In SituHigh-Resolution Electron Spectroscopic Imaging and Real-Time Image Simulation of Precipitate Growth Mechanisms

1997 ◽  
Vol 3 (S2) ◽  
pp. 627-628
Author(s):  
J. M. Howe ◽  
M. M. Tsai ◽  
A. A. Csontos
Keyword(s):  
Atomic Level ◽  
Interface Motion ◽  
Bonding Structure ◽  
Transmission Electron ◽  
Resolution Electron ◽  
Precipitate Growth ◽  
The Matrix ◽  
Interphase Boundaries ◽  
Transformation Mechanisms ◽  
Kinetics Of

Precipitate interfaces are ideal for studying the relationship between atomic bonding, structure and composition at internal interfaces and the mechanisms and kinetics of their motion as a function of temperature or driving force for reaction. The crystallography between coherent and semicoherent precipitates and the matrix is well-defined and the precipitate interfaces are often planar and grow by a terrace-ledge-kink mechanism, making them well-suited for study by conventional and high-resolution transmission electron microscopy (HRTEM).Motion of precipitate interfaces, or more generally, interphase boundaries, involves a change in lattice, composition or both. In order to understand the mechansims of interfacial motion, it is necessary to determine the structural and compositional changes that occur at the highest possible resolution, i.e., as close to the atomic level as possible, and also, to determine the corresponding kinetics of interface motion. HRTEM is an excellent technique for determining the atomic structure of transformation interfaces and in situhot-stage HRTEM is deal for determining interface dynamics at the atomic level, provided the transformation mechanisms are not altered by the thinness of the TEM foil.

scholarly journals TEM Studies of Precipitate Growth at the Atomic Level

1985 ◽  
Vol 62 ◽  
Author(s):  
J. M. Howe ◽  
R. Gronsky
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
High Resolution Electron Microscopy ◽  
Atomic Level ◽  
Atomic Structures ◽  
Transmission Electron ◽  
Resolution Electron ◽  
Precipitate Growth ◽  
Convergent Beam ◽  
Microscopy Techniques

ABSTRACTRecent advances in transmission electron microscopy instrumentation and technique now make it possible to study the shape-evolution of precipitates in metallic alloys at the atomic level. This investigation demostrates how a combination of transmission electron microscopy techniques; namely, high-resolution electron microscopy, image simulation, energy-dispersive x-ray spectroscopy and convergent-beam electron diffraction are used to characterize the atomic structures, chemistry and growth mechanisms of γ' precipitate plates in an Al-4.2 a/o Ag alloy aged for 30 min. at 350°C. The complimentary information obtained from each of these techniques allows modelling of the growth process at the atomic level, thus providing insight into the basic precipitation behavior of alloys.

The effect of composition and cooling rate on the structure of rapidly solidified (Fe, Ni)3Al–C alloys

1989 ◽  
Vol 4 (1) ◽  
pp. 44-49 ◽  
Author(s):  
S. A. Myers ◽  
C. C. Koch
Keyword(s):  
Cooling Rate ◽  
Base Alloy ◽  
Weight Percent ◽  
Quench Rate ◽  
Transmission Electron ◽  
Metastable Structures ◽  
Metastable Structure ◽  
The Matrix ◽  
Rapidly Solidified ◽  
Kinetics Of

There is controversy in the literature regarding the existence of the metastable γ′ phase with an ordered Ll2 structure in rapidly solidified Fe–Ni–Al–C alloys. In this study, the quench rate–metastable structure dependence was examined in the Fe–20Ni–8Al–2C (weight percent) alloy. The effect of silicon on the kinetics of phase formation was studied by adding two weight percent silicon to a base alloy of Fe–20Ni–8Al–2C. Samples were rapidly solidified in an arc hammer apparatus and examined by transmission electron microscopy. In the Fe–20Ni–8Al–2C alloy, the nonequilibrium γ′ and γ phases were found in foils 65 to 100 μm thick. At higher quench rates, i.e., thinner samples, the matrix was observed to be disordered fcc γ with K-carbide precipitates. Samples containing silicon were found to have a matrix composed of γ′ and γ structures when the foils were thicker than 40 μm. At higher quench rates, the matrix was disordered fcc γ with K-carbide precipitates. The nonequilibrium γ′ and γ structures are present in samples with or without silicon, but are observed at higher cooling rates with the addition of silicon. This sensitivity to cooling rate and composition in resulting metastable structures may explain the differences reported in the literature for these rapidly solidified materials.

scholarly journals Thermal Kinetics of SiCp Reinforced Al-Zn-Mg-Cu Alloy Composite

2021 ◽  
Author(s):  
Saikat Das ◽  
R. Govinda Rao ◽  
Prasanta Kumar Rout
Keyword(s):  
Base Alloy ◽  
Accelerated Aging ◽  
Stir Casting ◽  
Hardness Profile ◽  
Scanning Calorimetry ◽  
Transmission Electron ◽  
The Matrix ◽  
Aging Kinetics ◽  
Aging Phenomena ◽  
Kinetics Of

Abstract In the present work, the artificial aging kinetics of SiCp particles reinforced AA7075-SiCp composite fabricated by stir casting method was investigated. The aging behavior of AA7075-SiCp composite was investigated by Rockwell hardness tests and differential scanning calorimetry (DSC). Results show there are no changes in the sequences of formation and dissolution of precipitate. Reinforced particles are uniformly distributed throughout the matrix. The hardness profile shows increase in hardness with the comparison of AA7075 base alloy. In addition to SiCp in the matrix, precipitation kinetics has changed compared with base alloy since higher dislocations present in composite, hence requires lower activation energy to form ή precipitate and takes less time to reach the maximum hardness. In contrast, the addition of SiCp at low volume percent also showing accelerated aging phenomena in the composite during the aging process. High-resolution transmission electron microscope (HRTEM) micrograph of peak age (T6) condition divulges that enormous fine and plate-like ή (MgZn2) precipitates are uniformly distributed in the composite.

Temporal Evolution of Bimodal Distribution of γ’ Precipitates in Ni-Al-Mo Alloys under the Influence of Coherency Strains

1995 ◽  
Vol 398 ◽  
Author(s):  
A.D. Sequeira ◽  
H.A. Calderon ◽  
G. Kostorz
Keyword(s):  
Lattice Mismatch ◽  
Bimodal Distribution ◽  
X Ray Diffraction ◽  
Double Step ◽  
Bimodal Size Distribution ◽  
Elastic Fields ◽  
Transmission Electron ◽  
The Matrix ◽  
Kinetics Of ◽  
Coherency Strains

ABSTRACTThe influence of coherency strains produced by the γ-γ’ lattice mismatch, δ, on the decomposition process of Ni-Al-Mo alloys with a bimodal size distribution is presented. Samples with δ ranging from positive to negative, were investigated in a double-step aging procedure. The evolution of the microstructure and the kinetics of coarsening were studied using transmission electron microscopy (TEM). The lattice mismatch between the matrix and the different classes of precipitates was determined by high-resolution high-temperature x-ray diffraction. It is shown that the strain fields produced by the lattice mismatch can influence dramatically the decomposition of metallic alloys. It is suggested that the reduction of the coarsening rate of the large precipitates, the fast coarsening rate of the small precipitates and the distortions detected in the matrix are all direct consequences of the elastic fields produced by the γ-γ’ lattice mismatch.

Advanced Computing in Electron Microscopy, Earl J. Kirkland 1998. Plenum Press, New York and London. 260 pages. ($72.50)

1999 ◽  
Vol 5 (5) ◽  
pp. 371-372
Author(s):  
John Spence
Keyword(s):  
Electron Microscopy ◽  
New York ◽  
Recent Observation ◽  
High Resolution Electron Microscopy ◽  
Atomic Level ◽  
Phase Identification ◽  
Transmission Electron ◽  
Resolution Electron ◽  
New Material ◽  
Advanced Computing

The recent observation of Bucky-tubes by S. Iijima using a transmission electron microscope (TEM) represents the first occasion in which a useful new material, subsequently available in commercial quantities, has been discovered by high-resolution electron microscopy (HREM). More commonly, the HREM method has been used for microcharacterization of materials at the atomic level, and for phase identification of submicrometer-sized microphases and polytypes.

scholarly journals Specimen Charging on Thin Films with One Conducting Layer: Discussion of Physical Principles

2004 ◽  
Vol 10 (6) ◽  
pp. 790-796 ◽  
Author(s):  
Robert M. Glaeser ◽  
Kenneth H. Downing
Keyword(s):  
Electron Microscopy ◽  
Carbon Film ◽  
Image Resolution ◽  
Conducting Layer ◽  
Conducting Film ◽  
Transmission Electron ◽  
Resolution Electron ◽  
Optical Effects ◽  
Charging Effect ◽  
Kinetics Of

Although the most familiar consequences of specimen charging in transmission electron microscopy can be eliminated by evaporating a thin conducting film (such as a carbon film) onto an insulating specimen or by preparing samples directly on such a conducting film to begin with, a more subtle charging effect still remains. We argue here that specimen charging is in this case likely to produce a dipole sheet rather than a layer of positive charge at the surface of the specimen. A simple model of the factors that control the kinetics of specimen charging, and its neutralization, is discussed as a guide for experiments that attempt to minimize the amount of specimen charging. Believable estimates of the electrostatic forces and the electron optical disturbances that are likely to occur suggest that specimen bending and warping may have the biggest impact on degrading the image quality at high resolution. Electron optical effects are likely to be negligible except in the case of a specimen that is tilted to high angle. A model is proposed to explain how both the mechanical and electron-optical effects of forming a dipole layer would have much greater impact on the image resolution in a direction perpendicular to the tilt axis, a well-known effect in electron microscopy of two-dimensional crystals.

Analysis of Interface Dynamics in Solid-State Phase Transformations by In Situ Hot-Stage High-Resolution Transmission Electron Microscopy

1994 ◽  
Vol 332 ◽  
Author(s):  
James M. Howe ◽  
W. E. Benson ◽  
A. Garg ◽  
Y.-C. Chang
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Solid State ◽  
High Resolution ◽  
Phase Transformations ◽  
Interface Motion ◽  
Transmission Electron ◽  
Kinetics Of ◽  
Dynamics Of Interfaces

ABSTRACTIn situ hot-stage high-resolution transmission electron microscopy (HRTEM) provides unique capabilities for quantifying the dynamics of interfaces at the atomic level. Such information is critical for understanding the theory of interfaces and solid-state phase transformations. This paper provides a brief description of particular requirements for performing in situ hot-stage HRTEM, summarizes different types of in situ HRTEM investigations and illustrates the use of this technique to obtain quantitative data on the atomic mechanisms and kinetics of interface motion in precipitation, crystallization and martensitic reactions. Some limitations of in situ hot-stage HRTEM and future prospects of this technique are also discussed.

The growth kinetics of ledged interphase boundaries: transient motion, an analytical treatment

1989 ◽  
Vol 426 (1871) ◽  
pp. 377-389 ◽  
Keyword(s):  
State Theory ◽  
Single Step ◽  
Analytical Treatment ◽  
Transient Motion ◽  
Step Motion ◽  
The Matrix ◽  
Interphase Boundaries ◽  
Finite Difference Solution ◽  
Kinetics Of ◽  
Finite Extent

An analysis of the transient motion of ledged interphase boundaries is presented where volume diffusion of solute in the matrix to the riser of the step is assumed to control the growth rate. The analysis leads to a nonlinear integral equation governing step motion and can be applied in principle to situations involving many interacting steps. Detailed attention is given to the case of a single step in an infinite medium where comparisons are made with numerical results of Enomoto (obtained by finite difference solution of the diffusion equation). Attention is also given to transient motion in a medium of finite extent. The treatment here thus generalizes the steady-state theory of Atkinson.

Microstructural Comparison of an Al-8.0Zn-1.8Mg-2.0Cu Alloy with Typical T6 and T76 Tempers

2018 ◽  
Vol 941 ◽  
pp. 753-758
Author(s):  
Bai Qing Xiong ◽  
Kai Wen ◽  
Yong An Zhang ◽  
Zhi Hui Li ◽  
Xi Wu Li ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Structural Information ◽  
High Resolution Electron Microscopy ◽  
Precipitate Size ◽  
Imaging Analysis ◽  
Bright Field ◽  
Transmission Electron ◽  
Resolution Electron ◽  
Precipitate Size Distribution ◽  
The Matrix

In order to analyze aging behavior of an Al-8.0Zn-1.8Mg-2.0Cu alloy, the microstructure of the alloy subjected to T6 and T76 states are investigated by transmission electron microscopy (TEM) and high-resolution electron microscopy (HREM). Based on the precipitate observations, precipitate size distributions and average precipitate size are extracted from bright-field TEM images projected along 〈110〉Alorientation with the aid of an imaging analysis. The results indicate that the main precipitates are GPI zone, GPII zone and η' phase in the T6 alloy while η' phase and η phase in the T76 alloy. The bright-field TEM observations reveal that the matrix precipitates for the T6 alloy have small size and dispersive distribution while that for the T76 alloy has big size and sparse distribution. Both have discontinuously distributed grain boundary precipitates. Quantitative structural information including precipitate size distribution and average precipitate size has been calculated by an image analysis based on the bright-field TEM images projected along 〈110〉Alorientation. The results show that the T6 alloy has a narrower precipitate size range than the T76 alloy and thus the T6 alloy possesses a smaller average precipitate size than the T76 alloy.

scholarly journals Precipitation Process in a Cu-Ni-Be Alloy

2011 ◽  
Vol 172-174 ◽  
pp. 432-436 ◽  
Author(s):  
Chihiro Watanabe ◽  
Ryoichi Monzen
Keyword(s):  
Electron Microscopy ◽  
Precipitation Process ◽  
Average Thickness ◽  
Precipitation Sequence ◽  
Transmission Electron ◽  
The Matrix ◽  
Precipitated Phases ◽  
Kinetics Of ◽  
Ledge Mechanism ◽  
Habit Planes

The precipitation process in an aged Cu-1.9wt%Ni-0.3wt%Be alloy has been examined by high-resolution transmission electron microscopy. The precipitation sequence found is: Guinier- Preston (G.P.) zones → γ'' → γ' → stable γ. The disk-shaped G.P. zones and the disk-shaped γ'', γ' and γ precipitated phases are composed of monolayers of Be atoms on {100}αof the Cu matrix and alternative Be and Ni matrix layers parallel to {100}α. The γ'' phases consisting of two to eight Be-layers has a body-centered tetragonal (bct) lattice witha=b=0.24 nm andc=0.28 nm. The γ' or γ phase is bct witha=b=0.24 nm andc=0.26 nm ora=b=0.26 nm andc=0.27 nm. The γ'', γ' or γ phase aligns with the matrix according to the Bain orientation relationship. The growth kinetics of disk-shaped γ precipitates on aging at 500°C has been also investigated. The {001}αhabit planes of the γ precipitates migrate by a ledge mechanism. The average thickness of the γ disks increases with aging timetast1/2. An analysis of experimental data using a kinetic model yields the diffusivity of solute in the Cu matrix, which is in agreement with the reported diffusivity of Ni in Cu.

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