Showing 1–23 of 23 results for author: Fensin, S

Leveraging mechanical resonances for the selection of promising materials in complex phase spaces

Authors: Christopher A. Mizzi, Osman El-Atwani, Tannor T. J. Munroe, Saryu Fensin, Boris Maiorov

Abstract: The "high-entropy" paradigm has been applied to a central challenge in materials science, the design of new functional materials with enhanced performance for targeted applications, with some notable successes over the last twenty years. However, the immensity of the high-entropy design space remains a major impediment to discovering optimal compositions with tailored microstructures. Suites of hi… ▽ More The "high-entropy" paradigm has been applied to a central challenge in materials science, the design of new functional materials with enhanced performance for targeted applications, with some notable successes over the last twenty years. However, the immensity of the high-entropy design space remains a major impediment to discovering optimal compositions with tailored microstructures. Suites of high-throughput computational tools have been developed to address this problem, but there is a compelling need to inform these models with fast, economical, non-destructive, and versatile experimental guidance. In this work, we demonstrate mechanical resonance measurements can address this need. Mechanical resonance measurements enable the rapid, non-destructive assessment of materials created by novel syntheses and/or processes and provide high-accuracy determinations of elastic constants to directly benchmark models. We exemplify these capabilities on W-Ta-Cr-V-Hf and Mo-Nb-Ti-V-Zr refractory high-entropy alloys and suggest methodologies for the wider adoption and application of mechanical resonance measurements. △ Less

Submitted 19 February, 2026; originally announced February 2026.

Thicker amorphous grain boundary complexions reduce plastic strain localization in nanocrystalline Cu-Zr

Authors: Esther C. Hessong, Nicolo Maria della Ventura, Tongjun Niu, Daniel S. Gianola, Hyosim Kim, Nan Li, Saryu Fensin, Brad L. Boyce, Timothy J. Rupert

Abstract: Amorphous grain boundary complexions have been shown to increase the plasticity of nanocrystalline alloys as compared to ordered grain boundaries. Here, the effect of an important structural descriptor, amorphous complexion thickness, on the plasticity and failure modes of nanocrystalline Cu-Zr is studied with in-situ compression testing, with over 50 micropillars tested. Two model materials were… ▽ More Amorphous grain boundary complexions have been shown to increase the plasticity of nanocrystalline alloys as compared to ordered grain boundaries. Here, the effect of an important structural descriptor, amorphous complexion thickness, on the plasticity and failure modes of nanocrystalline Cu-Zr is studied with in-situ compression testing, with over 50 micropillars tested. Two model materials were created that differ only in their complexion thickness, with one having a thicker complexion population than the other. The sample with thinner complexions was more likely to experience non-uniform plastic deformation in the form of localized plastic flow or shear banding. In contrast, the sample with thicker complexions displayed more homogeneous plasticity and higher damage tolerance; thicker amorphous complexions suppress localization by absorbing defects. This work demonstrates that increasing complexion thickness can be beneficial for stable plastic flow in nanocrystalline alloys, by improving resistance to strain localization and premature failure. △ Less

Submitted 25 January, 2026; originally announced January 2026.

Bayesian inference and uncertainty quantification for modeling of body-centered-cubic single crystals

Authors: Seunghyeon Lee, Thao Nguyen, Darby J. Luscher, Saryu J. Fensin, John S. Carpenter, Hansohl Cho

Abstract: Uncertainties in the high-dimensional space of material parameters pose challenges for the predictive modeling of bcc single crystals, especially under extreme loading conditions. In this work, we identify the key physical assumptions and associated uncertainties in constitutive models that describe the deformation behavior of bcc single crystal molybdenum subjected to quasi-static to shock loadin… ▽ More Uncertainties in the high-dimensional space of material parameters pose challenges for the predictive modeling of bcc single crystals, especially under extreme loading conditions. In this work, we identify the key physical assumptions and associated uncertainties in constitutive models that describe the deformation behavior of bcc single crystal molybdenum subjected to quasi-static to shock loading conditions. We employ two representative physics-based bcc single crystal plasticity models taken from our previous work (Nguyen et al. 2021a; Lee et al. 2023b), each prioritizing different key deformation mechanisms. The Bayesian model calibration (BMC) is used for probabilistic estimates of material parameters in both bcc crystal plasticity models. In conjunction with the BMC procedure, the global sensitivity analysis is conducted to quantify the impact of uncertainties in the material parameters on the key simulation results of quasi-static to shock responses. The sensitivity indices at various loading conditions clearly illustrate the physical basis underlying the predictive capabilities of the two distinct bcc crystal plasticity models at low to high strain rates. Both of the calibrated bcc models are then further validated beyond the calibration regime, by which we further identify critical physical mechanisms that govern the transient elastic-plastic responses of single crystal molybdenum under shock loading. The statistical inference framework demonstrated here facilitates the further development of continuum crystal plasticity models that account for a broad range of deformation mechanisms. △ Less

Submitted 29 December, 2025; originally announced December 2025.

Achieving DFT accuracy in short range ordering and stacking fault energy using moment tensor potential for CoCrFeNi and CoCrNi

Authors: Mashroor S. Nitol, Artur Tamm, Subah Mubassira, Shuozhi Xu, Saryu J. Fensin

Abstract: Medium-entropy alloys (MEAs) such as CoCrFeNi and CoCrNi are promising structural materials owing to their outstanding mechanical and thermal properties, which arise from complex chemical disorder and atomic-scale interactions. Although density functional theory (DFT) has provided fundamental insights into these systems, its high computational cost limits exploration of large-scale phenomena. Clas… ▽ More Medium-entropy alloys (MEAs) such as CoCrFeNi and CoCrNi are promising structural materials owing to their outstanding mechanical and thermal properties, which arise from complex chemical disorder and atomic-scale interactions. Although density functional theory (DFT) has provided fundamental insights into these systems, its high computational cost limits exploration of large-scale phenomena. Classical interatomic potentials have been used to address this gap but often lack the fidelity needed to capture many-body interactions and chemical short-range ordering (CSRO) effects. In this work, we developed a machine-learned Moment Tensor Potential (MTP) to bridge accuracy and efficiency. The MTP was trained on a comprehensive DFT database spanning unary to quaternary configurations and reproduces energies, forces, and stresses with near-DFT accuracy across diverse structural and chemical environments. It accurately predicts elastic properties and recovers compositional trends in bulk and shear moduli in agreement with DFT. Hybrid Monte Carlo/molecular dynamics simulations capture CSRO, reproducing key DFT-reported features including Cr-Cr and Fe-Fe repulsion and Ni-Cr ordering. Stacking fault energetics were modeled, yielding ISF energies near 54 mJ/m2 for CoCrNi and 36 mJ/m2 for CoCrFeNi, consistent with DFT predictions. Local chemical environment effects on stacking faults were also resolved: Co-rich planes reduce, whereas Cr- or Fe-rich planes increase, the stacking fault energy. By enabling large-scale, high-fidelity simulations at a fraction of DFT's cost, the developed MTP provides a robust framework for predictive modeling of thermodynamic stability, defect behavior, and mechanical response of FCC MEAs. △ Less

Submitted 14 September, 2025; originally announced September 2025.

Predicting void nucleation in microstructure with convolutional neural networks

Authors: Abhijith Thoopul Anantharanga, Jackson Plummer, Saryu Fensin, Brandon Runnels

Abstract: Void nucleation in ductile materials subjected to high strain-rate loading remains a critical yet elusive phenomenon to understand. Traditional methods to understand void nucleation typically rely on experiments and molecular dynamics and do not capture the underlying factors leading to void nucleation. In this study, a convolutional neural network, specifically a U-Net enhanced with attention gat… ▽ More Void nucleation in ductile materials subjected to high strain-rate loading remains a critical yet elusive phenomenon to understand. Traditional methods to understand void nucleation typically rely on experiments and molecular dynamics and do not capture the underlying factors leading to void nucleation. In this study, a convolutional neural network, specifically a U-Net enhanced with attention gates is developed, to predict void nucleation probability in pristine tantalum microstructures. The approach leverages a multi-channel input, incorporating four channels of grain orientations and an additional channel of grain boundary energy calculated via the lattice matching method. Void nucleation probability fields are determined from post-mortem micrographs and serve as ground truth, distinguishing void from no-void regions at the pixel level. Pixel-level class imbalance, commen in such images, is addressed by using Focal loss to guide the network's training to predict void nucleation sites more effectively. The model not only predicts void nucleation sites consistent with ground-truth but also reveals additional potential void nucleation sites, capturing the stochastic nature of void nucleation. This study shows that CNN-based models can predict void nucleation sites while considering combined interplay of factors such as grain boundary energy and grain orientation. In this way, machine learning can serve as a means to understand the underlying factors leading to void nucleation thereby contributing to a fundamental understanding of failure due to spallation in ductile materials. △ Less

Submitted 11 September, 2025; originally announced September 2025.

Evaluating Moment Tensor Potential in Ag-Cu Alloy: Accuracy, Transferability, and Phase Diagram Fidelity

Authors: Mashroor S. Nitol, Marco J. Echeverría Iriarte, Doyl E. Dickel, Saryu J. Fensin

Abstract: A Moment Tensor Potential (MTP) has been developed for the Cu-Ag binary alloy and its accuracy, transferability, and thermodynamic fidelity evaluated. The model was trained on a diverse dataset encompassing solid, liquid, and interfacial configurations derived from density functional theory (DFT) calculations. Benchmarking against experiment and DFT data demonstrated significant improvements over… ▽ More A Moment Tensor Potential (MTP) has been developed for the Cu-Ag binary alloy and its accuracy, transferability, and thermodynamic fidelity evaluated. The model was trained on a diverse dataset encompassing solid, liquid, and interfacial configurations derived from density functional theory (DFT) calculations. Benchmarking against experiment and DFT data demonstrated significant improvements over the widely used classical Embedded Atom Method (EAM) potential, particularly in predicting defect energetics, surface properties, and the eutectic phase diagram. Despite a slight underestimation of Ag's melting point, the MTP model achieved consistent accuracy across elemental and binary systems without direct fitting to high-temperature phase transitions. The predicted eutectic temperature and composition were found in close agreement with experimental observations. These results establish MTP as a robust framework for modeling immiscible metallic systems and pave the way for its integration into large-scale atomistic simulations where both fidelity and generalizability are essential. △ Less

Submitted 25 August, 2025; originally announced August 2025.

The structure and migration of twin boundaries in tetragonal $β$-Sn: an application of machine learning based interatomic potentials

Authors: Ian Chesser, Mashroor Nitol, Esther C. Hessong, Himanshu Joshi, Nikhil Admal, Brandon Runnels, Daniel N. Blaschke, Khanh Dang, Abigail Hunter, Saryu Fensin

Abstract: Although atomistic simulations have contributed significantly to our understanding of twin boundary structure and migration in metals and alloys with hexagonal close packed (HCP) crystal structures, few direct atomistic studies of twinning have been conducted for other types of low symmetry materials, in large part due to a lack of reliable interatomic potentials. In this work, we examine twin bou… ▽ More Although atomistic simulations have contributed significantly to our understanding of twin boundary structure and migration in metals and alloys with hexagonal close packed (HCP) crystal structures, few direct atomistic studies of twinning have been conducted for other types of low symmetry materials, in large part due to a lack of reliable interatomic potentials. In this work, we examine twin boundary structure and migration in a tetragonal material, $β$-Sn, comparing high resolution Transmission Electron Microscopy (TEM) images of deformation twins in $β$-Sn to the results of direct atomistic simulations using multiple interatomic potentials. ML-based potentials developed in this work are found to give results consistent with our experimental data, revealing faceted twin boundary structures formed by the nucleation and motion of twinning disconnections. We use bicrystallographic methods in combination with atomistic simulations to analyze the structure, energy and shear coupled migration of observed twin facets in $β$-Sn. In analogy to Prismatic-Basal (PB/BP) interfaces in HCP metals, we discover low energy asymmetric Prismatic-A-plane (PA/AP) interfaces important to twin growth in $β$-Sn. A Moment Tensor Potential (MTP) and Rapid Artificial Neural Network (RANN) interatomic potential suitable for studying twinning and phase transformations in Sn are made publicly available as part of this work. △ Less

Submitted 13 May, 2025; originally announced May 2025.

Predicting Ti-Al Binary Phase Diagram with an Artificial Neural Network Potential

Authors: Micah Nichols, Christopher D. Barrett, Doyl E. Dickel, Mashroor S. Nitol, Saryu J. Fensin

Abstract: The microstructure of the Ti-Al binary system is an area of great interest as it affects material properties and plasticity. Phase transformations induce microstructural changes; therefore, accurately modeling the phase transformations of the Ti-Al system is necessary to describe plasticity. Interatomic potentials can be a powerful tool to model how materials behave; however, existing potentials l… ▽ More The microstructure of the Ti-Al binary system is an area of great interest as it affects material properties and plasticity. Phase transformations induce microstructural changes; therefore, accurately modeling the phase transformations of the Ti-Al system is necessary to describe plasticity. Interatomic potentials can be a powerful tool to model how materials behave; however, existing potentials lack accuracy in certain aspects. While classical potentials like the Embedded Atom Method (EAM) and Modified Embedded Atom Method (MEAM) perform adequately for modeling dilute Al solute within Ti's $α$ phase, they struggle with accurately predicting plasiticity. In particular, they struggle with stacking fault energies in intermetallics and to some extent elastic properties. This hinders their effectiveness in investigating the plastic behavior of formed intermetallics in Ti-Al alloys. Classical potentials also fail to predict the $α$ to $β$ phase boundary. Existing machine learning (ML) potentials reproduce the properties of formed intermetallics with density functional theory (DFT) but do not examine the $α$ to $β$ or $α$ to D0$_{19}$ phase boundaries. This work uses a rapid artificial neural network (RANN) framework to produce a neural network potential for the Ti-Al binary system. This potential is capable of reproducing the Ti-Al binary phase diagram up to 50$\%$ Al concentration. The present interatomic potential ensures stability and allows results near the accuracy of DFT. Using Monte Carlo simulations, RANN potential accurately predicts the $α$ to $β$ and $α$ to D0$_{19}$ phase transitions. The current potential also exhibits accurate elastic constants and stacking fault energies for the L1$_0$ and D0$_{19}$ phases. △ Less

Submitted 12 November, 2024; originally announced November 2024.

Exploring the relation between transonic dislocation glide and stacking fault width in FCC metals

Authors: Kathryn R. Jones, Khanh Dang, Daniel N. Blaschke, Saryu J. Fensin, Abigail Hunter

Abstract: Theory predicts limiting gliding velocities that dislocations cannot overcome. Computational and recent experiments have shown that these limiting velocities are soft barriers and dislocations can reach transonic speeds in high rate plastic deformation scenarios. In this paper we systematically examine the mobility of edge and screw dislocations in several face centered cubic (FCC) metals (Al, Au,… ▽ More Theory predicts limiting gliding velocities that dislocations cannot overcome. Computational and recent experiments have shown that these limiting velocities are soft barriers and dislocations can reach transonic speeds in high rate plastic deformation scenarios. In this paper we systematically examine the mobility of edge and screw dislocations in several face centered cubic (FCC) metals (Al, Au, Pt, and Ni) in the extreme large-applied-stress regime using MD simulations. Our results show that edge dislocations are more likely to move at transonic velocities due to their high mobility and lower limiting velocity than screw dislocations. Importantly, among the considered FCC metals, the dislocation core structure determines the dislocation's ability to reach transonic velocities. This is likely due to the variation in stacking fault width (SFW) due to relativistic effects near the limiting velocities. △ Less

Submitted 12 December, 2024; v1 submitted 16 September, 2024; originally announced September 2024.

Comments: 14 pages, 6 figures; revised version

Report number: LA-UR-24-29632

Journal ref: Modelling Simul. Mater. Sci. Eng. 33 (2025) 025020

Enhancing Irradiation Resistance in Refractory Medium Entropy Alloys with Simplified Chemistry

Authors: M. A. Tunes, D. Parkison, B. Sun, P. Willenshofer, S. Samberger, B. K. Derby, J. K. S. Baldwin, S. J. Fensin, D. Sobieraj, J. S. Wróbel, J. Byggmästar, S. Pogatscher, E. Martinez, D. Nguyen-Manh, O. El-Atwani

Abstract: Refractory High-Entropy Alloys (RHEAs) hold promising potential to be used as structural materials in future nuclear fusion reactors, where W and its alloys are currently leading candidates. Fusion materials must be able to withstand extreme conditions, such as (i) severe radiation-damage arising from highly-energetic neutrons, (ii) embrittlement caused by implantation of H and He ions, and (iii)… ▽ More Refractory High-Entropy Alloys (RHEAs) hold promising potential to be used as structural materials in future nuclear fusion reactors, where W and its alloys are currently leading candidates. Fusion materials must be able to withstand extreme conditions, such as (i) severe radiation-damage arising from highly-energetic neutrons, (ii) embrittlement caused by implantation of H and He ions, and (iii) exposure to extreme high-temperatures and thermal gradients. Recent research demonstrated that two RHEAs - the WTaCrV and WTaCrVHf - can outperform both coarse-grained and nanocrystalline W in terms of its radiation response and microstructural stability. Chemical complexity and nanocrystallinity enhance the radiation tolerance of these new RHEAs, but their multi-element nature, including low-melting Cr, complicates bulk fabrication and limits practical applications. We demonstrate that reducing the number of alloying elements and yet retain high-radiation tolerance is possible within the ternary system W-Ta-V via synthesis of two novel nanocrystalline refractory medium-entropy alloys (RMEAs): the W$_{53}$Ta$_{44}$V$_{3}$ and W$_{53}$Ta$_{42}$V$_{5}$ (in at.\%). We experimentally show that the radiation response of the W-Ta-V system can be tailored by small additions of V, and such experimental result was validated with theoretical analysis of chemical short-range orders (CSRO) from combined ab-initio atomistic Monte-Carlo modeling. It is predicted from computational analysis that a small change in V concentration has a significant effect on the Ta-V CRSO between W$_{53}$Ta$_{44}$V$_{3}$ and W$_{53}$Ta$_{42}$V$_{5}$ leading to radiation-resistant microstructures in these RMEAs from chemistry stand-point of views. We deviate from the original high-entropy alloy concept to show that high radiation resistance can be achieved in systems with simplified chemical complexity. △ Less

Submitted 21 June, 2024; originally announced June 2024.

Learning from metastable grain boundaries

Authors: Avanish Mishra, Sumit A. Suresh, Saryu J. Fensin, Nithin Mathew, Edward M. Kober

Abstract: Grain boundaries (GBs) govern critical properties of polycrystals. Although significant advancements have been made in characterizing minimum energy GBs, real GBs are seldom found in such states, making it challenging to establish structure-property relationships. This diversity of atomic arrangements in metastable states motivates using data-driven methods to establish these relationships. In thi… ▽ More Grain boundaries (GBs) govern critical properties of polycrystals. Although significant advancements have been made in characterizing minimum energy GBs, real GBs are seldom found in such states, making it challenging to establish structure-property relationships. This diversity of atomic arrangements in metastable states motivates using data-driven methods to establish these relationships. In this study, we utilize a vast atomistic database (~5000) of minimum energy and metastable states of symmetric tilt copper GBs, combined with physically-motivated local atomic environment (LAE) descriptors (Strain Functional Descriptors, SFDs) to predict GB properties. Our regression models exhibit robust predictive capabilities using only 19 descriptors, generalizing to atomic environments in nanocrystals. A significant highlight of our work is integration of an unsupervised method with SFDs to elucidate LAEs at GBs and their role in determining properties. Our research underscores the role of a physics-based representation of LAEs and efficacy of data-driven methods in establishing GB structure-property relationships. △ Less

Submitted 31 May, 2024; originally announced June 2024.

Effect of helium bubbles on the mobility of edge dislocations in copper

Authors: Minh Tam Hoang, Nithin Mathew, Daniel N. Blaschke, Saryu Fensin

Abstract: Helium bubbles can form in materials upon exposure to irradiation. It is well known that the presence of helium bubbles can cause changes in the mechanical behavior of materials. To improve the lifetime of nuclear components, it is important to understand deformation mechanisms in helium-containing materials. In this work, we investigate the interactions between edge dislocations and helium bubble… ▽ More Helium bubbles can form in materials upon exposure to irradiation. It is well known that the presence of helium bubbles can cause changes in the mechanical behavior of materials. To improve the lifetime of nuclear components, it is important to understand deformation mechanisms in helium-containing materials. In this work, we investigate the interactions between edge dislocations and helium bubbles in copper using molecular dynamics (MD) simulations. We focus on the effect of helium bubble pressure (equivalently, the helium-to-vacancy ratio) on the obstacle strength of helium bubbles and their interaction with dislocations. Our simulations predict significant differences in the interaction mechanisms as a function of helium bubble pressure. Specifically, bubbles with high internal pressure are found to exhibit weaker obstacle strength as compared to low-pressure bubbles of the same size due to the formation of super-jogs in the dislocation. Activation energies and rate constants extracted from the MD data confirm this transition in mechanism and enable upscaling of these phenomena to higher length-scale models. △ Less

Submitted 3 September, 2024; v1 submitted 14 May, 2024; originally announced May 2024.

Comments: 9 pages, 10 figures; v2+v3 minor revision

Report number: LA-UR-24-24506

Journal ref: Mod. Simul. Mater. Sci. Eng. 32 (2024) 075011

The structure and migration of heavily irradiated grain boundaries and dislocations in Ni in the athermal limit

Authors: Ian Chesser, Peter M. Derlet, Avanish Mishra, Sarah Paguaga, Nithin Mathew, Khanh Dang, Blas Pedro Uberuaga, Abigail Hunter, Saryu Fensin

Abstract: The microstructural evolution at and near pre-existing grain boundaries (GBs) and dislocations in materials under high radiation doses is still poorly understood. In this work, we use the creation relaxation algorithm (CRA) developed for atomistic modeling of high-dose irradiation in bulk materials to probe the athermal limit of saturation of GB and dislocation core regions under irradiation in FC… ▽ More The microstructural evolution at and near pre-existing grain boundaries (GBs) and dislocations in materials under high radiation doses is still poorly understood. In this work, we use the creation relaxation algorithm (CRA) developed for atomistic modeling of high-dose irradiation in bulk materials to probe the athermal limit of saturation of GB and dislocation core regions under irradiation in FCC Ni. We find that, upon continuously subjecting a single dislocation or GB to Frenkel pair creation in the athermal limit, a local steady state disordered defect structure is reached with excess properties that fluctuate around constant values. Case studies are given for a straight screw dislocation which elongates into a helix under irradiation and several types of low and high angle GBs, which exhibit coupled responses such as absorption of extrinsic dislocations, roughening and migration. A positive correlation is found between initial GB energy and the local steady state GB energy under irradiation across a wide variety of GB types. Metastable GB structures with similar density in the defect core region but different initial configurations are found to converge to the same limiting structure under CRA. The mechanical responses of pristine and irradiated dislocations and GB structures are compared under an applied shear stress. Irradiated screw and edge dislocations are found to exhibit a hardening response, migrating at larger flow stresses than their pristine counterparts. Mobile GBs are found to exhibit softening or hardening responses depending on GB character. Although some GBs recover their initial pristine structures upon migration outside of the radiation zone, many GBs sustain different flow stresses corresponding to altered mobile core structures. △ Less

Submitted 7 May, 2024; originally announced May 2024.

Transcending the MAX phases concept of nanolaminated early transition metal carbides/nitrides -- the ZIA phases

Authors: M. A. Tunes, S. M. Drewry, F. Schmidt, J. A. Valdez, M. M. Schneider, C. A. Kohnert, T. A. Saleh, C. G. Schön, S. Fensin, O. El-Atwani, N. Goossens, S. Huang, J. Vleugls, S. A. Maloy, K. Lambrinou

Abstract: A new potential class of nanolaminated and structurally complex materials, herein conceived as the Zigzag IntermetAllic (ZIA) phases, is proposed. A study of the constituent phases of a specific Nb--Si--Ni intermetallic alloy revealed that its ternary H-phase, \textit{i.e.}, the Nb$_3$SiNi$_2$ intermetallic compound (IMC), is a crystalline solid with the close-packed \textit{fcc} Bravais lattice,… ▽ More A new potential class of nanolaminated and structurally complex materials, herein conceived as the Zigzag IntermetAllic (ZIA) phases, is proposed. A study of the constituent phases of a specific Nb--Si--Ni intermetallic alloy revealed that its ternary H-phase, \textit{i.e.}, the Nb$_3$SiNi$_2$ intermetallic compound (IMC), is a crystalline solid with the close-packed \textit{fcc} Bravais lattice, the 312 MAX phase stoichiometry and a layered atomic arrangement that may define an entire class of nanolaminated IMCs analogous to the nanolaminated ceramic compounds known today as the MAX phases. The electron microscopy investigation of the Nb$_{3}$SiNi$_{2}$ compound -- the first candidate ZIA phase -- revealed a remarkable structural complexity, as its ordered unit cell is made of 96 atoms. The ZIA phases extend the concept of nanolaminated crystalline solids well beyond the MAX phases family of early transition metal carbides/nitrides, most likely broadening the spectrum of achievable material properties into domains typically not covered by the MAX phases. Furthermore, this work uncovers that both families of nanolaminated crystalline solids, \textit{i.e.}, the herein introduced \textit{fcc} ZIA phases and all known variants of the \textit{hcp} MAX phases, obey the same overarching stoichiometric rule $P_{x+y}A_xN_y$, where $x$ and $y$ are integers ranging from 1 to 6. △ Less

Submitted 11 August, 2023; originally announced August 2023.

Properties of accelerating edge dislocations in arbitrary slip systems with reflection symmetry

Authors: Daniel N. Blaschke, Khanh Dang, Saryu Fensin, Darby J. Luscher

Abstract: We discuss the theoretical solution to the differential equations governing accelerating edge dislocations in anisotropic crystals. This is an important prerequisite to understanding high speed dislocation motion, including an open question about the existence of transonic dislocation speeds, and subsequently high rate plastic deformation in metals and other crystals. We discuss the theoretical solution to the differential equations governing accelerating edge dislocations in anisotropic crystals. This is an important prerequisite to understanding high speed dislocation motion, including an open question about the existence of transonic dislocation speeds, and subsequently high rate plastic deformation in metals and other crystals. △ Less

Submitted 17 May, 2023; v1 submitted 18 March, 2023; originally announced March 2023.

Comments: 14 pages, 3 figures; v2 expanded introduction and additional refs

Report number: LA-UR-22-22567

Journal ref: Materials 16 (2023) 4019

Machine Learning Based Approach to Predict Ductile Damage Model Parameters for Polycrystalline Metals

Authors: Daniel N. Blaschke, Thao Nguyen, Mashroor Nitol, Daniel O'Malley, Saryu Fensin

Abstract: Damage models for ductile materials typically need to be parameterized, often with the appropriate parameters changing for a given material depending on the loading conditions. This can make parameterizing these models computationally expensive, since an inverse problem must be solved for each loading condition. Using standard inverse modeling techniques typically requires hundreds or thousands of… ▽ More Damage models for ductile materials typically need to be parameterized, often with the appropriate parameters changing for a given material depending on the loading conditions. This can make parameterizing these models computationally expensive, since an inverse problem must be solved for each loading condition. Using standard inverse modeling techniques typically requires hundreds or thousands of high-fidelity computer simulations to estimate the optimal parameters. Additionally, the time of a human expert is required to set up the inverse model. Machine learning has recently emerged as an alternative approach to inverse modeling in these settings, where the machine learning model is trained in an offline manner and new parameters can be quickly generated on the fly, after training is complete. This work utilizes such a workflow to enable the rapid parameterization of a ductile damage model called TEPLA with a machine learning inverse model. The machine learning model can efficiently estimate the model parameters much faster, as compared to previously employed methods, such as Bayesian calibration. The results demonstrate good accuracy on a synthetic test dataset and is validated against experimental data. △ Less

Submitted 18 July, 2023; v1 submitted 18 January, 2023; originally announced January 2023.

Comments: 13 pages, 9 figures; v2 minor revision

Report number: LA-UR-23-20468

Journal ref: Comput. Mater. Sci. 229 (2023) 112382

Perspectives on Novel Refractory Amorphous High-Entropy Alloys in Extreme Environments

Authors: Matheus A. Tunes, Hi T. Vo, Jon K. S. Baldwin, Tarik A. Saleh, Saryu J. Fensin, Osman El-Atwani

Abstract: Two new refractory amorphous high-entropy alloys (RAHEAs) within the W--Ta--Cr--V and W--Ta--Cr--V--Hf systems were herein synthesized using magnetron-sputtering and tested under high-temperature annealing and displacing irradiation using \textit{in situ} Transmission Electron Microscopy. While the WTaCrV RAHEA was found to be unstable under such tests, additions of Hf in this system composing a n… ▽ More Two new refractory amorphous high-entropy alloys (RAHEAs) within the W--Ta--Cr--V and W--Ta--Cr--V--Hf systems were herein synthesized using magnetron-sputtering and tested under high-temperature annealing and displacing irradiation using \textit{in situ} Transmission Electron Microscopy. While the WTaCrV RAHEA was found to be unstable under such tests, additions of Hf in this system composing a new quinary WTaCrVHf RAHEA was found to be a route to achieve stability both under annealing and irradiation. A new effect of nanoprecipitate reassembling observed to take place within the WTaCrVHf RAHEA under irradiation indicates that a duplex microstructure composed of an amorphous matrix with crystalline nanometer-sized precipitates enhances the radiation response of the system. It is demonstrated that tunable chemical complexity arises as a new alloy design strategy to foster the use of novel RAHEAs within extreme environments. New perspectives for the alloy design and application of chemically-complex amorphous metallic alloys in extreme environments are presented with focus on their thermodynamic phase stability when subjected to high-temperature annealing and displacing irradiation. △ Less

Submitted 17 November, 2022; originally announced November 2022.

Journal ref: Applied Materials Today 2023

An innovative materials design protocol for the development of novel refractory high-entropy alloys for extreme environments

Authors: O. El Atwani, H. T. Vo, M. Tunes, C. Lee, A. Alvarado, N. Krienke, J. D. Poplawsky, A. A. Kohnert, J. Gigax, W. -Y. Chen, M. Li, Y. Wang, J. S. Wróbel, Duc Nguyen-Manh, J. K. S. Baldwin, U. Tukac, E. Aydogan, S. Fensin, E. Martinez

Abstract: In the quest of new materials that can withstand severe irradiation and mechanical extremes for advanced applications (e.g. fission reactors, fusion devices, space applications, etc), design, prediction and control of advanced materials beyond current material designs become a paramount goal. Here, though a combined experimental and simulation methodology, the design of a new nanocrystalline refra… ▽ More In the quest of new materials that can withstand severe irradiation and mechanical extremes for advanced applications (e.g. fission reactors, fusion devices, space applications, etc), design, prediction and control of advanced materials beyond current material designs become a paramount goal. Here, though a combined experimental and simulation methodology, the design of a new nanocrystalline refractory high entropy alloy (RHEA) system is established. Compositions of this alloy, assessed under extreme environments and in situ electron-microscopy, revealed both high mechanical strength and thermal stability, grain refinement under heavy ion irradiation and outstanding irradiation resistance to dual-beam irradiation and helium implantation, marked by remarkable resistance to defect generation, growth and coalescence. The experimental and modeling results, which demonstrated notable agreement, can be applied to design and rapidly assess other alloys subjected to extreme environmental conditions. △ Less

Submitted 28 October, 2022; originally announced October 2022.

Limiting velocities and transonic dislocations in Mg

Authors: Khanh Dang, Daniel N. Blaschke, Saryu Fensin, Darby J. Luscher

Abstract: To accurately predict the mechanical response of materials, especially at high strain rates, it is important to account for dislocation velocities in these regimes. Under these extreme conditions, it has been hypothesized that dislocations can move faster than the speed of sound. However, the presence of such dislocations remains elusive due to challenges associated with measuring these experiment… ▽ More To accurately predict the mechanical response of materials, especially at high strain rates, it is important to account for dislocation velocities in these regimes. Under these extreme conditions, it has been hypothesized that dislocations can move faster than the speed of sound. However, the presence of such dislocations remains elusive due to challenges associated with measuring these experimentally. In this work, molecular dynamics simulations were used to investigate the dislocation velocities for the basal edge, basal screw, prismatic edge, and prismatic screw dislocations in Mg in the sub-, trans-, and supersonic regimes. Our results show that only prismatic edge dislocations achieve supersonic velocities. Furthermore, this work demonstrates that the discrepancy between the theoretical limiting velocity and the MD results for Mg is due to its sensitivity to large hydrostatic stress around the dislocation core, which was not the case for fcc metals such as Cu. △ Less

Submitted 25 August, 2022; v1 submitted 23 May, 2022; originally announced May 2022.

Comments: 7 pages, 4 figures; v2 clarifications and additional results

Report number: LA-UR-22-22557

Journal ref: Comput. Mater. Sci. 215 (2022) 111786

Clarifying the definition of 'transonic' screw dislocations

Authors: Daniel N. Blaschke, Jie Chen, Saryu Fensin, Benjamin A. Szajewski

Abstract: A number of recent Molecular Dynamics (MD) simulations have demonstrated that screw dislocations in face centered cubic (fcc) metals can achieve stable steady state motion above the lowest shear wave speed ($v_\text{shear}$) which is parallel to their direction of motion (often referred to as transonic motion). This is in direct contrast to classical continuum analyses which predict a divergence i… ▽ More A number of recent Molecular Dynamics (MD) simulations have demonstrated that screw dislocations in face centered cubic (fcc) metals can achieve stable steady state motion above the lowest shear wave speed ($v_\text{shear}$) which is parallel to their direction of motion (often referred to as transonic motion). This is in direct contrast to classical continuum analyses which predict a divergence in the elastic energy of the host material at a crystal geometry dependent `critical' velocity $v_\text{crit}$. Within this work, we first demonstrate through analytic analyses that the elastic energy of the host material diverges at a dislocation velocity ($v_\text{crit}$) which is greater than $v_\text{shear}$, i.e. $v_\text{crit} > v_\text{shear}$. We argue that it is this latter derived velocity ($v_\text{crit}$) which separates `subsonic' and `supersonic' regimes of dislocation motion in the analytic solution. In addition to our analyses, we also present a comprehensive suite of MD simulation results of steady state screw dislocation motion for a range of stresses and several cubic metals at both cryogenic and room temperatures. At room temperature, both our independent MD simulations and the earlier works find stable screw dislocation motion only below our derived $v_\text{crit}$. Nonetheless, in real-world polycrystalline materials $v_\text{crit}$ cannot be interpreted as a hard limit for subsonic dislocation motion. In fact, at very low temperatures our MD simulations of Cu at 10 Kelvin confirm a recent claim in the literature that true `supersonic' screw dislocations with dislocation velocities $v>v_\text{crit}$ are possible at very low temperatures. △ Less

Submitted 30 October, 2020; v1 submitted 31 August, 2020; originally announced August 2020.

Comments: 19 pages, 8 figures; v2 minor revision and changed title

Report number: LA-UR-20-25514

Journal ref: Phil. Mag. 101 (2021) 997-1018

Automated discovery of a robust interatomic potential for aluminum

Authors: Justin S. Smith, Benjamin Nebgen, Nithin Mathew, Jie Chen, Nicholas Lubbers, Leonid Burakovsky, Sergei Tretiak, Hai Ah Nam, Timothy Germann, Saryu Fensin, Kipton Barros

Abstract: Accuracy of molecular dynamics simulations depends crucially on the interatomic potential used to generate forces. The gold standard would be first-principles quantum mechanics (QM) calculations, but these become prohibitively expensive at large simulation scales. Machine learning (ML) based potentials aim for faithful emulation of QM at drastically reduced computational cost. The accuracy and rob… ▽ More Accuracy of molecular dynamics simulations depends crucially on the interatomic potential used to generate forces. The gold standard would be first-principles quantum mechanics (QM) calculations, but these become prohibitively expensive at large simulation scales. Machine learning (ML) based potentials aim for faithful emulation of QM at drastically reduced computational cost. The accuracy and robustness of an ML potential is primarily limited by the quality and diversity of the training dataset. Using the principles of active learning (AL), we present a highly automated approach to dataset construction. The strategy is to use the ML potential under development to sample new atomic configurations and, whenever a configuration is reached for which the ML uncertainty is sufficiently large, collect new QM data. Here, we seek to push the limits of automation, removing as much expert knowledge from the AL process as possible. All sampling is performed using MD simulations starting from an initially disordered configuration, and undergoing non-equilibrium dynamics as driven by time-varying applied temperatures. We demonstrate this approach by building an ML potential for aluminum (ANI-Al). After many AL iterations, ANI-Al teaches itself to predict properties like the radial distribution function in melt, liquid-solid coexistence curve, and crystal properties such as defect energies and barriers. To demonstrate transferability, we perform a 1.3M atom shock simulation, and show that ANI-Al predictions agree very well with DFT calculations on local atomic environments sampled from the nonequilibrium dynamics. Interestingly, the configurations appearing in shock appear to have been well sampled in the AL training dataset, in a way that we illustrate visually. △ Less

Submitted 24 August, 2020; v1 submitted 10 March, 2020; originally announced March 2020.

Combining Laue diffraction with Bragg coherent diffraction imaging at 34-ID-C

Authors: Anastasios Pateras, Ross Harder, Wonsuk Cha, Jonathan G. Gigax, J. Kevin Baldwin, Jon Tischler, Ruqing Xu, Wenjun Liu, Mark J. Erdmann, Robert Kalt, Richard L. Sandberg, Saryu Fensin, Reeju Pokharel

Abstract: Measurement modalities in Bragg coherent diffraction imaging (BCDI) rely on finding signal from a single nanoscale crystal object, which satisfies the Bragg condition among a large number of arbitrarily oriented nanocrystals. However, even when the signal from a single Bragg reflection with (hkl) Miller indices is found, the crystallographic axes on the retrieved three-dimensional (3D) image of th… ▽ More Measurement modalities in Bragg coherent diffraction imaging (BCDI) rely on finding signal from a single nanoscale crystal object, which satisfies the Bragg condition among a large number of arbitrarily oriented nanocrystals. However, even when the signal from a single Bragg reflection with (hkl) Miller indices is found, the crystallographic axes on the retrieved three-dimensional (3D) image of the crystal remain unknown, and thus, localizing in reciprocal space other Bragg reflections becomes in reality impossible or requires good knowledge of the orientation of the crystal. We report the commissioning of a movable double-bounce Si (111) monochromator at the 34-ID-C end station of the Advanced Photon Source, which aims at delivering multi-reflection BCDI as a standard tool in a single beamline instrument. The new instrument enables this through rapid switching from monochromatic to broadband (pink) beam permitting the use of Laue diffraction to determine crystal orientation. With a proper orientation matrix determined for the lattice, one can measure coherent diffraction near multiple Bragg peaks, thus providing sufficient information to image the full strain tensor in 3D. We discuss the design, concept of operation, the developed procedures for indexing Laue patterns, and automated measuring of Bragg coherent diffraction data from multiple reflections of the same nanocrystal. △ Less

Submitted 12 March, 2020; v1 submitted 26 February, 2020; originally announced February 2020.

Structural disjoining potential for grain boundary premelting and grain coalescence from molecular-dynamics simulations

Authors: Saryu Fensin, David Olmsted, Dorel Buta, Mark Asta, Alain Karma, J. J. Hoyt

Abstract: We describe a molecular dynamics framework for the direct calculation of the short-ranged structural forces underlying grain-boundary premelting and grain-coalescence in solidification. The method is applied in a comparative study of (i) a Sigma 9 <115> 120 degress twist and (ii) a Sigma 9 <110> {411} symmetric tilt boundary in a classical embedded-atom model of elemental Ni. Although both bound… ▽ More We describe a molecular dynamics framework for the direct calculation of the short-ranged structural forces underlying grain-boundary premelting and grain-coalescence in solidification. The method is applied in a comparative study of (i) a Sigma 9 <115> 120 degress twist and (ii) a Sigma 9 <110> {411} symmetric tilt boundary in a classical embedded-atom model of elemental Ni. Although both boundaries feature highly disordered structures near the melting point, the nature of the temperature dependence of the width of the disordered regions in these boundaries is qualitatively different. The former boundary displays behavior consistent with a logarithmically diverging premelted layer thickness as the melting temperature is approached from below, while the latter displays behavior featuring a finite grain-boundary width at the melting point. It is demonstrated that both types of behavior can be quantitatively described within a sharp-interface thermodynamic formalism involving a width-dependent interfacial free energy, referred to as the disjoining potential. The disjoining potential for boundary (i) is calculated to display a monotonic exponential dependence on width, while that of boundary (ii) features a weak attractive minimum. The results of this work are discussed in relation to recent simulation and theoretical studies of the thermodynamic forces underlying grain-boundary premelting. △ Less

Submitted 4 January, 2010; originally announced January 2010.

Comments: 24 pages, 8 figures, 1 table