共查询到20条相似文献,搜索用时 15 毫秒
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Layer type GeAsSe crystals have been investigated by High Resolution Electron Microscopy (HREM). Structure images observed along the [001] direction allow a straightforward interpretation. The image contrast was calculated using the multi-slice approximation. 相似文献
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Manikprage Jayaratna Masahiro Yoshimura Shigeyuki Sōmiya 《Journal of Materials Science》1987,22(6):2011-2016
The electrical conductivity of Cr2O3-doped Y2O3-stabilized ZrO2 (YSZ) has been studied as functions of composition, temperature and oxygen pressure. The specimens have been prepared by hot preoning of co precipitated oxides to yield >99.7% density. The Cr2O3 added above the solubility limit ( 0.7 mol %) precipitated as a secondary phase at the grain boundaries. The conductivity of Cr2O3-doped YSZ was almost independent of the oxygen pressure in the range 1018 to 105 Pa, indicating a dominant ionic condition. The electronic conductivity of dopant CR2O3 would be hindered by the higher ionic conductivity in thep
O2 ranges studied. The conductivity and the activation energy for conduction decreased slightly with the addition of Cr2O3. These phenomena seemed to be caused by vacancy trapping or polarization at the grain boundaries with the Cr2O3 precipitates. The samples with 1 mol % Cr2O3 addred to zirconia containing various Y2O3 contents showed similar conduction behaviour to those without Cr2O3 addition; that is, the conductivity maxima are observed at around 8 mol % Y2O3 addition to zirconia, and the activation energies increased with tha Y2O3 addition. 相似文献
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S. F. Horvath M. P. Harmer D. B. Williams M. R. Notis 《Journal of Materials Science》1989,24(3):863-872
Analytical electron microscopy has been used to study the precipitation reactions in sintered samples of 9 mol% La2O3-Y2O3 samples upquenched from the single phase cubic region into the cubic and hexagonal phase field. Samples annealed just inside the two-phase cubic-cubic and hexagonal solvus exhibited predominantly grain boundary precipitation. Small La2O3 rich second phases formed within the first ten minutes and developed into strained, facetted precipitates after 300 min. Intergranular and intragranular precipitation occurred in samples annealed further into the two-phase field. Strained, lathlike La2O3-rich monoclinic precipitates, exhibiting a preferrred orientation in the matrix, appeared as the dominant morphology for long times at temperature. Chemical microanalyses of the strained structures obtained in samples annealed for 300 min revealed La2O3 matrix concentrations in agreement with phase diagram predictions. However, the La2O3 concentrations in the second-phase precipitates were found to be far in excess of the cubic and hexagonal-hexagonal solvus. This discrepancy is believed to arise from a re-equilibration of the second phase in the cubic and monoclinic phase field during quenching. 相似文献
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The anodic polarization and corrosion properties of commercial WC-Co hardmetals with different grain sizes and containing small amounts of Cr3C2 and/or VC in acid (pH 2.8), acid/3% NaCl, and neutral 3% NaCl solutions, have been measured using potentiokinetic and linear polarization conductance techniques. An increase in grain size increased the passive current density. Small additions of Cr3C2 increased substantially the corrosion resistance. Small additions of VC had little effect on the corrosion resistance, but in the presence of small additions of Cr3C2 it reduced the beneficial effects of chromium. 相似文献
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High resolution electron microscopy (HREM) has emerged as a very powerful tool for probing the structure of metals and alloys.
It has not only helped in unravelling the structure of materials which have been at the forefront of novel materials development
such as quasicrystalline phases and high temperature superconducting compounds, but also is fast becoming a technique for
solving some outstanding issues in the case of the commercial alloys thereby helping alloy development. In addition to the
determination of the structures of phases, this tool is used for obtaining a first hand information of the arrangement of
atoms around the various types of crystallographic defects and interphase interfaces. This mode of microscopy allows direct
observation of orientation relationships between two phases across interfaces. HREM can be used for the direct examination
of the prenucleation process. Initial stages of nucleation can also be studied readily in amorphous alloys, precipitation
hardening alloys like maraging steels and in those systems where the formation of the omega phase occurs.
This presentation describes some results of HREM studies on various alloys, commercial as well as alloys of scientific interest,
where some of the aforementioned aspects have been examined. The specific examples cited pertain to metallic glasses, NiTi
shape memory alloys, Ni-Mo, Zr-Nb and Ti-Al alloys. 相似文献
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C S Pande 《Bulletin of Materials Science》1984,6(3):453-458
Until recently, in the field of superconductivity, electron microscopy has played only a minor role in studies of structure
and properties of existing superconductors (except Nb and its alloys) and in the development of new and improved superconductors.
This situation has changed in recent years. Electron microscopy is now being extensively used to study the growth, microstructure,
and kinetics of many superconductors, especially of A15 type. Electron microscopy has also contributed to the understanding
of the nature of radiation damage in these materials. These contributions will be reviewed with selected examples. 相似文献
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J. C. Jones 《Journal of Materials Science》1984,19(2):533-544
Although facilities for high resolution electron microscopy (HREM) are available, interpretation of micrographs at high magnifications
is far from unambiguous. The interpretation of the micrographs using a computed structure analysis program is therefore necessary.
The paper presents the theory behind HREM, together with a computer method for image interpretation. Special reference is
made to the JEOL JEM 200CX transmission electron microscope used in the study of sodium beta-alumina. 相似文献
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Powdered samples of polycrystalline Nb3Sn superconductor filaments with cubic A 15-structure have been investigated by high resolution electron microscopy (HREM). Structure images representing the projected electric potential of the structure in the (001)- plane are presented. The constrast pattern shows the position of the individual chains of Nb-atoms arranged parallel to the electron beam. This pattern is compared with the contrast calculated on the basis of the dynamical theory of electron diffraction by the multislice method. The observed contrast agrees with the calculated pattern. A structure image made in the [012]-projection containing one dislocation reveals a large region of strain in the crystal lattice surrounding that defect. 相似文献
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Thermal conduction behaviour of Cr3C2/SiC composite is investigated in terms of temperature and SiC content. Experimental results showed that thermal diffusivity of the composite increases with SiC content up to 20 vol%, corresponding to a conductivity maximum, then decreases with further increase of SiC. The reduction in diffusivity and conductivity at higher SiC content may due to formation of small amounts of solid solution at the interface and/or of interfacial gaps due to lack of perfect contact among SiC aggregates leading to increased phonon scattering. The thermal conductivity demonstrates a positive temperature dependence but becomes temperature-independent when SiC content is above 30 vol%. A correlation with composite theory is present. 相似文献
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In this paper a survey is given of the application of high resolution electron microscopy and selected area electron diffraction
to the study of long range ordered alloys. The characteristic features of the diffraction effects and of the imaging of ordered
alloys are discussed. Group theoretical considerations allow prediction of microtexture of such alloys.
A number of simple alloy structures are imaged and it is shown, by means of simulated images, that under suitable diffraction
conditions the columns of minority atoms are represented as bright dots. The columns of majority atoms are only visible at
very small thicknesses. Subsequently a number of one- and two-dimensional long period superstructures derived from these simple
structures are analysed, using high resolution micrographs. Finally the observed microtexture of the same alloy superstructures
is compared with the predictions of group theory. Strongly non-conservative antiphase boundaries are found to dissociate inapb’s which are as close to conservative as is compatible with thefcc lattice. 相似文献
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热压烧结制备了Al2O3/Cr3C2/(W,Ti)C复合陶瓷材料(以下简称ACW复合材料),对其Vickers硬度及组织形貌进行了研究,分析了Cr3C2及(W,Ti)C对Vickers硬度的影响.结果表明,(W,Ti)C和Cr3C2的添加利于阻止晶界迁移,抑制晶粒长大,Cr、W、Ti离子在Al2O3基体晶粒中的固溶起强化作用.每一相的添加量在10%~20%(体积分数,下同)为宜,添加总量在30%左右ACW复合材料硬度最佳. 相似文献
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Enhancement of the fracture toughness of Al2O3 was achieved by the additions of 10–40 vol% Cr3C2 particulates through a hot-pressing process. The dependence of Cr3C2 particle size (0.5, 1.5 and 7.5 m) on the toughening effect was investigated. The maximum fracture toughness of composites could be improved to 5.9, 7.6 and 8.0 MPa m1/2 for fine, medium and coarse Cr3C2 particle reinforced composites, respectively. Both the quantitative analysis of toughening contributions and experimental observations are extensively discussed in terms of Cr3C2 particle size, microcracks, as well as thermal residual stress between Al2O3 and Cr3C2. 相似文献