Sample preparation of sub-micron precipitates in rapidly solidified Mg-20Nd

1988 ◽  
Vol 46 ◽  
pp. 984-985
Author(s):  
Ralph E. Omlor ◽  
Lt Erica Robertson ◽  
Pamela F. Lloyd
Keyword(s):  
Melt Spinning ◽  
Volume Fraction ◽  
Carbon Film ◽  
Large Volume Fraction ◽  
The Matrix ◽  
Carbon Coated ◽  
Order Of Magnitude ◽  
Rapidly Solidified ◽  
Oxide Precipitate ◽  
A Current

The Mg-20Nd melt spun ribbonsare being examined in depth because of their potentiodynamic polarization response as compared to that of 7075-T73 aluminum. The Mg-20Nd ribbon exhibited pseudopassivation behavior at a current density approximately one order of magnitude less than the aluminum alloy. In previous work, this was found to be due to the presence of a tessellatal precipitated network which formed in the ribbons during melt spinning. EDS results on TEM foils gave similar compositional values on both matrix and precipitates. These results were not trusted due to the small size and large volume fraction of the precipitates.The Mg-20Nd ribbon was swabbed with a dilute solution of sulfuric acid to loosen the particles in the matrix. A heavy oxide film was also formed on the surface at this time. Plastic replication solution was then applied to this surface and stripped away when dry. The particle side of the plastic film was then carbon coated. This film was placed on 3mm grids and the plastic dissolved away leaving the carbon film and the oxide precipitate mixture.

Microstructure of Rapidly Solidified Cu-Fe Alloys

1983 ◽  
Vol 28 ◽  
Author(s):  
Uwe Köster ◽  
Christoph Caesar
Keyword(s):  
Cross Sections ◽  
Contact Surface ◽  
Iron Content ◽  
Melt Spinning ◽  
Volume Fraction ◽  
Thermal Contact ◽  
Lattice Parameter ◽  
Good Thermal Contact ◽  
Fe Alloys ◽  
Rapidly Solidified

ABSTRACTRapidly solidified ribbons of Cu-Fe alloys with iron contents up to 20 at.−% have been prepared by melt-spinning. Optical and electron microscopy as well as x-ray and electron diffraction techniques were used to characterize quantitatively the microstructure, i.e., grain size and shape, solubility of iron, lattice parameter, volume fraction and distribution of precipitated iron-particles, etc.Whereas the free surfaces of melt-spun Cu-Fe ribbons have been found to be very smooth, the contact surfaces usually consist of isolated areas of good thermal contact with small equiaxed grains separated by bands without contact during casting and therefore poor heat transfer. The cross sections of the ribbons generally exhibit a strong anisotropy in their microstructure: very fine crystals adjacent to the contact surface develop into narrow columnar grains, generally significantly elongated and extending across the whole section. The average columnar width of the grains has been found to decrease significantly with increasing iron content. Precipitation of iron not only depends on the iron content but also on the distance from the contact surface.

scholarly journals Effects of Annealing on Microstructure and Mechanical Properties of Metastable Powder Metallurgy CoCrFeNiMo0.2 High Entropy Alloy

Entropy ◽  
2019 ◽  
Vol 21 (5) ◽  
pp. 448 ◽  
Author(s):  
Cui Zhang ◽  
Bin Liu ◽  
Yong Liu ◽  
Qihong Fang ◽  
Wenmin Guo ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Powder Metallurgy ◽  
Volume Fraction ◽  
High Entropy Alloy ◽  
High Entropy ◽  
Large Volume Fraction ◽  
The Matrix ◽  
Coarse Precipitation ◽  
Precipitation Enhancement ◽  
Precipitation Phase

A CoCrFeNiMo0.2 high entropy alloy (HEA) was prepared through powder metallurgy (P/M) process. The effects of annealing on microstructural evolution and mechanical properties of P/M HEAs were investigated. The results show that the P/M HEA exhibit a metastable FCC single-phase structure. Subsequently, annealing causes precipitation in the grains and at the grain boundaries simultaneously. As the temperature increases, the size of the precipitates grows, while the content of the precipitates tends to increase gradually first, and then decrease as the annealing temperature goes up to 1000 °C. As the annealing time is prolonged, the size and content of the precipitates gradually increases, eventually reaching a saturated stable value. The mechanical properties of the annealed alloys have a significant correspondence with the precipitation behavior. The larger the volume fraction and the size of the precipitates, the higher the strength and the lower the plasticity of the HEA. The CoCrFeNiMo0.2 high entropy alloy, which annealed at 800 °C for 72 h, exhibited the most excellent mechanical properties with the ultimate tensile strength of about 850 MPa and an elongation of about 30%. Nearly all of the annealed HEAs exhibit good strength–ductility combinations due to the significant precipitation enhancement and nanotwinning. The separation of the coarse precipitation phase and the matrix during the deformation process is the main reason for the formation of micropores. Formation of large volume fraction of micropores results in a decrease in the plasticity of the alloy.

HREM of Rapidly Solidified Al-Li-Zr Based Alloys

1990 ◽  
Vol 48 (1) ◽  
pp. 54-55
Author(s):  
V. Radmilovic ◽  
G. Thomas ◽  
R. Kilaas ◽  
N. J. Kim
Keyword(s):  
Volume Fraction ◽  
Solution Treatment ◽  
Aging Treatment ◽  
High Resolution Electron Microscopy ◽  
Image Simulation ◽  
Large Volume Fraction ◽  
Heat Treated ◽  
Resolution Electron ◽  
Rapidly Solidified

During aging of Al-Li-Zr based alloys δ'(Al3Li) precipitates heterogeneously around β'(Al3Zr), forming so-called composite precipitate[l-4], that has important effects on the mechanical behavior of these alloys. As has been observed in several investigations, the addition of small amount of Zr results in a fairly large volume fraction of β' in the microstructure, and this suggests that there may be a partitioning of Li in the β'. In the present investigation, high resolution electron microscopy (HREM) and image simulation have been used to perform detailed characterization of the chemistry and structure of β' precipitate.The alloy Al-3Li-1Cu-0.5Mg-0.5Zr (wt.%) has been heat treated as follows: a) solution treatment at 550°C for 2 hours and water quenching, b) aging treatment at 150°C for 4 hours or at 200°C for 8 hours and c) 10% cold working followed by aging at 175°C for 64 hours. HREM images were taken on a JEOL ARM electron microscope operating at 400 and 800kV. Simulated HREM images of the composite δ'/β' precipitate were calculated using CEMPAS multislice program described by Kilaas[5].

Bi2Te3 Nanowire Array/Epoxy Composites for Thermoelectric Power Generators and Microcoolers

2007 ◽  
Author(s):  
Kalapi G. Biswas ◽  
Vijay Rawat ◽  
Manuel DaSilva ◽  
Timothy D. Sands
Keyword(s):  
Thermal Conductivity ◽  
Thermoelectric Power ◽  
Structural Integrity ◽  
Volume Fraction ◽  
Nanowire Array ◽  
Scanning Electron Micrographs ◽  
Transmission Electron Microscopy Analysis ◽  
Power Generators ◽  
The Matrix ◽  
Order Of Magnitude

The thermal conductivity of a nanowire array composite is controlled by the matrix thermal conductivity and volume fraction, thus the effective thermoelectric figure-of-merit (ZT) of the composite will be reduced relative to that of the thermoelectric nanowire material alone. In this report, we demonstrate a process for fabricating nanowire array /epoxy composite with high structural integrity and low effective thermal conductivity required for thermoelectric power generation applications. Using galvanostatic electrodeposition into sacrificial porous anodic alumina (PAA) templates of 50 micron thickness, we synthesized dense (∼75% volume fraction) self-supporting nanowire arrays of textured Bi2Te3. X-ray diffraction and transmission electron microscopy analysis showed that the nanowires have <11.0> texture, the orientation that yields the highest ZT in single crystals. The nanowire array was infiltrated with SU-8 epoxy resin, a low thermal conductivity material (0.2 W/m-K) with a thermal conductivity that is about an order of magnitude lower than that of PAA (1.7 W/m-K). Scanning electron micrographs of fractured composites confirm nearly complete infiltration of SU-8 epoxy in nanowire array with good adhesion and high structural integrity.

Effect of Different Cooling Speed and Rare Earth La on the Microstructures and Phase Constitution of Al-Fe Alloy

2010 ◽  
Vol 44-47 ◽  
pp. 2126-2130 ◽  
Author(s):  
Guo Fa Mi ◽  
Cui Fen Dong ◽  
Da Wei Zhao
Keyword(s):  
Rare Earth ◽  
Melt Spinning ◽  
Metastable Phase ◽  
Melting Furnace ◽  
High Melting Point ◽  
The Matrix ◽  
Cooling Speed ◽  
Matrix Morphology ◽  
Rapidly Solidified ◽  
Rare Earth La

The casting, sub-rapid solidified and rapidly solidified A1-5Fe alloys, with or without rare earth La have been respectively prepared by vacuum melting furnace, suction casting and melt spinning furnace. And the alloys were investigated with OM, TEM and XRD. The results show that the microstructure was apparently refined by the increasing of cooling rate. Meanwhile, the acicular Al3Fe phase transferred to flower-like phase in casting A1-5Fe alloy and the matrix morphology of the alloy also was changed in sub-rapidly solidified Al-5Fe alloy, while 1.5wt% La was added. The metastable phase A16Fe and Al11La3 phase with high melting point were found in Al-5Fe alloy and A1-5Fe-1.5La alloy.

Extrinsic viscous anisotropy in two-phase aggregates, fabric parametrisation and application to mantle convection

2020 ◽  
Author(s):  
Albert de Montserrat Navarro ◽  
Manuele Faccenda
Keyword(s):  
Volume Fraction ◽  
Three Dimensional ◽  
Two Phase ◽  
Mantle Dynamics ◽  
Mineral Phases ◽  
Viscosity Contrast ◽  
The Matrix ◽  
Order Of Magnitude ◽  
Convection Patterns ◽  
Strong Inclusion

&lt;p&gt;Earth's mantle rocks are poly-aggregates where different mineral phases coexist.&amp;#160; These rocks may often be approximated as two-phase aggregates with a dominant phase and less abundant one (e.g. bridgmanite-ferropericlase aggregates in the lower mantle). Severe shearing of these rocks leads to a non-homogeneous partitioning of the strain between the different phases. The resulting bulk rock is mechanically not isotropic, and the elastic and the viscous tensor depend on the volume fraction and viscosity contrast between the mineral phases and the fabric.&lt;/p&gt;&lt;p&gt;Here we employ three-dimensional mechanical models to reproduce and parametrise fabrics typical of mantle rocks and quantify the evolution of the viscous tensor. These fabrics are produced by shearing a mechanically heterogeneous medium comprised by randomly distributed isotropic inclusions embedded in: i) a weak inclusion-strong matrix aggregate where strain is mainly accommodated by the weak phase, that flattens and yields a penetrative foliation; and, ii) a strong inclusion-weak matrix where strain is mainly accommodated by the matrix, in this case, the strong phase deforms primarily parallel to the direction of the flow, producing cigar-shaped inclusions.&lt;/p&gt;&lt;p&gt;Finally, we combine the fabric parametrisation of a two-phase aggregate with the Differential Effective Medium (DEM) theory to study the evolution of the viscous tensor and its effects in mantle dynamics. The results of two-dimensional models of thermal convection show that a viscosity contrast of one order of magnitude between the two mineral phases is enough to deflect mantle plumes and produce convection patterns that differ considerably from the ideal isotropic media.&lt;/p&gt;

The strengthening of metals by dispersed particles

1964 ◽  
Vol 282 (1388) ◽  
pp. 63-79 ◽  
Keyword(s):  
Metal Matrix ◽  
Volume Fraction ◽  
Dislocation Motion ◽  
Model Systems ◽  
Dispersed Phase ◽  
Strong Phase ◽  
Large Volume Fraction ◽  
Density Of Dislocations ◽  
Dispersed Particles ◽  
The Matrix

A review is made of the yield strength attainable by dispersing particles in a metal matrix in order to hinder dislocation motion. The advantages and drawbacks of the various methods used to introduce the particles are considered. The greatest strengths are found in materials containing a large volume fraction of dispersed phase coupled with a high density of dislocations in the matrix. The greatest strengths should be achieved if the dispersed particles are very strong and are loaded to fracture. To load the particles they must be needle-shaped. Experiments on model systems of a metal containing wires to simulate the strong phase are described. These indicate some of the conditions necessary to obtain maximum strength and suggest how extreme brittleness can be avoided.

Rare Earth Oxide Dispersoid Stability and Microstructural Effects in Rapidly Solidified Ti3Al and Ti3A1-Nb

1985 ◽  
Vol 58 ◽  
Author(s):  
J. A. Sutliff ◽  
R. G. Rowe
Keyword(s):  
Rare Earth ◽  
Titanium Aluminide ◽  
Melt Spinning ◽  
Analytical Electron Microscopy ◽  
Rare Earth Oxide ◽  
Microstructural Effects ◽  
Analytical Electron ◽  
The Matrix ◽  
Rapidly Solidified ◽  
Titanium Aluminide Alloys

ABSTRACTThe microstructures of titanium aluminide alloys containing a rare earth oxide dispersion have been characterized using analytical electron microscopy. The alloys, based on Ti3A1 (alpha-2), contained 0 to 10.7 atom% Nb and 0.5 atom% Er. Alloys were rapidly solidified by melt spinning and were subsequently consolidated by HIP and extrusion. The microstructure of each alloy was examined in the as-cast, as-HIP'ed, and as-extruded conditions. A fine dispersoid spaced less than 100 nm apart was observed in ribbon aged at 750°C. The effects of processing conditions on the dispersoid distribution as a function of matrix chemistry were studied. Hot deformation was also examined to investigate the nature of the interaction between the dispersoids and the matrix during deformation.

Stress Analysis of Carbon Nanotubes Reinforced Nanocomposites

2013 ◽  
Vol 284-287 ◽  
pp. 357-361
Author(s):  
Shiuh Chuan Her ◽  
Shou Jan Liu
Keyword(s):  
Carbon Nanotubes ◽  
Carbon Nanotube ◽  
Stress Analysis ◽  
Volume Fraction ◽  
Interfacial Shear Stress ◽  
Stress Transfer ◽  
Large Volume Fraction ◽  
Concentric Cylinders ◽  
The Matrix ◽  
Lag Model

Stress transfer in the carbon nanotube reinforced nanocomposites is investigated in this work. The model consists of two concentric cylinders, namely, a single-walled carbon nanotube cylinder (SWCNT) and a matrix cylinder, as the representative volume element (RVE). The stress analysis is performed using the shear lag model for the axisymmetric RVE. Analytical solutions for the axial normal stresses in the SWCNT and matrix, and the interfacial shear stress across the SWCNT/matrix interface are obtained. Numerical results show that using a large volume fraction improves the efficiency of the stress transfer from the matrix to the carbon nanotubes.

Formation and Stability of Quasicrystalline and Hexagonal Approximant Phases in an Al–Mn–Be Alloy

2002 ◽  
Vol 17 (7) ◽  
pp. 1671-1677 ◽  
Author(s):  
G. S. Song ◽  
E. Fleury ◽  
S. H. Kim ◽  
W. T. Kim ◽  
D. H. Kim
Keyword(s):  
Thermal Stability ◽  
Phase Formation ◽  
Melt Spinning ◽  
Volume Fraction ◽  
Icosahedral Phase ◽  
Primary Phase ◽  
Solid Matrix ◽  
Two Phase ◽  
Large Volume Fraction ◽  
Faceted Particles

Phase formation and thermal stability for an Al–Mn–Be alloy have been investigated by melt-spinning and conventional casting. Significant differences in the phase formation and the thermal stability of the microstructure were found as a result of the different cooling rates. In the melt-spun ribbons, a large volume fraction of a metastable icosahedral phase was found to coexist with an Al solid solution. In the bulk cast ingots, the primary phase formed in the two-phase microstructure was a hexagonal approximant phase of quasicrystals. This phase that solidified in the form of faceted particles embedded in the Al solid matrix proved to be thermodynamically stable during annealing at 540 °C for 100 h. The effect of Be addition on the formation of the stable approximant phase is discussed in terms of the Hume–Rothery mechanism.

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