Hume-Rothery Symposium: Thermodynamics, Phase Equilibria and Kinetics for Materials Design and Engineering: Building CALPHAD Databases: Essential Experiments
Sponsored by: TMS Structural Materials Division, TMS: Alloy Phases Committee, TMS: Integrated Computational Materials Engineering Committee
Program Organizers: Carelyn Campbell, National Institute of Standards and Technology; Michael Gao, National Energy Technology Laboratory; Wei Xiong, University of Pittsburgh
Wednesday 8:30 AM
February 26, 2020
Room: 32A
Location: San Diego Convention Ctr
Session Chair: Michael Gao, National Energy Technology Laboratory; Yongho Sohn, University of Central Florida
8:30 AM Invited
Improvement of a CALPHAD Database for the Development of Next Generation TiAl Alloys by Targeted Key Experiments on High-temperature Phase Equilibria – The EU Project Advance: Frank Stein1; Benedikt Distl1; Zahra Kahrobaee1; Martin Palm1; Katja Hauschildt2; Marcus Rackel2; Florian Pyczak2; Svea Mayer3; Yang Yang4; Hai-Lin Chen4; Anders Engström4; 1Max-Planck-Institut fuer Eisenforschung; 2Helmholtz-Zentrum Geesthacht; 3Montanuniversität Leoben; 4Thermo-Calc Software AB
After many years of intensive research, TiAl-based alloys finally became the first light-weight intermetallic materials that were successfully transferred into industrial high-temperature applications, e.g., as energy-saving turbine blades in the low-pressure range of jet engines. Properties such as the high-temperature creep strength and corrosion resistance still might be improved and the development of the next generation of TiAl-based alloys is going on. Materials design today is no longer a classical trial and error approach. Time and costs of industrial alloy developments can be significantly reduced by making use of predictions obtained by the CALPHAD method applied on thermodynamic databases such as TCTI2. The goal of the EU-project ADVANCE is to improve and update this database by generating new experimental data on phase equilibria and phase transformations in a series of ternary systems Ti-Al-X (X = Nb, Mo, W, Si, Zr, O, B, C) and two quaternary systems, Ti-Al-Nb-Mo and Ti-Al-Nb-W.
9:10 AM Invited
Measurements of Thermophysical Properties of Metals and Alloys as Input for Computational Thermodynamics: Erhard Kaschnitz1; 1Austrian Foundry Research Institute
Thermophysical data are essential for computational thermodynamics to establish valid models. A variety of measurement techniques to obtain thermophysical properties has evolved the past decades, but not many of them are useful to investigate metals and alloys in the high temperature solid and liquid regions, especially if materials are reactive. An overview of current state-of-the-art measurement approaches for high temperature metallic specimens is given, outlining the expected benefit of each method. Measurements of thermophysical properties are performed under conditions close to, but also far from thermodynamic equilibrium, which influences the obtained results. Kinetic effects have always to be considered when thermophysical data is used as input for computational thermodynamics, as well as inevitable measurement uncertainties; in particular when data is extrapolated.Examples of obtained results of different measurement techniques for solid and liquid metallic specimens are presented; the significance of kinetic and measurement uncertainties is discussed.
9:50 AM Break
10:20 AM Invited
The Application of Metastable Equilibria in the Analysis of Transformation Behavior: John Perepezko1; 1University of Wisconsin-Madison
Metastable states can be accessed experimentally due to limitations on the nucleation and growth kinetics of stable phases. The kinetic limitations are enabled by large undercooling, high supersaturation, rapid transformation and during the initial stage of interface reactions. At the same time the application of metastable phase equilibrium data can serve as valuable input in the evaluation of stable phase equilibria and in the analysis of microstructure development. For example, during solidification of undercooled liquids metastable phase equilibrium data has allowed for the formulation of more accurate Gibbs energy functions for the stable equilibria and has uncovered previously missed stable equilibria. During rapid transformation, thermodynamics sets the limit on the supersaturation in the product phase in terms of the T0 curves. Similarly, during the initial stage of interface reaction the phase selection including amorphous phase formation can be effectively analyzed by the relevant metastable phase equilibria.
11:00 AM Invited
Selected Observations of Microstructural Development in Additively Manufactured Metallic Alloys: Yongho Sohn1; Le Zhou1; 1University of Central Florida
Additive manufacturing of metallic alloys is a disruptive technology that can produce net-shape components with nearly unlimited geometrical complexity and customization. This technology also brings an opportunity to design new and modified alloys based on robust understanding of phase equilibria and kinetics so that the dependent process variables are desensitized and thermo-kinetic environments associated with additive manufacturing are utilized effectively. In this presentation, experimental research efforts using gas atomization and laser powder bed fusion for metallic alloy development will be first introduced. Selected observations of microstructural development from solidification, micro-segregation, homogenization, and precipitation will be highlighted for additively manufactured Al-, Ni-, and Fe-base alloys, both commercially available and new/modified compositions. Use of computational methods in designing and modifying the alloy composition for printability/buildability and properties/performance will be presented to identify the critical development needs for methods and databases for both thermodynamics and kinetics.