Numerical Simulation of Solidified Structure Formation of Al-Si Alloy Casting Using Cellular Automaton Method

2008 ◽  
Vol 575-578 ◽  
pp. 154-163 ◽  
Author(s):  
Kenichi Ohsasa ◽  
Kiyotaka Matsuura ◽  
Kazuya Kurokawa ◽  
Seiichi Watanabe
Keyword(s):  
Numerical Simulation ◽  
Cellular Automaton ◽  
Structure Formation ◽  
Nucleation Rate ◽  
Heterogeneous Nucleation ◽  
Big Bang ◽  
Grain Structure ◽  
Alloy Casting ◽  
Undercooled Melt ◽  
Columnar To Equiaxed Transition

For the purpose of the prediction of casting structures, heterogeneous nucleation rate in the undercooled melt of solififying Al-Si alloys were evaluated by comparing experimentally observed macrostructures of solidified ingots with numerically simulated ones. Molten alloys were unidirectionally solidified in an adiabatic mold from a steel chill block located at the bottom of the mold. In the experiment, columnar to equiaxed transition (CET) was observed. A numerical simulation for grain structure formation of the sample ingots was carried out using a cellular automaton (CA) method, and heterogeneous nucleation rate in the solidifying alloys were evaluated by producing the similar structures to experimental ones. An attempt was made to predict the grain structure of conventionally cast ingots using the evaluated heterogeneous nucleation rate. However, the simulation could not predict the structure of ingot with low superheat due to crystal multiplication near the mold wall. The crystal multiplication mechanism, so-called "Big Bang mechanism", was introduced into the simulation and the simulation could predict the grain macrostructure composed of columnar and equiaxed crystals that were similar to experimentally observed one.

Grain Structure Formation Ahead of Tool during Friction Stir Welding of AZ31 Magnesium Alloy

2010 ◽  
Vol 160 ◽  
pp. 313-318 ◽  
Author(s):  
Uceu Suhuddin ◽  
Sergey Mironov ◽  
H. Takahashi ◽  
Yutaka S. Sato ◽  
Hiroyuki Kokawa ◽  
...  
Keyword(s):  
Friction Stir Welding ◽  
Magnesium Alloy ◽  
Structure Formation ◽  
Material Flow ◽  
Boundary Migration ◽  
Deformation Mode ◽  
Grain Structure ◽  
Az31 Magnesium Alloy ◽  
Structure Evolution ◽  
Friction Stir

The “stop-action” technique was employed to study grain structure evolution during friction-stir welding of AZ31 magnesium alloy. The grain structure formation was found to be mainly governed by the combination of the continuous and discontinuous recrystallization but also involved geometric effect of strain and local grain boundary migration. Orientation measurements showed that the deformation mode was very close to the simple shear associated with the rotating pin and material flow arose mainly from basal slip.

scholarly journals Controlling Condensation of Water Using Hybrid Hydrophobic-Hydrophilic Surfaces

2010 ◽  
Author(s):  
Kripa K. Varanasi ◽  
Tao Deng
Keyword(s):  
Nucleation Rate ◽  
Heterogeneous Nucleation ◽  
Energy Barrier ◽  
Superhydrophobic Surfaces ◽  
Industrial Processes ◽  
Spatial Control ◽  
Hydrophilic Surfaces ◽  
Wide Range ◽  
First Time ◽  
Control Water

Heterogeneous nucleation of water plays an important role in wide range of natural and industrial processes. Though heterogeneous nucleation of water is ubiquitous and everyday experience, spatial control of this important phenomenon is extremely difficult. Here we show, for the first time, that spatial control in the heterogeneous nucleation of water can be achieved by manipulating the local nucleation energy barrier and nucleation rate via the modification of the local intrinsic wettability of a surface by patterning hybrid hydrophobic-hydrophilic regions on a surface. Such ability to control water nucleation could address the condensation-related limitations of superhydrophobic surfaces, and has implications for efficiency enhancements in energy and desalination systems.

Effect of Homogenization Treatment on Superplastic Properties of Aluminum Based Alloy with Minor Zr and Sc Additions

2018 ◽  
Vol 385 ◽  
pp. 84-90 ◽  
Author(s):  
Anna Kishchik ◽  
Anastasia V. Mikhaylovskaya ◽  
Anton D. Kotov ◽  
Vladimir K. Portnoy
Keyword(s):  
Strain Rate ◽  
Heterogeneous Nucleation ◽  
Constant Strain Rate ◽  
Grain Structure ◽  
Treatment Mode ◽  
Homogenization Treatment ◽  
Superplastic Behaviour ◽  
One Step ◽  
Cold Rolled ◽  
Superplastic Properties

Effect of one-step and two-step homogenization treatment on precipitation of Al3(Sc,Zr) dispersoids, grain structure after annealing of cold rolled sheets and superplastic behaviour of a novel Al-Mg based alloy were studied. Heterogeneous nucleation of Al3(Sc,Zr) phase on dislocations and subboundaries dominated at one-step annealing and both homogeneous and heterogeneous nucleation of Al3(Sc,Zr) were observed at two-step annealing modes. It was shown that two-step treatment mode provides high density of Al3(Sc,Zr) precipitates and 650 % of elongation at the constant strain rate of 10-2 s-1 in the studied alloy.

scholarly journals The holographic spacetime model of cosmology

2018 ◽  
Vol 27 (14) ◽  
pp. 1846005 ◽  
Author(s):  
Tom Banks ◽  
W. Fischler
Keyword(s):  
Dark Matter ◽  
Gravitational Waves ◽  
Structure Formation ◽  
Big Bang ◽  
Baryon Asymmetry ◽  
Gaussian Fluctuations ◽  
Primordial Gravitational Waves ◽  
Conventional Models ◽  
Non Gaussian ◽  
The Big Bang

This essay outlines the Holographic Spacetime (HST) theory of cosmology and its relation to conventional theories of inflation. The predictions of the theory are compatible with observations, and one must hope for data on primordial gravitational waves or non-Gaussian fluctuations to distinguish it from conventional models. The model predicts an early era of structure formation, prior to the Big Bang. Understanding the fate of those structures requires complicated simulations that have not yet been done. The result of those calculations might falsify the model, or might provide a very economical framework for explaining dark matter and the generation of the baryon asymmetry.

Simulation of crystallization of the melt modified by nanoscale particles during laser treatment of a metal surface

2021 ◽  
Vol 1 ◽  
pp. 5-14
Author(s):  
V.N. Popov ◽  
Keyword(s):  
Numerical Simulation ◽  
Surface Layer ◽  
Stokes Equations ◽  
Solid Phase ◽  
Laser Action ◽  
Heat Removal ◽  
Boussinesq Approximation ◽  
Grain Structure ◽  
Homogeneous Distribution ◽  
Dissolved Carbon

A 2D mathematical model is proposed for the modification of an iron-based alloy with refractory nanosized particles. Numerical simulation of the processes during the modification of the surface layer of the substrate metal using the energy of a laser pulse has been carried out. Within the framework of the proposed model, the processes of heating and melting of metal on a substrate covered with a layer of nanosized refractory particles penetrating into the molten metal, convective heat transfer in the melt, and solidification after the end of the pulse are considered. Metal melting is considered in the Stefan approximation, and when the melt is cooled, the model of heterogeneous nucleation and subsequent crystallization is used. The fluid flow is described by the Navier-Stokes equations in the Boussinesq approximation. The distribution of nanoparticles in the melt is modeled by moving markers. Based on the results of calculations, the mode of pulsed laser action is determined, in which a flow is formed for a homogeneous distribution of particles of the modifying substance in the presence of a surfactant in the metal. The volume of the solid phase formed around the nucleus determines the size of the grain structure in the solidified alloy. The liquidus temperature changes depending on the concentration of dissolved carbon in the melt. In the numerical simulation of the solidification of the surface layer of the metal, it was found that the conditions of nucleation and crystallization differ significantly in the volume of the melt. It is determined that the duration of nucleation in a supercooled melt is several tens of microseconds. The maximum number of crystallization centers occurs in areas where heat removal occurs most rapidly. With the growth of the solid phase in the melt and the release of the latent heat of crystallization, the value of supercooling decreases, the nucleation stops and the number of formed crystallization centers does not change further. The distribution of the dispersion of the crystal structure over the volume of the melted metal is estimated. It was found that as the melt cools, sequential-volume crystallization occurs.

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