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Search the history of over billion web pages on the Internet. Greer, MD All rights reserved. No part of this book may be reproduced in any form or by any electronic or mechanical means including information and retrieval systems without prior permission from the publisher in writing.
Hidden truth, forbidden knowledge: Center for the Study of Extraterrestrial Intelligence—Biography 3. Unidentified flying objects—Sightings and encounters.
Box Crozet, VA Produced by: The Evidence and Implications" ''Disclosure: Greer's books or for more information about the Disclosure Project: Box Crozet, VA Acknowledgements My heartfelt thanks to the following people who directly helped with "Hidden Truth - Forbidden Knowledge" and to the many, many others - too numerous to count - who have supported my work over the years.
Norm Fletcher who took his time at the book dictation to take care of all the taping; Joan Korenbilt and Vicki Longhofer for their help with the editing; Brian O'Leary for the foreword; Ron Russell for his artwork for the cover; Joel Howard for his graphic skills; Jan Bravo for her devoted support in every way and my wife, Emily for her support and love and her help in her position as - as one of the witnesses called her - "Chief of Staff".
Allen Hynek The human experiment on planet Earth is on the verge of self- destruction. Looking at the threats of nuclear war, the chemical and bio- logical ecocide, global climate change, proliferating weapons on Earth and in space, the greed of corpora- tions, and the gross cronyism and mis- management of the U.
Barely Do we have any hope? My answer is, we can only try And if we do try, where can we find the answers? Having left my career as a mainstream space sci- entist at Princeton University and Science Applications International Corporation, I was then beginning to liberate myself from the confines and expectations of West- ern science. Now I felt free to explore and express our transcen- dent reality So was Steve. Greer and I talked into the night when we first met.
We began to make connections we were both just beginning to understand: Since then, Steve has provided amazing leadership in penetrating the mysteries not only of the phenomenon itself, but the shadowy corners of U. As a result, Dr. Greer has proven himself time and time again as a fearless and energetic warrior on the leading edge of planetary change.
First he founded the Center for the Study of Extraterrestrial Intelligence CSETI , in which he introduced the concept of ambassadorship between hu- mans and off-planet cultures — but this time not merely science fiction. Holding all- night expeditions in UFO hot spots around the world, his groups would vector in viii craft through the use of lights, sounds and visualization which he coined as Close Encounters of a Fifth Kind, aka.
The workshops continue to be offered to in- terested students. These revelations under- score a long, sordid history of governmental and media secrecy and the acquisition of technologies such as microelectronics, anti-gravity propulsion and zero-point, or "free" energy, from our visitors. This massive cover-up has been going on for almost six decades, since the UFO crash near Roswell, New Mexico in July , an event which was certainly not caused by balloons, as alleged by the U.
Such myths are only accepted by the ignorant or the powerful and their subjects. Greer's pioneering work on disclosure inevitably led to further understand- ing the depth and credibility of ET contact accounts as well as the cover-up itself, for example, the "above top secret" research going on near the infamous Groom Lake, Nevada and elsewhere.
Steve Greer is a spiritual warrior of high calling, juxtaposed against those forces identifying themselves as the "United States". The latter are criminals who must be brought to justice, for so many reasons evident to ever more of us, as we watch the fall of the American empire. It's a story about disclosure of the greatest mysteries of our time from a courageous soul unbeholden to the tyrannies that grip us in the most powerful nation on Earth.
Just as importantly, it provides us with a narrative of the benign nature of these off-planet cultures, that we are being visited by those who are empathetic about the human condition, while at the same time not directly interfering the so-called Prime Directive made famous by Star Trek.
It is sobering to think that, only since the United States pioneered the nuclear age in , causing the most frightening devastation of Hiroshima and Nagasaki, the modern sightings, contacts and technology transfers have been taking place. The long-range atomic bombers were stationed in Roswell, the bomb was created in Los Alamos, the first one ex- ploded in Alamagordo, and missiles to deliver future bombs were test- ed in White Sands — all in New Mexico, a nexus of the military-industrial complex.
Was it just coincidence that the Roswell UFO crash also happened there? We Earthlings need all the help we can get, so why not embrace the phenomenon for what it is, to marvel at the wonder, leaving behind our cultural biases? Only through expanding our knowledge and taking political action can we make the needed shifts, and that is what Dr.
Greer is so good at doing. In many ways, the UFO phenomenon tells us more about ourselves than about our mysterious visitors, and the mirror they hold in front of us is frightening — yet hopeful, if we listen to Dr. For example, his founding of Space En- ergy Access Systems SEAS is providing support to inventors with revolutionary new energy technologies that could give the world clean, cheap and decentralized energy, thus ending the oil, coal, and nuclear Age and the virtual end of human- caused pollution and climate change.
On the evening of my first meeting with Dr. Greer, the Unity min- ister Chad O'Shea presented me with a bumper sticker, "The truth shall set you free but first if will piss you off. This courageous work is not for the meek. Many cutting-edge scientists have been threatened, murdered, and otherwise suppressed by cascades of disinforma- tion and personal attacks.
Greer has endured all this, to our benefit. This book could be the most important you will read. It is not only full of tran- scendent truths, it is a call to action to shift the paradigm from terrestrial tyranny to peaceful, sustainable and just cosmic community Apollo Astronaut, Dr.
Brian O'Leary 14 Sept. The purpose was for me to provide an oral history, over the course of a week, of the events of my life. This book is the result of that gathering. To be honest, this book is released with more than a little trepidation.
It reveals personal experiences and events that frankly seem incredible. Even reading through the transcript of the tapes was at times a tearful and emotionally difficult experience. And I know that much of it can be used to attack me personally But it is time for you to know: Why did an emergency physician who had been chairman of a busy ER leave his career to get out to the world the information that we are not alone? What had I personally experienced -from childhood onwards - that gave me the knowledge of cosmic cultures, cos- mic consciousness and a glimpse of the wondrous future that awaits humanity?
What are the new energy and propulsion technologies that can give us a new world, free of pollution, poverty and conflict? What is the nexus where Mind, Space, Time and Matter all come together- and how might this be used technologi- cally by an advanced civilization? What does the blue-print of the next , years of human civilization on earth look like - and how can we transition to that time?
What did I find- and experience - as I met with heads of state, CIA offi- cials, billionaires and covert operatives who in turns are desperate to maintain the secrecy and yet pray for relief from the black box they have nailed shut around them? Who has been keeping this Hidden Truth and Forbidden Knowledge secret - and most importantly, why? This book addresses all this - and more.
It is my own Disclosure. Having founded and led The Disclosure Project, I feel it is time that the millions of people who follow our work know the truth about how I got here - and what I have found. I do not expect the general reader to accept all of this -or perhaps any of it. I ex- pect nothing in fact. It is the truth as I have found it and this is my heartfelt effort xi to share that truth.
I hope you find some meaning in this sharing from my heart and mind. A meeting I had with a senior General at the Pentagon a few years ago illustrates the gravity of the situation. I had been asked by this General, who at the time was head of a major intelligence operation in the Pentagon, to brief him and some of his staff on the UFO issue.
As our military advisor and I waited in the Gen- eral's reception room, we noticed a female officer looking up from her papers at us, curiously Finally she asked if I was Dr. Greer, and I said yes. She then proceeded to explain that they were very excited about the briefing and that she and her col- leagues had drawn straws to see who could be in attendance! Apparently, only one officer from her office could be present. We were escorted into the General's conference room and some time into the briefing this General said, "Well, I have no doubt that what you are sharing is true, but I have made inquiries through channels in my Agency and nobody can tell me anything!
He said, "This is all I have gotten - ridicule- for inquiring about this through channels This senior General then told me a disturbing and exquisitely per- sonal story: When he was young, his father had discovered a corrupt enterprise and conspir- acy in the government that was deeply disturbing- but nobody would listen to him.
It was a matter of enormous importance - but even the General admitted he just thought his father was a kook. Eventually, his father committed suicide or was murdered and made to look like a suicide over the matter.
Then the General said, "It wasn't until I got into this position at the Pentagon that I realized the old man was right! So how can I expect you to believe me? All I can do is share with you the truth as I know it and the rest is up to you.
A few comments on the book: It is not a written book, but merely an edited tran- script of over 45 hours of audio tape that were created in April of during my oral presentations at our farm. I ask that the reader forgive any errors or editing oversights. This book should be viewed as an oral history, transcribed and edited into a narrative. I had no notes or text as I made these oral presentations. Between and , I kept a diary via transcribed audio tape that was over pages just up to that time.
Clearly this book, which encompasses experi- ences that span half a century, can only reflect the major highlights and lessons gleaned over that time. It is by no means meant to be all-inclusive or recall all the xii information conveyed to me by thousands of conversations and meetings with cov- ert contacts within the Shadow Government.
Many of the names of these covert operatives are changed or abbreviated. How- ever, the original tapes and transcripts, which are in multiple secure locations, con- tain all of the names, corporations and entities involved with these illegal clandes- tine operations and will be released, if needed, at a later time.
Also, this book is not a recapitulation or even summary of the extensive documen- tation which exists in my two prior books. Moreover, a nearly page book of government documents and tran- scripts of over 60 top- secret witness testimonies to official government projects and events is available in "Disclosure". These books may be obtained at www. It is time for one chapter in human history to close and another to open.
Do we have the courage to embrace this new world, the hallmarks of which are univer- sal peace, enlightenment, and a genuinely high technology civilization on earth that is sustainable for thousands of years?
A monistic framework is set up where energy is the only fundamental substance. Different states of energy are ordered by a set of scalar fields. The dual elements of matter, mass and space, are described as volume- and gradient-energy contributions of the set of fields, respectively.
Time and space are formulated as background-independent dynamic variables. The evolution equations of the body of the universe are derived from the first principles of thermodynamics.
Gravitational interaction emerges from quantum fluctuations in finite space. Application to a large number of fields predicts scale separation in space and repulsive action of masses distant beyond a marginal distance. The predicted marginal distance is compared to the size of the voids in the observable universe.
Full-field simulation of solidification and forming of polycrystals. The phase-field method has emerged as the method of choice for simulation of microstructure evolution and phase-transformations in material science. It has wide applications in solidification and solid state transformations in general.
Recently, the method has been generalized to treat large deformation and damage in solids. A through process full-field simulation will be presented starting from solidification and ending with the evolution of damage during large deformation. Aspects of numerical discretization, efficient numerical integration and massive parallelization will be discussed. Modelling of flow behaviour and dynamic recrystallization during hot deformation of MS-W using the phase field framework.
A new simulation environment is developed to simulate the evolution of microstructure and the corresponding flow stress during rolling. An orientation dependent crystal plasticity hardening model is coupled to grain evolution-, recovery- and recrystallization kinetics within a phase field framework.
Hardening and softening kinetics are treated consecutive to differentiate between individual effects. From wetting to melting along grain boundaries using phase field and sharp interface methods.
Dec Computational Materials Science. We investigate the ability of a multi-order parameter phase field model with obstacle potentials to describe grain boundary premelting in equilibrium situations. The predictions for premelting are confirmed by simulations using the phase field package OpenPhase. For the prediction of the kinetics of melting along grain boundaries in pure materials, taking into account the short ranged interactions which are responsible for the grain boundary premelting, a sharp interface theory is developed.
It confirms that for overheated grain boundaries the melting velocity is reduced increased for non-wetting wetting grain boundaries. Numerical steady state predictions are in agreement with a fully analytical solution in a subset of the parameter space. Phase field simulations confirm the predictions of the sharp interface theory. Gamma-channel stabilization mechanism in Ni-base superalloys.
Dec Philosophical Magazine Letters. A mechanism is presented which opposes coalescence of Formula presented. The mechanism is based on the non-linear behaviour of the elastic energy in Formula presented. Variation of the channel width causes a disjoining pressure dependent on the density of misfit dislocations.
Nov International Journal of Thermophysics. In this paper, we present the simulation of the eutectic phase transitions in the Pt—C system, in terms of both freezing and melting, using the multi-phase-field model. The experimentally obtained heat-extraction and -injection rates associated with the induction of freezing and melting are converted into the corresponding rates for microstructure-scale simulations. In spite of the extreme differences in the volume fractions of the FCC—Pt-rich phase on the one hand and graphite C on the other, satisfactory results for the kinetics of solidification and melting have been obtained, involving reasonable offsets in temperature, inducing freezing and melting, with respect to the equilibrium eutectic temperature.
The seemingly anomalous peak characterizing the simulated freezing curves is ascribed to the speed up of the solidification process due to the curvature effect. Similarly, a peak is observed in the experimental freezing curves, also showing up more clearly with increasing freezing rates. Melting was simulated starting from a frozen structure produced by a freezing simulation.
The simulations reproduce the experimental melting curves and, together with the simulated freezing curves, help to understand the phase transition of the Pt—C eutectic. Finally, the effect of metallic impurities was studied. As shown for Au, impurities affect the morphology of the eutectic structure, their impact increasing with the impurity content, i. Large deformation framework for phase-field simulations at the mesoscale. Oct Computational Materials Science. Abstract A large-strain plasticity framework is set up for phase-field simulations at the mesoscopic scale.
The approach is based on an Eulerian setting with remeshing after each time step to keep a fixed structured mesh. Rotations, as evaluated from the antisymmetric part of the deformation gradient tensor, are integrated to capture the process history. Special emphasis is also given to the homogenization of the diffuse interface region to ensure the Hadamard jump condition and 2-dimensional scaling of the interface. The approach is applied to deformation of a polycrystal.
A continuum mechanical, bi-phasic, two-scale model for thermal driven phase transition during solidification. This articel focuses on a bi-scale numerical description for solidification process simulation.
The macro-scale implies two phases which are the solid and liquid metallic alloy physical states described using the theory of porous media TPM enhanced by strong thermal coupling and finite elastic-plastic-creep temperature dependent material behaviour. Furthermore, a linear viscous melt as well as a laminar melt flow are adopted. The thermal driven physics of solidification is covered by a microscopic phase-field model. Therefore, a Ginzburg-Landau type free energy function is employed.
After discussing the main model details, a real Bridgman oven numerical pre-model will demonstrate the principal performance. Phase-field study of the effect of creep on the rafts formation in Ni-base superalloys.
Stability of the microstructure at elevated temperatures is the major factor controlling the performance of Ni-base superalloys. At high temperatures rafting and creep phenomena become important.
We investigate the effects of external loading on the rafts formation with and without considering the creep phenomenon. Classical creep models were incorporated in the Phase-field modeling for precipitates evolution simulation involving creep. In this study we investigate the kinetics of raft formation considering the effect of inelastic strain during high-temperature creep.
We also investigate the effect of varying misfit strain on the rafts formation. The results of microstructure evolution and creep rate versus time are compared with experiments. Modeling the flow in diffuse interface methods of solidification. Sep Physical Review E. Fluid dynamical equations in the presence of a diffuse solid-liquid interface are investigated via a volume averaging approach.
The resulting equations exhibit the same structure as the standard Navier-Stokes equation for a Newtonian fluid with a constant viscosity, the effect of the solid phase fraction appearing in the drag force only. This considerably simplifies the use of the lattice Boltzmann method as a fluid dynamics solver in solidification simulations.
Galilean invariance is also satisfied within this approach. Further, we investigate deviations between the diffuse and sharp interface flow profiles via both quasiexact numerical integration and lattice Boltzmann simulations. It emerges from these studies that the freedom in choosing the solid-liquid coupling parameter h provides a flexible way of optimizing the diffuse interface-flow simulations. Once h is adapted for a given spatial resolution, the simulated flow profiles reach an accuracy comparable to quasiexact numerical simulations.
Primary combination of phase-field and discrete dislocation dynamics methods for investigating athermal plastic deformation in various realistic Ni-base single crystal superalloy microstructures. The phase-field method is used to generate realistic microstructures as the boundary conditions for DDD simulations in which a constant high uniaxial tensile load is applied along different crystallographic directions. Due to the high antiphase boundary energy and the rare formation of superdislocations, precipitate cutting is not observed in the present simulations.
A zoomed-in region of a melt channel under eutectic conditions is investigated and compared with experiments. The presented simulations allow prediction of the final properties of an alloy based on process parameters. The obtained results give insight into the solidification processes governing the microstructure formation of Mg-Al alloys, allowing their targeted design for different applications. Dual-scale phase-field simulation of Mg-Al alloy solidification.
In order to further enhance the resolution of the interdendritic region a high-performance computing approach has been used allowing significant simulation speed gain when using supercomputing facilities. Texture evolution in deformed AZ31 magnesium sheets: Experiments and phase-field study. Jun Computational Materials Science. Geometrical grounds of mean field solutions for normal grain growth.
May Acta Materialia. The classical mean field approach for normal grain growth in polycrystalline materials is revisited. We re-drive and study possible self-similar solutions and show that the grain size distribution can be determined only by the geometry of neighbouring grains for any given configuration. In three dimensions, it is shown that a single index can represent the geometrical characteristic of grains and has a one-to-one relationship with the mean field parameter.
Apr Acta Materialia. In binary alloys, the sublattice models can be classified into two types i. Internal minimization of sublattice occupancy and solute evolution during microstructure transformation leads, in general, to a solution superior to the separate solution of the individual problems. The present coupling technique is validated for Fe—C and Ni—Al alloys. Finally, the model is extended into multicomponent alloys and applied to simulate the nucleation process of VC monocarbide from austenite matrix in a steel containing vanadium.
This articel focuses on a thermo-mechanical model for numerical simulation of solidification processes considering two different scales, both in time and space. The macro-scale implies two phases solid and liquid steel , and is described by use of the theory of porous media TPM.
Moreover, a strong thermal coupling is addressed as well as finite J2 elastic-plastic solid behavior. The physics of solidification during heat dissipation is covered on the micro-scale in the framework of phase-field modeling. Therefore, a Ginzburg-Landau type free energy function is used. After discussing the main model details, a numerical example will demonstrate the principal performance of the presented model.
A meso-scale aproach to superalloys microstructure modeling. It is known that the mechanical properties strongly depend on the distribution and size of the precipitates. Knowledge of the precipitate growth kinetics and identifying the controlling parameters is an important aspect of the design and development of superalloys.
The microstructure evolution during different heat treatment cycles and under service conditions are numerically simulated using our in-house open-source library OpenPhase. Phase-field modeling of grain-boundary premelting using obstacle potentials.
Jul Physical Review E. We investigate the multi-order parameter phase field model of Steinbach and Pezzolla [I. Pezzolla, A generalized field method for multiphase transformations using interface fields, Physica D ] concerning its ability to describe grain boundary premelting. For a single order parameter situation solid-melt interfaces are always attractive, which allows to have unstable equilibrium solid-melt-solid coexistence above the bulk melting point.
The temperature dependent melt layer thickness and the disjoining potential, which describe the interface interaction, are affected by the choice of the thermal coupling function and the measure to define the amount of the liquid phase. Due to the strictly finite interface thickness also the interaction range is finite. For a multi-order parameter model we find either purely attractive or purely repulsive finite-ranged interactions.
The premelting transition is then directly linked to the ratio of the grain boundary and solid-melt interfacial energy. Large scale 3-D phase-field simulation of coarsening in Ni-base superalloys.
We numerically simulated precipitation hardening heat treatment cycles. A detailed analysis of obtained result is presented emphasizing the effect of elastic interaction on the coarsening kinetics in Ni-base superalloy.
Large strain elasto-plasticity for diffuse interface models. Most solid-state phase transformations are accompanied by large deformations, stemming either from external load, transformation strains or plasticity. The consideration of such large deformations will affect the numerical treatment of such transformations. In this paper, we present a new scheme to embed large deformations in an explicit phase-field scheme and its implementation in the open-source framework OpenPhase.
The suggested scheme combines the advantages of a spectral solver to calculate the mechanical boundary value problem in a small strain limit and an advection procedure to transport field variables over the calculation grid. Since the developed approach should be used for various sets of problems, e. However, to ensure compatibility with phase-field methods using the concept of diffuse interface, the latter is treated with special care in the present work. Phase-field modeling for 3D grain growth based on a grain boundary energy database.
A 3D phase-field model for grain growth combined with a grain boundary GB energy database is proposed. The phase-field model is applied to a grain growth simulation of polycrystalline bcc Fe to investigate the effect of anisotropic GB energy on the microstructural evolution and its kinetics. It is found that the anisotropy in the GB energy results in different microstructures and slower kinetics, especially when the portion of low-angle, low-energy GBs is large.
We discuss the applicability of the proposed phase-field simulation technique, based on the GB or interfacial energy database to simulations for microstructural evolution, including abnormal grain growth, phase transformations, etc. DFT-supported phase-field study on the effect of mechanically driven fluxes in Ni4Ti3 precipitation. Formation of the Ni4Ti3 precipitate has a strong effect on the shape memory properties of NiTi alloys.
In this work, growth of this precipitate is studied using phase-field modelling and density functional theory DFT calculations. Using first-principles calculations, the composition-dependent stability and elastic properties of the B2 phase are obtained. Composition-dependent elastic constants are incorporated into our phase-field model to investigate the interplay between stress and concentration fields around the precipitate.
The results are discussed in light of previous experimental and simulation studies. Applications of scale-bridging to computational materials design. Phase field modelling of grain boundary premelting using obstacle potentials.
Tertiary dendritic instability in late stage solidification of Ni-based superalloys. Derivatives of the commercial alloy CMSX-4 were directionally solidified and characterized with respect to their final dendrite microstructure.
The results indicate that Ni-based superalloys with high segregation levels show significant instability in secondary dendrite arms and an increased tendency for tertiary arm formation, respectively. Phase-field simulations were used to explore the impact of chemical composition on morphological instability and tertiary arm formation during the directional solidification of Ni-based superalloys. It is found that an increase in specific alloying elements in the overall alloy composition leads to pronounced segregation at the end of solidification.
This causes strong growth restriction of the secondary arms and triggers tertiary arm formation. The proposed mechanism explains experimental microstructures found in modifications of the base alloy CMSX A detailed analysis of obtained result is presented emphasising the effect of elastic interaction on the coarsening kinetics in Ni-base superalloy.
The study is performed using the phase-field modelling library "OpenPhase" which is based on a multi-phase field multi-component model. Simulating Mobile Dendrites in a Flow. We propose a scheme for simulation of the solute-driven dendritic solidification which accounts for the flows of liquid and motion of growing dendrites.
The scheme is based on the multiphase-field method for calculating the solidification and the lattice Boltzmann method to simulate the fluid flows. Motion and rotation of solid grains is possible. Solutal gradients in strained equilibrium. We demonstrate that the distortion of a crystal, caused by secondary phase precipitates, can stabilize a solutal gradient around the precipitate. The gradient persists in the quasi-static state stabilized by the gradient of the elastic energy around the precipitate.
The peak concentration at the interface between precipitate and matrix hereby is independent of the radius of the precipitate and no mechanism of ripening is active in an arrangement of precipitates of different size. The model offers an explanation of experimental observations of the anomalous stability of nano-precipitates in Al—Cu. Stability of the microstructure at elevated temperatures is the major factor controlling the performance of Ni-base super-alloys. During phase transformation, elastic stresses arise due to the lattice misfit among the phases.
Elastic anisotropy in turn has a strong influence on the microstructure and its evolution, due to which the precipitates grow as cuboids. The processing conditions are numerically simulated with our in-house software 'OpenPhase' which is based on a multi-phase field multi-component model [Steinbach et al.
Several studies related to the processes with analysis of the obtained microstructure are presented. Phase-eld simulation of microstructure evolution in Ni-Based superalloys. One effect could be that the finer grains produce a more brittle material [Callister, ]. During phase transformation, elastic stresses arise due to this lattice misfit among the phases. Hence, knowledge of the growth process is an important aspect for the design and development of superalloys.
A permeation model for the electrochemical interface. We show the transferability of the recently introduced concept of permeation from the context of finite dissipation in simple metallic interfaces to much more complicated electrochemical interfaces. The phenomenological bridge is formed by the exchange current, which can be measured by either impedance spectroscopy or by cyclic voltammetry.
In a proof-of-concept phase field model, Nernst-Planck diffusion and transport of charged species in a potential gradient as the solution of the Poisson equation are considered. It is shown that charges build up on the outer electrode surface in a fashion resembling the electrochemical double layer. This strange combination of basic and applied research is reviewed against its historical background: The main achievements in both fields are highlighted, and future perspectives are briefly discussed.
Jul Annual Review of Materials Research. This review presents a phase-field model that is generally applicable to homogeneous and heterogeneous systems at the mesoscopic scale.
Reviewed first are general aspects about first-and second-order phase transitions that need to be considered to understand the theoretical background of a phase field. The mesoscopic model equations are defined by a coarse-graining procedure from a microscopic model in the continuum limit on the atomic scale. Special emphasis is given to the question of how to separate the interface and bulk contributions to the generalized thermodynamic functional, which forms the basis of all phase-field models.
Numerical aspects of the discretization are discussed at the lower scale of applicability. The model is applied to spinodal decomposition and ripening in Ag-Cu with realistic thermodynamic and kinetic data from a database. Diffuse-interface modeling of solute trapping in rapid solidification: Predictions of the hyperbolic phase-field model and parabolic model with finite interface dissipation. Jun Acta Materialia. Two recently developed phase-field models, a hyperbolic model and a parabolic model with finite interface dissipation, are employed to study the solute trapping in a Si The physical conditions are numerically simulated with our in-house software 'OpenPhase' which is based on a multi-phase field multi-component model [Steinbach et al.
Cuboidal microstructure formation in Ni-base superalloys. Multi phase field simulation of coarsening in Ni-base superalloy. Microstructure and its mechanical properties at elevated temperatures are the major factor controlling the performance of Ni-base super-alloys.
In this study we present a numerical simulation of microstructure evolution of Ni-base super alloy using multi-phase field method. The microstructure evolution during the heat treatment cycle is numerically simulated with our in-house software 'OpenPhase' which is based on a multi-phase field multi-component model [Steinbach et al.
We discuss on the coarsening kinetics, parameters influencing it and identify directions for future work. Dec Metallurgical and Materials Transactions A. A multicomponent phase-field method coupled to thermodynamic calculations according to the CALPHAD method was used to simulate microstructural evolution during directional solidification of the LEK94 commercial single-crystal Ni-based superalloy using a two-dimensional unit cell approximation.
We demonstrate quantitative agreement of calculated microsegregation profiles and profiles determined from casting experiments as well as calculated fraction solid curves with those determined in differential thermal analysis DTA measurements. Finally, the role of solidification rate on dendrite morphology and precipitation of the secondary phases is investigated and a new measure of the dendrite morphology is presented to quantify the effect of back diffusion on the amount of secondary phases.
Ni-base superalloys are widely used materials for turbine blades in gas turbines in aerospace and power industries. These alloys have very high mechanical strength and creep resistance at high temperatures which allows using of such material at temperatures up to K. Our simulations are based on the multi-phase field model implemented in the open source phase field simulation library OpenPhase.
Phase field simulation of microstructural evolution in Ni-base superalloys. Viscous coalescence of droplets: May Physics of Fluids. The coalescence of two resting liquid droplets in a saturated vapor phase is investigated by Lattice Boltzmann simulations in two and three dimensions.
Our results differ significantly from the predictions of existing analytical theories of viscous coalescence as well as from experimental observations. While the underlying reason for these deviations is presently unknown, a simple scaling argument is given that describes our results well. Topological analysis versus mean-field approximations. The characteristics of 3-D grain growth are investigated by a topological analysis of phase-field simulation results compared with theoretical mean-field theories.
We found that the size distribution of the grains starting from an arbitrary narrow distribution crosses the self-similar Hillert distribution, and ends in a distribution with relatively longer tails of large grains in which the central peak shifted towards smaller grain size. The distribution of topological classes, as characterized by the number of facets per grain, is found to be time-invariant for the process as a whole.
The obtained shape function is in good agreement with the analytical distribution function derived based on the average N-hedron model [Rios PR, Glicksman ME.
The volumetric growth rate per topological class also correlates well with the analytical approach obtained by Mullins [Mullins WW. The relationship between grain size and its shape, however, deviates from theoretical predictions.
Phase-field model with finite interface dissipation. In rapid phase transformations, interfaces are often driven far from equilibrium, and the chemical potential may exhibit a jump across the interface.
We develop a model for the description of such situations in the framework of the phase-field formalism, with separate concentration fields in each phase. The key novel feature of this model is that the two concentration fields are linked by a kinetic equation which describes the exchange of components between the phases, instead of an equilibrium partitioning condition.
The associated rate constant influences the interface dissipation. For rapid exchange between the phases, the chemical potentials are equal in both coexisting phases at the interface as in previous models, whereas in the opposite limit strong non-equilibrium behavior can be modeled.
This is illustrated by simulations of a diffusion couple and of solute trapping during rapid solidification. Phase-field model with finite interface dissipation: Extension to multi-component multi-phase alloys. A previously developed phase-field model with finite interface dissipation for binary dual-phase alloys out of chemical equilibrium is generalized to a multi-component multi-phase model in the framework of the multi-phase-field formalism, allowing the description of multiple junctions with an arbitrary number of phases and components.
In multiple junctions, each phase concentration is assigned to a dynamic equation to account for finite interface dissipation, and its formulation is proposed in two different models. The overall mass conservation between the phases of a multiple junction is used in model I, whereas the concentrations of each pair of phases have to be conserved during the transformations for model II.
Both models demonstrate the decomposition of the nonlinear interactions between different phases into pairwise interaction of phases in multiple junctions. They converge to the same equilibrium state while in non-equilibrium states different predictions are given. Nov Continuum Mechanics and Thermodynamics. It links principles of thermodynamics and kinetics to the scale of the microstructure.
In addition it solves a very practical problem: How the hardness of steel is correlated to the conditions of processing. Although the model is well established since the s, quantitative explanation of growth kinetics was missing until very recently. The present paper will shortly review the classical model of pearlite transformation. Finally, an explanation of the growth kinetics observed in experiments is proposed based on diffusion fluxes driven by stress gradients due to large transformation strain.
Contact angle dependence of the velocity of sliding cylindrical drop on flat substrates. Via numerical simulations, we investigate the dynamics of cylindrical drops on flat substrates. In agreement with the common understanding, in the limit of Stokes flow and negligible drop deformation, the drop's centre-of-mass velocity scales linearly with the applied force and with the second power of drop radius.
In this paper, we go a step further and perform a detailed study of dissipation loss inside the drop. An important result is that the dominant part of viscous dissipation arises from the region below the drop's centre of mass. Based on this observation, we propose a simple analytic model which allows capturing the dependence of the steady-state drop velocity on the equilibrium contact angle.
Simulation results are in good agreement with the predictions of this model. The phase field method has been applied to simulate the microstructural evolution of a commercial single crystal Ni-based superalloy during both, HIP and annealing treatments. The effects of applying high isostatic pressure on the microstructural evolution, which mainly retards the diffusion of the alloying elements causing the loss of the orientational coherency between the phases is demonstrated by the simulation and experimental results.
Phase-field modelling of microstructure evolution in solids: Phase-field modelling is maturing to become a universal tool for modelling microstructure evolution in materials science. In solidification applications it has been proven to give quantitative predictions. In solid state, however, the mechanisms of phase transformation and microstructure evolution in are much more involved due to the existence of mechanical interactions, high interface anisotropies, large densities of defects, and retarded kinetics of diffusion and growth.
The paper gives an overview of actual developments in phase-field modelling of solid-state microstructure evolution and highlights necessary directions of future development in order to meet the challenge of quantitative predictions.
Stability and dynamics of droplets on patterned substrates: Insights from experiments and lattice Boltzmann simulations.
May Journal of Physics Condensed Matter. The stability and dynamics of droplets on solid substrates are studied both theoretically and via experiments. Focusing on our recent achievements within the DFG-priority program Nano- and Microfluidics , we first consider the case of large droplets on the so-called gradient substrates.
Here the term gradient refers to both a change of wettability chemical gradient or topography roughness gradient. While the motion of a droplet on a perfectly flat substrate upon the action of a chemical gradient appears to be a natural consequence of the considered situation, we show that the behavior of a droplet on a gradient of topography is less obvious.
Nevertheless, if care is taken in the choice of the topographic patterns in order to reduce hysteresis effects , a motion may be observed. Interestingly, in this case, simple scaling arguments adequately account for the dependence of the droplet velocity on the roughness gradient Moradi et al Europhys. Another issue addressed in this paper is the behavior of droplets on hydrophobic substrates with a periodic arrangement of square shaped pillars.
Here, it is possible to propose an analytically solvable model for the case where the droplet size becomes comparable to the roughness scale Gross et al Europhys. Two important predictions of the model are highlighted here. These predictions are confirmed via independent numerical simulations. Moreover, we also address the fundamental issue of the internal droplet dynamics and the terminal center of mass velocity on a flat substrate.
Morphologies of small droplets on patterned hydrophobic substrates. For situations, in which the size of a droplet is comparable to the roughness scale of the solid substrate, we explore possible wetting morphologies on patterned hydrophobic substrates and investigate their dependence on the initial droplet position, droplet volume and the surface geometry.
For a regular array of cubical pillars, small perturbations of a symmetric droplet state are restored by capillary forces. Larger deviations, on the other hand, may lead to completely new morphologies. Our studies also suggest that the previously reported 'reentrant transition' upon quasi-static evaporation a transition from the suspended state to partial penetration and then back to the suspended state Gross et al Europhys.
In contrast, a change in the substrate geometry may lead to a completely different behavior, fully precluding the reentrant transition. This underlines the importance of substrate design for the use of reentrant transition as a self-cleaning mechanism.
On the effect of superimposed external stresses on the nucleation and growth of Ni4Ti3 particles: A parametric phase field study. The effect of a superimposed stress on the coarsening of interacting Ni4Ti3 particles is studied using the multi-phase field method. The particle shape can change from a disk to a sphere with increasing applied stress. It is also found that diffusional and mechanical interactions between two Ni4Ti3 particles can promote the nucleation of new particles.
This provides an explanation for the autocatalytic nature of nucleation reported previously. Compressive stresses along [1 1 1]B2 increase the volume fraction and growth velocity of the Ni4Ti3 particles of the 1 1 1 B2 plane.
Misoriented particles disappear during particle growth. The simulation results are discussed in the light of previous experimental results. Phase-field simulation of diffusion couples in the Ni—Al system.
By linking thermodynamic and atomic mobility databases with two-dimensional phase-field simulation, the evolution of interdiffusion microstructures in a series of Ni-Al diffusion couples associated with the gamma, gamma', and beta-phases was studied. The phase-field simulated concentration profiles of some of the Ni-Al diffusion couples were also compared with the corresponding experimental data and the results of one-dimensional DICTRA Diffusion Controlled TRAnsformations simulations.
A discussion of the rafting direction was also made by comprehensively comparing the phase-field simulations with the predicted results from an elastic model. Dynamics of cylindrical droplets on flat substrate: Lattice Boltzmann modeling versus simple analytic models. The steady state motion of cylindrical droplets under the action of external body force is investigated both theoretically and via lattice Boltzmann simulation. As long as the shape-invariance of droplet is maintained, the droplet's center-of-mass velocity linearly scales with both the force density and the square of droplet radius.
However, a non-linear behavior appears as the droplet deformation becomes significant. This deformation is associated with the drop elongation occurring at sufficiently high external forcing. Yet, independent of either the force density or the droplet size, the center-of-mass velocity is found to be linear in terms of the inverse of dynamic viscosity. In addition, it is shown that the energy is mainly dissipated in a region near the substrate particularly close to the three phase contact line.
The total viscous dissipation is found to be proportional to both the square of force density and the inverse of dynamic viscosity. Moreover, the dependence of the center-of-mass velocity on the equilibrium contact angle is investigated. A simple analytic model is provided reproducing the observed behavior.
An analytical study of the static state of multi-junctions in a multi-phase field model. Feb Physica D Nonlinear Phenomena. We investigate the properties of the multi-order parameter phase field model of Steinbach and Pezzolla [I. Pezzolla, A generalized field method for multi-phase transformations using interface fields, Physica D —] with respect to the behavior in triple and higher order junctions.
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