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.

Composition Fluctuations in the Ostwald Ripening

2008 ◽  
Vol 277 ◽  
pp. 187-192
Author(s):  
G.V. Lutsenko ◽  
Andriy Gusak
Keyword(s):  
Computer Simulation ◽  
Particle Size ◽  
Large Volume ◽  
Ostwald Ripening ◽  
Volume Fraction ◽  
Size Distributions ◽  
Particle Size Distributions ◽  
Two Phase ◽  
Large Volume Fraction ◽  
Composition Fluctuations

The Ostwald ripening of a two-phase binary alloy has been considered for case of “large” volume fraction of precipitating phase. The approach is proposed in which the composition fluctuations into the vicinity of particles are considered. In this approach the evolution of particle size distributions is analyzed using the computer simulation.

Icosahedral Phase Formation Domain in Al–Cu–Fe System by Mechanical Alloying

2002 ◽  
Vol 17 (3) ◽  
pp. 653-659 ◽  
Author(s):  
P. Barua ◽  
B. S. Murty ◽  
B. K. Mathur ◽  
V. Srinivas
Keyword(s):  
Mechanical Alloying ◽  
Phase Formation ◽  
Volume Fraction ◽  
Structural Evolution ◽  
Icosahedral Phase ◽  
X Ray Diffraction ◽  
Transmission Electron ◽  
Metal Ratio ◽  
First Time ◽  
Systematic Composition

A systematic composition dependence study on icosahedral phase (i-phase) formation in the Al–Cu–Fe system has been carried out. Structural evolution during mechanical alloying and on subsequent heat treatment has been investigated by x-ray diffraction and transmission electron microscopy. The i-phase is observed to evolve from the reaction between the Al2Cu and b phases. The influence of the Cu to Fe ratio (RCuFe), Al to transition metal ratio (RAlTM), and the electron to atom ratio (e/a) on the volume fraction of the i-phase has been studied. The analysis of the present results and those published earlier indicates that quasicrystal-forming ability correlates better with the RAlTM and e/a ratios. The volume fraction of the i-phase is maximum when the RAlTM ˜ 2.3 and e/a ratio ˜ 2.0. Formation of the i-phase in Al65Cu25Fe10 by mechanical alloying is reported for the first time.

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.

Analysis of Steady Compaction Waves in Porous Materials

1989 ◽  
Vol 56 (1) ◽  
pp. 15-24 ◽  
Author(s):  
J. M. Powers ◽  
D. S. Stewart ◽  
Herman Krier
Keyword(s):  
Porous Materials ◽  
Volume Fraction ◽  
Matrix Material ◽  
Wave Structure ◽  
Solid Matrix ◽  
Tait Equation ◽  
Two Phase ◽  
Piston Velocity ◽  
Zone Length ◽  
Compaction Waves

A two-phase continuum mixture model is used to analyze steady compaction waves in porous materials. It is shown that such a model admits both subsonic and supersonic steady compaction waves in response to a piston-driven boundary condition when a Tait equation is used to describe a solid matrix material and a generic static compaction relation is used to describe collapse of the matrix. Parameters for the Tait equation are chosen to match shock and compaction wave data. The model is able to predict compaction wave speed, final pressure, and final volume fraction in porous HMX. The structure of the compaction wave is also studied. A shock preceding the compaction wave structure is predicted for compaction waves travelling faster than the ambient sound speed of the solid. For subsonic compaction waves no leading shock is predicted. The compaction zone length is studied as a function of initial volume fraction, piston velocity, and compaction viscosity.

In situ TEM observations of melting in nanosized eutectic Pb-Cd inclusions embedded in Al

1996 ◽  
Vol 54 ◽  
pp. 986-987
Author(s):  
S. Hagège ◽  
U. Dahmen ◽  
E. Johnson ◽  
A. Johansen ◽  
V.S. Tuboltsev
Keyword(s):  
Electron Microscope ◽  
Melt Spinning ◽  
Ternary Alloys ◽  
Solid Matrix ◽  
Eutectic System ◽  
In Situ Tem ◽  
In Situ Observation ◽  
Orientation Relationships ◽  
Transmission Electron

Small particles of a low-melting phase embedded in a solid matrix with a higher melting point offer the possibility of studying the mechanisms of melting and solidification directly by in-situ observation in a transmission electron microscope. Previous studies of Pb, Cd and other low-melting inclusions embedded in an Al matrix have shown well-defined orientation relationships, strongly faceted shapes, and an unusual size-dependent superheating before melting.[e.g. 1,2].In the present study we have examined the shapes and thermal behavior of eutectic Pb-Cd inclusions in Al. Pb and Cd form a simple eutectic system with each other, but both elements are insoluble in solid Al. Ternary alloys of Al (Pb,Cd) were prepared from high purity elements by melt spinning or by sequential ion implantation of the two alloying additions to achieve a total alloying addition of up to lat%. TEM observations were made using a heating stage in a 200kV electron microscope equipped with a video system for recording dynamic behavior.

scholarly journals Numerical Study on an Interface Compression Method for the Volume of Fluid Approach

Fluids ◽  
2021 ◽  
Vol 6 (2) ◽  
pp. 80
Author(s):  
Yuria Okagaki ◽  
Taisuke Yonomoto ◽  
Masahiro Ishigaki ◽  
Yoshiyasu Hirose
Keyword(s):  
Linear Theory ◽  
Volume Fraction ◽  
Numerical Study ◽  
Volume Of Fluid ◽  
Interfacial Wave ◽  
Validation Process ◽  
Two Phase ◽  
Numerical Diffusion ◽  
Mesh Resolution ◽  
Water Reactors

Many thermohydraulic issues about the safety of light water reactors are related to complicated two-phase flow phenomena. In these phenomena, computational fluid dynamics (CFD) analysis using the volume of fluid (VOF) method causes numerical diffusion generated by the first-order upwind scheme used in the convection term of the volume fraction equation. Thus, in this study, we focused on an interface compression (IC) method for such a VOF approach; this technique prevents numerical diffusion issues and maintains boundedness and conservation with negative diffusion. First, on a sufficiently high mesh resolution and without the IC method, the validation process was considered by comparing the amplitude growth of the interfacial wave between a two-dimensional gas sheet and a quiescent liquid using the linear theory. The disturbance growth rates were consistent with the linear theory, and the validation process was considered appropriate. Then, this validation process confirmed the effects of the IC method on numerical diffusion, and we derived the optimum value of the IC coefficient, which is the parameter that controls the numerical diffusion.

scholarly journals Effects of Polydispersity on the Phase Behavior of Additive Hard Spheres in Solution

Molecules ◽  
2021 ◽  
Vol 26 (6) ◽  
pp. 1543
Author(s):  
Luka Sturtewagen ◽  
Erik van der Linden
Keyword(s):  
Phase Behavior ◽  
Critical Point ◽  
Volume Fraction ◽  
Hard Spheres ◽  
Second Virial Coefficient ◽  
Two Phase ◽  
Different Types ◽  
Asymmetric Partitioning ◽  
Average Size ◽  
Liquid Liquid Phase Separation

The ability to separate enzymes, nucleic acids, cells, and viruses is an important asset in life sciences. This can be realised by using their spontaneous asymmetric partitioning over two macromolecular aqueous phases in equilibrium with one another. Such phases can already form while mixing two different types of macromolecules in water. We investigate the effect of polydispersity of the macromolecules on the two-phase formation. We study theoretically the phase behavior of a model polydisperse system: an asymmetric binary mixture of hard spheres, of which the smaller component is monodisperse and the larger component is polydisperse. The interactions are modelled in terms of the second virial coefficient and are assumed to be additive hard sphere interactions. The polydisperse component is subdivided into sub-components and has an average size ten times the size of the monodisperse component. We calculate the theoretical liquid–liquid phase separation boundary (the binodal), the critical point, and the spinodal. We vary the distribution of the polydisperse component in terms of skewness, modality, polydispersity, and number of sub-components. We compare the phase behavior of the polydisperse mixtures with their concomittant monodisperse mixtures. We find that the largest species in the larger (polydisperse) component causes the largest shift in the position of the phase boundary, critical point, and spinodal compared to the binary monodisperse binary mixtures. The polydisperse component also shows fractionation. The smaller species of the polydisperse component favor the phase enriched in the smaller component. This phase also has a higher-volume fraction compared to the monodisperse mixture.

Sol-Gel Derived Titania/Hydroxyapatite Layer on Titanium Substrate

2011 ◽  
Vol 117-119 ◽  
pp. 332-334 ◽  
Author(s):  
Wen Yan Wang ◽  
Yu Wu ◽  
Jing Pei Xie ◽  
Gao Lu ◽  
Xiao Ming Dong ◽  
...  
Keyword(s):  
Heat Treatment ◽  
Surface Quality ◽  
Phase Formation ◽  
Volume Fraction ◽  
Sol Gel ◽  
Calcium Nitrate ◽  
Titanium Substrate ◽  
Gel Method ◽  
Good Surface ◽  
Coating Method

In this study, calcium nitrate(Ca(NO3)2•4H2O) and phosphorus pentoxide(P2O5) were used as precursor to prepare hydroxyapatite(HA) layer by sol-gel method, followed by a dipping-coating method to coat HA layer onto Ti. Phase formation and microstructure were investigated by XRD and SEM to study the influence of atmosphere on the property of HA layer. The results revealed that there exists no large cracks in the layer which was heated in the nitrogen, leading to a good surface quality compared with the layer which was heated in the air. And there is no obvious difference in crystallinity and volume fraction of HA in the layer when adopting heat treatment in different atmospheres.

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