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Yang Y.,Oak Ridge National Laboratory | Chen S.-L.,CompuTherm LLC
Calphad: Computer Coupling of Phase Diagrams and Thermochemistry | Year: 2017

Phosphorus is a primary contributor to interface fracture and embrittlement in steels because of its strong segregation tendency at grain boundaries (GBs). The lack of consistency in literature data imposes great difficulties in performing segregation modeling that is compatible with both the Langmuir-Mclean segregation theory and the thermodynamic description of the Bcc(Fe,P) phase. This work carefully evaluated experimental data for phosphorus segregation at GBs in α-Fe and provided a new formula for converting the auger electron spectroscopy (AES) peak height ratio to GBs. Based on newly assessed literature data, this work proposes that the major driving force for phosphorus segregation is the formation of Fe3P-type clusters at GBs, which is supported not only by the almost equivalent Gibbs energy of α_Fe using the Bcc(Fe,P) substitutional model and the Bcc(Fe,Fe3P, P) associate model, but also by the good agreement between thermodynamic/kinetic modeling results and experimental data. © 2017 Elsevier Ltd


Wen Y.H.,Air Force Research Lab | Wen Y.H.,UES, Inc. | Lill J.V.,High Performance Technologies Inc. | Chen S.L.,CompuTherm LLC | Simmons J.P.,Air Force Research Lab
Acta Materialia | Year: 2010

A ternary phase-field model was developed that is linked directly to commercial CALPHAD software to provide quantitative thermodynamic driving forces. A recently available diffusion mobility database for ordered phases is also implemented to give a better description of the diffusion behavior in alloys. Because the targeted application of this model is the study of precipitation in Ni-based superalloys, a Ni-Al-Cr model alloy was constructed. A detailed description of this model is given in the paper. We have considered the misfit effects of the partitioning of the two solute elements. Transformation rules of the dual representation of the γ + γ′ microstructure by CALPHAD and by the phase field are established and the link with commercial CALPHAD software is described. Proof-of-concept tests were performed to evaluate the model and the results demonstrate that the model can qualitatively reproduce observed γ′ precipitation behavior. Uphill diffusion of Al is observed in a few diffusion couples, showing the significant influence of Cr on the chemical potential of Al. Possible applications of this model are discussed. © 2009 Acta Materialia Inc.


Senkov O.N.,Air Force Research Lab | Zhang F.,CompuTherm LLC | Miller J.D.,Air Force Research Lab
Entropy | Year: 2013

Microstructure and phase composition of a CrMo0.5NbTa0.5TiZr high entropy alloy were studied in the as-solidified and heat treated conditions. In the as-solidified condition, the alloy consisted of two disordered BCC phases and an ordered cubic Laves phase. The BCC1 phase solidified in the form of dendrites enriched with Mo, Ta and Nb, and its volume fraction was 42%. The BCC2 and Laves phases solidified by the eutectic-type reaction, and their volume fractions were 27% and 31%, respectively. The BCC2 phase was enriched with Ti and Zr and the Laves phase was heavily enriched with Cr. After hot isostatic pressing at 1450 °C for 3 h, the BCC1 dendrites coagulated into round-shaped particles and their volume fraction increased to 67%. The volume fractions of the BCC2 and Laves phases decreased to 16% and 17%, respectively. After subsequent annealing at 1000 °C for 100 h, submicron-sized Laves particles precipitated inside the BCC1 phase, and the alloy consisted of 52% BCC1, 16% BCC2 and 32% Laves phases. Solidification and phase equilibrium simulations were conducted for the CrMo0.5NbTa0.5TiZr alloy using a thermodynamic database developed by CompuTherm LLC. Some discrepancies were found between the calculated and experimental results and the reasons for these discrepancies were discussed. © 2013 by the authors.


Sun Z.,Northwestern Polytechnical University | Guo X.,Northwestern Polytechnical University | Zhang C.,CompuTherm LLC
Calphad: Computer Coupling of Phase Diagrams and Thermochemistry | Year: 2012

A thermodynamic description for the NbSiSn system has been developed on the basis of the constituent binaries and critically reviewed ternary experimental data. The published thermodynamic descriptions for the NbSi and NbSn binaries were directly used and that for the SiSn binary was remodeled in the present study. A two-sublattice model, (Nb,Si,Sn) 3 (Nb, Si, Sn), was applied to the A15 phase considering its crystal structure and homogeneity range. The isothermal sections at 1600 °C, 1500 °C, 1200 °C and 900 °C, the liquidus projection and the solidification path of the alloy (Nb18Si5Sn) were calculated accordingly based on the currently obtained thermodynamic description and compared with the experimental results. Comparison between the calculated results and the experimental measurements shows that the present modeling can provide a satisfactory account of the experimental information for the Nb-rich corner of the NbSiSn ternary phase diagram. © 2011 Elsevier Ltd. All rights reserved.


Luo A.A.,General Motors | Zhang C.,CompuTherm LLC | Sachdev A.K.,General Motors
Scripta Materialia | Year: 2012

The limited extrudability of AZ31 (Mg-3Al-1Zn) alloy is reported to be caused by incipient melting of the Mg 17Al 12 binary phase with a eutectic temperature of 438°C. Computational phase equilibria and microstructural examination, however, show that Mg-Al-Zn ternary phases with eutectic temperatures as low as 338°C are actually present in the AZ31 alloy, which is indeed the real limitation to its extrudability. The significantly improved extrudability of AM30 alloy (Mg-3Al-0.3Mn) is due to the absence of these zinc-containing eutectic phases. © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.


Zhang C.,CompuTherm LLC | Zhang F.,CompuTherm LLC | Chen S.,CompuTherm LLC | Cao W.,CompuTherm LLC
JOM | Year: 2012

Thermodynamic calculation is used to shed light on the design and development of high-entropy alloys (HEAs) in this article. A thermodynamic database for the Al-Co-Cr-Fe-Ni was developed, and phase diagrams of this system were calculated. The calculated results, such as primary solidified phases, which are fractions of stable phases at a given alloy composition, explain the published experimental observations fairly well for both as-cast and homogenized alloys. These calculations also confirm the effect of each element on the face-centered cubic (fcc)/body-centered cubic (bcc) structure transition as published in the literature. The role of thermodynamic calculation in aiding effective design of HEAs is clearly demonstrated by this work. © 2012 TMS.


Tan L.,University of Wisconsin - Madison | Allen T.R.,University of Wisconsin - Madison | Yang Y.,CompuTherm LLC
Corrosion Science | Year: 2011

The effect of testing conditions (temperature, time, and oxygen content) and material's microstructure (the as-received and the grain boundary engineered conditions) on the corrosion behavior of alloy 800H in high-temperature pressurized water was studied using a variety of characterization techniques. Oxidation was observed as the primary corrosion behavior on the samples. Oxide exfoliation was significantly mitigated on the grain boundary engineered samples compared to the as-received ones. The oxide formation, including some " mushroom-shaped oxidation" , is predicted via a combination of thermodynamics and kinetics influenced by the preferential diffusion of specific species using short-cut diffusion paths. © 2010 Elsevier Ltd.


Zhang F.,CompuTherm LLC | Zhang C.,CompuTherm LLC | Chen S.L.,CompuTherm LLC | Zhu J.,CompuTherm LLC | And 2 more authors.
Calphad: Computer Coupling of Phase Diagrams and Thermochemistry | Year: 2014

The concept of High Entropy Alloy (HEA) is understood from the point of view of phase diagram calculation. The role of entropy of mixing on the phase stability is discussed for both ideal and non-ideal solid solution phases. The relative stability of a solid solution phase and line compounds is illustrated using hypothetical systems. Calculated binary and multicomponent phase diagrams are used to explain the phenomena observed experimentally for HEAs. The potential of using the CALPHAD (CALculation of PHAse Diagrams) approach in aiding the design of alloys with multiple key components is also discussed. © 2013 Elsevier Ltd.


Grant
Agency: Department of Defense | Branch: Air Force | Program: SBIR | Phase: Phase II | Award Amount: 750.00K | Year: 2010

CompuTherm, LLC proposes a pilot project to develop a modeling tool that can be used to assess the durability of environmental barrier coatings (EBCs) for ceramic matrix composites (CMCs) under combustion environment. This modeling tool is a package that integrates thermodynamic databases for the gas phase and silica-oxide EBC systems, and robust computer software dealing with complicated systems involving gas, oxide liquid and solid. With this modeling tool, we can predict the phase stability and compatibility of EBCs with the SiC-based substrate, the durability and high temperature capability of a selected EBC, the volatility of the SiO2 scale, and the recession of the SiC-based ceramic materials under given combustion environment. All this information provides valuable guidance for the intelligent selection of EBCs of CMCs, which is crucial for the development of next generation hot section structural components. CompuTherm, LLC has significant capabilities for developing modeling tools from its past experience with software and thermodynamic databases development. In Phase I, have demonstrated the feasibility of the proposed approach by developing a tool for a simplified model system, whilst a powerful tool, which can be applied to practical complicated system, will be developed in Phase II. BENEFIT: A major breakthrough in gas turbine engine performance requires a new generation of hot section structural materials having a temperature capability considerably higher than current metallic hot section structural materials. Si-based ceramics, such as ceramic matrix composites (CMCs), exhibit superior high-temperature strength and durability, indicating their potential to revolutionize gas turbine engine technology. However, their usage as turbine engine hot-section components is limited due to their lack of environmental durability in high velocity combustion environments. Development of advanced EBCs for CMCs is therefore an essential, yet challenging task for materials scientists/engineers due to the complexity of the system. Traditional trial-and-error approach is costly and time-consuming, computational approach, on the other hand, becomes more and more important in materials development/enhancement and durability assessment. Successful completion of the proposed work will provide the US Air Force, other federal agencies, aerospace, and related industries with a valuable tool to accelerate the development of advanced environmental barrier coatings (EBCs) for ceramic matrix composites (CMCs) to be used in combustion environment. In addition, research centers such as government laboratories and universities will find this tool useful for basic materials research. This will result in significant cost savings for the US government and aerospace industry in the development of next generation hot section structural materials.


Grant
Agency: Department of Defense | Branch: Air Force | Program: STTR | Phase: Phase I | Award Amount: 149.99K | Year: 2015

ABSTRACT: CompuTherm, LLC proposes a pilot project to develop an innovative modeling tool for rapid deployment of thermodynamic capability for Integrated Computational Materials Engineering (ICME). To be developed on the basis of CompuTherms current capability, Pandat software, the proposed modeling tool represents the next generation of CALPHAD software. The significant advances of the proposed modeling tool are threefold: (1) a subroutine based on Bayesian method will be implemented to consider the errors of the experimental data, which propagate to the thermodynamic model parameters, and eventually to the predicted properties; (2) a novel optimization module, which includes a system for experimental data management and an automated optimizer, will be developed to accelerate the process of thermodynamic database development; (3) advanced thermodynamic models will be adopted to develop more accurate thermodynamic databases with better extendibility. In Phase I, a prototype modeling tool targeting a ternary system will be developed to examine the feasibility of the proposed approach, while a full functioning software package for multi-component systems will be developed in Phase II. The final product will be an easy to use tool for DoD, other federal agencies, and private sectors to develop their own ICME applications.; BENEFIT: Understanding the phase stability of a multi-component system is an essential part for alloy design and process development. The CALPHAD method for calculating phase diagrams of multi-component systems is therefore fundamentally important for the development of Integrated Computational Materials Engineering (ICME) tools. Current generation CALPHAD software packages have been applied to many technically important alloys containing more than 10 components. Although successful, the weaknesses of these software packages have limited further extension and application of the CALPHAD approach. Developing and maintaining a multi-component database is costly and time-consuming due to the current software limitations. The proposed next generation CALPHAD modeling tool has significant advantages over those currently available tools. Successful completion of the proposed work will provide US Air force, other federal agencies, industrial companies, government laboratories and research institutes with a user-friendly tool for rapid deployment of thermodynamic capability for ICME. The linkage of the modeling tool to be developed in this work with other physics-based tools, microstructural evolution prediction tools, and property prediction tools will certainly extend the current CALPHAD capability and lead to the development of more powerful ICME tools.

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