Track B
Computational Mesoscale Structure and Physico-chemical Property Evolution of Solid Materials


Session B-1 Databases of physico-chemical properties of materials

B-1:IL02  Ab-initio Accurate Simulation of Plasticity and Thermodynamics
P. Grigorev, T.D. Swinburne, CNRS / Aix-Marseille University, Marseille, France; M.C. MARINICA, CEA Saclay, France; J.R. KERMODE, University of Warwick, UK; R. DSOUZA, J. NEUGEBAUER, Max-Planck-Institut für Eisenforschung GmbH, Germany

Atomic simulations of plasticity or thermodynamics require large system sizes or long sampling campaigns, far beyond the computational limits of ab initio methods. However, the chemical (meV/atom) accuracy of ab initio is essential to predict e.g. solute hardening effects or phase stability. I first discuss a novel coupling scheme that seamlessly embeds small ab initio regions in large atomic simulations[1], allowing general chemical accuracy in the vicinity of e.g. a foreign impurity atom for controllable cost. This enables ab initio accurate simulations of e.g. segregation and depinning mechanisms at dislocations, demonstrated on helium and hydrogren in tungsten. If time permits I will also present a recent sampling-free mean field approach to calculate meV/atom accurate vibrational free energies beyond the quasiharmonic approximation, for orders of magnitude less computational effort[2]. Implications for high throughput alloy design will be discussed. [1] P Grigorev et al. 10.1016/j.actamat.2023.118734 & in prep. [2] TDS et al. 10.1103/PhysRevB.102.100101 & R Dsouza et al., in prep.

B-1:IL03  Thermodynamic Databases for Multicomponent Materials - CALPHAD, ab initio and ML
M. TO BABEN, C. Früh, GTT-Technologies, Herzogenrath, Germany

CALPHAD databases are the state-of-the-art for thermodynamic modelling of inorganic materials (metals, ceramics, slags, salts). However, the CALPHAD methodology is still a very manual process and requires the existence and human evaluation of large amounts of experimental data. Commercial CALPHAD databases therefore cover “only” few tens of elements with a focus on some application (such as steels, metallurgy or non-oxide ceramics). Ab initio databases on the other hand, such as materialsproject.org or oqmd.org, are not limited by the existence of experimental data and therefore cover larger parts of chemical space. The use of these databases for thermodynamic modelling is however restricted by both the temperature range (usually 0K), limited accuracy with respect to phase equilibria and the difficulty in describing solution phase thermodynamics. Here, it is demonstrated that ML techniques can be used to bridge the gap between CALPHAD and ab initio databases. This is especially important to model processing of mew functional materials or recovery of minority elements during recycling of complex end-of-life products.

B-1:IL04  Atomic Cluster Expansion for a Unified Approach to Machine Learning Potentials
R. DRAUTZ, Ruhr-University Bochum, Bochum, Germany

Efficient implementations of Density Functional Theory (DFT) enabled high-throughput calculations for tens of thousands of atomic structures. The resulting large DFT datasets then drove the development of a variety of different machine learning potentials. The Atomic Cluster Expansion (ACE) may be seen to unify many of the different machine learning potentials, from traditional approaches based on empirical descriptors and neural networks to graph-based architectures. In my talk I will introduce ACE and relate it to other descriptors and machine learning potentials. I will then demonstrate the accuracy of ACE, briefly discuss its implementation and highlight its efficiency. I will further show recent applications of ACE, for example, to pipe diffusion in tungsten or the carbon phase diagram. Next I will discuss generalizations of ACE to multi-component materials, magnetism, charge transfer and semi-local interactions, before showing how ACE can be used together with active learning for efficient exploration of composition-structure spaces.

B-1:IL05  Creating an Efficient Alloy Database Infrastructure and Detecting Abnormal Data
A.M. KRAJEWSKI, A. Debnath, S. Lin, M. Ahn, H. Sun, W. Reinhart, A. Beese, Z.-K. Liu, Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA, USA

Humanity spent 5000 years advancing alloys, first through empirical breakthroughs and then through scientific understanding, which requires expert knowledge and support of high-quality datasets, which can then be used to harvest advances in data analysis and machine learning (ML). As our community moves towards large-scale multi-source data collection, new challenges appear, including (1) high presence of erroneous data, sometimes over 5% caused by nonstandardized notations or general human errors, (2) complex structure (schema) of the data making it hard to homogenize, and (3) bottlenecks in data passing between experiment and modeling teams. In this talk, we present a set of open-source tools for alloy datasets that solve these challenges through (1) robust infrastructure setup, (2) data abnormalities screening (PyQAlloy), and (3) design space optimization (nimCSO). They apply to any complex materials datasets, and we demonstrate them on our HEA database (ULTERA.org) developed under the ARPA-E ULTIMATE program, to facilitate rapid discovery using forward and inverse ML methods. ULTERA efficiently processes 6,300+ experimental points from 537 publications with automated integration of the literature, our experiments, generative modeling, predictive modeling, and validations.

B-1:L06  Reactive Sintering of Boron Carbides: Dependence on Elemental Precursors
D. OLEVANO, S. Lionetti, U. Martini, Rina Consulting Centro Sviluppo Materiali S.p.A., Rome, Italy; S. Lemonnier, F. Moitrier, ISL, Institut Franco-Allemand de recherches de Saint-Louis, Saint-Louis, France

Reactive sintering approach is a promising route for improving ballistic efficiency of well-known ceramics such as B4C. Indeed, B4C is difficult to sinter and this approach makes it possible to selectively choose different precursors on the basis of their specific properties such as purity, morphology, reactivity and particle size. All these properties have an influence on the crystalline phase synthesis and sintering behaviours and by consequence on the final properties of the ceramics. The main idea of this work is to collect all information (for database) on the characteristics of the raw materials and link them to the synthesis and densification behaviours of the ceramics and further to the failure behaviour of the dense ceramics during the ballistic event. To set up a complete methodology of boron carbide ceramic development by the reactive sintering approach, two types of Boron precursors (i.e., B and B’) and two types of Carbon precursors (i.e., C and C’) have been selected and thoroughly characterized by means of SEM, XRD, BET, chemical analyses and TEM. Then precursors were mixed and their reactivity evaluated through DTA/TG thermal analyses combined with XRD analyses. This research activity is part of the EDA CERAMBALL II project.

Session B-2 Theory of phase transitions

B-2:IL01  Quantitative Predictive Theories for Physico-chemical Property of Solid Phases

ZI-KUI LIU, Pennsylvania State University, University Park, PA, USA

Thermodynamics is a science concerning the state of a system, whether it is stable, metastable, or unstable[1]. It is commonly divided into four categories: equilibrium thermodynamics by Gibbs, statistical thermodynamics by Gibbs and Landau, and irreversible thermodynamics by Onsager and Prigogine. The development of density function theory (DFT) enabled the quantitative prediction of properties of the ground state of a system from quantum mechanics. Their integration into predictive theories[2] will be discussed in this presentation along with future perspectives[3]. The zentropy theory combines the bottom-up DFT predictions with the revised top-down statistical thermodynamics, while the theory of cross phenomena keeps the entropy production due to irreversible processes in the combine law of thermodynamics to revise the Onsager flux equations. The zentropy theory is capable of quantitatively predicting free energy landscape, singularity and emergent divergences of properties at critical point free of parameters, while the theory of cross phenomena can predict the coefficients of internal processes between non-conjugate variables [2].
[1] Z.K. Liu, Acta Mater. 200 (2020) 745–792.
[2] Z.K. Liu, Mater. Res. Lett. 10 (2022) 393–439. [3] Z.K. Liu, CALPHAD 82 (2023) 102580.

B-2:IL02  Phase-field Modelling of Nonequilibrium Interface Dynamics in Diffusion-controlled Phase Transition of Alloys  
MUNEKAZU OHNO, Hokkaido University, Sapporo, Hokkaido, Japan

Quantitative phase-field models have been developed as a method for solving free boundary problems in diffusion-controlled phase transformations, and are used as a powerful means of computer experiments, especially in the field of solidification. However, existing quantitative phase-field models are generally based on local equilibrium condition regarding solute distribution in the diffuse interfaces. However, it is known that the local equilibrium condition does not hold true when the interfacial velocity is very high as in additive manufacturing and laser welding. In other words, existing quantitative models cannot describe the solute trapping and solute drag effect emerging in interface dynamics at high velocity, and thereby cannot reproduce the related microstructural formation processes. In this study, we attempted to develop a quantitative phase-field model that describes the nonequilibrium interfacial dynamics and applied it to simulation of alloy solidification.

B-2:IL03  Moire Patterns and Inversion Boundaries in Graphene/Hexagonal Boron Nitride Bilayers 
K.R. ELDER, Oakland University, Rochester, MI, USA; Z.-F. Huang, Wayne State University, Detroit, MI, USA; T. Ala-Nissila, Aalto University, Espoo, Finland

In this talk I would to discuss modeling out of plane deformation in two dimensional sheets and bilayers of such sheets. In particular the focus will be on graphene and hexagonal boron nitride (hBN). As proof of principle the model is shown analytically to reduce to standard models of flexible sheets in the small deformation limit. Applications to strained sheets, dislocation dipoles and grain boundaries are used to validate the behavior of a single flexible graphene layer. For the multi-layer systems, parameters are obtained to closely match existing theoretical density functional theory calculations on layer spacing and stacking energies for graphene/graphene, hBN/hBN and graphene/hBN bilayers. Simulations of graphene/hBN twisted bilayers are presented that reveal the structure, energy, and elastic properties of the corresponding Moire patterns, and show a crossover, as the misorientation angle between the layers increases, from the well-defined hexagonal network of domain boundaries and junctions to smeared-out patterns. The transition occurs when the thickness of domain walls approaches the size of the Moire patterns, and coincides with the peaks in the average von Mises and volumetric stresses of the bilayer.

B-2:IL04  Advancing MOCVD Synthesis of Wafer-scale 2D Materials: A Computational Framework
k. momeni, Department of Mechanical Engineering, University of Alabama, Tuscaloosa, AL, USA; Materials Research Institute, Pennsylvania State University, University Park, PA, USA

Achieving consistent growth of two-dimensional (2D) materials across wafer-scale dimensions using Chemical Vapor Deposition (CVD) encounters obstacles due to limited comprehension of growth mechanisms across various length scales and the susceptibility of synthesis to subtle condition alterations. In response, we devised a comprehensive computational model known as the CPM framework, which integrates Computational Fluid Dynamics (CFD), Phase-Field (PF), and reactive Molecular Dynamics (MD), and subsequently validated its accuracy through experimentation. Through a meticulous alignment of theoretical projections with extensive empirical evaluations of WSe2 synthesized via Metal-Organic CVD (MOCVD), we have successfully demonstrated the efficacy of our methodology. Leveraging this computational framework, we have achieved the successful fabrication of uniform large-area 2D materials using MOCVD, guided by computational insights. Our study lays a robust groundwork for precise manipulation of coverage, morphology, and characteristics of 2D materials across wafer-scale dimensions, thus facilitating their application in electronic, optoelectronic, and quantum computing devices.

Session B-3 Strain and size effects on phase equilibria, phase transitions, and mesoscale domain states

B-3:IL01  Hydride Formation in Superconducting Q-Bits

T. Leibengood, P. VOORHEES, Department of Materials Science and Engineering, Northwestern University, Evanston, IL, USA; P.-C. Simon, Idaho National Laboratory, USA

The fabrication process for superconducting qubits that are based on 2D transmons frequently involves the deposition of niobium thin films on silicon substrates. The properties of superconducting qubits using Nb can also be affected by the formation of Nb hydrides. These phases have a significant lattice parameter mismatch with Nb implying that stress plays an important role on the formation of the hydrides, their shape, and the growth process. Stress can both prevent and promote the formation of these hydrides. Unlike most hydride precipitation processes, Nb hydrides in transmons form in an approximately 30-nanometer thick film of Nb. As a result, the effect of the free surface on the precipitation process can be profound. We find that due to the large diffusion coefficient of H in Nb, the Nb hydrides can precipitate in the film and then migrate quickly to the surface. A discussion of the critical role of stress and free surfaces on Nb-hydride formation in Nb thin films will be given.

B-3:IL02  Explaining Anomalous Low-temperature Irradiation Creep with Predictive Atomistic Simulations: A Case Study of Developing a Quantitative Virtual Experiment  
M. BOLEININGER, S.L. Dudarev, D.R. Mason, L. Reali, UK Atomic Energy Authority, Oxfordshire, UK; A. Feichtmayer, J. Riesch, T. Höschen, M. Fuhr, R. Neu, T. Schwarz-Selinger, Max Planck Institute for Plasma Physics, Garching, Germany

Realising economically viable fusion reactors requires developing a full-scale “virtual reactor” representation of an operating tokamak device, informed by predictive materials models spanning the parameter space of simultaneous thermal, mechanical, and radiation loads. This work describes a combined in silico and in vivo study focused on quantifying deformation under stress and irradiation at low temperature. While it is well known that irradiation accelerates creep deformation in metals, the phenomenon of irradiation creep becoming more pronounced at low temperature defies conventional understanding. We have designed an experiment for measuring stress-relaxation in a tensioned tungsten wire under irradiation and developed a virtual representation of the experiment consisting of a multiscale model driven by predictive atomistic simulations, allowing us to quantitatively predict the outcome of the experiment ahead of the actual observation. We discover that stresses up to 2GPa relax in minutes where, as opposed to conventional irradiation creep, temperature does not drive the process. Instead, the effect stems from the coalescence of athermally migrating, nanoscale radiation defects into dislocation networks and internal crystal planes aligned to compensate the external stress.

B-3:L03  Mechanisms of Nanostructure Formation During Dealloying 
G. HENKELMANN, J. Weissmüller, Hamburg University of Technology, Institute of Materials Physics and Technology, Hamburg, Germany

Electrochemical dealloying of dilute solid solutions with a low fraction of noble metals x has been shown to generate an interconnected nanoscale network of the master alloy, covered by the noble metal. KMC simulations qualitatively reproduce this phenomenon. Current theoretical models explain the highest x, at which dealloying can be observed, that is the parting limit at x≈45%, as well as the lowest potential, at which dealloying can be observed, the critical potential ϕ_c (x). However, these models describe the limits of dealloying and fail to predict the resulting structure and elemental composition in the case of x and ϕ far from the limits. Specifically of interest is the structure size L and its dependence on the dealloying potential ϕ. The expanded theoretical model should predict an x-ϕ-phase-diagram distinguishing regions of passivation and network formation. In the region of network formation, contour lines L(x,ϕ) in the phase diagram show points of equal structure size.

B-3:IL04  Strain Phase Thermodynamics and Phase-field Modeling of Strain Phase Equilibria and Mesoscale Transformations in Ferroelectric Heterostructure
B. Wang, T.N. Yang, C. Dai, M.H. Zhang, LONG-QING CHEN, Materials Research Institute and Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA, USA

It has now been well established that strains can be utilized to tune solid state phase and domain microstructures and thus physical properties. In this presentation, it is shown that one can efficiently construct multidomain and multiphase diagrams of arbitrarily strained or stressed ferroelectric thin films, in analogy to the well-known temperature-composition phase diagrams by ignoring the coherency strain energy contribution. Such strain/stress phase diagrams can be refined through phase-field simulations by incorporating the coherency strain energy contributions as well as electrostatic interactions and domain wall energy contributions. It is demonstrated that mesoscale ferroelectric domain structures may undergo phase transformations under external mechanical and electric fields as well as light. A combination of thermodynamic stability analysis and phase-field method offers a powerful theoretical tool for understanding the thermodynamic driving forces for the formation of thermodynamically stable mesoscale polar structures and for guiding the tuning of their properties using strains.

B-3:IL05  Coherent Phase Change in Interstitial Solutions – a Hierarchy of Instabilities 
J. Weissmüller, Hamburg University of Technology, Hamburg, Germany and Helmholtz-Center Hereon, Geesthacht, Germany

Many modern energy storage schemes rely on the reversible insertion and removal of interstitials in crystalline hosts, e.g. hydrogen in metals or lithium in battery electrodes. Scenarios in which the ex-change retains the crystalline coherency even when there are phase transformations can be particular-ly favorable. Yet, theory for those scenarios does not readily predict the nature of phase transfor-mations nor their concrete location in transformation mechanism maps spanning the temperature-composition space. This talk revisits the underlying continuum theory of chemo-mechanically coupled phenomena. The Bitter-Crum theorem – relevant for computer experiments with periodic boundary conditions – suggests drastically different behavior in open as opposed to closed systems. More realis-tic approaches – allowing for stress relaxation at free surfaces – find modified effective solute-solute interaction energies, with simple consequences for constrained equilibrium alloy phase diagrams. In-triguingly, instabilities in the coherent chemo-elastically coupled system also relate to open-system elastic parameters. Dual-phase or single-fees states with compositional heterogeneity and with me-chanical deformation – for instance buckling – then form spontaneously at no external load.

B-3:IL06  Modeling of Microstructure Formation in FePt High-density Magnetic Recording Media Based on a Phase-field Method Enhanced by Machine Learning Techniques 
TOSHIYUKI KOYAMA, Nagoya University, Nagoya, Japan

It has widely known that the recording density in magnetic recording media is strongly affected by the size and the microstructure morphology of magnetic particles on the disk. In this study, we propose a phase-field model for microstructure formation during sputtering in the FePt - X (X is, for example, carbon) system to clarify the mechanism of the characteristic microstructure development, and search for the condition to optimize the microstructure morphology for magnetic recording media through machine learning techniques. The results obtained are as follows. The characteristic microstructure, i.e. the FePt fine grains are covered with a thin film of X phase, is stabilized by the energy balance between the grain boundary energy of FePt phase and the FePt/X interface energy. During the growth process of a thin film composed of FePt phase and X phase, a phase with low surface energy prefers to cover the film surface, and a phase with higher concentration in the gas phase tends to cover the surface. In conclusion, the optimal microstructure morphology for magnetic recording media can be achieved by kinetically controlling the microstructure, which is energetically regulated by the surface and interface energies, with the concentration in the gas phase.

B-3:IL08  Microstructure Evolution with Elastic Strains: Recent Phase Field Results 
Y. LE BOUAR, A. Finel, Université Paris-Saclay, ONERA, CNRS, LEM, Châtillon, France; M. Cottura, B. Appolaire, Institut Jean Lamour, Université de Lorraine - CNRS, Nancy, France

Mechanical properties of metallic materials depend strongly on their microstructure, i.e. on the shape and spatial arrangement of the different phases in the materials. The phase field method has emerged as the most powerful method for modeling microstructure evolutions during phase transformations, especially when elastic coherency stresses are generated in solids. In this work, I will first present recent three-dimensional phase field results on the rafting in nickel-based superalloys. Several creep conditions will be analyzed such as tensile loadings along the [001], [011] and [111] directions, as well as shear loadings. The importance of elastic stresses and of the plastic relaxation will be discussed. Then, I will present the new discrete phase field approach proposed in [1] and show that this method significantly reduces the computational cost of phase field simulations. Such an improvement is highly desirable for three-dimensional simulations, as well as for the construction of large microstructure databases for machine learning based approaches.
[1] A. Finel, Y. Le Bouar, Phys. Rev. Lett. 121 (2018) 025501

B-3:IL09  First-principles Study on Alloy Phase Equilibria with Lattice Strain Relaxation 
YING CHEN, Tohoku University, Sendai, Japan; T. Horiuchi, Hokkaido University of Science, Sapporo, Japan; T. MOHRI, Hokkaido University, Sapporo, Japan

The lattice strain relaxation induced by the different sizes of constituent elements in an alloy influences various material properties, and also has direct effect on phase equilibrium and the formation process of microstructure. However, since there is neither direct measurement experimentally nor a clear definition theoretically on an atomic size, it is rare to include the lattice strain effect explicitly in the phase equilibria calculations. We proposed a theoretic method to describe the atomic sizes in the solid solution based on Bader analysis. We further incorporated the lattice strain relaxation explicitly to evaluate the phase transition temperature using the first-principles cluster variation method (CVM). The local atomic relaxation energy from the electronic structures within the microscopic elasticity theory has been also calculated. Cu-Au has been adopted as an example of the solid solution with a large atomic size difference. Computer simulation of the local lattice relaxation yielded the relaxation energy which resolved the large discrepancy of the Cu3Au L12-disorder transition temperature between previous CVM calculation and experiments. As a comparison, another binary alloy Cu-Ni in which the two elements have closed atomic sizes has been also investigated.

Session B-4 Structural, electric, and magnetic domain structures and their evolution under external stimuli

B-4:IL01  Understanding and Design of metallic Alloys Guided by Integrated Phase-field Simulation

YUHONG ZHAO, North University of China, University of Science and Technology Beijing, Taiyuan, China

Phase-field method has become a mainstream computational method for predicting the evolution of nano and mesoscopic microstructures and properties during materials processes. Many recent advances have been achieved in applying PFM to understanding the thermodynamic driving forces and mechanisms underlying microstructure evolution in metallic materials and related processes, including casting, aging, deformation, additive manufacturing, and defects, etc. Several examples are presented to demonstrate the potential of integrated PFM in discovering new multi-scale phenomena and designing high-performance alloys, such as a new Mg-14Li-7Al (wt.%) alloy with ultra-high specific strength (470-500 kNmkg−1) strengthened by spinodal decomposition at low temperature quenching, another high strength and ductility Cu-Ni-Al alloy, etc.

B-4:L03  Charged Dislocations in Ionic Ceramics: Equilibrium and Kinetics 
E. GARCIA, Purdue University, West Lafayette, IN, USA

The multifuncional properties of ionic ceramics has led to a great deal of applications ranging from memories, materials with runnable and switchable electrical conductivity, sensors and actuators, to technologies for energy storage and conversion applications. The possibilities seem endless, only limited by their processing, formability, and structural integrity. At its core, the presence of defects, including grain boundaries, dislocations, vacancies, and insterstitials has a central role on delivering tailored properties. In this paper, a thermodynamics-based variational formulation will be presented to rationalize the effects of electrical charge, stresses, and thermochemistry (including its couplings) and their effect on the stability and time-dependent behavior of dislocations in ionic ceramics. Applications to Yttria Stabilized Zirconia will be presented, highlighting the electro-chemo-mechanical interactions of point defects on the vicinity of the dislocation core and its impact on the observed non-elastic behavior. Comparisons against experiments will be made.

B-4:L04  Magnetic Structures Stimulated by External Mechanical Stress and Temperature Distribution in Amorphous Microwires used in Magnetic Sensors
A. CHIZHIK1, V. Zhukova1, P. Corte-Leon1, A. Zhukov1, 2, 1Universidad del País Vasco, UPV/EHU, San Sebastián, Spain; 2IKERBASQUE, Basque Foundation for Science, Bilbao, Spain

Magnetic amorphous microwires are of interest for research from technical and fundamental points of view. Here we study magnetic wires subjected to the effect of bending. The samples were bended and annealed in this state. Then the samples were unbent and examined in the straightened state. Also we present the results on the study of the magnetic structure and magnetization reversal in microwires with distributed anisotropy caused by distributed annealing temperature.
The hysteresis loops were obtained using the fluxmetric and MOKE methods. The MOKE technique was applied to get the images of surface magnetic domain structures.
The effect of magnetic bistability induced by bending annealing was discovered. Without annealing and after the annealing without bending, this effect was not observed. The induced bistability was accompanied by the rapid movement of a single longitudinal domain wall. In microwires with longitudinally distributed properties, the most significant result obtained is that we managed to recognize a wide variety of the complex magnetic structures in various longitudinal locations on the surface of the microwire. All this helps to optimize the properties of the active elements of magnetic sensors.

B-4:IL05  Giant Begative Compressibility of Flexible Banoporous Materials under High-pressure Intrusion-extrusion Process: From Energy Applications to Biological Channels 
D. Caprini1,F. Battista2, P. Zajdel3, G. Di Muccio2, C. Guardiani2, B. Trump4, M. Carter4, A.A. Yakovenko5, E. Amayuelas6, L. Bartolome6, S. Meloni7, Y. Grosu6, 8, C.M. Casciola2, A. Giacomello2, 1Center for Life Nano- & Neuro-Science, Istituto Italiano di Tecnologia, Rome, Italy; 2Dipartimento di Ingegneria Meccanica e Aerospaziale, Sapienza Universita di Roma, Rome, Italy; 3A. Chełkowski Institute of Physics, University of Silesia, Chorzow,  Poland; 4Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD, USA; 5X-Ray Science Division, Advanced Photon Source, Argonne National Laboratory, Argonne, IL, USA; 6Centre for Cooperative Research on Alternative Energies (CIC energiGUNE), Basque Research and Technology Alliance (BRTA), Alava Technology Park, Vitoria-Gasteiz, Spain; 7Dipartimento di Scienze Chimiche e Farmaceutiche, Universita degli Studi di Ferrara, Ferrara, Italy; 8Institute of Chemistry, University of Silesia, Katowice, Poland

This report highlights synergetic effect between computational methods and experiment in discovering the giant negative compressibility in metastable electrocapillary systems. Although coveted in applications, few materials expand when subject to compression or contract under decompression, i.e., exhibit negative compressibility. We proposed a simple strategy to obtain negative compressibility which exploits capillarity both to pre-compress the elastic material and to release such precompression by a threshold phenomenon – the reversible intrusion of a liquid into a lyophobic flexible cavity. The metastable elastocapillary system we designed according to these principles achieved the largest negative compressibility ever reported. Experiments demonstrate that the concept is effective all the way from hydrophobic subnanometre porous materials to millimetre-sized metamaterials and is relevant for diverse fields, including materials science and biology, providing a simple, cross-scale, and flexible platform to endow materials with negative compressibility for technological and biomedical applications.

B-4:IL06  Computational Modeling for Prediction of Material Topology by Quantum Annealing 
K. Endo, Mayu Muramatsu, Keio University, Yokohama, Kanagawa, Japan

In this study, we propose an objective function for exploring the phase-separated structure of diblock polymers by annealing, with an eye toward the use of quantum annealing. On the basis of the obtained results, we confirm the tendency of the microstructure and the simulation performance by comparison with the phase-field simulation. The approach is based on the use of a global optimization metaheuristic algorithm, called simulated annealing, to directly minimize the Helmholtz free energy instead of minimizing it analytically and then solving the resulting nonlinear, partial differential equation, i.e., the governing equation of the phase-field model. In this paper, we illustrate the use of simulated annealing in the solution of the phase-field model by applying it to the formation of a microstructure in a diblock polymer.
[1] Endo, K., Matsuda, Y., Tanaka, S. and Muramatsu, M. A phase-field model by an Ising machine and its application to the phase-separation structure of a diblock polymer. Sci. Rep. 12:10794.

Session B-5 Thermodynamics of mesoscale states and phase transitions

B-5:IL01  Grain Boundaries are Natural Brownian Ratchets: Directional GB Anisotropy

C. Qiu1, M. Punke2, 3, S. Wang1, Y. Su4, Y. Tian5, X. Pan5, M. Salvalaglio2, 3, J. Han1, D.J. Srolovitz6, 1Department of Materials Science and Engineering, City University of Hong Kong, Hong Kong SAR, China; 2Institute of Scientific Computing, TU Dresden, Dresden, Germany; 3Dresden Center for Computational Materials Science, TU Dresden, Dresden, Germany; 4School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai, China; 5Department of Physics and Astronomy, University of California, Irvine, CA, USA; 6Department of Mechanical Engineering, The University of Hong Kong, Hong Kong SAR, China

The motion of grain boundaries (GBs, i.e., natural defects in polycrystals separating single-crystal grains of different orientations) gives rise to microstructure evolution of polycrystalline materials. Classical models for GB motion posit that GB velocity, v=MF, where M is a constant (temperature-dependent) mobility and F is the driving force. Reversing the sign of F implies that the magnitude of the GB velocity is unchanged but with motion in the opposite direction. We show that this proposition is true only under a very restrictive set of conditions and a large population of GBs possess directionally-anisotropic migration behavior. We develop a Markov-chain Monte Carlo method that explains this phenomena and demonstrates that the inequivalence of back and forth motion leads to akin to ``Brownian ratchets''. We demonstrate how non-equilibrium thermal/mechanical perturbations can give rise to directional GB migration and show how oscillating stress or temperature accelerates grain growth. Finally, we demonstrate this effect through a novel set of experiments in-situ in a transmission electron microscope.

B-5:IL02  Grain Boundary Segregation and Solute Drag in Multicomponent Alloys  
F. Abdeljawad, M. Taghizadeh, Lehigh University, Bethlehem, PA, USA

High entropy alloys (HEAs) are a new class of materials that are composed of multiple elemental species in equal or near equal compositions. HEAs exhibit unique combinations of engineering properties that are not encountered in conventional alloys. Recent experimental findings revealed sluggish grain coarsening in HEAs and attributed it to segregation of elemental species to grain boundaries (GBs) and resultant solute drag. While GB segregation has been the subject of active research, most studies focus on binary alloys; very little is known about GB segregation and solute drag in multicomponent systems. Herein, we present a theoretical and computational model of GB segregation and dynamic solute drag in HEAs. The model accounts for bulk thermodynamics and the interaction of various elemental species with GBs, and it captures various mass transport processes. As a demonstration, the case of concentrated ternary alloys will be presented. Simulation results reveal a plethora of segregation behaviors, including synergistic co-segregation and induced de-segregation, that are dependent on alloy-alloy interactions within the GB. Our approach provides avenues to employ GB segregation engineering as a strategy to design HEAs with tailored microstructures.

B-5:IL03  Mesocanonical Ensemble as a Rationale for Studying Metastability and Hysteretic Transitions in Confined Nanophases 
A.V. NEIMARK, Department of Chemical and Biochemical Engineering, Rutgers, The State University of New Jersey, Piscataway, NJ, USA

Phase transitions in confined fluids are affected by geometric constraints and guest-host interactions. Nanophase transitions often involve long-lasting metastable states and hysteresis that have been well-documented in gas adsorption-desorption and nonwetting fluid intrusion-extrusion experiments with various micro- and mesoporous materials. The mesoscopic canonical, or mesocanonical, ensemble (MCE) is devised to study the nanophase behavior under conditions of controlled fluctuations that allows to stabilize metastable and labile states. In the MCE, the system of interest (a nanopore, or a system of nanopores) is considered in equilibrium with a reservoir of limited volume, called the gauge cell, which me controls the allowable level of density fluctuations. In this respect, the MCE is a middle ground between the grand canonical ensemble, which permits unlimited fluctuations, and the canonical ensemble, which considers a close system. The MCE Monte Carlo simulations produce van der Waals type isotherms with distinctive swings around the phase transitions regions. The constructed isotherms determine the positions of phase equilibrium, spinodals, and nucleation barriers. Advantages of the MCE method is demonstrated on various examples of gas adsorption on nanoporous systems.

Session B-6 Thermal, mechanical, electric, magnetic, and multifunctional properties of mesoscale structures

B-6:IL01  Multiphysics-multiscale Simulations of Additive Manufactured Fe-Ni Permalloy
BAI-XIANG XU, Y. Yang, Division Mechanics of Functional Materials, Institute of Materials Science, Technische Universität Darmstadt, Darmstadt, Germany

Designing microstructure in use of the unique additive manufacturing thermal conditions opens new avenues to tailor its magnetic properties. Yet, AM-produced parts suffer from spatially inhomogeneous thermal-mechanical and magnetic responses, which are less investigated. We present a powder-resolved multiphysics-multiscale simulation scheme for tailoring magnetic materials of Fe-Ni permalloy produced from powder bed fusion additive manufacturing (Yang et al. npj Comp. Mat., 9, 103, 2023). It integrates four important elements: finite element method (FEM)-based phase-field simulations of the thermal structural evolution during powder bed fusion, subsequent thermo-elasto-plastic FEM calculation, nanoscale chemical order-disorder transitions, and the finite difference based micromagnetic simulations. By employing this scheme, we investigate the dependence of the fusion zone size, the residual stress and plastic strain, and the magnetic hysteresis of AM-produced FeNi on beam power and scan speed. The residual stress is identified as the key thread in connecting the physical processes and phenomena across scales. We suggest a phenomenological relation between magnetic coercivity and average residual stress, which guides the hysteresis design of 3D printed soft magnetic materials.

B-6:IL02  Thermomechanical Properties of Highly Defective Metals for Fusion Power  
F. HOFMANN, A. Reza, K. Song, I. Tolkachev, G. He, Department of Engineering Science, University of Oxford, Oxford, UK; D.R. Mason, S.L. Dudarev, P.W. Ma, UK Atomic Energy Authority, Culham Science Centre, UK; S. Das, Department of Mechanical Engineering, University of Bristol, Bristol, UK; H. YU, Canadian Nuclear Laboratories, Chalk River, Canada

Nuclear fusion promises a safe, clean and almost inexhaustible energy source. Great progress has been made in controlling the fusion reaction. For commercially viable fusion power, materials are needed that can survive the intense in-reactor irradiation conditions for decades. Tungsten-based alloys are the main candidates for fusion armour components, while ferritic-martensitic steels will be used for structural components. We examine tungsten and iron-chromium model alloys to gain fundamental insight into the accumulation of irradiation-induced defects, and their effect on thermomechanical properties. By combining X-ray and electron diffraction measurements of lattice strain with TEM observations and molecular dynamics simulations we gain insight into the nature of the defects formed. Using transient grating spectroscopy we probe irradiation-induced changes in elastic properties and thermal transport, while nano-indentation allows us to explore changes in plastic deformation behaviour. Informed by molecular dynamics and continuum simulations, we can interpret these changes in terms of the underlying defect population. As such, as joined up picture of the structure-function relationship in highly defective irradiation-damaged materials begins to emerge.

B-6:IL03  Physics-based Data-driven Modeling to Accelerate Materials Design 
I. ROSLYAKOVA, Materials Discovery and Interfaces (MDI), Institute for Materials, Ruhr-Universität Bochum, Bochum, Germany

A hybrid modeling strategy that combines data-driven methods with existing physical laws is presented. The proposed hybrid data-driven modeling not only uses well-established methods from data science, such as statistics, machine learning, deep learning, etc., but also tries to keep as much physics as possible to analyze heterogeneous simulated and experimental data. In this hybrid modeling strategy, physics-based models and data-driven methods are combined to identify statistically sound correlations between material chemistry, thermodynamics, microstructures, and mechanical data [1-7]. Such a materials modeling and design strategy allows to identify the influence of individual physical effects from the considered contributions on selected material properties, which is necessary to accelerate the computer-aided design of new materials and alloys.
[1] Y. Jiang, et al., MSMSE, 2023, 31(3), 035005.
[2] U. Nwachukwu, et al., MSMSE, 2022, 30 (2), 025009
[3] E. Zhang, et al., Int. J. of Refractory Metals and Hard Materials, 2022, 103, 105780
[4] M. Ahmed, et al., MSMSE, 2021, 29, 055012
[5] K. Abrahams, et al., MSMSE, 2021, 29, 055007
[6] S. Zomorodpoosh, et al., Journal of Physics Communications, 2020, 4, 075024
[7] B. Bocklund, et al., MRS Communications, 2019, 9, 618-6

B-6:IL04  Phase-field Simulation of Elastocaloric and Magneto-elastocaloric Effect 
MIN YI, Nanjing University of Aeronautics and Astronautics, Nanjing, China

Modelling elastocaloric effect (eCE) is crucial for the design of environmentally friendly and energy-efficient eCE based solid-state cooling devices. Here, a thermodynamically consistent non-isothermal phase-field model (PFM) coupling martensitic transformation with mechanics and heat transfer is developed and applied for simulating eCE and magneto-eCE. To avoid the numerical issue related to the non-differentiable energy barrier function across the transition point, the austenite-martensite transition energy barrier in PFM is constructed as a smooth function of temperature. Both the indirect method using isothermal PFM with Maxwell relations and the direct method using non-isothermal PFM are applied to calculate the elastocaloric properties. It is found that the discrepancy of ∆Tadmax by indirect and direct method is within 10% at stress less than 150 MPa, confirming the feasibility of both methods in evaluating eCE at low stress. However, at higher stress, ∆Tadmax obtained from the indirect method is notably larger than that from the direct one. The results demonstrate the developed PFM herein, combined with both indirect and direct method for eCE calculations, as a practicable toolkit for the computational design of elastocaloric devices.


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