Review of Phonon Behavior and Microstructural Development Leading to Martensitic Transformations in NixAl(100-x) Alloys

1991 ◽  
Vol 246 ◽  
Author(s):  
L. E. Tanner ◽  
S. M. Shapiro ◽  
D. Schryvers ◽  
Y. Noda
Keyword(s):  
Phonon Mode ◽  
Inelastic Neutron Scattering ◽  
Dynamical Behavior ◽  
Martensitic Transformations ◽  
High Resolution Electron Microscopy ◽  
Inelastic Neutron ◽  
Microstructural Development ◽  
Martensitic Transformation Temperature ◽  
Resolution Electron ◽  
Structural Configurations

AbstractElastic and inelastic neutron-scattering and high-resolution electron-microscopy examinations of the β2 (B2) phase of NixAl(100-x) alloys show a direct relationship between the anomalous changes in lattice dynamical behavior and the evolution of static premartensitic structural configurations as the β2 cools toward its martensitic transformation temperature, Ms. The resulting microstructure is a fine-scale mosaic assembly of nonuniformly distorted and modulated domains, in which {110}<110> shear-plus-shuffle displacements give rise to the {110}B2 micromodulations of ∼1.3 nm wavelength. These displacements are derived from the unusually low energy of the Σ4<ζζ0>–TA2 phonon mode and its anomalous temperaturedependent incomplete softening at ζ = 0 (viz., the elastic constant C) and at ζ ≈ 0.16. These inhomogeneously strained domains (ISDs) are believed to be centered on low strain-amplitude defects. They are viewed as strain embryos of the product 7M(5, 2) martensite but are generally too weak to act as potent nucleation centers. Similar ISD configurations develop at defects with higher strain amplitudes (e.g., dislocations, grain boundaries) and these are the most likely sites for heterogeneous nucleation to occur.

AlN Nanorods synthesized by a Mechanothermal Process

2011 ◽  
Vol 1288 ◽  
Author(s):  
G. Rosas ◽  
J. Chihuaque ◽  
C. Patiño-Carachure ◽  
R. Esparza ◽  
R. Pérez
Keyword(s):  
Electron Microscopy ◽  
Mechanical Milling ◽  
Annealing Treatment ◽  
High Resolution Electron Microscopy ◽  
Dynamical Theory ◽  
Transmission Electron ◽  
Resolution Electron ◽  
Structural Configurations ◽  
Simulated Images

ABSTRACTWell-crystallized AlN nanorods have been produced by mechanical milling and subsequent annealing treatment of the milling powders (mechanothermal process). High purity AlN powders were used as the starting material. Mechanical milling was carried out in a vibratory SPEX mill for 30 h, using vials and balls of silicon nitride. The annealing treatment was carried out at 1200 ºC for 10 min. The characterization of the samples was performed by X-ray diffractometry and transmission electron microscopy (TEM). TEM observations indicated that the synthesized nanorods consisted of 30 nm in diameter and 100 nm in length. High resolution electron microscopy observations have been used in the structural characterization. AlN nanorods exhibit a well-crystallized structure. The growing direction of the nanorods is close to the [001] direction. The structural configurations have been explored through comparisons between experimental HREM images and theoretically simulated images obtained with the multislice method of the dynamical theory of electron diffraction.

On the Grain Refinement Mechanisms in SPD – Applying High Resolution Electron Microscopy and the LEDS Approach

2006 ◽  
Vol 503-504 ◽  
pp. 45-50 ◽  
Author(s):  
Jens C. Werenskiold ◽  
Hans Jørgen Roven
Keyword(s):  
High Resolution ◽  
Strain Tensor ◽  
Advanced Characterization ◽  
High Resolution Electron Microscopy ◽  
Microstructural Development ◽  
Flow Paths ◽  
Characterization Methods ◽  
Angular Pressing ◽  
Deformation Banding ◽  
Resolution Electron

The present work is an attempt to contribute the current understanding of the operating mechanisms responsible for the development of ultrafine grains during severe plastic deformation (SPD) in aluminium. Equal channel angular pressing (ECAP) at room temperature has been applied to a commercial Al-Mg-Si alloy. Route A was used in all pressings and the first two passes were studied in most detail. Advanced characterization methods such as FEG-SEM with a state-of-the-art microdiffraction unit has been applied when characterizing samples carefully prepared from different positions along certain flow paths in the process shear zone. Intrinsic strain measurements are done in parallel in order to describe the actual strain tensor in each position studied. Detailed information on phenomena involved in the grain break-up mechanisms has been obtained by high resolution EBSD data collected through the deformation zone. The microstructural development seems to be dominated by deformation banding and may be explained in terms of the LEDS theory.

DYNAMICAL BEHAVIOR OF APERIODIC INTERGROWTH CRYSTALS

1996 ◽  
Vol 10 (17) ◽  
pp. 2049-2080 ◽  
Author(s):  
D. SCHMICKER ◽  
SANDER VAN SMAALEN
Keyword(s):  
Inelastic Neutron Scattering ◽  
Sliding Mode ◽  
Current Knowledge ◽  
Equations Of Motion ◽  
Dynamical Behavior ◽  
Experimental Information ◽  
Inelastic Neutron ◽  
Theory Of Elasticity ◽  
Theoretical Understanding ◽  
Elastic Tensor

An overview is given of the current knowledge pertaining to the sliding mode in incommensurate intergrowth compounds. It is found that both theoretical understanding and experimental information is wanting. Responsible for the latter is the lack of high-quality, very pure crystals of incommensurate intergrowth compounds, thus destroying the sliding mode by the effect of pinning. A phenomenological description is presented of the sliding mode in the long wavelength limit, using an extension of the theory of elasticity. The six by six elastic tensor is extended to a nine by nine elastic tensor describing the elastic waves in (3+1)-dimensional aperiodic crystals. The equations of motion are solved and symmetry restrictions on the components of this elastic tensor are given for all superspace groups. Experimental information as obtained by Brillouin scattering, inelastic neutron scattering and X-ray diffraction is discussed against the background of the present theoretical knowledge. Particular attention is given to pinning, to damping and the existence of propagating and overdamped regimes, and to the polarization of the sliding mode.

scholarly journals Observation of soft phonon mode in TbFe3(BO3)4 by inelastic neutron scattering

2018 ◽  
Vol 97 (5) ◽  
Author(s):  
M. S. Pavlovskiy ◽  
K. A. Shaykhutdinov ◽  
L. S. Wu ◽  
G. Ehlers ◽  
V. L. Temerov ◽  
...  
Keyword(s):  
Neutron Scattering ◽  
Phonon Mode ◽  
Inelastic Neutron Scattering ◽  
Inelastic Neutron ◽  
Soft Phonon Mode

Synthesis of AlFe Intermetallic Nanoparticles by High-Energy Ball Milling

2015 ◽  
Vol 1766 ◽  
pp. 181-186
Author(s):  
G. Rosas ◽  
J. Chihuaque ◽  
E. Bedolla ◽  
R. Esparza ◽  
R. Pérez
Keyword(s):  
Electron Microscopy ◽  
Ball Milling ◽  
High Resolution Electron Microscopy ◽  
High Energy ◽  
Dynamical Theory ◽  
High Energy Ball Milling ◽  
Resolution Electron ◽  
Energy Ball ◽  
Structural Configurations ◽  
Diffraction Patterns

ABSTRACTIn this investigation, the chemical and microstructural characteristics of nanostructured AlFe intermetallic produced by high-energy ball milling have been explored. High purity elemental powders were used as the starting material. The ball milling was carried out at room temperature using a SPEX-8000 mixer/mill. The structure, morphology and compositions of the powders were obtained using X-ray diffraction patterns (XRD), scanning and transmission electron microscopy (STEM). High resolution electron microscopy observations have been used in the nanostructured materials characterization. The structural configurations have been explored through comparisons between experimental HREM images and theoretically simulated images obtained with the multislice method of the dynamical theory of electron diffraction.

Recent Applications of High Resolution Electron Microscopy to Crystalline Arrays of Virus Particles

1978 ◽  
Vol 36 (3) ◽  
pp. 470-482 ◽  
Author(s):  
R.W. Horne
Keyword(s):  
Electron Microscopy ◽  
Image Processing ◽  
Analytical Techniques ◽  
Staining Technique ◽  
High Resolution Electron Microscopy ◽  
Optical Diffraction ◽  
Full Potential ◽  
Virus Particles ◽  
Resolution Electron ◽  
Wide Range

The technique of surrounding virus particles with a neutralised electron dense stain was described at the Fourth International Congress on Electron Microscopy, Berlin 1958 (see Home & Brenner, 1960, p. 625). For many years the negative staining technique in one form or another, has been applied to a wide range of biological materials. However, the full potential of the method has only recently been explored following the development and applications of optical diffraction and computer image analytical techniques to electron micrographs (cf. De Hosier & Klug, 1968; Markham 1968; Crowther et al., 1970; Home & Markham, 1973; Klug & Berger, 1974; Crowther & Klug, 1975). These image processing procedures have allowed a more precise and quantitative approach to be made concerning the interpretation, measurement and reconstruction of repeating features in certain biological systems.

One Million Direct Magnification Microscopy

1971 ◽  
Vol 29 ◽  
pp. 166-167
Author(s):  
J. A. Hugo ◽  
V. A. Phillips
Keyword(s):  
Electron Microscopy ◽  
High Resolution Electron Microscopy ◽  
Illumination Level ◽  
Level Of Detail ◽  
Photographic Emulsion ◽  
Low Contrast ◽  
Fluorescent Screen ◽  
Resolution Electron ◽  
Lattice Images ◽  
Electron Microscopes

A continuing problem in high resolution electron microscopy is that the level of detail visible to the microscopist while he is taking a picture is inferior to that obtainable by the microscope, readily readable on a photographic emulsion and visible in an enlargement made from the plate. Line resolutions, of 2Å or better are now achievable with top of the line 100kv microscopes. Taking the resolution of the human eye as 0.2mm, this indicates a need for a direct viewing magnification of at least one million. However, 0.2mm refers to optimum viewing conditions in daylight or the equivalent, and certainly does not apply to a (colored) image of low contrast and illumination level viewed on a fluorescent screen through a glass window by the dark-adapted eye. Experience indicates that an additional factor of 5 to 10 magnification is needed in order to view lattice images with line spacings of 2 to 4Å. Fortunately this is provided by the normal viewing telescope supplied with most electron microscopes.

Lattice Imaging of Twin, Lath and α/Martensite Boundaries in Duplex Low Carbon Steels

1977 ◽  
Vol 35 ◽  
pp. 118-119
Author(s):  
J. Y. Koo ◽  
G. Thomas
Keyword(s):  
High Resolution Electron Microscopy ◽  
Ferrite Matrix ◽  
Carbon Steels ◽  
Bright Field Image ◽  
Low Carbon ◽  
Lattice Imaging ◽  
Bright Field ◽  
Lattice Image ◽  
New Information ◽  
Resolution Electron

High resolution electron microscopy has been shown to give new information on defects(1) and phase transformations in solids (2,3). In a continuing program of lattice fringe imaging of alloys, we have applied this technique to the martensitic transformation in steels in order to characterize the atomic environments near twin, lath and αmartensite boundaries. This paper describes current progress in this program.Figures A and B show lattice image and conventional bright field image of the same area of a duplex Fe/2Si/0.1C steel described elsewhere(4). The microstructure consists of internally twinned martensite (M) embedded in a ferrite matrix (F). Use of the 2-beam tilted illumination technique incorporating a twin reflection produced {110} fringes across the microtwins.

Structural analysis of the surface-layer protein of spirillum serpens by high-resolution electron microscopy

1983 ◽  
Vol 41 ◽  
pp. 738-739
Author(s):  
W. H. Wu ◽  
R. M. Glaeser
Keyword(s):  
Electron Microscopy ◽  
Surface Layer ◽  
Structural Analysis ◽  
High Resolution ◽  
Low Dose ◽  
High Resolution Electron Microscopy ◽  
Optical Diffraction ◽  
Surface Layer Protein ◽  
Morphological Unit ◽  
Resolution Electron

Spirillum serpens possesses a surface layer protein which exhibits a regular hexagonal packing of the morphological subunits. A morphological model of the structure of the protein has been proposed at a resolution of about 25 Å, in which the morphological unit might be described as having the appearance of a flared-out, hollow cylinder with six ÅspokesÅ at the flared end. In order to understand the detailed association of the macromolecules, it is necessary to do a high resolution structural analysis. Large, single layered arrays of the surface layer protein have been obtained for this purpose by means of extensive heating in high CaCl2, a procedure derived from that of Buckmire and Murray. Low dose, low temperature electron microscopy has been applied to the large arrays.As a first step, the samples were negatively stained with neutralized phosphotungstic acid, and the specimens were imaged at 40,000 magnification by use of a high resolution cold stage on a JE0L 100B. Low dose images were recorded with exposures of 7-9 electrons/Å2. The micrographs obtained (Fig. 1) were examined by use of optical diffraction (Fig. 2) to tell what areas were especially well ordered.

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