Computational Thermodynamics and Kinetics: Microstructural Evolution and Phase Stability II
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Computational Materials Science and Engineering Committee
Program Organizers: Nana Ofori-Opoku, Canadian Nuclear Laboratories; Jorge Munoz, University of Texas at El Paso; Sara Kadkhodaei, University Of Illinois Chicago; Vahid Attari, Texas A&M University; James Morris, Ames Laboratory
Monday 2:30 PM
February 24, 2020
Room: 33C
Location: San Diego Convention Ctr
Session Chair: Emily Moore, Lawrence Livermore National Laboratory; Daniela Wipp, TU Wien
2:30 PM Invited
Nonequilibrium Nanoscale Patterns and Negative Effective Interface Energy: A Phase Field Approach: Pascal Bellon1; Qun Li1; Robert Averback1; 1University of Illinois at Urbana-Champaign
Nanostructured states can be stabilized at equilibrium in alloys where attractive short-range interactions compete with repulsive long-range interactions. This nanostructuration can be extended to steady-state dynamical systems described by effective interactions, e.g., for alloys under irradiation. Nanostructuration is associated with the spontaneous formation of interfaces from a macroscopic phase, thus suggesting a negative effective interfacial energy. We analyze this hypothesis by considering a Cahn-Hilliard phase-field model augmented with a Laplacian-square inhomogeneity term to capture effective long-range interactions. Analytical modeling and phase field simulations indicate that, in the patterning regime the interface free energy is indeed negative but also scale-dependent, raising questions about defining interface energy as an excess quantity. It is proposed that a more consistent description is achieved by introducing an interfacial compressibility as a conjugate variable of the patterning lengthscale. This concept is used to predict capillary effects near curved interfaces and compared with phase field simulation results.
3:00 PM
Computing Grain Boundary Diagrams: Chongze Hu1; Jian Luo1; 1University of California San Diego
In this talk, we will review our most recent atomistic simulation studies to construct grain boundary (GB) “phase” (complexion) diagrams. Specifically, we have conducted hybrid Monte Carlo and molecular dynamics (hybrid MC/MD) simulations in semi-grand canonical ensembles to derive GB diagrams for several binaries, such as Ni-doped Mo [Yang et al. PRL 2018], Au-doped Si [Hu & Luo, Scripta 2019], and Ag-doped Cu systems. We find that the occurrence of first order GB transformations can be observed in Ni-doped Mo and Au-doped Si systems. For the latter case, our simulation shows that 1st order GB adsorption from Si “clean” GB to Au bilayer occurs at low temperature, but it becomes continuous at high temperature. Furthermore, the hexagonal Au segregation patterns identified by MC/MD simulations are verified by first-principles calculations. Finally, differential charge density maps show that strong charge transfer can prompt Au segregation at Si GBs. Most recent work systematically constructs GB diagrams for Ag-doped Cu via data-driven machine learning methods.
3:20 PM Cancelled
Formation of Conducting Filament due to the Electrochemical Changes in the Memresistive Systems: a Phase Field Study: Arijit Roy1; Pil-Ryung Cha1; 1Kookmin University
In recent years, a variety of organic or inorganic systems promising for the application of non-volatile memory (resistive RAM or ReRAM) are investigated. Due to application of electric field in metal-insulator-metal (MIM) system, charged ionic species migrate and are accumulated at counter electrode to form the conducting filament (CF). Morphological evolution of CF leading to the electrical properties of such systems are studied using phase field modelling. Two cases – 1) system with ionic species of intrinsic and electrode origin, and 2) system with electric field assisted generation of new defects – are considered. Crucial physiochemical and process parameters assisting the CF formation are investigated and identified. Our study is compared qualitatively with reported experimental observations, facilitating the validation of our model. We believe that presented correlation between various physiochemical parameters and measured I-V characteristics is important to develop the new generation of non-volatile ReRAM.
3:40 PM
Simulating Precipitation of Detrimental Boron Nitrides in Micro-alloyed Steels Based on Experimental Elemental Distributions: Daniela Wipp1; Maximilian Weiss2; Andreas Limbeck2; Tomasz Wojcik3; Sabine Zamberger4; Matthew Galler5; Erwin Povoden-Karadeniz1; 1Christian Doppler Laboratory for Interfaces and Precipitation Engineering CDL-IPE, Institute of Materials Science and Technology, TU Wien; 2Institute of Chemical Technologies and Analytics, TU Wien; 3Institute of Materials Science and Technology, TU Wien; 4voestalpine Forschungsservicegesellschaft Donawitz GmbH; 5voestalpine Wire Rod Austria GmbH
Boron in solid solution increases considerably the hardenability of micro-alloyed steel. To control a complex microstructure and consequently the mechanical properties, a deep understanding of the distribution of elements and the limiting composition for boron nitride (BN) precipitation in steel is essential. In particular, heterogeneities in terms of local boron concentrations need to be evaluated. LA-ICP-MS revealed heterogeneous elemental distributions in the studied steel. Boron enrichment led to BN nucleation, closely related to TiN, as found by TEM analysis. This is reproduced by precipitation simulation, where BN nucleates in the boron enriched case only. Even though TiN is present in the simulation result, confirming experimental observation, its volume fraction seems not sufficiently high for complete N-binding and related “boron protection”. The present study reveals the great potential of determining threshold quantities of boron alloying for its complete solid solution by the coupling of quantitative element distribution analysis with thermokinetic simulation.
4:00 PM Break
4:20 PM Invited
CALPHAD for Complex Concentrated Alloy Development: New Opportunities: Wei Xiong1; 1University of Pittsburgh
The CALPHAD method has been developed for several decades with wide applications in materials design and discovery. It has demonstrated advantages in predicting phase stability of multicomponent alloys, and can further integrate with other phase transformation models. The emerging markets of advanced alloy manufacturing require further development of the CALPHAD-based materials design/discovering approaches. One of the cases is the complex concentrated alloys, which has significantly extended the composition space from single-component rich corner to a much broader composition range with much more unknowns. Therefore, the CALPHAD modeling itself still requires considerable improvements in terms of model and database development, which will also help the accelerated insertion of materials. In this work, the state-of-the-art CALPHAD modeling for alloy design is reviewed such as prediction of metastable phases and stacking fault energy. New opportunities in the complex concentrated alloy development indicate a critical need to improve the low-temperature thermodynamic models and databases.
4:50 PM Invited
Thermodynamics, Structure, and the 3D Geometry of Bendable 2D Materials: Joel Berry1; 1Lawrence Livermore National Laboratory
The ease with which thin elastic sheets can deform out-of-plane leads to many interesting and some unusual phenomena that arise from couplings between in-plane/2D structure & thermodynamics and the 3D shape of the sheet. I will discuss two studies in which such couplings are exploited to design materials with novel and tailored properties. The first involves a new approach to form nanoscale 3D objects by patterned alloying of 2D transition metal dichalcogenide monolayers and to compositionally pattern monolayers using non-flat substrates. The second involves a new geometry-based mechanism for controlling the relative atomic stacking of layered 2D sheets, applied to stabilizing ABC-stacked trilayer-graphene. First principles-informed thermodynamic and mechanical models will be presented and used to explore the interplay between 2D states and 3D geometry. Comparisons will be made with experiments, and applications spanning flexible electronics, catalysis, optical devices, responsive coatings, and soft robotics discussed. Prepared by LLNL under Contract DE-AC52-07NA27344.
5:20 PM
Thermodynamic Assessment of Actinide Alloys: the Pu-U-Al-Fe-Ga-Ni System: Emily Moore1; Alexander Landa1; Aurélien Perron1; 1Lawrence Livermore National Laboratory
Actinide alloys garner much interest across the nuclear community and knowledge of phase stability is paramount to predicting their behavior under normal and accident conditions. Using the CALPHAD (CALculation of PHAse Diagrams) method the development and application of a thermodynamic database comprising the multi-component system : Pu-U-Al-Fe-Ga-Ni is presented. Equilibrium calculations and Scheil solidification simulations are performed to demonstrate the effect of alloying elements such as iron and nickel. This work was performed under the auspices of the U.S Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344. LLNL-ABS-779999
5:40 PM
Theoretical Calculation of Atomic Size in a Solid Solution: Tetsuo Mohri1; 1Tohoku University
Experimentally, the atomic size in a solid solution has been well defined as a partial molar volume at a given concentration. Theoretically, however, it is not an easy task to provide a clear definition. We formulated the free energy of a Cu-Au system within the Cluster Variation Method in terms of atomic volumes of constituent elements, and minimized the free energy to optimize the equilibrium atomic volume. Interestingly, each element keeps the volume in the pure metal over the wide concentration range. This result is discussed in terms of local and global relaxations of the system.