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Computational Thermodynamics and Kinetics: Poster Session
Sponsored by: TMS Functional Materials Division, TMS Materials Processing and Manufacturing Division, TMS: Chemistry and Physics of Materials Committee, TMS: Computational Materials Science and Engineering Committee, TMS: Integrated Computational Materials Engineering Committee, TMS: Solidification Committee
Program Organizers: Hesam Askari, University Of Rochester; Damien Tourret, IMDEA Materials Institute; Eva Zarkadoula, Oak Ridge National Laboratory; Enrique Martinez Saez, Clemson University; Frederic Soisson, Cea Saclay; Fadi Abdeljawad, Lehigh University; Ziyong Hou, Chongqing University

Monday 5:30 PM
March 20, 2023
Room: Exhibit Hall G
Location: SDCC

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H-29: A Machine Learned Spin-Lattice Potential for Bulk Iron: Benjamin Seddon¹; James Elliott¹; Christoph Ortner²; ¹University of Cambridge; ²University of British Columbia
    It is well known that magnetic effects stabilise the room temperature body-centred cubic (BCC) phase of iron, and so it is important to take these into account in computer simulations. Here, we describe our contribution to the recent set of machine learning potentials that incorporate magnetic effects by explicitly expressing the energy in terms of the atomic magnetic and spatial degrees of freedom. We use the Lagrangian formulation of Constrained Density Functional Theory (cDFT), as implemented in Abinit, to generate an open-source dataset of cDFT for bulk bcc iron. This dataset provides atomic position and spin configurations with the associated energy and energy derivatives (force, spin torque, pressure, etc.) for bulk bcc iron, including defects and spin fluctuations. We then use this dataset to parameterise a magnetic atomic cluster expansion potential using ACE.jl, and demonstrate its use by studying defect diffusion in BCC iron.

H-1: Accurate Evaluation of the Mechanical Properties of Ideal Single Crystals: A Comparative Ab Initio Study: Jaylan Elhalawani¹; Mostafa Youssef¹; ¹American University in Cairo
     The theoretical limit of the strength of materials is determined by the strength of a single crystal. The mechanical properties of an ideal single crystal set the bound for these properties for a real defective crystal. Experimental evaluation of the former is highly limited. Several computational techniques based on ab initio methods can be used to calculate the anisotropic properties of single crystals. This work aims at evaluating two approaches to calculating the direction-dependent young’s moduli, ultimate strengths, and Poisson's ratios for 13 BCC and 12 FCC elements. The first approach is based on the elastic constants tensor while the second is more elaborate and uses the full tensile stress-strain curves in 3 directions. Herein, we conducted the comparison based on density functional theory calculations. Our work highlights special cases in which one has to fully compute the stress-strain curve to reliably evaluate the direction-dependent mechanical properties of materials.

H-2: Application of Multi-Cell Monte Carlo Method to BCC Refractory Alloys: Junxin Wang¹; Maryam Ghazisaeidi¹; ¹Ohio State University
    We present the Multi-Cell Monte Carlo method for phase prediction for multicomponent alloys. This method is designed for simulating coexisting phases in many-component crystalline systems. A general introduction of the Multi-Cell Monte Carlo method as well as several successful applications are provided demonstrating its advantage over some common phase prediction methods and showing its strong ability when applied to multicomponent systems. Particularly, we apply the method to the BCC refractory alloys, exploring the thermodynamic stability in the composition space relevant to BCC “high entropy alloys”.

H-27: Atomistic Simulations of Liquid/Metal Interfaces with Applications to Active Brazing: Ian Winter¹; Michael Chandross¹; ¹Sandia National Laboratories
    Active brazing is a high temperature method for joining metal/ceramic parts. A particular issue affecting active-braze joints is runout, that occurs when the braze alloy flows out of the joint rather than fully wetting the metal substrate. Runout is a wetting instability with deleterious effects on strength and hermeticity. The wetting is determined by the surface energy of the metal, the surface tension of the braze alloy, and the braze/substrate interfacial energy, phenomena that are temperature and composition dependent. We present the results of interfacial thermodynamics and atomistic simulations that enable an understanding of the mechanisms controlling wetting in active brazing. We focus on the effects of the composition of the braze alloy and the metal substrate on the wetting behavior, with a goal of informing the design of new, better performing braze alloys. SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525 (SAND2022-1056 A).

H-28: CFD Informed Strategy for the 3D Printing of Crack-free High-strength Al-alloys: Giuseppe Del Guercio¹; David McCartney¹; Sebastien Faron¹; Adam Clare¹; Marco Simonelli¹; ¹University of Nottingham
    The densification of alloys manufactured by Laser Powder Bed Fusion (L-PBF) is influenced by the thermal history experienced by the material during processing. The cooling rates and thermal gradients caused by L-PBF regimes may result in detrimental hot cracking phenomena. The control of the thermal history and the prediction of the associated cracking tendency are key in highlighting processing regimes able to print crack-free components. Here, we discuss the cracking behaviour of a popular high-strength aluminium alloy (AA2024) computing established cracking indices informed by computational fluid dynamics (CFD). The study is conducted as a function of multiple process parameters investigating the temporal and spatial evolution of the alloy’s crack propensity. The results highlight L-PBF regimes able to avoid hot cracks and shed light on the thermo-physical dynamics involved in their nucleation. This work proves how pairing CFD and material science can result in crack-free high-strength aluminium components without material modification.

Deducing Surface-scale Chemical Conditions from Equilibrium Nanoparticle Shapes: Mujan Seif¹; T. John Balk¹; Matthew Beck¹; ¹University of Kentucky
    As applications of nanoparticles continue to expand, precise control of their functional surfaces becomes increasingly valuable. While the macroscopic or average environmental chemical conditions in which nanoparticles are equilibrated can be controlled and the resulting shapes observed via SEM, the details of local, nanoscale conditions present during particle evolution remain unclear and, in some cases, prohibitively difficult to establish. Here, we use density functional [perturbation] theory to build a computational thermodynamic framework by which we “reverse engineer” nanoscale chemical conditions and map them back to controllable macroscopic environmental conditions. The case study presented here highlights scandate thermionic cathodes—next-generation electron emitters repeatedly observed to be composed of W nanoparticles with a highly-faceted, unique characteristic shape. We demonstrate that the chemical composition of each facet can be predicted as a function of temperature and oxygen availability and use these results to hypothesize the origin of scandate cathodes’ exceptional electron emission properties.

H-3: Driving Force Induced Transition in Thermal Behavior of Grain Boundary Migration in Ni: Xinyuan Song¹; Chuang Deng¹; ¹University of Manitoba
    The mobility of grain boundaries (GBs) has been long assumed to follow the Arrhenius relation. However, in recent years, many GBs have been found to behave anti-thermally, i.e., the mobility of the GBs would decrease with the increase of the temperature. Based on our atomistic simulation results in Ni, the thermal behavior of the GBs is found to be highly related to their energy barrier for migration, and the anti-thermal behavior of GBs can be accurately predicted by the equation considering configuration entropy, which means that the configuration entropy at high temperature is the main cause that slows down the movement of the GBs. Furthermore, we found that the driving force we applied in the simulation could lower the energy barrier of the GBs, which would have a drastic effect on the thermal behavior of the GBs. Choosing an appropriate driving force is thus critical in future studies.

H-4: Thermodynamic and Elastic Properties of Body-centered-cubic Refractory, High-entropy Alloys: NbTaTiV, TaNbHfZrTi, VNbMoTaW: Danielsen Moreno¹; Chelsey Hargather¹; ¹New Mexico Institute of Mining and Technology
    Body-centered cubic (BCC) refractory high-entropy alloys (HEAs) are potential candidates for high-performance engineering material applications. At high temperatures, these HEAs show potential to outperform traditional engineering alloys such as nickel-base superalloys. By implementing first principles calculations based on density functional theory, thermodynamic and elastic properties of several refractory HEA systems are investigated. Special quasirandom structures are employed, and the thermodynamic properties are calculated with a Debye model code written for this study. Thermodynamic properties such as entropy, enthalpy, heat capacity, and thermal expansion as a function of temperature are presented, as well as elastic properties such as elastic constants, bulk, shear, and Young’s moduli, and Poisson’s ratio. The BCC refractory HEAs in this study are NbTaTiV, TaNbHfZrTi, and VNbMoTaW. The results are compared to experimental or computational values from the existing literature for validation.

H-5: Time-cone Based Models of Nucleation and Growth in Polycrystalline Systems: Siu Sin Jerry Quek¹; Jing Xiang Ng²; David Wu¹; ¹Institute of High Performance Computing; ²Nanyang Technological University
     Nucleation and growth during phase transformation can be described by the classical works of Johnson and Mehl, Avrami and Kolmogorov (JMAK)¹, which is rigorously derived within the assumptions of isotropic & interface-limited growth, random nucleation in space and an infinite system. However, in most solid-state transformation, precipitation occurs in a polycrystalline domain and is diffusion-limited, violating JMAK’s assumptions. Therefore, we address the effects of a grain boundary network on nucleation and growth kinetics using time-cone based theories and simulations. Specifically, we consider the two limiting cases of grain boundaries that are permeable² and impermeable³ to phase transformation. We also elucidated the effects of grain aspect ratio on the transformation kinetics in these contexts. ¹ W.A. Johnson and R.F. Mehl (1939); M. Avrami (1939-1941); A.N. Kolmogorov (1937) ² J.W. Cahn, Acta Metallurgica (1956) 4, 449-459.³ E. Villa and P.R. Rios, Acta Materialia 58 (2010), 2752-2768.

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