Electron microscopy of modulated and ordered alloys

1988 ◽  
Vol 46 ◽  
pp. 768-769
Author(s):  
J. Bentley
Keyword(s):  
Electron Microscopy ◽  
Elastic Anisotropy ◽  
Data Interpretation ◽  
Transformation Process ◽  
Complex Nature ◽  
Quantitative Measurements ◽  
Transmission Electron ◽  
Coarsening Behavior ◽  
Modulated Structures ◽  
Ordered Alloys

Modulated and ordered alloys are of interest not only from a basic standpoint but also because they often possess interesting properties or form the basis of commercial materials. Transmission electron microscopy (TEM) provides much unique and valuable information in the study of phase transformations in such alloys but, as this overview of the applicable methods will try to illustrate, the experimental work is often challenging and data interpretation is rarely straightforward.In alloys with a modulated structure, spinodal decomposition is the transformation process of most interest. In cubic crystals, elastic anisotropy usually leads to triaxially modulated structures with composition modulations along <100>, whereas in isotropic systems, randomly oriented, highly interconnected structures are formed. TEM has most commonly been used to image the spinodal microstructure and to measure wavelength and waveshape. The observations are often only qualitative because of the complex nature of the image, but quantitative measurements of coarsening behavior have been attempted.

Transmission Electron Microscopy study of Bi-based superconducting phases

1990 ◽  
Vol 48 (4) ◽  
pp. 50-51
Author(s):  
J.G. Wen ◽  
K.K. Fung
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Single Crystals ◽  
Microscopy Study ◽  
Electron Microscopy Study ◽  
Space Groups ◽  
Superconducting Phases ◽  
Ceramic Samples ◽  
Transmission Electron ◽  
Modulated Structures

Bi-based superconducting phases have been found to be members of a structural series represented by Bi2Sr2Can−1Cun−1On+4, n=1,2,3, and are referred to as 2201, 2212, 2223 phases. All these phases are incommensurate modulated structures. The super space groups are P2/b, NBbmb 2201, 2212 phases respectively. Pb-doped ceramic samples and single crystals and Y-doped single crystals have been studied by transmission electron microscopy.Modulated structures of all Bi-based superconducting phases are in b-c plane, therefore, it is the best way to determine modulated structure and c parameter in diffraction pattern. FIG. 1,2,3 show diffraction patterns of three kinds of modulations in Pb-doped ceramic samples. Energy dispersive X-ray analysis (EDAX) confirms the presence of Pb in the three modulated structures. Parameters c are 3 0.06, 38.29, 30.24Å, ie 2212, 2223, 2212 phases for FIG. 1,2,3 respectively. Their average space groups are all Bbmb.

Solution-Based Synthesis of Magnesium Oxide Nanorods

1999 ◽  
Vol 581 ◽  
Author(s):  
Q. Wei ◽  
C.M. Lieber
Keyword(s):  
Electron Microscopy ◽  
Magnesium Oxide ◽  
Magnesium Chloride ◽  
Low Cost ◽  
Industrial Applications ◽  
Transformation Process ◽  
Matrix Composites ◽  
X Ray ◽  
Transmission Electron ◽  
Oxide Nanorods

ABSTRACTA solution-based synthesis route was developed to produce large quantities of MgO nanorods. Hydrated basic magnesium chloride, which has needle-like crystal structure, was used as a precursor. A subsequent two-step transformation process with magnesium hydroxide as an intermediate product was used to preserve the morphology of the precursor to yield magnesium oxide nanorods. Scanning electron microscopy, powder X-ray diffraction and energy dispersive X-ray spectroscopy show that the products are very pure (>95%) crystalline MgO nanorods with diameters from 40 nm to 200 nm and lengths 10 microns or longer. High-resolution transmission electron microscopy and electron diffraction further reveal that these MgO nanorods are single crystals and that the rod axis is along the <110> crystal direction. A model for the structural transformation from hydrated basic magnesium chloride to magnesium oxide has been developed and compared to our experimental results. This solution-based process can be easily scaled-up, and is a low-cost source of pure magnesium oxide nanorods needed in many industrial applications, for example, as reinforcing agents in matrix composites and as flux-pinning centers in high-TC superconductors.

Quantitative Measurements of Segregation In Co-Cr-X Magnetic Recording Media by Energy-Filtered Transmission Electron Microscopy

1998 ◽  
Vol 517 ◽  
Author(s):  
J. Bentley ◽  
J.E. Wittig ◽  
T.P. Nolan
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Magnetic Recording ◽  
Core Loss ◽  
Specimen Thickness ◽  
Recording Media ◽  
Magnetic Recording Media ◽  
Quantitative Measurements ◽  
Transmission Electron ◽  
Random Angle

AbstractReliable core-loss spectroscopic methods have been developed for mapping elemental segregation in Co-Cr-X magnetic recording media by energy-filtered transmission electron microscopy. Extraction of quantitative compositions at a spatial resolution approaching 1 nm involves sophisticated treatments for diffraction contrast, variations in specimen thickness, and closely-spaced oxygen K and chromium L23 ionization edges. These methods reveal that intergranular chromium levels are ∼25 at.% for random-angle boundaries and ∼15 at.% for 90° boundaries in films of Co84Cr12Ta4 d.c. magnetron sputtered at 250°C.

scholarly journals The origin of striation in the metastable β phase of titanium alloys observed by transmission electron microscopy

2017 ◽  
Vol 50 (3) ◽  
pp. 795-804 ◽  
Author(s):  
Jiangkun Fan ◽  
Jinshan Li ◽  
Yudong Zhang ◽  
Hongchao Kou ◽  
Jaafar Ghanbaja ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Dark Field ◽  
Atomic Scale ◽  
Intermediate Structure ◽  
Atomic Displacements ◽  
Β Phase ◽  
Transmission Electron ◽  
Modulated Structures ◽  
High Resolution Tem

For the β phase of Ti-5553-type metastable β-Ti alloys, striations in transmission electron microscopy (TEM) bright- and dark-field images have been frequently observed but their origin has not been sufficiently investigated. In the present work, this phenomenon is studied in depth from the macroscopic scale by neutron diffraction to the atomic scale by high-resolution TEM. The results reveal that the β phase contains homogeneously distributed modulated structures, intermediate between that of the β phase (cubic) and that of the α phase or the ω phase (hexagonal), giving rise to the appearance of additional diffraction spots at 1/2, 1/3 and 2/3 β diffraction positions. The intermediate structure between β and α is formed by the atomic displacements on each second {110}βplane in the \langle 1{\overline 1}0\rangle_{\beta} direction, whereas that between β and ω is formed by atomic displacements on each second and third {112}βplane in the opposite \langle 11{\overline 1}\rangle_{\beta } direction. Because of these atomic displacements, the {110}βand {112}βplanes become faulted, resulting in the streaking of β diffraction spots and the formation of extinction fringes in TEM bright- and dark-field images, the commonly observed striations. The present work reveals the origin of the striations and the intrinsic correlation with the additional electron reflections of the β phase.

Quantitative measurements in in situ straining experiments in transmission electron microscopy

2001 ◽  
Vol 203 (1) ◽  
pp. 47-56 ◽  
Author(s):  
F. Pettinari ◽  
A. Couret ◽  
D. Caillard ◽  
G. Molenat ◽  
N. Clement ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Quantitative Measurements ◽  
Transmission Electron

Study of modulated structures by transmission electron microscopy

1985 ◽  
Vol 18 (1-4) ◽  
pp. 97-110 ◽  
Author(s):  
J.W. Steeds ◽  
D.M. Bird ◽  
D.J. Eaglesham ◽  
S. McKernan ◽  
R. Vincent ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Transmission Electron ◽  
Modulated Structures

Modulated Structures in Ion Implanted Al-Fe System

1983 ◽  
Vol 27 ◽  
Author(s):  
K.V. Jata ◽  
D. Janoff ◽  
E.A. Starke
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
High Purity ◽  
Annealing Treatment ◽  
Modulated Structure ◽  
Transmission Electron ◽  
Modulated Structures ◽  
Ion Energies ◽  
High Purity Aluminum ◽  
Al Matrix

ABSTRACTThe results of transmission electron microscopy studies of iron implantation into high purity aluminum foils are described. For both 50 and 100 + 50 keV incident ion energies, modulated structure has been detected in the as-implanted foils. Upon annealing at 793 K the modulated structure decomposes into the Al matrix and Al3Fe precipitates for the 50 keV implantation. A similar annealing treatment for the 100 + 50 keV implantation indicates that the modulated structure is more stable, although some Fe3Al precipitation occurs.

TEM study of dislocation core configurations in Ni3(Al,l%Ta) deformed at high temperatures

1990 ◽  
Vol 48 (4) ◽  
pp. 474-475
Author(s):  
N. Baluc
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Yield Strength ◽  
Constant Strain Rate ◽  
Dislocation Core ◽  
Anomalous Increase ◽  
Weak Beam ◽  
Transmission Electron ◽  
Ordered Alloys ◽  
High Resolution Tem

The Ni3Al intermetallic compound of the ordered L12 structure with various alloying elements (such as Ta or Ti) reinforces most of the industrial superalloys which are designed for high temperature applications. Therefore, the understanding of its mechanical properties is of primary importance. The yield strength, measured in constant strain rate tests, exhibits an anomalous behaviour as a function of temperature: it increases up to a peak temperature above which it finally decreases. The anomalous increase has been extensively studied during the last 30 years, including weak-beam and high resolution transmission electron microscopy (TEM) observations and computer simulations. Numerous models have been proposed to explain this anomalous variation in which the structure of the dislocation core plays a fundamental role. A review of core effects on the plasticity of ordered alloys was given by Vitek (1985). In the present investigation, the Ni3(Al,l%Ta) phase was deformed at temperatures above the yield strength peak and the detailed core configurations of dislocations have been analyzed using weak-beam and high resolution TEM techniques.

Modulated structures of (Bi1−xPbx)2Sr2CoOy examined by high-resolution transmission electron microscopy

1992 ◽  
Vol 196 (1-2) ◽  
pp. 34-42 ◽  
Author(s):  
Kasumi Yanagisawa ◽  
Yoshio Matsui ◽  
Kaoru Shoda ◽  
Eiji Takayama-Muromachi ◽  
Shigeo Horiuchi
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
High Resolution ◽  
Transmission Electron ◽  
Modulated Structures
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