PANDAT and Thermo-Calc software, attempts to model the early stages of precipitation are present. The calculated particle size and composition of  M₂₃C₆  carbide is in good agreement with 3DAP data.

关键词: Nucleation and growth

Inter-conversion of M(n+1)AX(n) phases in the Ti-Al-C system

Journal of the American Ceramic Society

It is demonstrated that the M(n+1)AX(n) phase Ti3AlC2 may be readily synthesized by sintering a stoichiometric mixture of the lower order MAX phase Ti2AlC mixed with a stoichiometric amount of TiC in the temperature range 1350 degrees-1450 degrees C. High-quality Ti3AlC2 was readily produced using sintering times in the range 2-5 h. In general, < 2% of unwanted or remnant phases were found to be present and in some samples none could be detected at all.

关键词: resolved neutron-diffraction;ti3sic2 synthesis;mechanical-properties;powder diffraction;crystal-chemistry;ti3alc2;temperature;ceramics;carbide;ti2alc

Introduction to atmospheric corrosion research in China

Science and Technology of Advanced Materials

In this paper, we introduce the research on atmospheric corrosion in China. We describe the climate characteristics and the classification of atmospheric corrosivity across the whole country. We also describe the rusting evolution under simulated wet/dry cyclic conditions. (C) 2007 NIMS and Elsevier Ltd. All rights reserved.

关键词: atmospheric corrosion;corrosivity;rusting evolution;weathering steels;rust;mechanism;so2;o-3;no2

ON THE M_7C_3 IN Cr27 CAST IRON

LI Yuqing WANG Cirong GU Zhaofeng Research Institute of Daye Steel Works , Huangshi , China Senior Engineer , Research Institute of Daye Steel Works , Huangshi 435001 , China

金属学报(英文版)

Determination of(Fe,Cr)_7C_3 in Cr27 cast iron results about 30 v.-%.Minor Si and Mn are present.Sectional area of the M_7C_3 grains is 1—50μm~2.Combining matrix analysis of elec- tron diffraction pattern with calculated angle between plane traces,{011}twins and also {013}twins producing local environment for Ru_7B_3 are observed in the orthorhombic M_7C_3. A crystallographic model for M_7C_3 is proposed.

关键词: cast iron , null , null , null , null

Zn-5%Al合金超塑性的m-C-δ(或m-k-δ)关系

刘勤 , 夏锄 , 刘晓东

金属学报

在170,190,210,230,250℃的温度下,采用3.7×10~2,7.4×10~2和1.1×10~(-1)min(-1)的应变速率(平均)对Zn-5%Al共晶合金的m-C-δ(或m-k-δ)关系曲线(简称m-δ关系曲线)进行了测定.所有的曲线均随应变的δ增加而快速上升.俟达到某一定的应变量(极限应变量δ1)后。开始缓慢下降并保持平稳直至断裂.Zn-5%A1共晶合金的m-δ关系曲线不存在k_(?)=k_I(k_(I 1),k_(I 2),k_(I 3),……)=k_F(或C_0=C_I(C_(I 1),C_(I 2),C_(I 3),……)=C_F=1)的简单情况.可应用m-δ方程式[4,5]对曲线上各点C值(包括所有的C_I和C_F值)进行计算.C值随δ值的增加成近似的直线上升.直线的斜率在极限应变(δ1)处突然减小.

关键词:

C60、M@C60(M=Si,Ge)富勒烯分子的压缩力学特性

沈海军

功能材料

采用基于Tersoff势的分子动力学方法,模拟了温度T=300、700和1100K下C60、M@C60(M=Si,Ge)富勒烯分子的对径压缩过程.根据模拟结果,讨论了温度T对3种富勒烯分子压缩力学特性的影响以及它们压缩力学特性的差异.研究表明,在300～1100K范围内,温度T对C60、M@C60(M=Si,Ge)分子压缩力学特性无显著影响;当压缩应变至8%～16%左右,各富勒烯分子在加载点处开始"塌陷",当压缩应变至28%～32%左右,各富勒烯达到承载极限;C60、Si@C60、Ge@C60分子依次具有由低到高的承载能力.

关键词: 富勒烯 , 分子动力学 , 力学特性 , 内嵌M@C60富勒烯

Coarsening of M23C6 Precipitates in an Fe-Cr-C Ternary Alloy

ZHU Na-qiong , LU Li , HE Yan-lin , LI Lin , LU Xiao-gang

钢铁研究学报(英文版)

Coarsening of M23C6 precipitates in an Fe-12.4Cr-0.13C ternary alloy has been investigated ageing at 780 ℃ up to 200 h. Evolution of M23C6 carbides at different ageing times was determined experimentally using transmission electron microscopy. Particle size distribution was obtained with different measuring methods. Simulations of coarsening of M23C6 precipitates were carried out using computational thermodynamics and kinetics. Results showed low coarsening rates for M23C6 precipitates in the Fe-Cr-C ternary alloy. Interfacial energy of M23C6/ferrite interface is between 0.1 and 0.3 J·m-2 for the coarsening of M23C6 ageing at 780 ℃.

关键词: M23C6 , coarsening , PSD , interfacial energy