Oxygen induced chemical ordering and ultrafine lamellar structure formation in a Ti-48 at. % Al alloy

2002 ◽  
Vol 753 ◽  
Author(s):  
Williams Lefebvre ◽  
Annick Loiseau ◽  
Alain Menand
Keyword(s):  
Structure Formation ◽  
Lamellar Structure ◽  
Atom Probe ◽  
Nucleation And Growth ◽  
Al Alloy ◽  
Microstructure Development ◽  
Chemical Ordering ◽  
Transmission Electron ◽  
Critical Oxygen ◽  
Means Of Transmission

ABSTRACTInfluence of oxygen on the microstructure development of a Ti-48 at. % Al alloy has been investigated by means of transmission electron microscopy and 1D atom probe. Oxygen is found to significantly increase the temperature of the α → α2 chemical ordering reaction. As a consequence, above a critical oxygen content, the α → α2 transformation is substituted to the α → γm massive transformation when the Ti-48 Al alloy is quenched from the single a-phase field. In such a case, our pervious work has shown that the alloy exhibits a fully (α2 + γ) ultrafine lamellar structure. The present work gives a complete description of the ultrafine lamellar structure formation which, in opposition to the classical lamellar structure formation, involves an intragranular nucleation and growth of the γ phase within the α2 matrix.

Decomposition of Unstable Supersaturated Cu90Co10 Solid Solutions

1995 ◽  
Vol 400 ◽  
Author(s):  
Ralf Busch ◽  
Frank Gärtner ◽  
Christine Borchers ◽  
Peter Haasen ◽  
Rüdiger Bormann
Keyword(s):  
Heterogeneous Nucleation ◽  
Atom Probe ◽  
Nucleation And Growth ◽  
Growth Behavior ◽  
Nanometer Scale ◽  
Probe Field ◽  
Chemical Ordering ◽  
Transmission Electron ◽  
Composition Profiles ◽  
Ion Microscopy

AbstractHomogeneous Cu90Co10 alloys were prepared by rapid solidification using the meltspin technique. The decomposition process of this highly supersaturated unstable solid solution was investigated on a nanometer scale using a combination of atom probe field ion microscopy (AP/FIM) analyses and transmission electron microscopy.Annealing of the Cu90Co10 alloys at 440°C for various times leads to the formation of a compositional modulated microstructure within the grains. The composition profiles determined by AP/FIM analyses clearly exclude a classical nucleation and growth behavior of Co-rich particles. The microstructure is modulated with two different wavelengths. In addition, chemical ordering perpendicular to [111] directions of the fee lattice is observed.At the grain boundaries of this alloy, heterogeneous nucleation of pure Co particles is observed. This heterogeneous nucleation process competes with the decomposition within the grains.

Microstructure Evolution in the Atomized Droplets of Mg-9wt%Al Alloy

2010 ◽  
Vol 146-147 ◽  
pp. 1094-1101
Author(s):  
Fei Ding ◽  
Xiao Feng Wang
Keyword(s):  
Droplet Size ◽  
Microstructure Evolution ◽  
Eutectic Reaction ◽  
Solidification Process ◽  
Nucleation And Growth ◽  
Al Alloy ◽  
Microstructure Development ◽  
The Common ◽  
Kinetics Of ◽  
Common Action

A numerical model is developed to describe the kinetics of the microstructure evolution in an atomized droplet of Mg-9wt%Al alloy. The model is coupled with the heat transfer controlling equations to simulate the solidification process of the atomized droplets. The numerical results show that the microstructure development is a result of the common action of the nucleation and growth of grains. The nucleation events take place at a critical supercooling for a given droplet. As the droplet size decreases, the critical supercooling increases significantly. The volume fractions of the phases formed during the period of the recalescence, the segregated solidification and the eutectic reaction are sensitive to the droplet size. It is demonstrated that the developed model describes the microstructure evolution process well.

scholarly journals The Transport System of Nacre Components through the Surface Membrane of Gastropods

2016 ◽  
Vol 672 ◽  
pp. 103-112 ◽  
Author(s):  
Elena Macías-Sánchez ◽  
Antonio G. Checa ◽  
Marc G. Willinger
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Calcium Carbonate ◽  
Lamellar Structure ◽  
Surface Membrane ◽  
Organic Matrix ◽  
X Ray ◽  
Transmission Electron ◽  
Means Of Transmission ◽  
Electron Energy Loss

The surface membrane is a lamellar structure exclusive of gastropods that is formed during the shell secretion. It protects the surface of the growing nacre and it is located between the mantle epithelium and the mineralization compartment. At the mantle side of the surface membrane numerous vesicles provide material, and at the nacre side, the interlamellar membranes detach from the whole structure. Components of nacre (glycoproteins, polysaccharides and calcium carbonate) cross the structure to reach the mineralization compartment, but the mechanism by which this occurs is still unknown. In this paper we have investigated the ultrastructure of the surface membrane and the associated vesicle layer by means of Transmission Electron Microscopy. Electron Energy Loss Spectroscopy and Energy-dispersive X-ray Spectroscopy were used for elemental analysis. The analyses revealed the concentration of calcium in the studied structures: vesicles, surface membrane, and interlamellar membranes. We discuss the possible linkage of calcium to the organic matrix.

Substitution Effect of the Third Element X on the Morphology of A1/L12/D022 Three-Phase Microstructure in Ni-V-X (X=Si, Al) Alloy

2011 ◽  
Vol 172-174 ◽  
pp. 236-241
Author(s):  
Takao Kozakai ◽  
Daisuke Sakurai ◽  
Minoru Doi
Keyword(s):  
Electron Microscopy ◽  
Lamellar Structure ◽  
Lattice Mismatch ◽  
Morphological Changes ◽  
Substitution Effect ◽  
Al Alloy ◽  
The Third ◽  
Transmission Electron ◽  
Three Phase ◽  
Long Time

Morphology of phase-separated microstructure consisting of cubic disordered A1 and ordered L12 phases and tetragonal ordered D022 phase in Ni-V-X (X=Al, Si) alloys has been investigated by transmission electron microscopy. Ternary Ni-V-Al alloy showed the lamellar structure of D022 phase with spherical L12 particles, while Ni-V-Si ternary alloy indicated the anisotropic microstructure consisting of plate- or diamond-shaped D022 and plate-shaped L12 phases. When a part of element Al is substituted by Si, the morphology of three-phase microstructure (A1/L12/D022) varied depending on the amount of element substitution. When Ni-16.1V-4.0Al-2.8Si (at.%) alloy was aged at 1173K for long time, D022 plate-like particle aligned along <110> direction and L12 particles formed between them in the shape of sphere. In the case of Ni-16.6V-2.8Al-4.0Si (at%) alloy more substituted for Al by Si, cuboidal L12 phases were first formed aligning along <100> direction and then plate-shaped D022 phases precipitated along the <100> direction in the channel of cuboidal L12 particles. Such morphological changes with the substitution of the third elements X by Al or Si were able to be explained based on lattice mismatch.

Precipitation in AA2195 by Atom Probe Tomography and Transmission Electron Microscopy

2019 ◽  
Author(s):  
Muna Khushaim
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Atom Probe Tomography ◽  
Minimum Weight ◽  
Cost Effective ◽  
Atom Probe ◽  
Design Strategies ◽  
Transmission Electron ◽  
Consumption Cost ◽  
Means Of Transmission

The transportation industries are constantly striving to achieve minimum weight to cut fuel consumption and improve overall performance. Different innovative design strategies have been placed and directed toward weight saving combined with good mechanical behavior. Among different materials, aluminum-based alloys play a key role in modern engineering and are widely used in construction components because of their lightweight and superior mechanical properties. Introduction of different nanostructure features can improve the service and the physical properties of such alloys. In this study, alloy AA2195 has been selected and characterized by means of transmission electron microscopy and atom probe tomography. Quantitative chemical analyses reveal that applying the rolling deformation on the specimen causes the uniform distribution of different platelet precipitates such as T1(Al2CuLi) and θ′(Al2Cu), which increases the hardening behavior of such alloys. Applying a plastic deformation on such alloys has been highlighted as an important engineering tool for the manipulation with second-phase precipitates in the microstructure. In this study, the findings of the characterization analysis were translated to construct a robust microstructure with an excellent hardness behavior (hardness value of 209 HV) by applying a low-energy consumption, cost-effective method.

Atomic-Scale Segregation and Fluctuations in Chemical Ordering FePt Thin Films

2007 ◽  
Vol 1032 ◽  
Author(s):  
Karen L Torres ◽  
Chandan Srivastava ◽  
Richard L Martens ◽  
Gregory B Thompson
Keyword(s):  
Thin Films ◽  
Grain Boundaries ◽  
Atom Probe ◽  
Density Fluctuations ◽  
Atomic Scale ◽  
Chemical Ordering ◽  
Transmission Electron ◽  
Deposited Film ◽  
Deposited Films ◽  
Fept Thin Films

AbstractA series of atom probe and transmission electron microscopy (TEM) studies have been performed to quantify minute compositional fluctuations in Fe55Pt45 thin films during the A1 to L10 phase transformation. The atom probe specimens were analyzed in an Imago Local Electrode Atom Probe (LEAP®) at a target evaporation of 0.5%, a pulse fraction of 20% and a temperature of 120K. We noted a propensity of fracture failures in the LEAP with this material at lower temperatures. The atom probe reconstruction showed small levels of Pt segregation at grain boundaries in the as-deposited films. Fresnel-contrast TEM imaging confirmed high density fluctuations in these boundaries. Upon annealing at 600°C for 10 minutes, the film transformed from A1 to L10 and the grain boundaries become Fe enriched as compared to the as-deposited film.

scholarly journals THE MICROSTRUCTURE DEVELOPMENT DURING ISOTHERMAL AGEING STUDY OF AN Al-Mg-Si ALUMINUM ALLOY

2016 ◽  
Vol 22 (3) ◽  
pp. 138 ◽  
Author(s):  
Toufik Ziar ◽  
Hichem Farh ◽  
Rebai Guemini
Keyword(s):  
Aluminum Alloy ◽  
Early Stage ◽  
Alloy Sample ◽  
Microstructure Development ◽  
Transmission Electron ◽  
Ageing Study ◽  
The Matrix ◽  
Different Shapes ◽  
Isothermal Ageing ◽  
Means Of Transmission

<p class="Articletitle"><span lang="EN-US">The effects of isothermal ageing on the microstructure development of an Al-Mg-Si aluminum alloy have been investigated by means of transmission electron microscopy. From micrographs illustrating the micro structural change of the  alloy during iso­thermal ageing ; we can observe  in the water quenched alloy sample aged for 50 and 75 hours at 350</span><span lang="EN-GB">°</span><span lang="EN-US">C, dispersoid particles that were aligned along &lt;100&gt; matrix direction loosing their distribution at their early stage of precipitation with an increase in holding times. For the microstructure of the alloy ramp heated and aged at 450</span><span lang="EN-GB">°</span><span lang="EN-US">C for different holding times, we can clearly see dispersoid particles in their early stages of formation heterogeneously distributed with different shapes after an increase in holding times. These dispersoid particles exhibited strain field contrast when they are heated at low temperatures, that indicating they are coherent or semi-coherent with the matrix. A loss of coherency was observed for most of the dispersoid particles when they were aged with high holding times. </span></p>

Nucleation and growth processes of silicon nanowires

2004 ◽  
Vol 832 ◽  
Author(s):  
Seiji Takeda ◽  
Nobuhiko Ozaki ◽  
Kohei Ueda ◽  
Hideo Kohno ◽  
Jun Kikkawa ◽  
...  
Keyword(s):  
Silicon Nanowires ◽  
Nucleation And Growth ◽  
Scanning Tunneling ◽  
Present Moment ◽  
Tunneling Microscopy ◽  
Growth Processes ◽  
Transmission Electron ◽  
Vapor Liquid Solid Mechanism ◽  
Three Stages ◽  
Means Of Transmission

ABSTRACTWe have studied the nucleation and growth processes of silicon nanowires (SiNWs) by means of transmission electron microscopy and scanning tunneling microscopy. SiNWs are grown on hydrogen-terminated Si surface via the VLS (Vapor-Liquid-Solid) mechanism using silane (SiH4) as source gas. We have classified the growth process of SiNWs into three stages: the formation of nanocatalysts on a substrate, the nucleation of SiNWs in nanocatalysts, followed by the growth of SiNWs. We have shown that the structures of SiNWs are varied in several ways in each stage, and accordingly the structural properties of grown SiNWs can be modified to great extents. At the present moment, the phenomena at the each stage are not fully controlled, and this prevents us utilizing silicon nanowires more effectively.

TEM Observations of Precipitation of Coherent L12 and D022 Ordered Phases in Ni-V-Ge Alloys

2007 ◽  
Vol 561-565 ◽  
pp. 2365-2368 ◽  
Author(s):  
Yusuke Inuzuka ◽  
Shogo Ito ◽  
Takao Kozakai ◽  
Minoru Doi
Keyword(s):  
Electron Microscopy ◽  
Solid Solution ◽  
Transmission Electron Microscopy ◽  
Lamellar Structure ◽  
Supersaturated Solid Solution ◽  
Early Stage ◽  
Phase Separations ◽  
Transmission Electron ◽  
Ordered Phases ◽  
Means Of Transmission

Phase separations of A1 (γ) supersaturated solid solution into γ, cubic-L12 (γ') and tetragonal-D022 (γ") phases were investigated in Ni-V-Ge alloys by means of transmission electron microscopy (TEM). When Ni-15.8at%V-9.0at%Ge alloy is aged at 1073 K, at the early stage of ageing γ" phases are observed in the γ matrix as triangle- or diamond-shaped precipitates. With further ageing, colonies of lamellar structure consisting of two variants of γ" phase are dispersedly formed in the γ matrix and then γ" plates grow along the <110> direction. When Ni-14.5at%V-8.8.at%Ge alloy is isothermally annealed at 1023 K, first spherical γ' particles precipitate homogeneously in the γ matrix, followed by the formation of lamellar structure of γ" phases. In the course of further ageing, the lamellar structure develops, and only γ' particles around the lamellar structure grow and others gradually fade out.

Multiscale Characterization of the Ultrastructure of Normal and Osteoporotic Human Trabecular Bone

2002 ◽  
Author(s):  
Matthew A. Rubin ◽  
Iwona Jasiuk
Keyword(s):  
Electron Microscopy ◽  
Trabecular Bone ◽  
Hierarchical Structure ◽  
Lamellar Structure ◽  
Inbred Mice ◽  
Osteoporotic Bone ◽  
Human Trabecular Bone ◽  
Transmission Electron ◽  
The Hierarchical Structure ◽  
Means Of Transmission

In this paper we characterized hierarchical structure of healthy and osteoporotic human trabecular bone from microscale down to nanoscale. To characterize the hierarchical structure, trabecular bone was investigated at the microstructural level (i.e. trabecula, trabecular packets), sub-microstructural level (lamellar structure) and the nanostructural level (crystal-collagen collagen composite). There was an emphasis on evaluating the sub-microstructure and nanostructure of trabecular bone since detailed descriptions of the lamellar structure and of the crystal-collagen relationship in osteoporotic bone are relatively unknown. The ultrastructure of healthy and osteoporotic human trabecular bone was characterized experimentally by means of transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The experiments also involved studying trabecular bone from C57BL/6J and C3H/HeJ mice. These mice have nearly the same size and weight, but have very different bone density. Thus, they were good candidates for a comparative study of healthy and osteoporotic human trabecular bone. TEM and SEM were used to characterize the hierarchical microstructure of trabecular bone in the inbred mice. The understanding of the hierarchical nature of healthy and osteoporotic bone microstructure is needed for a deeper understanding of the state of bone health and its mechanical properties.

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