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Image analysis and modeling of spherical and channel microstructures of fuel-cell materials

IEEE TRANSACTIONS ON NANOTECHNOLOGY 2005年第5期4卷 616-631页

作者： Zhang, JZ Wu, QMJ Shi, ZQ Holdcroft, S Natl Res Council Canada Inst Fuel Cell Innovat MicroTechnol & Sensing Grp Vancouver BC V6T 1W5 Canada Univ Windsor Dept Elect & Comp Engn Windsor ON N9B 3P4 Canada Natl Res Council Canada Inst Fuel Cell Innovat Membrane Electrode Assembly Grp Vancouver BC V6T 1W5 Canada Simon Fraser Univ Dept Chem Burnaby BC V5A 1S6 Canada

The development of novel fuel-cell materials demands accurate and flexible microstructure characterization techniques. Conventional electron microscopy-based microstructural morphology analysis is carried out through the conceptual interpretation of transmission electron microscope images. With this method, only qualitative information on material morphologies can usually be obtained. This paper presents a digital image analysis system that deals with the automatic measurement and quantitative characterization of the microstructural morphologies of polymer electrolyte membrane fuel-cell materials. In this approach, two types of essential microstructural morphologies (spheral particles and interconnected graft channels) are modeled based on statistical geometry theory, and the statistical analysis schemes of the microstructural morphologies are designed and applied to the characterization of the phase-separated microstruclures in fuel-cell components such as solid electrolyte ionomers, catalyst layers, and gas diffusion layers. Experimental results on real fuel-cell materials specimens demonstrate the effectiveness of the method.

关键词： fuel-cell materials image analysis microstructure modeling statistical analysis stochastic geometry system implementation

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Simulation of diffusion-limited lateral growth of dendrites during solidification via liquid metal cooling

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ACTA MATERIALIA 2014年 69卷 47-59页

作者： Miller, J. D. Yuan, L. Lee, P. D. Pollock, T. M. AFRL RXCM Wright Patterson AFB OH USA Univ Michigan Dept Mat Sci & Engn Ann Arbor MI 48109 USA GE Global Res Niskayuna NY 12309 USA Univ Manchester Sch Mat Manchester Xray Imaging Facil Manchester M13 9PL Lancs England Univ Calif Santa Barbara Dept Mat Engn Santa Barbara CA 93106 USA

Directional solidification via the liquid metal cooling process results in refined microstructure and reduced defects, thus providing improved mechanical performance of single crystal (SX) materials. However, the enhanced heat extraction inherent to the process results in a curved solidification front that may lead to non-axial growth of dendrites near the casting walls. The mechanism by which the lateral growth occurs has been investigated by microstructure modeling via solute-adjusted, diffusional growth of dendrites. Local thermal profiles derived from continuum solidification models were used as inputs to a dendrite-growth model capable of simulations in both two and three dimensions. A finite difference calculation of the diffusion field and volume of fluid tracking for the growth of the dendrite front was coupled to predict the microstructure evolution during directional solidification. Model predictions were compared to experimentally observed dendritic structures. In addition, a parametric analysis was conducted to evaluate the sensitivity of the dendrite-growth mode to changes in thermal, structural (such as dendrite position and spacing) and model parameters. The inclination angle of the solidification front strongly influenced the evolution of dendritic structure. The degree of misorientation of the < 0 0 1 > SX orientation from the withdrawal axis significantly contributed to the onset of lateral dendritic growth. Published by Elsevier Ltd. on behalf of Acta Materialia Inc.

关键词： LMC directional solidification microstructure modeling Dendrite growth

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modeling OF TWO-PHASE GRAIN STRUCTURE IN THE TITANIUM ALLOY TI-6AL-4V USING CELLULAR AUTOMATA

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INTERNATIONAL JOURNAL FOR MULTISCALE COMPUTATIONAL ENGINEERING 2014年第1期12卷 23-31页

作者： Krumphals, Alfred Poletti, Cecilia Warchomicka, Fernando Stockinger, Martin Sommitsch, Christof Graz Univ Technol Inst Mat Sci & Welding Christian Doppler Lab Mat Modelling & Simulat A-8010 Graz Austria Vienna Univ Technol Inst Mat Sci & Technol A-1040 Vienna Austria Bohler Schmiedetech GmbH & Co KG Kapfenberg Austria

The static coarsening behavior of the alpha-beta titanium alloy Ti-6A1-4V during heat treatments is modeled using a probabilistic cellular automata model (CA). For this purpose the kinetics of grain growth is described via transformation probabilities which are determined by diffusion mechanisms at grain and phase boundaries. For temperature changes an algorithm is implemented which adjusts the fraction of alpha and beta phase to reach equilibrium phase values. Hence, the CA is capable of calculating grain coarsening as well as grain dissolution in the two-phase area during heating and isothermal treatments at forging temperature. For these calculations, an initial microstructure is used as input and it can be imported from either virtual created microstructures, real micrographs, or electron bacicscatter diffraction (EBSD) maps. The model output includes mean diameter, grain size distribution, and virtually simulated microstructures which can be easily compared with experimental micrographs. Examples showing a good correlation between the predicted microstructures and experimental results, as well as data from literature, are presented in this work. The successful implementation of this model will lead to predictions of behavior in other dual-phase alloys.

关键词： microstructure modeling grain growth Ti-6A1-4V cellular automata

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Simulation of Dendritic Growth with Different Orientation by Using the Point Automata Method

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CMC-COMPUTERS MATERIALS & CONTINUA 2010年第1期18卷 69-103页

作者： Lorbiecka, A. Z. Sarler, B. Univ Nova Gorica Lab Multiphase Proc Nova Gorica Slovenia

The aim of this paper is simulation of thermally induced liquid-solid dendritic growth in two dimensions by a coupled deterministic continuum mechanics heat transfer model and a stochastic localized phase change kinetics model that takes into account the undercooling, curvature, kinetic and thermodynamic anisotropy The stochastic model receives temperature information from the deterministic model and the deterministic model receives the solid fraction information from the stochastic model The heat transfer model is solved on a regular grid by the standard explicit Finite Difference Method (FDM) The phase-change kinetics model is solved by the classical Cellular Automata (CA) approach and a novel Point Automata (PA) approach The PA method was developed and introduced in this paper to circumvent the mesh anisotropy problem, associated with the classical CA method Dendritic structures are in the CA approach sensitive on the relative angle between the cell structure and the preferential crystal growth direction which is not physical The CA approach is established on quadratic cells and Neumann neighborhood The PA approach is established on randomly distributed points and neighbourhood configuration, similar as appears in meshless methods Both methods provide same results in case of regular PA node arrangements and neighborhood configuration with five points A comprehensive comparison between both stochastic approaches has been made with respect to curvature calculations, dendrites with different orientations of crystallographic angles and types of the node arrangements randomness It has been shown that the new method can be used for calculation of the dendrites in any direction

关键词： microstructure modeling solidification dendritic growth cellular automata method (CA) point automata method (PA) random node arrangement

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Evaluation of an Al-Ce alloy for laser additive manufacturing

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ACTA MATERIALIA 2017年 126卷 507-519页

作者： Plotkowski, A. Rios, O. Sridharan, N. Sims, Z. Unocic, K. Ott, R. T. Dehoff, R. R. Babu, S. S. Univ Tennessee Dept Mech Aerosp & Biomed Engn Knoxville TN 37996 USA Oak Ridge Natl Lab Mfg Demonstrat Facil Knoxville TN 37932 USA Oak Ridge Natl Lab Mat Sci Technol Div Oak Ridge TN 37831 USA Univ Tennessee Bredesen Ctr Interdisciplinary Res Knoxville TN 37996 USA Ames Lab Div Mat Sci Engn Ames IA 50011 USA Oak Ridge Natl Lab Energy & Transportat Sci Div Oak Ridge TN 37831 USA

This study focuses on the development of a design methodology for alloys in AM, using a newly developed Al-Ce alloy as an initial case study. To evaluate the candidacy of this system for directed energy deposition processes, single-line laser melts were made on cast Al-12Ce plates using three different beam velocities (100, 200, and 300 min/min). The microstructure was evaluated in the as melted and heat treated conditions (24 h at 300 degrees C). An extremely fine microstructure was observed within the melt pools, evolving from eutectic at the outer solid-liquid boundaries to a primary Al FCC dendritic/cellular structure nearer the melt-pool centerline. The observed microstructures were rationalized through the construction of a microstructure selection map for the Al-Ce binary system, which will be used to enable future alloy design. Interestingly, the heat treated samples exhibited no micro structural coarsening. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

关键词： Additive manufacturing Al alloys microstructure control microstructure modeling

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Exploring spatial beam shaping in laser powder bed fusion: High-fidelity simulation and in-situ monitoring

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ADDITIVE MANUFACTURING 2024年 93卷

作者： Bayat, Mohamad Rothfelder, Richard Schwarzkopf, Karen Zinoviev, Aleksandr Zinovieva, Olga Spurk, Christoph Hummel, Mark Olowinsky, Alexander Beckmann, Felix Moosmann, Julian Schmidt, Michael Hattel, Jesper H. Tech Univ Denmark DTU Dept Mech Engn Bldg 425 DK-2800 Lyngby Denmark Friedrich Alexander Univ Erlangen Nurnberg Lehrstuhlur Photon Technol LPT Prof Schmidt Konrad Zuse Str 3-5 D-91052 Erlangen Germany Grad Sch Adv Opt Technol SAOT Paul Gordan Str 6 DK-91052 Erlangen Denmark Rhein Westfal TH Aachen Chair Laser Technol LLT Steinbachstr 15 D-52074 Aachen Germany Fraunhofer Inst Laser Technol ILT Steinbachstr 15 D-52074 Aachen Germany Helmholtz Zentrum Hereon Inst Mat Phys Max Planck Str 1 D-21502 Geesthacht Germany Univ New South Wales UNSW Canberra Sch Engn & Technol Northcott Dr Campbell ACT 2612 Australia

Laser beam shaping is a novel and relatively unexplored method for controlling the melt pool conditions during metal additive manufacturing (MAM) processes, but even so it still holds good promise for achieving site-specific tailored properties. In this work, a comprehensive numerical and experimental campaign is carried out to explore this subject within metal laser powder bed fusion (LPBF). More specifically, a multiphysics numerical model is implemented for simulating the heat and fluid flow conditions during LPBF of Ti6Al4V using arbitrary circular beam shapes with various power distributions spanning from a pure Gaussian beam to a pure ring beam profile. The model is subsequently coupled with cellular automata to describe the beam shape effects on the microstructure evolution. Model validation is carried out in a two-fold manner. First, we compare the predicted melt pool cross-section with the one from ex-situ single track experiments, and we find a deviation of less than 9 % in melt pool dimensions. Secondly, advanced in-situ X-ray monitoring is carried out to unravel the melt pool dynamics and we find that the predicted morphology closely matches the in-situ X-ray results. Moreover, it is shown that at lower laser power, a bulge of liquid metal forms at the center of the melt pool when employing ring profiles, and this is ascribed to the absence of recoil pressure at the center of the ring beam. Furthermore, increasing the laser power seems to destabilize the melt pool regime, as the central bulge transforms into a liquid metal jet that periodically collapses and breaks up into hot spatter. Based on the results, we believe that our multiphysics modelling methodology, opens up new pathways for predicting how laser beam shaping influences porosity, surface roughness as well as microstructure formation in LPBF processes.

关键词： Beam shaping Ring-spot beam shape Laser powder bed fusion In-situ monitoring Multiphysics simulation microstructure modeling

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A three-dimensional sharp interface model for the quantitative simulation of solutal dendritic growth

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ACTA MATERIALIA 2010年第1期58卷 340-352页

作者： Pan, Shiyan Zhu, Mingfang Southeast Univ Sch Mat Sci & Engn Jiangsu Key Lab Adv Metall Mat Nanjing 211189 Peoples R China

A three-dimensional (3-D) sharp interface model is developed to simulate the solutal dendritic growth in the low Peclet number regime. The model adopts a previously proposed solutal equilibrium approach to calculate the evolution of the solid/liquidinterface. To describe specific crystallographic orientations of 3-D dendritic growth, a weighted mean curvature algorithm incorporated with the anisotropy of surface energy is proposed, allowing the simulation of 3-D dendrites with various orientations in a straightforward manner. The model validation is performed by comparing the simulations with the analytical predictions and experimental data for both single and multi-dendritic growth, which demonstrates the quantitative capabilities of the proposed model. The model efficiently reproduces realistic 3-D multi-equiaxed and columnar dendrites with various orientations and well-developed side branches. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

关键词： microstructure modeling Solutal dendritic growth Weighted mean curvature Three dimensions

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Understanding grain evolution in additive manufacturing through modeling

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ADDITIVE MANUFACTURING 2018年 21卷 255-268页

作者： Akram, Javed Chalavadi, Pradeep Pal, Deepankar Stucker, Brent 3DSIM LLC 1794 Olymp PkwySuite 110 Park City UT 84098 USA

Variability in the mechanical properties of additively manufactured metal parts is a key concern for their application in service. One of the parameters affecting the above-mentioned property is solidification texture which is driven by scan patterns and other process variables. Understanding of how these textures arise in the AM process can provide a pathway to control these features which ultimately decide the final structural material properties. In this work, a Cellular Automata (CA) based two-dimensional microstructure model is formulated and implemented to understand grain evolution in AM. Grain evolution in multilayer depositions using various scan patterns in Directed Energy Deposition (DED), Metal Laser Sintering/Selective Laser Melting (MLS/SLM), and Electron Beam Melting (EBM) is presented and qualitatively compared with reported literature. Results show strong correlation of scan patterns with evolving grain orientations. Variability in grain size and orientation evolution during SLM and EBM processing of metallic materials showed direct influence by exposure to different cooling rates and thermal gradients. The similarities between the simulated and reported results lead us to conclude CA based modeling for predicting grain orientation and size in metal AM processes is useful for prediction of continuum level structural properties at global and local length scales.

关键词： Additive manufacturing microstructure modeling Grain orientation Selective laser melting Electron beam melting

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Fundamental aspects of the martensite transformation curve in Fe-Ni-X and Fe-C alloys

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JOURNAL OF MATERIALS RESEARCH AND TECHNOLOGY-JMR&T 2018年第4期7卷 499-507页

作者： Costa Guimaraes, Jose Roberto Rios, Paulo Rangel Univ Fed Fluminense Escola Engn Ind Met Volta Redonda Trabalhadores420 BR-27255125 Volta Redonda RJ Brazil

This work initially reviews fundamental aspects of nucleation and growth of martensite. Next, based on previous work as well as on new unpublished work it proposes a probabilistic formalism to describe/analyze the martensite transformation curves. Furthermore, it discusses the autocatalysis that modulates the advance of martensite's nucleation determined by the stability of the alloy-system. The accommodation of the transformation strains that gives the volume fraction transformed refers to (local) interactions among growing units as well with the austenite matrix. The scarcity/randomness of martensite nucleation loci in the austenite, which promotes the initially scattered transformation, as well as underlies the microstructural evolution. The formalism was validated by fitting the transformation curves typical of the athermal as well as of the thermal-activated martensites. (C) 2018 Brazilian Metallurgical, Materials and Mining Association. Published by Elsevier Editora Ltda. This is an open access article under the CC BY-NC-ND license (https://***/licenses/by-nc-nd/4.0/).

关键词： Martensitic transformations microstructure modeling Phase transformations Steels Fe-Ni-X alloys

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Cellular automaton simulation of microstructure evolution during austenite decomposition under continuous cooling conditions

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BULLETIN OF MATERIALS SCIENCE 2001年第3期24卷 305-312页

作者： Varma, MR Sasikumar, R Pillai, SGK Nair, PK Reg Res Lab Trivandrum 695019 Kerala India Indian Inst Technol Dept Met Engn Madras 600036 Tamil Nadu India

A two-dimensional diffusion based model is developed to describe transformation of austenite into ferrite and pearlite under continuous cooling conditions. The nucleation of ferrite is assumed to occur over grain boundaries and the nucleation of pearlite is assumed to be taking place all over the grain and at growing ferrite-austenite interfaces, when the composition and temperature conditions are favourable. A cellular automaton algorithm with transformation rules based on this model is used for the growth of ferrite and pear-lite, Model predicted results for continuous cooling transformations are verified by comparing the model predicted microstructure features with the experimental measurements for two sets of plain carbon steels of different composition and austenite grain size. Using the model, it is possible to generate results like undercooling to start ferrite and pearlite transformations, which are difficult to obtain experimentally.

关键词： microstructure modeling CCT diagrams austenite ferrite pearlite nucleation and growth

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