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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. Source

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. Source

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. Source

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. Source

Agency: Department of Defense | Branch: Air Force | Program: SBIR | Phase: Phase I | Award Amount: 99.99K | Year: 2009

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. The modeling tool includes a thermodynamic database for the gas phase, a thermodynamic database for the silicate system (EBCs), and a computer software package that deals with thermodynamic equilibrium, gas-solid reaction, and volatile kinetics of silica. In particular, this tool would predict, given an EBC system and an environmental combustion condition, the partial pressure of each gaseous species in the system, the activity of silica in the EBC, the flux of volatile silicon species, such as SiO(g), and Si(OH)4(g), and the recession and glass formation of the EBC. This modeling tool would provide valuable guidance to the US Air Force and private sectors in the development of advanced EBCs for CMCs. CompuTherm, LLC has significant capabilities for developing modeling tools from its past experience with software and thermodynamic database development. In Phase I, we will examine the feasibility of developing such a tool using a simplified system, whilst a powerful tool, which can be applied to practical complicated systems, 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 the current metallic hot-section structural materials. Si-based ceramics, such as ceramic matrix composites (CMCs), exhibit superior high-temperature strength and durability, which indicates 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 the high velocity combustion environment. 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 DoD, 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 high temperature 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 saving for the US government and aerospace industry in the development of next generation hot-section structural materials.

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