COMPUTATION OF THERMODYNAMIC PARAMETERS OF BINARY METAL SYSTEMS WITH LIMITED SOLUBILITY OF COMPONENTS IN THE SOLID α-PHASE

The focus of discussion in Working Group 3 was on the Thermodynamic Properties as determined spectroscopically, including the observational techniques and the theoretical modeling of physical processes responsible for the emission spectrum. Recent advances in observational techniques and theoretical concepts make this discussion particularly timely. It is wise to remember that the determination of thermodynamic parameters is not an end in itself and that these are interesting chiefly for what they can tell us about the energetics and mass transport in prominences.

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Microtomy of spherical Al2O3 powders

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010007429x ◽

1983 ◽

Vol 41 ◽

pp. 74-75

Author(s):

E.J. Jenkins ◽

D.S. Tucker ◽

J.J. Hren

Keyword(s):

Thin Film ◽

Size Range ◽

Particle Aggregation ◽

Ion Milling ◽

Thin Sections ◽

Α Phase ◽

Convenient Means ◽

Van Der Waals Attraction ◽

Negative Feature ◽

Film Substrate

The size range of mineral and ceramic particles of one to a few microns is awkward to prepare for examination by TEM. Electrons can be transmitted through smaller particles directly and larger particles can be thinned by crushing and dispersion onto a substrate or by embedding in a film followed by ion milling. Attempts at dispersion onto a thin film substrate often result in particle aggregation by van der Waals attraction. In the present work we studied 1-10 μm diameter Al2O3 spheres which were transformed from the amprphous state to the stable α phase.After the appropriate heat treatment, the spherical powders were embedded in as high a density as practicable in a hard EPON, and then microtomed into thin sections. There are several advantages to this method. Obviously, this is a rapid and convenient means to study the microstructure of serial slices. EDS, ELS, and diffraction studies are also considerably more informative. Furthermore, confidence in sampling reliability is considerably enhanced. The major negative feature is some distortion of the microstructure inherent to the microtoming operation; however, this appears to have been surprisingly small. The details of the method and some typical results follow.

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Microstructural Evolution in Reduced TiO2

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100097089 ◽

1981 ◽

Vol 39 ◽

pp. 74-75

Author(s):

W. T. Donlon ◽

S. Shinozaki ◽

E. M. Logothetis ◽

W. Kaizer

Keyword(s):

Microstructural Evolution ◽

Point Defects ◽

Extended Defects ◽

Small Deviations ◽

Controlled Atmospheres ◽

Limited Solubility ◽

Thin Foils ◽

Heat Treated ◽

Porous Polycrystalline ◽

Crystallographic Shear

Since point defects have a limited solubility in the rutile (TiO2) lattice, small deviations from stoichiometry are known to produce crystallographic shear (CS) planes which accomodate local variations in composition. The material used in this study was porous polycrystalline TiO2 (60% dense), in the form of 3mm. diameter disks, 1mm thick. Samples were mechanically polished, ion-milled by conventional techniques, and initially examined with the use of a Siemens EM102. The electron transparent thin foils were then heat-treated under controlled atmospheres of CO/CO2 and H2 and reexamined in the same manner.The “as-received” material contained mostly TiO2 grains (∼5μm diameter) which had no extended defects. Several grains however, aid exhibit a structure similar to micro-twinned grains observed in reduced rutile. Lattice fringe images (Fig. 1) of these grains reveal that the adjoining layers are not simply twin related variants of a single TinO2n-1 compound. Rather these layers (100 - 250 Å wide) are alternately comprised of stoichiometric TiO2 (rutile) and reduced TiO2 in the form of Ti8O15, with the Ti8O15 layers on either side of the TiO2 being twin related.

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Ion Beam Mixing of Ni-Ti Bilayered Thin Films

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100118345 ◽

1985 ◽

Vol 43 ◽

pp. 290-291

Author(s):

A. K. Rai ◽

R. S. Bhattacharya ◽

M. H. Rashid

Keyword(s):

Crystal Structure ◽

Thin Films ◽

Amorphous Alloys ◽

Ion Beam ◽

Ion Bombardment ◽

High Energy ◽

Mixing Efficiency ◽

Ion Beam Mixing ◽

Enhanced Diffusion ◽

Binary Metal

Ion beam mixing has recently been found to be an effective method of producing amorphous alloys in the binary metal systems where the two original constituent metals are of different crystal structure. The mechanism of ion beam mixing are not well understood yet. Several mechanisms have been proposed to account for the observed mixing phenomena. The first mechanism is enhanced diffusion due to defects created by the incoming ions. Second is the cascade mixing mechanism for which the kinematicel collisional models exist in the literature. Third mechanism is thermal spikes. In the present work we have studied the mixing efficiency and ion beam induced amorphisation of Ni-Ti system under high energy ion bombardment and the results are compared with collisional models. We have employed plan and x-sectional veiw TEM and RBS techniques in the present work.

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High-resolution EM investigation about effect of stress on formation of ω-phase crystals in β-tttanium alloys

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100167494 ◽

1996 ◽

Vol 54 ◽

pp. 1006-1007

Author(s):

E. Sukedai ◽

M. Shimoda ◽

A. Fujita ◽

H. Nishizawa ◽

H. Hashimoto

Keyword(s):

High Resolution ◽

Titanium Alloys ◽

High Resolution Electron Microscopy ◽

Dark Field ◽

Zone Refining ◽

Ω Phase ◽

Α Phase ◽

Nucleation Sites ◽

Resolution Electron ◽

Bcc Structure

ω-phase particles formed in β-titanium alloys (bcc structure) act important roles to their mechanical properties such as ductility and hardness. About the ductility, fine ω-phase particles in β–titanium alloys improve the ductility, because ω-phase crystals becomes nucleation sites of α-phase and it is well known that (β+α) duplex alloys have higher ductility. In the present study, the formation sites and the formation mechanism of ω-phase crystals due to external stress and aging are investigated using the conventional and high resolution electron microscopy.A β-titanium alloy (Til5Mo5Zr) was supplied by Kobe Steel Co., and a single crystal was prepared by a zone refining method. Plates with {110} surface were cut from the crystal and were pressured hydrostatically, and stressed by rolling and tensile testing. Specimens for aging with tensile stress were also prepared from Ti20Mo polycrystals. TEM specimens from these specimens were prepared by a twin-jet electron-polishing machine. A JEM 4000EX electron microscope operated at 400k V was used for taking dark field and HREM images.

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High-resolution observations of metastable γ’ precipitation in Al-15at.%Ag

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100167482 ◽

1996 ◽

Vol 54 ◽

pp. 1004-1005

Author(s):

N. V. Larcher ◽

I. G. Solorzano

Keyword(s):

Discontinuous Precipitation ◽

Equilibrium Phase ◽

Quantitative Description ◽

Present Contribution ◽

Α Phase ◽

The Matrix ◽

Aging Sequence ◽

Matrix Precipitation ◽

Considerable Detail ◽

Kinetics Of

It is currently well established that, for an Al-Ag alloy quenched from the α phase and aged within the metastable solvus, the aging sequence is: supersaturated α → GP zones → γ’ → γ (Ag2Al). While GP zones and plate-shaped γ’ are metastable phases, continuously distributed in the matrix, formation of the equilibrium phase γ takes place at grain boundaries by discontinuous precipitation (DP). The crystal structure of both γ’ and γ is hep with the following orientation relationship with respect to the fee α matrix: {0001}γ′,γ // {111}α, <1120>γ′,γ, // <110>α.The mechanisms and kinetics of continuous matrix precipitation (CMP) in dilute Al-Ag alloys have been studied in considerable detail. The quantitative description of DP kinetics, however, has received less attention. The present contribution reports the microstructural evolution resulting from aging an Al-Ag alloy with Ag content higher than those previously reported in the literature, focusing the observations of γ' plate-shaped metastable precipitates.

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Direct imaging of order-disorder and antiphase domain structures in Ti3Al intermetallic compound

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100175533 ◽

1990 ◽

Vol 48 (4) ◽

pp. 480-481

Author(s):

H. Q. Ye ◽

T.S. Xie ◽

D. Li

Keyword(s):

Intermetallic Compound ◽

Volume Fraction ◽

Fundamental Problem ◽

Antiphase Domain ◽

Atomic Scale ◽

Orientation Relationships ◽

Domain Structures ◽

Α Phase ◽

Diffraction Patterns ◽

Two Phases

The Ti3Al intermetallic compound has long been recognized as potentially useful structural materials. It offers attractive strength to weight and elastic modulus to weight ratios. Recent work has established that the addition of Nb to Ti3Al ductilized this compound. In this work the fundamental problem of this alloy, i.e. order-disorder and antiphase domain structures was investigated at the atomic scale.The Ti3Al+10at%Nb alloys used in this study were treated at 1060°C and then aged at 700°C for 2 hours. The specimens suitable for TEM were prepared by standard jet electrolytic-polishing technique. A JEM-200CX electron microscope with an interpretable resolution of about 0.25 nm was used for HREM.The [100] and [001] projections of the α2 phase were shown in Fig.l.The alloy obtained consist of at least two phases-α2(Ti3Al) and β0 structures. Moreover, a disorder α phase with small volume fraction was also observed. Fig.2 gives [100] and [001] diffraction patterns of the α2 phase. Since lattice parameters of the ordered α2 (a=0.579, c=0.466 nm) and disorder α phase (a0=0.294≈a/2, c0=0.468 nm) are almost the same, their diffraction patterns are difficult to be distinguished when they are overlapped with epitaxial orientation relationships.

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MÖSSBAUER STUDY OF THE α-PHASE OF THE Ta-H SYSTEM

Le Journal de Physique Colloques ◽

10.1051/jphyscol:19746108 ◽

1974 ◽

Vol 35 (C6) ◽

pp. C6-515-C6-515 ◽

Cited By ~ 1

Author(s):

A. HEIDEMANN ◽

G. KAINDL ◽

D. SALOMON ◽

G. WORTMANN

Keyword(s):

Mössbauer Study ◽

Α Phase

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