Hrem Investigation of the Structure of the σ5(310)/[001] Symmetric Tilt Grain Boundary In Nb.*

1990 ◽  
Vol 209 ◽  
Author(s):  
Wayne E. King ◽  
G. H. Campbell ◽  
A. Coombs ◽  
M. J. Mills ◽  
M. RüHle
Keyword(s):  
Grain Boundary ◽  
High Vacuum ◽  
High Resolution Electron Microscopy ◽  
Ultra High Vacuum ◽  
Interatomic Potentials ◽  
Pseudopotential Theory ◽  
Tilt Axis ◽  
Embedded Atom ◽  
Symmetric Tilt ◽  
Bonding Method

ABSTRACTRecent atomistic simulations using interatomic potentials for Nb developed employing the embedded atom method (EAM) and the model generalized pseudopotential theory (MGPT) have indicated a possible cusp at the Σ5(310) orientation in the energy vs tilt angle curves for<001> symmetric tilt grain boundaries. In addition, the most stable structure predicted using EAM exhibits shifts of one crystal relative to the other along the tilt axis and along the direction perpendicular to the tilt axis lying in the boundary plane. The structure predicted using the MGPT was mirror symmetric across the plane of the grain boundary. This boundary has been prepared for experimental study using the ultra high vacuum diffusion bonding method. A segment of this boundary has been studied using high resolution electron microscopy.

Hrem Investigation of the Structure of the Σ5(210)/[001] Symmetric Tilt Grain Boundaries in Nb.

1991 ◽  
Vol 229 ◽  
Author(s):  
G. H. Campbell ◽  
S. M. Foiles ◽  
Wayne E. King ◽  
M. Rühle ◽  
W. Wien
Keyword(s):  
High Vacuum ◽  
High Resolution Electron Microscopy ◽  
Ultra High Vacuum ◽  
Experimental Result ◽  
Energy Structure ◽  
Interatomic Potentials ◽  
Pseudopotential Theory ◽  
Atomic Structures ◽  
Embedded Atom ◽  
Symmetric Tilt

AbstractWe have simulated the atomic structures of the Σ 5 (210)/[001 ] symmetric tilt grain boundary using interatomic potentials for Nb developed employing the embedded atom method (EAM) and the model generalized pseudopotential theory (MGPT). These potentials do not predict the same lowest energy structure for the Σ 5 (210)/[001]. Using the ultra high vacuum diffusion bonding process, we have fabricated Σ 5 (210)/[001] bicrystals. The samples have been observed using high resolution electron microscopy and the observed images have been compared with those simulated based on the structures predicted theoretically. The experimental result for the Σ 5 (210)/[001] is in close agreement with the structure predicted using the EAM.

Investigation of Copper Segregation to the Σ5(310)/[001] Symmetric Tilt Grain Boundary in Aluminum

1999 ◽  
Vol 589 ◽  
Author(s):  
Jürgen M. Plitzko ◽  
Geoffrey H. Campbell ◽  
Wayne E. King ◽  
Stephen M. Foiles
Keyword(s):  
Electron Microscopy ◽  
Grain Boundary ◽  
Low Voltage ◽  
Theoretical Calculations ◽  
High Vacuum ◽  
Analytical Electron Microscopy ◽  
Ultra High Vacuum ◽  
Face Centered Cubic ◽  
Symmetric Tilt ◽  
Tilt Grain Boundary

AbstractThe Σ5 (31O)/[001] symmetric tilt grain boundary (STGB) in the face centered cubic (FCC) metal aluminum with 1at% copper has been studied. The model grain boundary has been fabricated by ultra-high vacuum diffusion bonding of alloy single crystals. The segregation of the copper has been encouraged by annealing the sample after bonding at 200 °C. TEM samples of this FCCmaterial were prepared with a new low voltage ion mill under very low angles.The atomic structure of the Σ5(310)/[001] STGB for this system was modeled with electronic structure calculations. These theoretical calculations of the interface structure indicate that the Cu atoms segregate to distinct sites at the interface. High resolution electron microscopy (HRTEM) and analytical electron microscopy including electron energy spectroscopic imaging and X-ray energy dispersive spectrometry have been used to explore the segregation to the grain boundary. The HRTEM images and the analytical measurements were performed using different kinds of microscopes, including a Philips CM300 FEG equipped with an imaging energy filter. The amount of the segregated species at the interface was quantified in a preliminary way. To determine the atomic positions of the segregated atoms at the interface, HRTEM coupled with image simulation and a first attempt of a holographic reconstruction from a through-focal series have been used.

Atomic Structure of the (310) Twin in Niobium: Theoretical Predictions and Comparison with Experimental Observation

1992 ◽  
Vol 295 ◽  
Author(s):  
Geoffrey H. Campbell ◽  
S. M. Foiles ◽  
M. Rühle ◽  
W. E. King
Keyword(s):  
High Resolution ◽  
Grain Boundary ◽  
Atomic Structure ◽  
Mirror Symmetry ◽  
Interatomic Potentials ◽  
Pseudopotential Theory ◽  
Embedded Atom ◽  
Transmission Electron ◽  
Theoretical Predictions ◽  
Model Structures

AbstractHigh - resolution transmission electron microscopy (HREM) has been used to characterize the atomic structure of the symmetric 36.9° tilt grain boundary with [001] tilt axes forming a twin about (310) in Nb. The projected structure was imaged along two different directions in the plane of the boundary and was compared to model structures through high - resolution image simulation. The atomic structure of this Σ5 boundary was predicted with atomistic simulations using interatomic potentials derived from the Embedded Atom Method (EAM), Finnis-Sinclair (FS), and the Model Generalized Pseudopotential Theory (MGPT). The EAM and FS predicted structures with translations of the adjacent crystals which break mirror symmetry. The MGPT predicted one stable structure with mirror symmetry. The atomic structure of the (310) twin in Nb was found by HREM to be mirror symmetric. These findings indicate that the angular dependent interactions modeled in the MGPT are important for determining the grain boundary structures of bcc transition metals.

Hrem Study of Ultra Thin Titanium Films

1997 ◽  
Vol 472 ◽  
Author(s):  
T. Braisaz ◽  
P. Ruterana ◽  
G. Nouet ◽  
Ph. Komninou ◽  
Th. Kehagias ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
High Vacuum ◽  
High Resolution Electron Microscopy ◽  
Zone Axis ◽  
Ultra High Vacuum ◽  
Electron Gun ◽  
Mirror Plane ◽  
Planar Defects ◽  
Resolution Electron ◽  
Order Of Magnitude

ABSTRACTHigh resolution electron microscopy has been used to characterize the structure of ultra thin films of titanium deposited on KBr substrate by Ultra High Vacuum (UHV) electron-gun evaporation. The size of the grains has an order of magnitude of 10 nm whatever the substrate temperature. The observations have been carried out along <1123> zone axis. Some of the grains contain planar defects which were identified as the twin {1011}. The atomic structure of this twin is characterized by a mirror plane similar to that observed in polycrystalline titanium. Additionaly, this structure can be modified by a b2/2 twinning dislocation.

Effect of Crack on the Tensile Strength of a Bicrystal Zr - A MD Based Evaluation

2020 ◽  
Vol 978 ◽  
pp. 487-491
Author(s):  
Divya Singh ◽  
Avinash Parashar
Keyword(s):  
Molecular Dynamics ◽  
Tensile Strength ◽  
Grain Boundary ◽  
Tensile Loading ◽  
Strain Response ◽  
Tilt Axis ◽  
Symmetric Tilt ◽  
Tilt Grain Boundary ◽  
The One ◽  
Dynamics Simulations

In this article, molecular dynamics simulations have been performed to study the effect of crack on the tensile strength of a bicrystal of Zr. Bicrystal with a symmetric tilt grain boundary, with crack and without crack, are generated along [0001] tilt axis. This is further subjected to tensile loading and the stress strain response of the bicrystals with and without crack is studied. The strength of the bicrystal with crack is lower than the one without crack.

A Field Emission Electron Microscope

1971 ◽  
Vol 29 ◽  
pp. 6-7
Author(s):  
A. Tonomura ◽  
T. Komoda
Keyword(s):  
Electron Microscope ◽  
Field Emission ◽  
High Vacuum ◽  
High Resolution Electron Microscopy ◽  
Ultra High Vacuum ◽  
Electron Optics ◽  
Ion Pumps ◽  
High Brightness ◽  
Emission Electron ◽  
Resolution Electron

We have developed a field emission electron microscope. Although field emission gun requires ultra high vacuum and skillful technique, it brings about the favorable characteristics of high brightness and small energy spread. This characteristics will enable a significant progress in coherent electron optics and high resolution electron microscopy, especially in electron beam holography.Its column is Hitachi HU-11C Electron Microscope modified for ultra high vacuum operation, and it is evacuated with five ion pumps. Field emission gun is divided into two parts and is evacuated differentially with two ion pumps and a sublimation pump. The final pressures in these rooms are 5x10-10 Torr and 5x10-8 Torr respectively.

Characterization of structural units in tilt grain boundaries

1992 ◽  
Vol 50 (1) ◽  
pp. 120-121
Author(s):  
Stuart McKernan ◽  
C. Barry Carter
Keyword(s):  
High Resolution ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
High Resolution Electron Microscopy ◽  
Boundary Structure ◽  
Structural Units ◽  
Symmetric Tilt ◽  
Resolution Electron ◽  
Special Cases ◽  
High Resolution Electron Microscope

General tilt grain boundaries can be viewed in terms of small structural units of varying complexity. High-resolution electron microscope (HREM) images of these boundaries in many materials show this repetitive similarity of the atomic structure at the boundary plane. The structure of particular grain boundaries has been examined for several special cases and commonly observed configurations include symmetric tilt grain boundaries and asymmetric tilt grain boundaries with one grain having a prominent, low-index facet. Several different configurations of the boundary structure may possibly occur, even in the same grain boundary. There are thus many possible ways to assemble the basic structural units to form a grain boundary. These structural units and their distribution have traditionally been examined by high-resolution electron microscopy. The images of the projection of the atomic columns (or the tunnels between atomic columns) providing a template for constructing “ball-and-stick ” models of the interface.

Structure of Σ7 grain boundary in Al2O3

1994 ◽  
Vol 52 ◽  
pp. 718-719
Author(s):  
C. C. Chu ◽  
F.-R. Chen ◽  
C.-Y. Wang ◽  
L. Chang
Keyword(s):  
Grain Boundary ◽  
Atomic Structure ◽  
Coincidence Site Lattice ◽  
High Vacuum ◽  
Three Dimensional ◽  
High Resolution Electron Microscopy ◽  
Boundary Structure ◽  
Cubic Symmetry ◽  
Grain Boundary Structure ◽  
Resolution Electron

In the past, extensive high resolution electron microscopy has been applied to the atomic structure of grain boundaries of cubic symmetry. In order to have a better understanding of generalization of the grain boundary theory, it could be fruiful to study grain boundary structure of non-cubic and low symmetry crystals in which case the exact CSL’s may not exist. Al2O3 has a hexagonal crystal structure ( non-cubic). In the case of hexagonal crystals, three dimensional coincidence site lattices (CSL’s) are only possible for rational values of (c/a), except for rotations about the [0001] axis. The (c/a) of α-Al2O3 is very close to a rational number (15/2) such that constrained coincidence-site lattice (CCSL) misorientations can be found. In this research, we study the atomic structure of Σ7 grain boundary. The misonentation of Σ7 is [011]/180°. The bicrystals of Σ7 were made by diffusion bonding in high temperature and high vacuum.Figs. 1 (a) and (b). show typical HRTEM images of Σ7 Al2O3 boundary recorded at the underfocus values -48 nm and -96 nm, respectively. The beam direction is parallel to a common axis [20].

Quantitative Hrem Study of the Atomic Structure of the Σ(310)/[001] Symmetric Tilt Grain Boundary in Nb

1992 ◽  
Vol 295 ◽  
Author(s):  
Wayne E. King ◽  
Geoffrey H. Campbell
Keyword(s):  
Grain Boundary ◽  
Atomic Structure ◽  
Optimization Method ◽  
Interatomic Potentials ◽  
Cubic Metals ◽  
Symmetric Tilt ◽  
Resolution Electron ◽  
Least Squares Optimization ◽  
Tilt Grain Boundary ◽  
High Resolution Electron Micrographs

AbstractWe have used a non-linear least squares optimization method to deduce a model for the atomic structure of the Σ(310)/[001] symmetric tilt grain boundary in Nb from high resolution electron micrographs (HREM) of a bicrystal prepared by diffusion bonding. The resultant model is similar to, but differs in detail from a theoretical prediction based on interatomic potentials which included angular forces thought to be important in the prediction of defect structures in body centered cubic metals. Results validate this approach as a step towards making HREM a quantitative technique.

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