A TEM STUDY OF ICOSAHEDRAL AND NEAR ICOSAHEDRAL PHASES IN 8090 ALLOY

1987 ◽  
Vol 48 (C3) ◽  
pp. C3-489-C3-495 ◽  
Author(s):  
G. LAPASSET ◽  
A. LOISEAU
Keyword(s):  
Icosahedral Phases

Microtwinning Evidence For The Apparent Five-Fold Symmetry in T2(Al6Li3Cu)

1987 ◽  
Vol 45 ◽  
pp. 24-25
Author(s):  
Kenneth S. Vecchio ◽  
David B. Williams
Keyword(s):  
Stable Equilibrium ◽  
Equilibrium Phase ◽  
Convergent Beam Electron Diffraction ◽  
Icosahedral Structure ◽  
Cubic Crystals ◽  
Icosahedral Phases ◽  
Heat Treated ◽  
Zero Layer ◽  
Convergent Beam ◽  
Zr Alloy

Since the discovery in 1984 by Shechtman et al. of crystals which display apparent five-fold symmetry, extensive effort has been given to establishing a theoretical basis for the existence of icosahedral phases (eg.2.). Several other investigations have been centered on explaining these observations based on twinning of cubic crystals (eg.3.). Recently, the existence of a stable, equilibrium phase T2Al6 Li3Cu) possessing an icosahedral structure has been reported in the Al-Li-Cu system(4-6).In the present study an Al-2.6wt.%Li-l.5wt.%Cu-0.lwt.%Zr alloy was heat treated at 300°C for 100hrs. to produce large T2 precipitates. Convergent Beam Electron Diffraction (CBED) patterns were obtained from two-fold, three-fold, and apparent five-fold axes of T2 particles. Figure 1 shows the five-fold symmetric zero layer CBED pattern obtained from T2 particles.

A Structural Model for a Quasi-Crystalline Material Derived from TEM

1990 ◽  
Vol 48 (1) ◽  
pp. 48-49
Author(s):  
Jan-Olov Bovin ◽  
Osamu Terasaki ◽  
Jan-Olle Malm ◽  
Sven Lidin ◽  
Sten Andersson
Keyword(s):  
High Resolution ◽  
Electron Diffraction ◽  
Structural Model ◽  
Image Intensifier ◽  
Crystalline Materials ◽  
Icosahedral Phases ◽  
Transmission Electron ◽  
Electron Microscopes ◽  
Diffraction Patterns ◽  
Quasi Crystals

High resolution transmission electron microscopy (HRTEM) is playing an important role in identifying the new icosahedral phases. The selected area diffraction patterns of quasi crystals, recorded with an aperture of the radius of many thousands of Ångströms, consist of dense arrays of well defined sharp spots with five fold dilatation symmetry which makes the interpretation of the diffraction process and the resulting images different from those invoked for usual crystals. The atomic structure of the quasi crystals is not established even if several models are proposed. The correct structure model must of course explain the electron diffraction patterns with 5-, 3- and 2-fold symmetry for the phases but it is also important that the HRTEM images of the alloys match the computer simulated images from the model. We have studied quasi crystals of the alloy Al65Cu20Fe15. The electron microscopes used to obtain high resolution electro micrographs and electron diffraction patterns (EDP) were a (S)TEM JEM-2000FX equipped with EDS and PEELS showing a structural resolution of 2.7 Å and a IVEM JEM-4000EX with a UHP40 high resolution pole piece operated at 400 kV and with a structural resolution of 1.6 Å. This microscope is used with a Gatan 622 TV system with an image intensifier, coupled to a YAG screen. It was found that the crystals of the quasi crystalline materials here investigated were more sensitive to beam damage using 400 kV as electron accelerating voltage than when using 200 kV. Low dose techniques were therefore applied to avoid damage of the structure.

Packing Characteristics of Atomic Structures of Model Icosahedral Phases

1989 ◽  
Vol 28 (Part 1, No. 10) ◽  
pp. 1893-1899 ◽  
Author(s):  
Tetsushoku Tei ◽  
Kaoru Kimura ◽  
Shin Takeuchi ◽  
Yutaka Mera ◽  
Koji Maeda
Keyword(s):  
Atomic Structures ◽  
Icosahedral Phases

Microstructural Characterization of Rapidly Solidified Ultrahigh Strength Aluminum Alloys

1998 ◽  
Vol 4 (S2) ◽  
pp. 98-99
Author(s):  
D. H. Ping ◽  
K. Hono ◽  
A. Inoue
Keyword(s):  
Rapid Solidification ◽  
Microstructural Characterization ◽  
Atom Probe ◽  
Probe Field ◽  
Amorphous Phases ◽  
Ultrahigh Strength ◽  
Icosahedral Phases ◽  
Transmission Electron ◽  
Solidification Processes ◽  
Rapidly Solidified

Recently, Inoue et al. succeeded in fabricating ultrahigh-strength Al-based alloys consisting of a nanoscale mixture of α-Al and amorphous phases or a mixture of a-Al, amorphous and icosahedral phases in Al-TM-Ce, Al-TM-Ln (TM: transition metals) and Al-Cr-Co-Ce systems by rapid solidification [1-3]. In order to understand the mechanism of the nanoscale microstructural evolution during the rapid solidification processes in these nanocomposite alloys, we have characterized the microstructures of rapidly solidified Al94.5Cr3Co1.5Ce1 and Al96V4Fe2 alloys by atom probe field ion microscopy (APFIM) and high resolution transmission electron microscopy (HREM).TEM investigations have revealed that the as-quenched Al94.5Cr3Co1.5Ce1 alloy is composed of a nanoscale mixture of amorphous and α-Al. A typical TEM bright field micrograph is shown in Fig. 1. The microdiffraction patterns taken at various locations in the darkly contrasted region have shown that the region consists of a few interconnected α-Al grains and many localized amorphous regions which are trapped within the Al grains.

Decagonal quasicrystal of a new structural type

2004 ◽  
Vol 219 (12) ◽  
Author(s):  
Sergiy Balanetskyy ◽  
Benjamin Grushko ◽  
Tamara Ya. Velikanova
Keyword(s):  
High Resolution ◽  
Structural Unit ◽  
Alloy System ◽  
Structural Type ◽  
Decagonal Quasicrystal ◽  
Decagonal Phase ◽  
Icosahedral Phases ◽  
Resolution Electron

AbstractA stable decagonal phase of a new structural type was discovered in Al—Pd—Re. This is the second Al-based alloy system after Al—Pd—Mn where both stable icosahedral and decagonal phases are formed. In contrast to the isostructural icosahedral phases of similar Al and Pd concentrations in both systems, the new decagonal phase exhibits periodicity of ∼2.57 vs. ∼1.25 nm in Al—Pd—Mn and is formed at significantly higher Al concentration than that in Al—Pd—Mn. In the tenfold plane, the structural unit of the Al—Pd—Re decagonal phase assumed from the high-resolution electron images is

Discommensurations in icosahedral phases

1986 ◽  
Vol 34 (11) ◽  
pp. 8202-8206 ◽  
Author(s):  
Bulbul Chakraborty ◽  
A. K. Sood ◽  
M. C. Valsakumar
Keyword(s):  
Icosahedral Phases

Features of the Mackay Clusters with and without a Center Atom in Al Based Approximants of Icosahedral Quasicrystals

2012 ◽  
Vol 508 ◽  
pp. 353-356 ◽  
Author(s):  
Shota Suzuki ◽  
Rayko Simura ◽  
Kazumasa Sugiyama
Keyword(s):  
The Other ◽  
Other Hand ◽  
Icosahedral Phases ◽  
Icosahedral Quasicrystals

The Packing Features of Mackay and Pseudo Mackay Clusters in Al Based Approximants to Icosahedral Phases Are Surveyed. The Cubic Approximants of α-AlMnSi, AlReSi, and α-(Al,Si)CuFe Indicate Typical Mackay Clusters Composed by the Dense Icosahedral Shell Packing. On the other Hand, the Cubic Approximants of α-Alcuru and α-(Al,Si)CuFe and the Non-Cubic Approximants of Ir9Al28, χ-AlPdRe, and R-AlPdCo Shows so-Called Pseudo Mackay Clusters in which the Icosahedral Packing Feature Is Disappeared at their First Shells. The Distorted First Shells Represent a Variation of Pseudo Mackay Clusters, which Could Be Classified into Three Subgroups Based on the Symmetry.

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