Rapidly solidified and thermally treated microstructures of beryllium-1wt.% Yttrium alloy

1988 ◽  
Vol 46 ◽  
pp. 782-783
Author(s):  
L. A. Jacobson ◽  
P.L. Martin ◽  
T. E. Mitchell
Keyword(s):  
Melting Point ◽  
Elevated Temperatures ◽  
Alloying Element ◽  
High Melting Point ◽  
Superplastic Behavior ◽  
Dilute Alloys ◽  
Arc Melting ◽  
Transmission Electron ◽  
Heat Treated ◽  
Rapidly Solidified

Renewed interest in the possible use of beryllium at elevated temperatures has led to the examination of several dilute beryllium alloys with elements that form high melting point beryllide intermetallic compounds. One such alloying element is yttrium, which forms a beryllide, YBe13, with a melting point of over 1900° C. This system has been reported to have a eutectic between Be and YBe13 at a composition under 1 wt% Y. 13 Dilute alloys in this system have been investigated as to their superplastic behavior.Samples were prepared by arc melting l0g buttons of Be-1wt% Y alloy, melting at least three times to promote homogeneity. Very small pieces of a button were then arc melted on a water cooled copper hearth and splat-quenched by means of a spring loaded hammer. Pieces of splat material were heat treated for 2h at 1000°C, and 3mm disks were punched out for subsequent twin jet electrolytic thinning and examination by transmission electron microscopy.

In situ transmission electron microscope measurements of solid Al-solid Pb and solid Al-liquid Pb surface-energy anisotropy in rapidly solidified Al-5% Pb (by mass)

1987 ◽  
Vol 414 (1847) ◽  
pp. 499-507 ◽  
Keyword(s):  
Electron Microscope ◽  
Melting Point ◽  
Surface Energy ◽  
Transmission Electron Microscope ◽  
Room Temperature ◽  
Transmission Electron ◽  
Increasing Temperature ◽  
Rapidly Solidified ◽  
Al Matrix

Alloys of Al-5% Pb and Al-5% Pb-0.5% Si (by mass) have been manufactured by rapid solidification and then examined by transmission electron microscopy. The rapidly solidified alloy microstructures consist of 5-60 nm Pb particles embedded in an Al matrix. The Pb particles have a cube-cube orientation relation with the Al matrix, and are cub-octahedral in shape, bounded by {100} Al, Pb and {111} Al, Pb facets. The equilibrium Pb particle shape and therefore the anisotropy of solid Al-solid Pb and solid Al-liquid Pb surface energies have been monitored by in situ heating in the transmission electron microscope over the temperature range between room temperature and 550°C. The ani­sotropy of solid Al-solid Pb surface energy is constant between room temperature and the Pb melting point, with a {100} Al, Pb surface energy about 14% greater than the {111} Al, Pb surface energy, in good agreement with geometric near-neighbour bond energy calculations. The {100} AI, Pb facet disappears when the Pb particles melt, and the anisotropy of solid Al-liquid Pb surface energy decreases gradually with increasing temperature above the Pb melting point, until the Pb particles become spherical at about 550°C.

Development of a Double Tilt Specimen Heating Holder and its Application for the Study of Phase Transformation of Si3N4 During Sintering

1997 ◽  
Vol 3 (S2) ◽  
pp. 1085-1086
Author(s):  
T. Kamino ◽  
T. Yaguchi ◽  
M. Tomita ◽  
Y. Yasutomi ◽  
K. Hidaka
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Elevated Temperatures ◽  
Heating Element ◽  
High Melting ◽  
High Melting Point ◽  
Transmission Electron ◽  
High Resolution Tem ◽  
Metal Wires ◽  
Very High

The results of our previous studies revealed that the specimen heating holder with the heating elements of spiral shaped fine metal wires of high melting point enable us to observe high resolution transmission electron microscopy(TEM) images at elevated temperatures.In fact, the holder was applied for high resolution TEM study of a formation of SiC crystal at 1500°C and a surface reconstruction of Au deposited Si particle at 1000°C successfully. However, because the heating holder was single tilt type, there was a certain limitation in its application.In this paper, development of a double tilt specimen heating holder with a heating element of spiral shaped fine metal wire and its application for the study of microstructural changes of Si3N4 during sintering at very high temperature.Photograph of the newly developed double tilt specimen heating holder is shown in Fig. 1. The heating element is mounted on the electrically isolated tilting frame of the holder and the heating current is supplied via tilting rod which is also electrically isolated from other parts of the holder.

Investigation on Fracture Mechanism of A356 during Thixo-Forging

2006 ◽  
Vol 116-117 ◽  
pp. 140-144 ◽  
Author(s):  
Kai Kun Wang ◽  
R. Kopp ◽  
Gerhard Hirt
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Melting Point ◽  
Fracture Mechanism ◽  
Liquid Fraction ◽  
Irregular Shape ◽  
High Melting ◽  
High Melting Point ◽  
Microstructural Changes ◽  
Transmission Electron

Transmission electron microscopy (TEM) was used to assess the microstructural changes accompanying semisolid molding of a creep resistant Mg-5%Al-2%Sr alloy. It was revealed that the processing created thixotropic morphologies with globular solids of α-Mg, having well-developed sub-structures. The quickly-solidified liquid fraction, enriched in Al and Sr, led to the formation of increased volumes of a lamellae type Al4Sr phase, surrounding the secondary α-Mg. Traces of Mg17Al12 still existed, predominantly as irregular shape compounds located mainly in grain interiors. Both the primary solid and high melting point precipitates of Mn-Al modified with Sr, acted as nucleation substrates for secondary α-Mg grains.

Synthesis of High-Temperature Silicides Via Rapid Solid-State Metathesis

1993 ◽  
Vol 322 ◽  
Author(s):  
Richard M. Jacubinas ◽  
Richard B. Kaner
Keyword(s):  
High Temperature ◽  
Solid State ◽  
Melting Point ◽  
Alkaline Earth ◽  
Elevated Temperatures ◽  
High Strength ◽  
Heat Of Formation ◽  
High Melting Point ◽  
Temperature Oxidation ◽  
Oxidation And Corrosion

AbstractMosi2 has a very favorable combination of materials properties, including a high melting point (2020°C), high strength at elevated temperatures, and resistance to high temperature oxidation and corrosion. These properties make it a good candidate for a hightemperature structural material; however, it has very poor ductility. A great deal of research has focused on improving the ductility of this alloy through various preparative routes. We have synthesized Mosi2, as well as WSi2, TaSi2, and NbSi2, using rapid solid-state metathesis reactions between a high oxidation state metal halide and an alkaline earth silicide. These reactions take advantage of the large exothermic heat of formation of the alkaline earth halide and can reach temperatures as high as the melting point of the product silicides. In addition, this approach yields crystalline products in seconds. The synthetic technique will be discussed along with characterization results.

TEM Study of a Creep-Resistant Mg-5Al-2Sr Alloy after Semisolid Molding

2006 ◽  
Vol 116-117 ◽  
pp. 136-139
Author(s):  
Frank Czerwinski ◽  
Anna Zielinska-Lipiec
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Melting Point ◽  
Liquid Fraction ◽  
Irregular Shape ◽  
High Melting ◽  
High Melting Point ◽  
Microstructural Changes ◽  
Transmission Electron

Transmission electron microscopy (TEM) was used to assess the microstructural changes accompanying semisolid molding of a creep resistant Mg-5%Al-2%Sr alloy. It was revealed that the processing created thixotropic morphologies with globular solids of α-Mg, having well-developed sub-structures. The quickly-solidified liquid fraction, enriched in Al and Sr, led to the formation of increased volumes of a lamellae type Al4Sr phase, surrounding the secondary α-Mg. Traces of Mg17Al12 still existed, predominantly as irregular shape compounds located mainly in grain interiors. Both the primary solid and high melting point precipitates of Mn-Al modified with Sr, acted as nucleation substrates for secondary α-Mg grains.

Phosphorus Precipitation in Si-Ge (30 at. %) Alloy

1973 ◽  
Vol 31 ◽  
pp. 146-147
Author(s):  
C. R. Hills ◽  
G. J. Thomas ◽  
J. K. Maurin
Keyword(s):  
Electron Microscopy ◽  
Strain Field ◽  
Structural Changes ◽  
Elevated Temperatures ◽  
Large Strain ◽  
Defect Clusters ◽  
Solution Treated ◽  
Transmission Electron ◽  
Heat Treated ◽  
Small Defect

Solution treated and quenched Si-Ge (30 at. %) alloy doped with phosphorus to a level of 1.54 × 1020 atoms/cm3 has been shown to increase in resistivity following aging at elevated temperatures. This effect is indicative of a loss of phosphorus from substitutional sites in the Si-Ge lattice and consequent precipitation of the excess phosphorus into electrically inactive centers. The structural changes occurring as a result of aging have been studied using transmission electron microscopy.Examination of the solution heat-treated material (1 hr. at 1000°C, then quenched) prior to aging revealed the presence of small defect clusters ranging in size from 20-80 Å, as well as larger defects approximately 200 Å in diameter exhibiting large strain field contrast.

A microstructural study of rapidly solidified and heat-treated austenitic Fe–Mn−Al–Mo–W–Nb–C alloys

1995 ◽  
Vol 10 (6) ◽  
pp. 1371-1378 ◽  
Author(s):  
Kwan H. Han ◽  
Hyun E. Lee
Keyword(s):  
Solidification Process ◽  
Vacancy Defect ◽  
Treatment Schedule ◽  
Depletion Effect ◽  
Transmission Electron ◽  
Heat Treated ◽  
Melt Spun ◽  
The Matrix ◽  
Means Of Transmission ◽  
Rapidly Solidified

The microstructural characteristics of melt-spun and heat-treated austenitic Fe−28Mn−8.6Al−0.5Mo−0.7W−0.5Nb−1.1C (in wt. %) alloys have been investigated by means of transmission electron microscopy. The melt-spun alloy contained fine austenitic cells and some intercelluar Nb(C, N) precipitates. Detailed observations revealed fine {100} modulations in the matrix of the cells, as well as a concomitant L′I2 atomic ordering arising from it. These observations indicate that the onset of decomposition of the initial austenite phase occurred during the rapid solidification process. Aging of the melt-spun alloy at 823–1173 K produced various microstructures, including a general precipitation of Nb(C, N) in the matrix. On isochronal annealing for 1 h, this matrix Nb(C, N) precipitation commenced at 1073 K with the formation of metastable coherent K-carbide (K′) near cell boundaries. On annealing at temperatures above 1123 K, only the Nb(C, N) precipitates were formed, on a fine scale, being accompanied by the formation of precipitate-free regions in the vicinity of cell and grain boundaries. Both intercellular and matrix Nb(C, N) precipitates obeyed a cube-to-cube orientation relationship with austenite. The general matrix precipitation of Nb(C, N) and formation of precipitate-free regions are discussed in terms of a vacancy (defect)-depletion effect. Finally, it was demonstrated that, by employing a double heat-treatment schedule of annealing at 1173 K followed by aging at 823 K, a novel microstructure consisting of fine dispersoids of Nb(C, N) carbo-nitride, distributed over the matrix of {100} modulated structure, could be produced.

HRTEM Study of Sputtered Cu-6at% Ta Films

1997 ◽  
Vol 3 (S2) ◽  
pp. 409-410
Author(s):  
Y. Liu ◽  
H. Wang ◽  
J. Mazumder ◽  
J.M. Rigsbee
Keyword(s):  
Research Laboratory ◽  
Elevated Temperatures ◽  
Cross Sectional ◽  
Metal Composites ◽  
University Of Illinois ◽  
High Mechanical Strength ◽  
Transmission Electron ◽  
Heat Treated ◽  
Materials Research ◽  
Cu Foil

Cu-refractory metal composites such as Cu-Ta alloys are attracting research interest because of their potential high electrical and thermal conductivity and high mechanical strength at elevated temperatures [1]. In the previous study, it has been shown that the hardness of Cu-Ta is three times of the Cu substrate [2] and the Ta was found to exist as discrete particle and aligned particles. In this presentation, we report the detailed study on the microstructure of the heat treated film and hot-pressed film.The Cu-6at%Ta films were deposited on Cu foil at 100°C by RF co-sputtering. The films examined in this study was hot-pressed under 35 MPa pressure at Ar atmosphere for 1 hour. Cross-sectional TEM samples were examined using a Hitachi 9000 high resolution transmission electron microscope (HRTEM) at the Center for Microanalysis, Materials Research Laboratory, University of Illinois at Urbana-Champaign.

Direct Observation of Crystalline Ordering In Naturally Graphitized Carbon Produced by Low Grade Metamorphism

1977 ◽  
Vol 35 ◽  
pp. 162-163
Author(s):  
Thomas R. McKee ◽  
Peter R. Buseck
Keyword(s):  
Crystallite Size ◽  
Sedimentary Rocks ◽  
Carbonaceous Material ◽  
Low Grade ◽  
X Ray ◽  
Graphitized Carbon ◽  
Transmission Electron ◽  
Heat Treated ◽  
Commercial Carbon ◽  
Metamorphic Zone

Sediments commonly contain organic material which appears as refractory carbonaceous material in metamorphosed sedimentary rocks. Grew and others have shown that relative carbon content, crystallite size, X-ray crystallinity and development of well-ordered graphite crystal structure of the carbonaceous material increases with increasing metamorphic grade. The graphitization process is irreversible and appears to be continous from the amorphous to the completely graphitized stage. The most dramatic chemical and crystallographic changes take place within the chlorite metamorphic zone.The detailed X-ray investigation of crystallite size and crystalline ordering is complex and can best be investigated by other means such as high resolution transmission electron microscopy (HRTEM). The natural graphitization series is similar to that for heat-treated commercial carbon blacks, which have been successfully studied by HRTEM (Ban and others).

Voids in Irradiated Tungsten and Molybdenum

1969 ◽  
Vol 27 ◽  
pp. 190-191
Author(s):  
Robert C. Rau ◽  
Robert L. Ladd
Keyword(s):  
Melting Point ◽  
Fast Neutron ◽  
Neutron Irradiation ◽  
Elevated Temperatures ◽  
Irradiation Temperature ◽  
The Body ◽  
Face Centered Cubic ◽  
Body Centered Cubic ◽  
Cubic Metals ◽  
Face Centered

Recent studies have shown the presence of voids in several face-centered cubic metals after neutron irradiation at elevated temperatures. These voids were found when the irradiation temperature was above 0.3 Tm where Tm is the absolute melting point, and were ascribed to the agglomeration of lattice vacancies resulting from fast neutron generated displacement cascades. The present paper reports the existence of similar voids in the body-centered cubic metals tungsten and molybdenum.

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