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arXiv 2022年

作者： Eren, Erdem Runnels, Brandon Mason, Jeremy Department of Materials Science and Engineering University of California at Davis DavisCA United States Department of Mechanical and Aerospace Engineering University of Colorado Colorado SpringsCO United States

The evolution of interfaces is intrinsic to many physical processes ranging from cavitation in fluids to recrystallization in solids. Computational modeling of interface motion entails a number of challenges, many of which are related to the range of topological transitions that can occur over the course of the simulation. Microstructure evolution in a polycrystalline material that involves grain boundary motion is a particularly complex example due to the extreme variety, heterogeneity, and anisotropy of grain boundary properties. Accurately modeling this process is essential to determining processing-structure-property relationships in polycrystalline materials though. Simulations of microstructure evolution in such materials often use diffuse interface methods like the phase field method that are advantageous for their versatility and ease of handling complex geometries but can be prohibitively expensive due to the need for high interface resolution. Discrete interface methods require fewer grid points and can consequently exhibit better performance but have received comparatively little attention, perhaps due to the difficulties of maintaining the mesh and consistently implementing topological transitions on the grain boundary network. This work explicitly compares a recently-developed discrete interface method to a multiphase field method on several classical problems relating to microstructure evolution in polcrystalline materials: a shrinking spherical grain, the steady-state triple junction dihedral angle, and the steady-state quadruple point dihedral angle. In each case, the discrete method is found to meet or outperform the multiphase field method with respect to accuracy for comparable levels of refinement, demonstrating its potential efficacy as a numerical approach for microstructure evolution in polycrystalline materials. © 2022, CC BY.

关键词： Finite element method

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Quantifying microstructural evolution via time-dependent reduced-dimension metrics based on hierarchical n-point polytope functions

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Physical Review E 2022年第2期105卷 025306-025306页

作者： Pei-En Chen Rahul Raghavan Yu Zheng Hechao Li Kumar Ankit Yang Jiao Mechanical and Aerospace Engineering Arizona State University Tempe Arizona 85287 USA Materials Science and Engineering Arizona State University Tempe Arizona 85287 USA Department of Physics Arizona State University Tempe Arizona 85287 USA

We devise reduced-dimension metrics for effectively measuring the distance between two points (i.e., microstructures) in the microstructure space and quantifying the pathway associated with microstructural evolution, based on a recently introduced set of hierarchical n-point polytope functions Pn. The Pn functions provide the probability of finding particular n-point configurations associated with regular n polytopes in the material system, and are a special subset of the standard n-point correlation functions Sn that effectively decompose the structural features in the system into regular polyhedral basis with different symmetries. The nth order metric Ωn is defined as the L1 norm associated with the Pn functions of two distinct microstructures. By choosing a reference initial state (i.e., a microstructure associated with t0=0), the Ωn(t) metrics quantify the evolution of distinct polyhedral symmetries and can in principle capture emerging polyhedral symmetries that are not apparent in the initial state. To demonstrate their utility, we apply the Ωn metrics to a two-dimensional binary system undergoing spinodal decomposition to extract the phase separation dynamics via the temporal scaling behavior of the corresponding Ωn(t), which reveals mechanisms governing the evolution. Moreover, we employ Ωn(t) to analyze pattern evolution during vapor deposition of phase-separating alloy films with different surface contact angles, which exhibit rich evolution dynamics including both unstable and oscillating patterns. The Ωn metrics have potential applications in establishing quantitative processing-structure-property relationships, as well as real-time processing control and optimization of complex heterogeneous material systems.

关键词： Classical statistical mechanics Microstructure

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Exotic Magnetism in Perovskite KOsO3

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Physical Review Letters 2024年第15期132卷 156701-156701页

作者： Jie Chen Hongze Li Javier Gainza Angel Muñoz Jose A. Alonso Jue Liu Yu-Sheng Chen Alexei A. Belik Kazunari Yamaura Jiaming He Xinyu Li John B. Goodenough J.-S. Zhou Materials Science and Engineering program Mechanical Engineering University of Texas at Austin Austin Texas 78712 USA Instituto de Ciencia de Materiales de Madrid CSIC Cantoblanco E-28049 Madrid Spain Universidad Carlos III Avenida Universidad 30 E-28911 Leganés-Madrid Spain Neutron Scattering Division Oak Ridge National Laboratory Oak Ridge Tennessee 37830 USA NSF’s ChemMatCARS The University of Chicago Chicago Illinois 60437 USA Research Center for Materials Nanoarchitectonics (MANA) National Institute for Materials Science Namiki 1-1 Tsukuba Ibaraki 305-0044 Japan Graduate School of Chemical Sciences and Engineering Hokkaido University North 10 West 8 Kita-ku Sapporo Hokkaido 060-0810 Japan

A new perovskite KOsO3 has been stabilized under high-pressure and high-temperature conditions. It is cubic at 500 K (Pm−3m) and undergoes subsequent phase transitions to tetragonal at 320 K (P4/mmm) and rhombohedral (R−3m) at 230 K as shown from refining synchrotron x-ray powder diffraction (SXRD) data. The larger orbital overlap integral and the extended wave function of 5d electrons in the perovskite KOsO3 allow to explore physics from the regime where Mott and Hund’s rule couplings dominate to the state where the multiple interactions are on equal footing. We demonstrate an exotic magnetic ordering phase found by neutron powder diffraction along with physical properties via a suite of measurements including magnetic and transport properties, differential scanning calorimetry, and specific heat, which provide comprehensive information for a system at the crossover from localized to itinerant electronic behavior.

关键词： Magnetic interactions Magnetic order Antiferromagnets Density functional theory First-principles calculations Neutron diffraction Sintering

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Computing Grain Boundary 'Phase' Diagrams

arXiv

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arXiv 2022年

作者： Luo, Jian Department of Nanoengineering Program of Materials Science and Engineering University of California La Jolla San DiegoCA United States

Grain boundaries (GBs) can be treated as two-dimensional (2-D) interfacial phases (also called 'complexions') that can undergo interfacial phase-like transitions. As bulk phase diagrams and calculation of phase diagram (CALPHAD) methods are a foundation for modern materials science, we propose to extend them to GBs to have equally significant impacts. This perspective article reviews a series of studies to compute the GB counterparts to bulk phase diagrams. First, a phenomenological interfacial thermodynamic model was developed to construct GB lambda diagrams to forecast high-temperature GB disordering and related trends in sintering and other properties for both metallic and ceramic materials. In parallel, an Ising-type lattice statistical thermodynamic model was utilized to construct GB adsorption diagrams, which predicted first-order GB adsorption (a.k.a. segregation) transitions and critical phenomena. These two simplified thermodynamic models emphasize on the GB structural (disordering) and chemical (adsorption) aspects, respectively. Subsequently, hybrid Monte Carlo and molecular dynamics atomistic simulations were used to compute more rigorous and accurate GB 'phase' diagrams. Computed GB diagrams of thermodynamic and structural properties were further extended to include mechanical properties. Moreover, machine learning was combined with atomistic simulations to predict GB properties as functions of four independent compositional variables and temperature in a 5-D space for a given GB in high-entropy alloys or as functions of five GB macroscopic (crystallographic) degrees of freedom (DOFs) plus temperature and composition for a binary alloy in a 7-D space. Relevant other studies are examined. Future perspective and outlook, including two emerging fields of high-entropy grain boundaries (HEGBs) and electrically (or electrochemically) induced GB transitions, are discussed. Copyright © 2022, The Authors. All rights reserved.

关键词： Grain boundaries

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A Computationally Derived Technique for the Precision Placement of Heterogeneous Nanoscale Species on a Single Substrate 17

A Computationally Derived Technique for the Precision Placem...

引用

17th Annual Conference on Foundations of Nanoscience: Self-Assembled Architectures and Devices, FNANO 2020

作者： Deluca, Marcello Gopinath, Ashwin Arva, Gaurav Department of Mechanical Engineering and Materials Science Duke University United States Department of Mechanical Engineering Massachusetts Institute of Technology United States

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Tailoring Anisotropy and Heterogeneity of Selective Laser Melted Ti6Al4V Alloys

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Transactions of the Indian National Academy of engineering 2023年第2期8卷 245-251页

作者： Karimi, J. Kollo, L. Prashanth, K. G. Department of Mechanical and Industrial Engineering Tallinn University of Technology Tallinn Estonia BIAS–Bremer Institut für angewandte Strahltechnik GmbH Bremen Germany Erich Schmid Institute of Materials Science Austrian Academy of Sciences Leoben Austria CBCMT School of Engineering Vellore Institute of Technology Vellore India

Selective laser melting (SLM) provides an opportunity to manufacture parts with complex geometry, minimal wastage, and no need for special tooling. However, the fabricated parts exhibit heterogeneity and anisotropy in mechanical properties and residual stresses, which have been long-term concerns of the SLM of metallic materials. The present study investigates the effect of melting sequence and heat treatment on such heterogeneous and anisotropic properties in the SLM Ti6Al4V alloys. As a relatively low-cost and effective approach, the application of melting sequence led to the homogenization of the microstructure and improvement of mechanical properties, though anisotropy in properties (residual stresses, hardness) remained. The application of the heat treatment process not only homogenized the hardness but also reduced the anisotropy. These approaches would be considered as the two potential strategies to overcome the shortcoming of the SLM process, depending on the required properties, possibility and performance, and the budget.

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High-entropy grain boundaries

arXiv

引用

arXiv 2022年

作者： Luo, Jian Zhou, Naixie Department of Nanoengineering Program of Materials Science and Engineering University of California La Jolla San DiegoCA United States

Do high-entropy alloys and ceramics have their grain boundary (GB) counterparts? As the concept of high-entropy grain boundaries (HEGBs) was initially proposed in 2016, this article provides the first complete and rigorous discussion of the underlying interfacial thermodynamics. A simplified segregation model can illustrate both GB and bulk high-entropy effects, which reduce GB energy with increasing temperature for saturated multicomponent (conventional and high-entropy) alloys. HEGBs can be utilized to stabilize nanocrystalline alloys at high temperatures via thermodynamic and kinetic effects. GB structural disordering and transitions offer further opportunities to attain higher effective GB entropies. Future perspective is discussed. Copyright © 2022, The Authors. All rights reserved.

关键词： Grain boundaries

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Educational trends post COVID-19 in engineering: Virtual laboratories

引用

materials today. Proceedings 2022年 49卷 155-160页

作者： Diego Vergara Pablo Fernández-Arias Jamil Extremera Lilian P Dávila Manuel P Rubio Department of Mechanical Engineering Catholic University of Ávila Ávila 05005 Spain. Department of Computer Science and Automatics University of Salamanca Salamanca 37008 Spain. Department of Materials Science and Engineering School of Engineering University of California at Merced Merced CA 95343 United States. Department of Construction University of Salamanca Zamora 49029 Spain.

The rapid advance of Information and Communication Technology (ICT) in recent times and the current pandemic caused by COVID-19 have profoundly transformed society and the economy in most of the world. The education sector has benefited from this ICT-driven revolution, which has provided and expanded multiple new tools and teaching methods that did not exist just a few decades ago. In light of this technological change, virtual laboratories (VLs) based on the use of virtual reality (VR) have emerged, which are increasingly used to facilitate the teaching-learning process in a wide range of training activities, both academic and professional types. The set of advantages offered by this type of VL, the main of which are listed in this article, has made its use increasingly common as support for engineering classes at universities. This paper presents a study involving 420 engineering students from Spanish and Portuguese universities and associated analyses on the assessment of different parameters in various VLs designed by the authors. The results obtained indicate that, in general, VR-based VLs are widely accepted and demanded by students, who likewise consider real laboratories (RLs) necessary in face-to-face teaching. In the current post-COVID-19 educational scenario, VLs and RLs will coexist within the new hybrid models that combine face-to-face and online teaching and learning.

关键词： COVID-19 Didactic tools engineering Hybrid education Virtual laboratories Virtual reality

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Thermally Conductive Electrically Insulating Electronics Packaging for Water Immersion Cooling

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IEEE Transactions on Components, Packaging and Manufacturing Technology 2025年

作者： Gebrael, Tarek Gamboa, Arielle R. Hoque, Muhammad Jahidul Aflatounian, Shayan Huitink, David Pilawa-Podgurski, Robert Miljkovic, Nenad University of Illinois Department of Mechanical Science and Engineering UrbanaIL61801 United States University of Arkansas Department of Mechanical Engineering FayettevilleAR72701 United States University of California Department of Electrical Engineering and Computer Sciences BerkeleyCA94720 United States University of Illinois Department of Electrical and Computer Engineering UrbanaIL61801 United States University of Illinois Materials Research Laboratory UrbanaIL61801 United States Institute for Sustainability Energy and Environment UrbanaIL61801 United States Air Conditioning and Refrigeration Center UrbanaIL61801 United States 744 Moto-oka Nishi-ku Fukuoka819-0395 Japan

Power densification is making thermal design a key step in the development of future electrical devices. Systems such as data centers and electric vehicles are generating more heat, which requires efficient cooling to maintain the electronics at temperatures below their limits and to ensure reliability. Immersion cooling has emerged as a promising thermal management technique that brings the coolant closer to the heat-generating elements, hence reducing thermal impedance and improving cooling. Although the dielectric liquid coolants used in immersion cooling do not compromise the electrical performance of the submerged electrical devices, their cooling performance is inferior compared to ideal coolants such as water. To use water as an immersion coolant, the electronics need to be encapsulated to prevent short circuits. Here, a packaging approach is developed that insulates the electronics from the surrounding water and spreads heat for better cooling. The package consists of an aluminum nitride (AlN) component for insulation and heat spreading, and a Parylene C coating for conformal electrical insulation. The package is characterized electrically by measuring the leakage current in water under DC voltages up to 600 V for periods up to 7 days. The thermal performance of this packaging method is also characterized by calculating the junction-to-coolant thermal resistance. The developed packaging design can be implemented in high power density applications where the heat flux is beyond what standard dielectric fluids can handle. © 2011-2012 IEEE.

关键词： Dielectric liquids

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Exciton-phonon coupling induces new pathway for ultrafast intralayer-to-interlayer exciton transition and interlayer charge transfer in WS2-MoS2 heterostructure: a first-principles study

arXiv

引用

arXiv 2024年

作者： Chan, Yang-Hao Naik, Mit H. Haber, Jonah B. Neaton, Jeffrey B. Louie, Steven G. Qiu, Diana Y. da Jornada, Felipe H. Institute of Atomic and Molecular Sciences Academia Sinica Taipei10617 Taiwan Physic Division National Center of Theoretical Physics Taipei10617 Taiwan Department of Physics University of California BerkeleyCA94720-7300 United States Materials Science Division Lawrence Berkeley National Laboratory BerkeleyCA94720 United States Department of Mechanical Engineering and Materials Science Yale University New HavenCT06520 United States Department of Materials Science and Engineering Stanford University StanfordCA94305 United States

Despite the weak, van-der-Waals interlayer coupling, photoinduced charge transfer vertically across atomically thin interfaces can occur within surprisingly fast, sub-50fs timescales. Early theoretical understanding of the charge transfer is based on a noninteracting picture, neglecting excitonic effects that dominate the optical properties of such materials. Here, we employ an ab initio many-body perturbation theory approach which explicitly accounts for the excitons and phonons in the heterostructure. Our large-scale first-principles calculations directly probe the role of exciton-phonon coupling in the charge dynamics of the WS2/MoS2 heterobilayer. We find that the exciton-phonon interaction induced relaxation time of photo-excited excitons at the K valley of MoS2 and WS2 is 67 fs and 15 fs at 300 K, respectively, which sets a lower bound to the intralayer-to-interlayer exciton transfer time and is consistent with experiment reports. We further show that electron-hole correlations facilitate novel transfer pathways which are otherwise inaccessible to non-interacting electrons and holes. © 2024, CC BY.

关键词： Tungsten compounds

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