CAO Jianchun
,
LIU Qingyou
,
YONG Qilong
,
SUN Xinjun
钢铁研究学报(英文版)
Using thermomechanical simulation experiment, the kinetics of the isothermal transformation of austenite to ferrite in two HSLA lowcarbon steels containing different amounts of niobium was investigated under the conditions of both deformation and undeformation. The results of optical microstructure observation and quantitative metallography analysis showed that the kinetics of the isothermal transformation of austenite to ferrite in lower niobium steel with and without deformation suggests a stage mechanism, wherein there exists a linear relationship between the logarithms of holding time and ferrite volume fraction according to Avrami equation, whereas the isothermal transformation of austenite to ferrite in high niobium steel proceeds via a two stage mechanism according to micrographs, wherein, the nucleation rate of ferrite in the initial stage of transformation is low, and in the second stage, the rate of transformation is high and the transformation of residual austenite to ferrite is rapidly complete. Using carbon extraction replica TEM, niobium carbide precipitation for different holding time was investigated and the results suggested that NbC precipitation and the presence of solute niobium would influence the transformation of austenite to ferrite. The mechanism of the effect of niobium on the isothermal transformation was discussed.
关键词:
niobium;transformation;ferrite;austenite
黄爱华
,
金鸣林
,
李和兴
,
房永征
材料导报
试验是以2种含不同QI的煤沥青为原料,采用变径反应管进行热转化反应制备有序性中间相的研究.试验采用偏光显微镜和扫描电镜(SEM)观察了原料各反应阶段的微观结构,考察了QI对热转化过程中中间相有序生长的影响,分析了热转化过程中软化点及族组分的变化.结果表明:少量的喹啉不溶物含量不会阻碍中间相有序的发展.高QI(2.03%)原料易生成镶嵌结构的中间相体,高温处理后样品呈轴状、短纤维、层片松散的石墨化焦结构;含低QI(0.11%)的原料能生成较好的、大区域的中间相体,域结构的中间相体在外力导向和内部裂解气流的作用下容易生成有序的半焦,高温处理后呈大区域、片层紧密、有序性强的细纤维焦结构.同时研究发现,在热转化过程中可通过测定软化点(SP)和TI含量来确定中间相转化程度.软化点约低于250℃、TI为75%左右时为初始中间相区域体形成阶段、半焦生成的前期.
关键词:
煤沥青
,
热转化反应
,
喹啉不溶物
,
中间相
Physical Review B
Longitudinal electron transport is investigated for a long-period semiconductor superlattice in the presence of a magnetic field applied along the growth direction of the superlattice. It is shown that the longitudinal magnetoresistance exhibits a complicated dependence on the magnetic-field strength. In contrast with the conventional Shubnikov-de Haas oscillations, the magnetoresistance shows periodic oscillations only in the region of low reciprocal magnetic field.
关键词:
magnetoresistance
F.M.Chu David P.Pope Dept.of Materials Science and Engineering
,
University of Pennsylvania
,
Philadelphia
,
PA 19104
,
USA
材料科学技术（英文）
In this paper the geometric description and general theory of mechanical twinning are reviewed, the twins in general lattices and superlattices are summarized, and the kinetic process by which mechanical twins form is revisited. A case study of mechanical twinning of HfV2+Nb, (cubic) Laves phase, is presented and the synchroshear of selected atomic layers is proposed to explain the physical process of twin formation. If the twins form in this way, then long shear vectors and / or atomicshuffles are not really necessary.
关键词:
twin
,
null
,
null
,
null
J.M. Gong
,
S.T. Tu
,
J. Xia and X. Ling (School of Mechanical Engineering
,
Nanjing University of Chemical Technology
,
Nanjing 210009
,
China)
金属学报(英文版)
Creep deformation localization is generally found in structures at high temperamture,typically in weldments. As the heat affected zone (HAZ) in a weldment is very narrow, deformation in HAZ region can hardly be measured by conventional displacement gauge. A new method for measuring long-term local creep deformation was developed by quartz optical fiber and technique of digital image analysis. The creep deformations of base metal, weld metal and HAZ in weldments are thereby determined with crossweld specimens.
关键词:
creep deformation
,
null
,
null
,
null
材料科学技术（英文）
A new type of long periodic structure has been found in ZrO2-Y2O3 ceramics in annealed states. High resolution electron microscopy (HREM), selected area electron diffraction, and computer simulation have been used to reveal the presence of the long periodic structure. The unit cell of the long periodic structure consists of a cubic ZrO2 unit cell and L1(0)- like phase one.
关键词:
ceramics;electron diffraction;electron microscopy;crystal structure;microstructure
Jiancun RAO
,
Yu ZHOU
,
Douxing LI
材料科学技术（英文）
A new type of long periodic structure has been found in ZrO2-Y2O3 ceramics in annealed states. High resolution electron microscopy (HREM), selected area electron diffraction, and computer simulation have been used to reveal the presence of the long periodic structure. The unit cell of the long periodic structure consists of a cubic ZrO2 unit cell and L10- like phase one.
关键词:
Ceramics
,
null
,
null
,
null
,
null
Applied Physics Letters
The dipole configuration of relaxor ferroelectrics (RFs) is investigated by numerically solving the time-dependent Ginzburg-Landau equation based on the dipole defect model. The domain structure of RFs is revealed to consist of dipole ordered clusters embedded in the paraelectric matrix. We demonstrate that the role of long-range elastic energy in RFs is much less important than in normal ferroelectrics, although the shape of the dipole clusters depends on the elastic energy. Based on the numerical results, a phase diagram of temperature-defect density for RFs is constructed, which identifies four distinct phase regimes. (c) 2006 American Institute of Physics.
关键词:
monte-carlo-simulation;dielectric-properties;computer-simulation;domain formation;defects;field;model;glass
