Computational Thermodynamics and Kinetics: Poster Session
Sponsored by: TMS: Chemistry and Physics of Materials Committee, TMS: Computational Materials Science and Engineering Committee
Program Organizers: Niaz Abdolrahim, University of Rochester; Stephen Foiles, Sandia National Laboratories; James Morris, Oak Ridge National Laboratory; Raymundo Arroyave, Texas A & M University

Monday 6:00 PM
February 27, 2017
Room: Hall B1
Location: San Diego Convention Ctr

B-9: A Mathematical Model for the Heat Preservation of Torpedo Ladle: Shiwei Liu1; 1Xi'an University of Architecture and Technology
    Torpedo ladle is mainly used as a holding, transport, storage vessel. In order to reduce the heat loss from a variety of factors, in the present work, a mathematical model was established. According to the simulation, a model of radiation heat transfer of slag surface was calculated to improve the data exactitude. A mathematical model based on the radiation heat transfer model was established to predict the heat loss and temperature variation of molten iron. The results show that the vessel will obtain better thermal insulation properties after the application of a nanoporous material thermal insulating lining which possesses smaller thermal conductivity. The temperature of the torpedo ladle shell can be reduced to 155℃ by using a 16mm thick nanoporous material lining as a thermal insulating lining.

B-11: Control Technique Study of Non-metallic Inclusions in Low Carbon Steel by Rare Earth Final Deoxidization: Peng Bowen1; 1Shanghai University
    Thermodynamic calculations were carried out to analyze the formation mechanism of inclusion in low carbon steel by rare earth final deoxidization. The deoxidization and alloying process of steelmaking was stimulated in laboratory. The inclusions in as-cast samples were extracted with the method of non-aqueous solution electrolysis. Scanning electron microscope (SEM) with energy dispersive spectrometer (EDS) was used to analyze the chemical composition, three-dimensional morphology and size distribution of the inclusions. The calculation result showed that the Al-Mg-Ce-O complex inclusions can be formed when the content of rare earth increases to a proper value, and it has lower melting point than magnesium aluminate spinel, which is harmful to the property of steel. The experimental result showed that, the three-dimensional morphology of Al-Mg-Ce-O complex inclusions is spherical, and the mean diameter of that is about 5 μm. Furthermore, the formation mechanism and the control technique of complex inclusion were discussed.

B-12: Developing Iridium-based Alloys as Effective Catalysts for Direct Ethanol Fuel Cells: Lida Mehdizadegan Namin1; Nathaniel Deskins1; Koretaka Yuge2; 1Worcester Polytechnic Institute; 2Kyoto University
    Fuel cells enable the conversion of different chemicals directly into electrical energy, and are much more efficient than conventional combustion engines. Direct ethanol fuel cells (DEFCs) use ethanol as a fuel source. However, DEFCs are not commercialized due to the lack of an efficient catalyst. Iridium alloys are promising catalysts as they possess high catalytic activity and are much cheaper than platinum, the traditional fuel cell catalyst. Synthesizing all possible alloys experimentally is a burdensome task which is not economically feasible. As a result, in this study we have developed realistic atomic models of iridium alloys in DEFCs. Since density functional theory (DFT) methods are limited by finite computation power, we used the combination of DFT with statistical physics methods such as cluster expansion (CE). Our results show that iridium alloys are really effective in the ethanol oxidation reaction in DEFCs.

B-13: Effect of Cooling Rate on Phase Transformation and Microstructure Evolution in a Large Size Forged Ingot of Medium Carbon Low Alloy Steel: Emna Ben Fredj1; Hadi Ghasemi Nanesa1; Davood Shahriari1; Jean-Benoit Morin2; Mohammad Jahazi1; 1ÉTS; 2FINKL STEEL - SOREL
    In the present study, the influence of cooling rate on the kinetics of phase transformation is investigated in large size forged ingots made of medium carbon low alloy steel. In particular, the volume fraction of martensite after quenching is determined. Dilatometry tests were conducted on Gleeble® 3800 thermomechanical simulator to determine the transformation temperatures and identify the phases after different heat treatment cycles. The heat treatment tests were carried out at 900 ºC with a heating rate of 5 ºC/s, followed by holding for 1800 s after which the samples were cooled at 3 and 15 ºC/s. Optical and electron microscopic analyses, X-Ray Diffraction and micro-hardness measurements were utilized to identify and quantify the volume fraction of martensite and retained austenite for each condition. The calculated volume fraction of martensite using mathematical analysis was compared with those calculated by Koistinen-Marburger equation.

B-14: First-principles Study on Interface Segregation for MoSi2-Mo5Si3 Pseudobinary Alloys: Koretaka Yuge1; Toshihiro Yamazaki2; Yuichiro Koizumi2; Kyosuke Kishida1; Haruyuki Inui1; 1Department of Materials Science and Engineering, Kyoto University; 2Tohoku University
    MoSi2-Mo5Si3 pseudobinary alloys can form C11b/D8m labyrinth structure, considered as the promising candidate for ultra-high temperature structural material improving gas turbine engine performance in power generation systems. To modify mechanical properties through changing the interface morphology, we have proposed strategy to add two elements, one can well solute to parent phases, and another exhibit strong segregation to the interface, where the former can effectively modify lattice misfit, and the latter can lead to structural refinement. It therefore becomes essentially important to understand the interface segregation behavior with a variety of combination of additive elements, which has not been theoretically well addressed so far. In the present study, based on first-principles calculation, we focus on how the segregation energy of one element changes with the existence of the second additive element, and quantitatively estimate interface segregation profile at finite temperature with a combination of statistical thermodynamics approach using Monte Carlo simulation.

B-15: Formation and Control of CaS Inclusion in Gear Steel 20MnCr5: Xu Jie1; Fu Jianxun1; Wu Yanxin1; Li Xu1; 1Shanghai University
    The modification of (CaO)m(Al2O3)n inclusion and the fact of CaS inclusion formation in gear steel 20MnCr5 after calcium treatment have been studied by thermodynamic equilibrium calculation using the Factsage. Based on the thermodynamic equilibrium, when the liquid steel containing 0.035% [Al],the mass fraction of sulfur is lower than 0.0077% and the ratio of w(Ca)/w(Al) is higher than 0.12,the lower melting point 12(CaO)·7(Al2O3) inclusion will form in the molten steel. The stable CaS inclusion can not form itself under the condition of this composition experimental steel. When the temperature of molten steel drop to 1725.5K and the sulfide content reached 0.0159% at the frontier of solidification, The CaS inclusions are precipitated by the reaction of sulfur with CaO of the surface layer of lower melting point 12(CaO)·7(Al2O3).To avoid it precipitate CaS inclusion in solidification processing, the mass fraction of sulfur must be controlled below 0.000522%.

B-16: Kinetics of the α/γ Interface Migration in Fe-Mn and Fe-Ni Alloys: Jianing Zhu1; Hao Chen1; Chi Zhang1; Zhigang Yang1; Haiwen Luo2; 1Tsinghua University; 2University of Science&Technology Beijing
    The austenite (γ)→ferrite(α) and ferrite(α)→austenite (γ) transformation in Fe-based alloys have received particular concern in the past decades due to their both theoretical and practical importance. In this work, kinetics of the α→γ and γ→α transformation in a series of Fe-xMn and Fe-xNi (x=1w.t.% to 12w.t.%) has been experimentally investigated. A so-called GEB model, in which chemical driving force at the migrating interfaces is assumed to be balanced by Gibbs energy dissipation due to alloying elements diffusion inside the interface and interface friction, has been applied to modeling the kinetics of the α→γ and γ→α transformation. A kinetic transition from partitioning to partitionless mode is predicted to occur during the α→γ and γ→α transformation, which is in good agreement with experimental results. Value of the intrinsic α/γ interface mobility is also derived from experiments.

B-17: Investigations on the Mechanical Deformation of Amorphous Alloy Nanowires Using Phase-field Modeling and Thermodynamics Avalanche Models: G.P. Zheng1; 1Hong Kong Polytechnic University
    In spite of the encouraging progresses in the preparations and applications of nano-glasses and nano-sized amorphous alloys, our understanding on their mechanical behaviours and the deformation mechanisms is still incomplete to the extent that impedes the progress in their practical applications. In this work, we investigate the size effects on the mechanical behaviors of amorphous alloys under tensile deformation using computer simulations such as phase-field modeling and a thermodynamics avalanche model. The relation between the mechanical properties of nano-glasses and nano-sized amorphous alloys and their intrinsic defects are elucidated. In particular, the size effects caused by the density of deformation defects on the boundaries of nano-glasses and on the surfaces of nano-wires are quantitatively determined in comparisons with the avalanche model. The simulation provides deep insights into the emergence of ductility in nano-glasses and amorphous nano-wires.

B-18: Modeling of the Molar Volume of the Al-Co-Ni-W System: Ursula Kattner1; Eric Lass1; Peisheng Wang1; 1National Institute of Standards and Technology
    The CALPHAD method, originally developed for modeling thermochemical properties and phase diagrams of alloy systems, has since its inception been expanded to describe diffusion mobilities for the simulation of diffusional processes. Molar volume and compressibility were only described for a few systems with much of the focus on temperature and pressure dependence. Although molar volume is a property that is needed for the simulation of numerous materials processes it has been included only in a handful of proprietary CALPHAD databases. A new thermodynamic database for Co-based gamma/gamma-prime which is being developed by CHiMaD (Center for Hierarchical Materials Design) and NIST will also include descriptions of the composition and temperature dependence of the molar volume for all phases. The Al-Co-Ni-W system is a fundamental subsystem for these alloys. Assessments of the model descriptions of the molar volume of the unaries and binaries of this subsystem will be presented.

B-19: Morphological Stability of Rods: Fei Wang1; Oleg Tschukin1; Michael Selzer1; Britta Nestler1; 1Karlsruhe Institute of Technology
    The classical well-known morphological stability criterion, according to Plateau-Rayleigh (PR) theory, was systematically corrected, considering both linear/non-linear stability analysis as well as energetic concept. Analyzing the initial curvature distribution, we propose an alternative stability which dramatically improves existing theories. We find a metastable region for the critical configuration from the energetic concept and further identify the stability criterion by examining the morphological changing mechanisms: surface diffusion and mean curvature flow. The thermodynamically consistent phase-field models capture these two mechanisms and strongly confirm the present criterion.

B-20: Role of the Particle Morphology on the Zener Pinning Effect: A Phase-field Approach: Kunok Chang1; Junhyun Kwon1; Chgan-Kyu Rhee1; 1Korea Atomic Energy Research Institute
    Incorporating second-phase particles is one of the most efficient way to prevent grain growth during the sintering process. Therefore, it is important to understand the grain boundary/second-phase particle interaction to design the material with the optimal mechanical properties. We investigated a role of the second-phase particle morphology on pinning effect using the phase-field approach. We performed large-scale 3D grain growth simulations with the presence of the various shape of the second-phase particles, such as spherical or cubical/cuboidal particles. We quantitatively measured the pinning effect depending particle orientation as well as particle morphology using the phase-field method. The obtained simulation results were compared with the experimental observation using HRTEM.

B-22: Studies on the Effect of Solution Heat Treatment on Surface and Subsurface Microstructure in Single Crystal Superalloys: Dimitra Spathara1; Duncan Putman2; Nils Warnken1; 1University of Birmingham; 2Rolls-Royce Plc.
    Single crystal superalloys are commonly solution heat treated under high vacuum conditions to remove microsegregation and dissolve secondary solidification phases. Microstructural modifications beneath the surface have been reported after heat treatment, which involve formation of TCP phases and melting of surface layers. The present study uses experimental and computational tools to demonstrate the extent of surface modification during heat treatment of CMSX-4 and CMSX-10. Both alloys show different response to heat treatment and the degree to which surface modification takes place differs. It is demonstrated that elemental loss is the cause for this kind of reaction. The proposed mechanism is rationalised using thermodynamic modelling, which involves using CALPHAD type databases. The differences in behaviour between CMSX-4 and CMSX-10 are explained.

B-23: The Environment Dependent Dynamic Charge Potential for III-V Materials: Abduljabar Alsayoud1; Abu Asaduzzaman1; Keith Runge1; Pierre Deymier1; Krishna Muralidharan1; 1University of Arizona
    The recently developed environment-dependent dynamic charge (EDD-Q) interatomic potential provides comprehensive framework for modeling molecules, nanostructures and the bulk counterparts. Specifically, EDD-Q incorporates a hierarchical approach towards potential parameterization where charge/electron density variations within a material system are systematically parameterized as a function of the chemical environment. This enables capturing the underlying chemistry of electrons. Further, the functional form of EDD-Q can be adapted to either the embedded atom or bond-order potential forms, enabling easy integration with already available atomistic modeling codes. The data-set for parameterization are generated from electron density and thermochemical data obtained from first-principles calculations. In this work, we present the development of EDD-Q potentials for a wide variety of materials that include the III-V semiconductors. We show that EDD-Q can successfully emulate the underlying first-principles calculations and model transport properties such as thermal conductivity, viscosity and diffusion properties that were not included in the training sets.

B-24: Thermodynamic Modeling of Al-Fe-Cr Ternary System: Shusen Wang1; Zhu Li1; Zhiwei Qin1; Shihua Wang1; Xionggang Lu1; Chonghe Li1; 1Shanghai University
    The Al-Fe-Cr ternary system is one of the most important systems to developing aluminum alloys. Up to now, although several reviews about this ternary system have been available, however no thermodynamic assessment was published. In this paper, previous work of the Al-Fe-Cr ternary system and its related binary systems are reviewed. Then, Al-Cr binary system was re-assessed in order to better describe the phases Al8(Cr, Fe)5 in ternary system. Based on the re-assessed Al-Cr binary system and Al-Fe, Fe-Cr binary systems assessed before, as well as the experimental data reported in the literature, the Al-Fe-Cr ternary system was assessed by means of CALPHAD method. Isothermal sections of 1433K, 1348K, 1273K, 1173K, 1073K and 973K in Al-rich corner and some invariant reactions are calculated. It is shown that the present calculations are in good agreement with the most of the experimental results.

B-25: Thermodynamically Based Comparisons of GMCE Refrigerant Performance: Timothy Brown1; Patrick Shamberger1; 1Texas A&M University
    Despite optimizing giant magnetocaloric effect (GMCE) in key material systems (MnFeX, La(Fe,Si)13, NiMnX Heusler alloys), practical GMCE-based magnetic refrigeration is unrealized. One problem is the lack of direct cycle-based performance comparisons between GMCE refrigerants, so that despite much magneto-thermal characterization, it remains unclear which material is optimal for a given application. Further experimental investigations are unfeasible, since performance metrics (e.g., cooling power, % Carnot efficiency) are both material- and cycle-dependent, with additional complications arising from hysteretic path-dependence. Here we present an alternative thermodynamic modeling approach, combining Preisach hysteresis models with experimental data sets to simulate GMCE alloys' state evolution under specified cyclic conditions. Performance metrics are calculated and compared for alloy compositions within each GMCE class undergoing magnetic Ericsson and Brayton cycles between 0 and 1.5 T. Hence for the first time, we directly compare the cycle-dependent performance of GMCE alloys, specifying trends in which are optimal for given applications.