Thermodynamics of Materials in Extreme Environments: Thermodynamics and Stabilities of Alloys and Ceramics
Sponsored by: ACerS Basic Science Division, ACerS Energy Materials and Systems Division
Program Organizers: Xiaofeng Guo, Washington State University; Kristina Lilova, Arizona State University; Kyle Brinkman, Clemson University; Alexandra Navrotsky, Arizona State University; Jake Amoroso, Savannah River National Laboratory; Xingbo Liu, West Virginia University; Gustavo Costa, NASA Glenn Research Center
Monday 4:00 PM
October 18, 2021
Room: A221
Location: Greater Columbus Convention Center
Session Chair: Kristina Lilova, Arizona State University; Xiaofeng Guo, Washington State University
4:00 PM Invited
Stability of Multicomponent Rare Earth Silicates for Environmental Barrier Coating Application: Mackenzie Ridley1; Cameron Miller1; Rebekah Webster1; Hans Olson1; Alejandro Salanova1; Kathleen Tomko1; Jon Ihlefeld1; Cormac Toher2; Patrick Hopkins1; Elizabeth Opila1; 1University of Virginia; 2Duke University
Environmental barrier coatings (EBCs) are required for application of SiC-based ceramic matrix composites (CMCs) in hot section turbine engine applications. State of the art EBCs are composed of ytterbium silicates. Multicomponent rare earth silicates offer the opportunity to reduce the thermal conductivity of the EBCs via phonon scattering mechanisms, reducing the surface temperatures of the underlying CMCs. The stability of these multicomponent rare earth silicates in high-temperature steam and calcium magnesium aluminosilicate (CMAS)-containing environments relevant for turbine environment were tested at temperatures between 1200 and 1400C. It was found that multicomponent rare earth silicates enable stabilization of nonequilibrium polymorphs, formation of nonequilibrium steam reaction products, and enhanced CMAS resistance. The tailoring of thermal and thermochemical properties of EBCs through choice of rare earth silicate component mixtures is described.
4:30 PM Invited
Directions of Zero Thermal Expansion in Anisotropic Oxides: Scott Mccormack1; William Wheeler2; Benjamin Hulbert2; Waltraud Kriven2; 1University of California, Davis; 2University of Illinois at Urbana-Champaign
Oxide materials often have anisotropic crystal structures, which can result in direction-dependent material properties. While they typically have positive coefficients of thermal expansion, it has been observed that some oxide materials can have directions of negative thermal expansion over certain temperature ranges. Such materials, having both positive and negative coefficients of thermal expansion must also have particular directions in which the thermal expansion is zero. In-situ high-temperature X-ray diffraction was used to track directions of zero thermal expansion in HfTiO4 from room temperature to melting. These experiments were performed using a Quadrupole Lamp Furnace (QLF) (T~ 200 - 2000 ˚C) at the National Synchrotron Light Source II (NSLS II) and a Conical Nozzle Levitator system equipped with CO2 laser (CNL) (T ~ 700 - 3400 ˚C) at the Advanced Photon Source (APS). These results have important implications for the design of directional near-zero thermal expansion materials.
5:00 PM
A First-principles-based Study of Oxidation Thermodynamics in Refractory High Entropy Alloys: Adib Samin1; 1Air Force Institute of Technology
In an effort to better characterize the oxidation behavior in refractory high entropy alloys (RHEAs), interstitial oxidation was studied in a Mo-Nb-Ta-W alloy using DFT-based Monte Carlo simulations. It was found that the interstitial oxygen had comparable stability at tetrahedral and octahedral sites. The interstitial oxygen was found to arrange in ordered clusters and was associated with slightly enhanced mechanical properties. The solubility of the interstitial oxygen in the alloy was found to decrease with temperature. Moreover, the thermodynamics of Ti-Nb alloys and their oxides were studied as a step towards improving our understanding of the oxidation behavior of RHEAs. The presence of titanium was found to favor the formation of TiO2 over Nb2O5 in large regions of the Ellingham diagram thereby contributing to enhanced oxidation resistance in Nb-containing alloys since Nb2O5 is typically associated with scale spallation and pore formation due to its anisotropic thermal expansion.