scholarly journals Direct observation of crystallization and melting with colloids

2019 ◽  
Vol 116 (4) ◽  
pp. 1180-1184 ◽  
Author(s):  
Hyerim Hwang ◽  
David A. Weitz ◽  
Frans Spaepen
Keyword(s):  
Energy Difference ◽  
Face Centered Cubic ◽  
Limited Growth ◽  
Free Energy Difference ◽  
Precise Control ◽  
Early Computer ◽  
Face Centered ◽  
Jump Frequencies ◽  
Kinetics Of ◽  
Kinetics Of Crystal Growth

We study the kinetics of crystal growth and melting of two types of colloidal crystals: body-centered cubic (BCC) crystals and face-centered cubic (FCC) crystals. A dielectrophoretic “electric bottle” confines colloids, enabling precise control of the motion of the interface. We track the particle motion, and by introducing a structural order parameter, we measure the jump frequencies of particles to and from the crystal and determine from these the free-energy difference between the phases and the interface mobility. We find that the interface is rough in both BCC and FCC cases. Moreover, the jump frequencies correspond to those expected from the random walk of the particles, which translates to collision-limited growth in metallic systems. The mobility of the BCC interface is greater than that of the FCC interface. In addition, contrary to the prediction of some early computer simulations, we show that there is no significant asymmetry between the mobilities for crystallization and melting.

Dynamic Transformation of Austenite at Temperatures above the Ae3

2018 ◽  
Vol 941 ◽  
pp. 633-638
Author(s):  
John Joseph Jonas ◽  
Clodualdo Aranas Jr. ◽  
Samuel F. Rodrigues
Keyword(s):  
Electron Microscopy ◽  
Driving Force ◽  
Energy Difference ◽  
Accelerated Cooling ◽  
Free Energy Difference ◽  
Dynamic Transformation ◽  
Plate Rolling ◽  
Temperature Transformation ◽  
Mn Steel ◽  
Kinetics Of

Under loading above the Ae3 temperature, austenite transforms displacively into Widmanstätten ferrite. Here the driving force for transformation is the net softening during the phase change while the obstacle consists of the free energy difference between austenite and ferrite as well as the work of shear accommodation and dilatation during the transformation. Once the driving force is higher than the obstacle, phase transformation occurs. This phenomenon was explored here by means of the optical and electron microscopy of a C-Mn steel deformed above their transformation temperatures. Strain-temperature-transformation (STT) curves are presented that accurately quantify the amount of dynamically formed ferrite; the kinetics of retransformation are also specified in the form of appropriate TTRT diagrams. This technique can be used to improve the models for transformation on accelerated cooling in strip and plate rolling.

scholarly journals Effects of Different Contents of Each Component on the Structural Stability and Mechanical Properties of Co-Cr-Fe-Ni High-Entropy Alloys

2021 ◽  
Vol 11 (6) ◽  
pp. 2832
Author(s):  
Haibo Liu ◽  
Cunlin Xin ◽  
Lei Liu ◽  
Chunqiang Zhuang
Keyword(s):  
Mechanical Properties ◽  
Structural Stability ◽  
High Entropy Alloys ◽  
Face Centered Cubic ◽  
Obvious Effect ◽  
High Entropy ◽  
Precise Control ◽  
Component Content ◽  
Face Centered ◽  
And Performance

The structural stability of high-entropy alloys (HEAs) is closely related to their mechanical properties. The precise control of the component content is a key step toward understanding their structural stability and further determining their mechanical properties. In this study, first-principle calculations were performed to investigate the effects of different contents of each component on the structural stability and mechanical properties of Co-Cr-Fe-Ni HEAs based on the supercell model. Co-Cr-Fe-Ni HEAs were constructed based on a single face-centered cubic (FCC) solid solution. Elemental components have a clear effect on their structure and performance; the Cr and Fe elements have an obvious effect on the structural stability and equilibrium lattice constant, respectively. The Ni elements have an obvious effect on stiffness. The Pugh ratios indicate that Cr and Ni addition may increase ductility, whereas Co and Fe addition may decrease it. With increasing Co and Fe contents or decreasing Cr and Ni contents, the structural stability and stiffness of Co-Cr-Fe-Ni HEAs are improved. The structural stability and mechanical properties may be related to the strength of the metallic bonding and covalent bonding inside Co-Cr-Fe-Ni HEAs, which, in turn, is determined by the change in element content. Our results provide the underlying insights needed to guide the optimization of Co-Cr-Fe-Ni HEAs with excellent mechanical properties.

Mechanical stability and strength of a single Au crystal

2008 ◽  
Vol 86 (7) ◽  
pp. 935-941 ◽  
Author(s):  
J -M Zhang ◽  
Y Yang ◽  
K -W Xu ◽  
V Ji
Keyword(s):  
Mechanical Stability ◽  
Energy Difference ◽  
Theoretical Strength ◽  
Stable Region ◽  
Embedded Atom Method ◽  
Face Centered Cubic ◽  
Embedded Atom ◽  
Free Body ◽  
Face Centered ◽  
Bcc Phase

The structural stability and theoretical strength of a Au face-centered cubic (FCC) crystal under uniaxial loading is investigated by combining the modified analytical embedded atom method (MAEAM) with Born stability criteria. The results show that under sufficient compression, there exists a stress-free body-centered cubic (BCC) phase, which is unstable and slips spontaneously to a stress-free metastable body-centered tetragonal phase by consuming internal energy. The structural energy difference between the BCC and FCC phases is in good agreement with the experimental value. The stable region ranged from –2.21 GPa to 6.31 GPa in the theoretical strength or from –9.83% to 7.87% in the strain correspondingly.PACS Nos.: 62.20.–x, 61.50.Ks, 81.05.Bx

scholarly journals Surface Induced Crystallization in Fibre Reinforced Nylon 6,6 Composites

1992 ◽  
Vol 1 (4) ◽  
pp. 096369359200100 ◽  
Author(s):  
N Klein ◽  
G Marom
Keyword(s):  
Fibre Surface ◽  
Energy Difference ◽  
Carbon Fibres ◽  
Free Energy Difference ◽  
Difference Function ◽  
Nylon 6,6 ◽  
Aramid Fibres ◽  
Transcrystalline Layer ◽  
Kinetics Of ◽  
Induced Crystallization

The present study deals with the growth of transcrystalline layer in Nylon 6,6 reinforced with HM pitch based carbon or aramid fibres. The kinetics of transcrystalline growth is investigated quantitatively. The surface energy parameters that are derived here, can be used to define a better criterion for the nucleation of transcrystallinity from the fibre surface. The free energy difference function, Δσ, as it appears in the classical theory of heterogeneous nucleation is calculated for both aramid and HM carbon fibres.

Effect of nanosilver on the thermal stability and thermal decomposition kinetics of poly(acetoacetoxyethyl methacrylate–styrene)

2018 ◽  
Vol 50 (8) ◽  
pp. 710-719
Author(s):  
Shengtao Gao ◽  
Honglong Xing
Keyword(s):  
Thermal Stability ◽  
Degradation Kinetics ◽  
Nitrate Solution ◽  
Silver Nitrate Solution ◽  
Thermal Degradation Kinetics ◽  
Face Centered Cubic ◽  
Transmission Electron ◽  
Face Centered ◽  
Kinetics Of ◽  
Better Than

Nanosilver/poly(acetoacetoxyethyl methacrylate–styrene) (nano-Ag/P(AAEM-St)) composites were synthesized via emulsifier-free emulsion with silver nitrate solution, AAEM, and St monomer copolymerization by ultrasonic. The morphology and structure of the composites were characterized by ultraviolet and visible spectroscopy, X-ray diffractometer, and transmission electron microscopy, respectively. The results show that Ag nanoparticles with face-centered cubic structure are homogeneously dispersed in the P(AAEM-St) matrix. The thermal stability and the thermal degradation kinetics of P(AAEM-St) were investigated using the thermogravimetric analysis and Kissinger and Flynn–Wall–Ozawa method, respectively. The results prove that the thermal stability of the pure P(AAEM-St) is better than that of the nano-Ag/P(AAEM-St) composites.

Structure of spinel/sesquioxide phase boundaries

1987 ◽  
Vol 45 ◽  
pp. 270-271
Author(s):  
L. A. Tietz ◽  
C. B. Carter
Keyword(s):  
Face Centered Cubic ◽  
Product Phase ◽  
Low Oxygen ◽  
Hexagonal Close Packed ◽  
Corundum Structure ◽  
Partial Pressures ◽  
Pure Matrix ◽  
Oxygen Anions ◽  
Face Centered ◽  
Kinetics Of

The spinel/sesquioxide ((A1-x,Bx)3O4/(A1-y,By)2O3) interphase interface can be formed by either an internal reduction or oxidation process. Internal reduction produces a dispersed product phase in the parent matrix instead of a continuous layer of product phase at the surface (external reduction). The kinetics of and thermodynamic criteria for internal reduction have been described. An (Al1-yFey) 2O3 solid solution, where y≤0.1, can be internally reduced at moderately high temperatures (T≥1300°C) and low oxygen partial pressures (pO2< 10-8) to produce a dispersion of nearly stoichiometric FeAl2O4 in an almost pure matrix of α-Al2C3 as can be seen by referring to a phase diagram of the second kind (pO2 vs. composition) for this system. FeAl2O4 has a cubic spinel structure which is based on a face-centered cubic (fee) arrangement of oxygen anions while α-Al2O3 has the corundum structure which is based on an hexagonal close-packed (hcp) arrangement of the oxygen anions. Alternatively, the spinel/sesquioxide phase boundary can be produced by oxidation, as in the oxidation of Nil-zFe2+zO4 to α-Fe2C3 (hematite) in a NiFe2O4 matrix.

Atomic structures and migration mechanisms of interphase boundaries during body- to face-centered cubic phase transformations

2019 ◽  
Vol 52 (5) ◽  
pp. 1176-1188 ◽  
Author(s):  
Yunhao Huang ◽  
Jincheng Wang ◽  
Zhijun Wang ◽  
Junjie Li
Keyword(s):  
Phase Transformations ◽  
Interphase Boundary ◽  
Cubic Phase ◽  
Face Centered Cubic ◽  
Orientation Relationships ◽  
Atomic Structures ◽  
Interphase Boundaries ◽  
Face Centered ◽  
And Migration ◽  
Kinetics Of

Atomic structures and migration mechanisms of interphase boundaries have been of scientific interest for many years owing to their significance in the field of phase transformations. Though the interphase boundary structures can be deduced from crystallographic investigations, the detailed atomic structures and migration mechanisms of interphase boundaries during phase transformations are still poorly understood. In this study, a systematic study on atomic structures and migration mechanisms of interphase boundaries in a body-centered cubic (b.c.c.) to face-centered cubic (f.c.c.) massive transformation was carried out using the phase-field crystal model. Simulation results show that the f.c.c./b.c.c. interphase boundaries can be classified into faceted interphase boundaries and side surfaces. The faceted interphase boundaries are semi-coherent with a group of dislocations, leading to a ledge migration mechanism, while the side surfaces are incoherent and thus migrate in a continuous way. After a careful analysis of the simulated migration process of interphase boundaries at atomic scales, a detailed description of the ledge mechanism based on the motion and nucleation of interphase boundary dislocations is presented. The ledge-forming process is accompanied by the nucleation of new heterogeneous dislocations and motions of original dislocations, and thus the barrier of ledge formation comes from the hindrance of these two dislocation behaviors. Once the ledge is formed, the original dislocations continue to advance until the ledge height reaches 1/|Δg|, where Δg represents the difference in reciprocal lattice vectors between two phases. The new heterogeneous dislocation moves along the radial direction of the interphase boundary, resulting in ledge extension. The interface dislocation behaviors greatly affect the migration of the interphase boundary, leading to different migration kinetics of faceted interphase boundaries under the Kurdjumov–Sachs and the Nishiyama–Wasserman orientation relationships. This study revealed the mechanisms and kinetics of complex structure transition during a b.c.c.–f.c.c. massive phase transformation and can shed some light on the process of solid phase transformations.

Theoretical Investigation of Carbon Atom Adsorption and Diffusion on the Surfaces of Cu

2014 ◽  
Vol 1082 ◽  
pp. 475-479
Author(s):  
Liang Qiao ◽  
Shu Jie Liu ◽  
Xiao Ying Hu ◽  
Li Li Wang ◽  
Dong Mei Bi
Keyword(s):  
Carbon Atom ◽  
First Principles ◽  
Density Functional ◽  
Energy Difference ◽  
Face Centered Cubic ◽  
Functional Theory ◽  
Hexagonal Close Packed ◽  
Adsorbed Carbon ◽  
Face Centered ◽  
And Diffusion

The adsorption and diffusion of carbon atom on Cu (111) and (100) surfaces have been investigated based on first-principles density-functional theory. For Cu (111) surface, the hexagonal close-packed and face-centered cubic sites are the most stable sites with little energy difference in the adsorption energy. For Cu (100) surface, the hollow site is the most stable. There is charge transfer from Cu surface to the adsorbed carbon atom. Moreover, the diffusions of carbon atom on Cu surfaces have been investigated, and the results show that the diffusion of carbon atom prefers to happen on Cu (111) surface.

scholarly journals Three-dimensional superlattice engineering with block copolymer epitaxy

2020 ◽  
Vol 6 (24) ◽  
pp. eaaz0002 ◽  
Author(s):  
Jiaxing Ren ◽  
Tamar Segal-Peretz ◽  
Chun Zhou ◽  
Gordon S. W. Craig ◽  
Paul F. Nealey
Keyword(s):  
Scanning Transmission Electron Microscopy ◽  
Three Dimensional ◽  
Honeycomb Lattice ◽  
Lattice Stability ◽  
Face Centered Cubic ◽  
Precise Control ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Face Centered ◽  
Atomic Lattices

Three-dimensional (3D) structures at the nanometer length scale play a crucial role in modern devices, but their fabrication using traditional top-down approaches is complex and expensive. Analogous to atomic lattices, block copolymers (BCPs) spontaneously form a rich variety of 3D nanostructures and have the potential to substantially simplify 3D nanofabrication. Here, we show that the 3D superlattice formed by BCP micelles can be controlled by lithographically defined 2D templates matching a crystallographic plane in the 3D superlattice. Using scanning transmission electron microscopy tomography, we demonstrate precise control over the lattice symmetry and orientation. Excellent ordering and substrate registration can be achieved, propagating through 284-nanometer-thick films. BCP epitaxy also showed exceptional lattice tunability, with a continuous Bain transformation from a body-centered cubic to a face-centered cubic lattice. Lattice stability was mediated by molecular packing frustration, and surface-induced lattice reconstruction was observed, leading to the formation of a unique honeycomb lattice.

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