Download or read book Large Scale Phase Field Simulations of Microstructure Evolution During Thermal Cycling of TI 6AL 4V written by and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Phase field Models of Microstructure Evolution and New Numerical Strategies written by Weiming Feng and published by . This book was released on 2009 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: A basic interest in materials science is the determination of microstructures of materials in order to understand why materials have the properties they exhibit and how these properties can be controlled to serve technological uses. In this dissertation, the phase-field approach is combined with other models and algorithms to study the effect of elastic energy, anisotropic mobility and structural defects on phase separation kinetics and morphological evolution in bulk systems. A multi-dimensional general phase-field model has been developed by combining the iteration method for calculating the elastic energy and a semi-implicit spectral method for solving the Cahn?Hilliard equation. The model can efficiently calculate the microstructure evolution for systems with rather general elastic anisotropies, arbitrarily large elastic inhomogeneity, general misfit strain, and large anisotropic mobility. The microstructure and structure functions have been studied to show the effect of large anisotropic mobility together with the elastic energy. To address the challenge of large scale simulations of microstructures which are still computationally expensive to date, an adaptive semi-implicit Fourier spectral (AFSIM) method is developed to solve Allen-Cahn equation by making grid points spatially adaptive in the physical domain via a moving mesh strategy, while maintaining a uniform grid in the computational domain for the spectral implementation. The moving mesh method is adopted since it is particularly efficient among recent efforts in developing advanced numerical algorithms. The newly developed approach not only provides more accurate treatment at the interfaces requiring higher resolution, but also retains the numerical efficiency of the semi-implicit Fourier spectral method. Numerical examples using the adaptive moving mesh semi-implicit Fourier spectral method are presented for both two and three space dimensional microstructure simulations, and they are compared with those obtained by other methods. By maintaining similar accuracy, the proposed method is shown to be far more efficient than the existing methods for microstructures with small ratios of interfacial width to the domain size. The AFSIM is further implemented to solve Cahn-Hilliard equation with inhomogeneous, anisotropic elasticity. Numerical implementations and test examples in both two and three dimensions are considered with a particular illustration using the well-studied example of mis-fitting particles in a solid as they approach to their equilibrium shapes. It is shown that significant savings in memory and computational time is achieved while accurate solutions are preserved. The dynamics of the structure defects such as dislocations generally control the material properties during non-equilibrium processing. In phase-fields description, the dislocations exist only along the dislocations lines parallel to the slip planes. The total dislocation line length to volume ratio in dislocation motion is expected to be significantly smaller than the total area to volume ratio for interface motion. Therefore, AFSIM is extended to study the dislocation motion. By comparing the results with analytical solutions for accuracy and with results from the uniform Fourier-spectral semi-implicit method (UFSIM) for efficiency, it is shown that AFSIM yields much more accurate results for the dislocation stress field and is an order magnitude more efficient than the UFSIM for the same accuracy.

Download or read book Phase Field Modeling of Microstructure Evolution in Thermal Barrier Coating Systems written by Karim E. Ahmed and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: ABSTRACT: The development of robust thermal barrier coating (TBC) systems is crucial in many high-temperature applications. The performance of a TBC system is significantly limited by microstructural evolution mechanisms, such as sintering at elevated temperatures. Sintering reduces the porosity of TBC and makes it denser which eventually increases the thermal conductivity and reduces the strain compliance of TBC. Understanding how sintering proceeds in TBC systems is thus important in improving the design of such systems. An elaborate phase field model was developed in order to understand the sintering behavior of columnar TBC structure. The model takes into account different sintering mechanisms, such as volume diffusion, grain boundary diffusion, surface diffusion, and grain boundary migration, coupled with elastic strain arising from the thermal expansion mismatch in thermal barrier coating system. Direct relations between model parameters and material properties were established. Such relations facilitate quantitative studies of the sintering process in any material of interest. The model successfully demonstrates a strong dependence of the sintering process in TBC on the initial morphology and dimensions of coatings, strain, and temperature.

Download or read book Unified Approach to Scale Transition in Simulations of Microstructure Evolution Using Phase field Crystal Model written by Matjaž Berčič and published by . This book was released on 2019 with total page 143 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Phase field Model for Interstitial Loop Growth Kinetics and Thermodynamic and Kinetic Models of Irradiated Fe Cr Alloys written by and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Computational Study of Microstructure Evolution During Phase Transformations written by Taiwu Yu and published by . This book was released on 2021 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Phase transformation is always a critical topic in the study of materials science. Most people have been familiar with some transformations between solid and liquid, such as ice to water, or transformations between liquid and gas, such as water to vapor. Besides, the phase transformations in solids also occur everywhere. Some solid phase transformations occur due to temperature variations. Those transformations may also be affected by external stress or strain, as seen in shape memory alloys (SMAs). The solid-solid transformation is considered to be the one of the most effective ways to tailor the microstructure and properties of the alloys, moreover, it sometimes strengthens the structural materials. There are some types of solid-state phase transformations that are hard to characterize in the traditional experiments. The difficulty mainly comes from two aspects. Firstly, some of the phase transformations happen too fast, such as martensitic transformation. The speed of the martensitic transformation is close to the speed of sound traveling in solids (~1000m/s), which makes it difficult to know how it starts and evolves. Secondly, some of the phase transformation processes are too slow, such as oxidation. It could take years to form a continuous layer of oxides in microns. With the fast development of high-performance computing, the study of phase transformations through computational tools attracts more and more attention. The objective of this thesis is to apply computational tools to study the two types of phase transformations and their corresponding mechanical properties: precipitation and martensitic transformation. As one of the most important structural phase transformations discovered in metallurgy and materials science, martensitic transformation (MT) has been attracting continued attention since its discovery in the late nineteenth century till today because it relates closely to the functional properties of NiTi-based alloy such as the superelasticity and shape memory effect. Most importantly, MT can be tailored through nano-scale defects in materials. Firstly, nano-scale defects in the B2 parent phase are known to have profound impacts on the properties of NiTi-based shape memory alloys. We employed the phase field models (PFM) to study the effects of two typical nano-scale defects, nano-scale precipitates and voids, on MT. The simulation of precipitation unveiled the mechanical and chemical effects on the behavior of MT in NiTi-Hf alloys. Moreover, the simulation of MT with the coexistence of precipitates explained the mechanism of two typical patterns of martensite. The results indicates that the stress-strain response has great dependence on the concentration heterogeneity in the matrix as well as precipitate microstructures. Through the simulation we proved the feasibility to achieve linear or quasi-linear superelasticity with high recoverable strain (up to 4%) in NiTi-Hf alloys after the precipitation. In the simulation of MT under the effects of nano voids in NiTi, we observed that martensite could be confined in the interspacing area between voids. Besides, MT could be triggered at lower critical stress with larger volume fraction of voids. This simulation may shed lights on the design of the porous NiTi alloys for the biomedical application. In superalloys, the microstructure of precipitates can be altered by the formation of an oxide layer on the surface. It is observed that the \gamma\prime precipitates dissolve at the near-surface region with the formation of the oxide layer in the alloy. We employed DICTRA module in Thermo-calc Software to solve the multicomponent diffusion equations in alloy H282 with an outward flux of chromium or aluminum due to oxidation and applied PFM to simulate the dissolution of precipitates. The local variation of precipitates’ volume fraction as a function of oxidation time has been quantitatively determined. The calculation of precipitates depletion depth shows good agreement with the experiments. The highly heterogeneous structure of \gamma\prime precipitates is expected to have a significant effect on the creep behavior of the alloy.

Download or read book Phase field Simulation of Microstructural Development Induced by Interdiffusion Fluxes Under Multiple Gradients written by Rashmi Ranjan Mohanty and published by . This book was released on 2009 with total page 225 pages. Available in PDF, EPUB and Kindle. Book excerpt: The diffuse-interface phase-field model is a powerful method to simulate and predict mesoscale microstructure evolution in materials using fundamental properties of thermodynamics and kinetics. The objective of this dissertation is to develop phase-field model for simulation and prediction of interdiffusion behavior and evolution of microstructure in multi-phase binary and ternary systems under composition and/or temperature gradients. Simulations were carried out with emphasis on multicomponent diffusional interactions in single-phase system, and microstructure evolution in multiphase systems using thermodynamics and kinetics of real systems such as Ni-Al and Ni-Cr-Al. In addition, selected experimental studies were carried out to examine interdiffusion and microstructure evolution in Ni-Cr-Al and Fe-Ni-Al alloys at 1000°C. Based on Onsager's formalism, a phase-field model was developed for the first time to simulate the diffusion process under an applied temperature gradient (i.e., thermotransport) in single- and two-phase binary alloys. Development of concentration profiles with uphill diffusion and the occurrence of zero-flux planes were studied in single-phase diffusion couples using a regular solution model for a hypothetical ternary system. Zero-flux plane for a component was observed to develop for diffusion couples at the composition that corresponds to the activity of that component in one of the terminal alloys. Morphological evolution of interphase boundary in solid-to-solid two-phase diffusion couples (fcc-[gamma] vs. B2-[beta]) was examined in Ni-Cr-Al system with actual thermodynamic data and concentration dependent chemical mobility. With the instability introduced as a small initial compositional fluctuation at the interphase boundary, the evolution of the interface morphology was found to vary largely as a function of terminal alloys and related composition-dependent chemical mobility. In a binary Ni-Al system, multiphase diffusion couples of fcc-[gamma] vs. L12-[gamma prime], [gamma] vs. [gamma]+[gamma prime] and [gamma]+[gamma prime] vs. [gamma]+[gamma prime] were simulated with alloys of varying compositions and volume fractions of second phase (i.e., [gamma prime]). Chemical mobility as a function of composition was employed in the study with constant gradient energy coefficient, and their effects on the final interdiffusion microstructure was examined. Interdiffusion microstructure was characterized by the type of boundaries formed, i.e. Type 0, Type I, and Type II boundaries, following various experimental observations in literature and thermodynamic considerations. Volume fraction profiles of alloy phases present in the diffusion couples were measured to quantitatively analyze the formation or dissolution of phases across the boundaries. Kinetics of dissolution of [gamma prime] phase was found to be a function of interdiffusion coefficients that can vary with composition and temperature. The evolution of interdiffusion microstructures in ternary Ni-Cr-Al solid-to-solid diffusion couples containing fcc-[gamma] and [gamma]+[beta] (fcc+B2) alloys was studied using a 2D phase-field model. Alloys of varying compositions and volume fractions of the second phase ([beta]) were used to simulate the dissolution kinetics of the [beta] phase. Semi-implicit Fourier-spectral method was used to solve the governing equations with chemical mobility as a function of compositions. The simulation results showed that the rate of dissolution of the [beta] phase (i.e., recession of [beta]+[gamma] two-phase region) was dependent on the composition of the single-phase [gamma] alloy and the volume fraction of the [beta] phase in the two-phase alloy of the couple. Higher Cr and Al content in the [gamma] alloy and higher volume fraction of [beta] in the [gamma]+[beta] alloy lower the rate of dissolution. Simulated results were found to be in good agreement with the experimental observations in ternary Ni-Cr-Al solid-to-solid diffusion couples containing [gamma] and [gamma]+[beta] alloys. For the first time, a phase-field model was developed to simulate the diffusion process under an applied temperature gradient (i.e., thermotransport) in multiphase binary alloys. Starting from the phenomenological description of Onsager's formalism, the field kinetic equations are derived and applied to single-phase and two-phase binary system. Simulation results show that a concentration gradient develops due to preferential movement of atoms towards the cold and hot end of an initially homogeneous single-phase binary alloy subjected to a temperature gradient. The temperature gradient causes the redistribution of both constituents and phases in the two-phase binary alloy. The direction of movement of elements depends on their atomic mobility and heat of transport values.

Download or read book Combined Molecular Dynamics and Phase Field Simulation of Crystal Melt Interfacial Properties and Microstructure Evolution During Rapid Solidification of TI NI Alloys written by Sepideh Kavousi and published by . This book was released on 2019 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Phase field Models of Microstructure Evolution in a System with Elastic Inhomogeneity and Defects written by Shenyang Hu and published by . This book was released on 2004 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Simulating Three dimensional Microstructure Evolution in the Region of Ultrahigh Volume Fractions of Coarsening Phase written by Hui Yan and published by . This book was released on 2014 with total page 300 pages. Available in PDF, EPUB and Kindle. Book excerpt: A three-dimensional (3D) phase-field model is developed to study the kinetic behavior and microstructure evolution by phase coarsening in the region of ultrahigh volume fractions. In this model, a two-phase system is described by concentration and orientation variables. The microstruture evolution is tracked by solving the time-dependent Cahn-Hilliard equation and Ginzburg-Landau equation. This 3D model is able to simulate the complex microstruture in the region of ultrahigh volume fractions. By employing the phase-field model, the 3D microstructure evolution by phase coarsening is studied over a series of volume fractions (Vv) between 0.9 and 1. Small-scale simulations are performed at the size of 128 x 128 x 128. It is found that the morphology of particles in the simulated microstructure shares some characteristic of that in grain growth. The scaling exponent m gradually decreases from 3 to 2, when the volume fraction approaches 1. These simulation predictions are different from previous research over lower volume fraction (Vv

Download or read book Fundamental and Practical Applications of Phase Field Method to the Study of Alloy Microstructure Evolutions written by Weiqi Luo and published by . This book was released on 2005 with total page 206 pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: The microstructure of a material has a great influence on its properties. Therefore, understanding underlying mechanisms of microstructural evolution is critical for developing desired properties. However, microstructural evolution is highly non-linear and, at this stage, fundamental quantitative understanding of it is limited. There has been an increasing demand lately for modeling and simulating microstructural evolution. That is not only because they have a relatively lower cost than experiment, and can be performed for arbitraries conditions, but also they can provide fundamental understanding of experimental observations, and its ability to predict the evolution. Moreover, a quantitative predictive model will be very usefully to guide process design in various industry applications. For this reason, many computer models have been developed. Among them, the phase field method has become a rigorous approach to simulating complex microstructural evolution, such as martensitic transformation, dendritic growth, dislocation movement and grain growth. The effect of nucleating ordered precipitates at dislocations and the subsequent growth on particle morphology in Ni-Al and Al-Li through phase field method study is presented in this thesis. Results show that this process yields the splitting pattern that is observed experimentally. In particular, the structural discontinuity associated with an edge dislocation may lead to the formation of an antiphase domain boundary within an ordered phase particle. At this stage, the application of phase field methods in industry is still limited because many phase field models are qualitative in nature. The development of a quantitative phase field model for the Fe-Cr-C system by designing an appropriate energy expression and linking the thermodynamic and kinetics parameters to quantitative databases is presented in this thesis. This model is validated and its capability is shown in the corresponding chapter.

Download or read book Titanium and Titanium Alloys written by Christoph Leyens and published by John Wiley & Sons. This book was released on 2006-03-06 with total page 532 pages. Available in PDF, EPUB and Kindle. Book excerpt: This handbook is an excellent reference for materials scientists and engineers needing to gain more knowledge about these engineering materials. Following introductory chapters on the fundamental materials properties of titanium, readers will find comprehensive descriptions of the development, processing and properties of modern titanium alloys. There then follows detailed discussion of the applications of titanium and its alloys in aerospace, medicine, energy and automotive technology.

Download or read book Microstructure Evolution During Warm Working of Ti 6Al 4V with a Colony Alpha Microstructure Preprint written by and published by . This book was released on 2008 with total page 25 pages. Available in PDF, EPUB and Kindle. Book excerpt: A high-resolution electron-backscatter-diffraction (EBSD) technique was employed to investigate microstructure evolution during warm working of Ti-6Al-4V with a colony alpha microstructure. Particular emphasis was paid to the specific mechanisms governing this process. Microstructure development was found to be driven mainly by the geometrical requirements of the imposed strain and by the kinking of alpha lamellae. For the most part, the lamellar microstructure was surprisingly stable during straining with limited globularization observed only in kinked alpha colonies. The kinking process was shown to be closely linked with the development of shear bands within the colonies. These observations suggest that changes in strain path may be beneficial in promoting globularization during warm working.

Download or read book Quantitative Study of Precipitate Growth in Ti 6al 4v Using the Phase Field Method written by Fan Yang and published by . This book was released on 2008 with total page 53 pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: Microstrucures play an important role in determining the properties of titanium alloys. This work employs the phase field method to study diffusional phase transformation and the accompanying microstructural evolutions in Ti-6Al-4V. The phase field method used in this work incorporated real thermodynamic and mobility data base and adopts the model proposed by Kim et al. to eliminate the inherent length scale problem in traditional phase field method. It also uses the sparse data structure and algorithm to achieve more efficient computing. Different initial microstructures are used to study how spatial and size distribution of the precipitate phase may influence the kinetics of precipitate growth. Compared to the case with particles of identical size, a normal size distribution of the alpha precipitates has little influence on the kinetics of precipitate growth. However, a uniform spatial distribution of the precipitates will slightly speed up the kinetics, compared to a system with a spatially random distributed precipitates. Grain boundary diffusion becomes dominant below to. It can speed up the kinetics much more and even alters the shapes of the grain boundary alpha phase during evolution. The grain boundary alpha layers developed by grain boundary diffusion may serve as nucleation sites for the secondary plate-like alpha precipitates. In this present study, a model is developed, which can capture the evolution of grain boundary alpha phase and its kinetics.

Download or read book Thermo Mechanical Modeling of Additive Manufacturing written by Michael Gouge and published by Butterworth-Heinemann. This book was released on 2017-08-03 with total page 296 pages. Available in PDF, EPUB and Kindle. Book excerpt: Thermo-mechanical Modeling of Additive Manufacturing provides the background, methodology and description of modeling techniques to enable the reader to perform their own accurate and reliable simulations of any additive process. Part I provides an in depth introduction to the fundamentals of additive manufacturing modeling, a description of adaptive mesh strategies, a thorough description of thermal losses and a discussion of residual stress and distortion. Part II applies the engineering fundamentals to direct energy deposition processes including laser cladding, LENS builds, large electron beam parts and an exploration of residual stress and deformation mitigation strategies. Part III concerns the thermo-mechanical modeling of powder bed processes with a description of the heat input model, classical thermo-mechanical modeling, and part scale modeling. The book serves as an essential reference for engineers and technicians in both industry and academia, performing both research and full-scale production. Additive manufacturing processes are revolutionizing production throughout industry. These technologies enable the cost-effective manufacture of small lot parts, rapid repair of damaged components and construction of previously impossible-to-produce geometries. However, the large thermal gradients inherent in these processes incur large residual stresses and mechanical distortion, which can push the finished component out of engineering tolerance. Costly trial-and-error methods are commonly used for failure mitigation. Finite element modeling provides a compelling alternative, allowing for the prediction of residual stresses and distortion, and thus a tool to investigate methods of failure mitigation prior to building. - Provides understanding of important components in the finite element modeling of additive manufacturing processes necessary to obtain accurate results - Offers a deeper understanding of how the thermal gradients inherent in additive manufacturing induce distortion and residual stresses, and how to mitigate these undesirable phenomena - Includes a set of strategies for the modeler to improve computational efficiency when simulating various additive manufacturing processes - Serves as an essential reference for engineers and technicians in both industry and academia

Download or read book Phase Transformations and Evolution in Materials written by Patrice E. A. Turchi and published by Minerals, Metals, & Materials Society. This book was released on 2000 with total page 432 pages. Available in PDF, EPUB and Kindle. Book excerpt: This is a collection of papers presented at the TMS Annual Meeting & Exhibition, held in Nashville, Tennessee, in March, 2000. The symposium emphasizes both theoretical and experimental aspects of phase transformations and evolutions in materials. Topics addressed in papers include: mechanical properties of structurally heterogeneous systems; simulations of structural transformations; large-scale modelling of microstructure evolution in martensites; applying the concentration wave method to predict ordering phenomena in substitutional alloys and ceramic materials; and use of the phase field method to study coherent transformations.

Download or read book Crystal Plasticity Finite Element Methods written by Franz Roters and published by John Wiley & Sons. This book was released on 2011-08-04 with total page 188 pages. Available in PDF, EPUB and Kindle. Book excerpt: Written by the leading experts in computational materials science, this handy reference concisely reviews the most important aspects of plasticity modeling: constitutive laws, phase transformations, texture methods, continuum approaches and damage mechanisms. As a result, it provides the knowledge needed to avoid failures in critical systems udner mechanical load. With its various application examples to micro- and macrostructure mechanics, this is an invaluable resource for mechanical engineers as well as for researchers wanting to improve on this method and extend its outreach.