Larry Aagesen

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• Doctor of Philosophy
• Computational Scientist at Idaho National Laboratory

A phase-field model to simulate the formation of both void and gas bubble superlattices is derived from a grand potential functional, assuming 1D diffusion of self-interstitial atoms. The model is capable of accounting for superlattice formation by either a nucleation and growth or spinodal decomposition mechanism; in this work, we focus on the nuc...

Nanopatterned microstructures in materials can have a profound impact on materials’ physical and chemical properties. While voids are typically considered as detrimental defects in irradiated materials, the patterning of nanoscale voids causes the formation of void superlattices and provides a highly efficient mechanism for gas storage. Despite the...

Self-organized microstructures and patterns have been widely observed in non-equilibrium physical systems. In particular, irradiation in metals creates far-from-equilibrium environments, in which the competing dynamics of defect production and annihilation can lead to unique self-organized superlattice structures, e.g., void and gas bubble superlat...

In this paper, we present a phase-field model of quasi-brittle fracture with pressurized cracks, with dedicated applications for polycrystalline materials. The model is formulated as a minimization problem within the variational framework. The external work done by pressure on the crack surfaces is included in the objective function. Several carefu...

The silicon carbide (SiC) layer in tristructural isotropic (TRISO) fuel particles serves as a barrier to prevent the escape of fission products produced and not retained in the fuel kernel. The release of silver (Ag) is a concern due to the long half-life of the 110mAg isotope. However, accurately determining the fission gas release rate requires k...

Uranium dioxide (UO2) is the primary fuel material that is used in current nuclear reactors. As one of the most fundamental material parameters, grain boundary (GB) energy strongly influences many fuel properties, and the influences depend on the characters and properties of individual GBs. Using molecular dynamics simulations, a high throughput su...

The growth and interconnection of fission gas bubbles in the hotter central regions of U-(Pu)-Zr nuclear fuel has been simulated with a phase-field model. The Cahn-Hilliard equation was used to represent the two-phase microstructure, with a single defect species. The volume fraction of the bubble phase and surface area of the bubble-matrix interfac...

Solidification is a significant step in the forming of crystalline structures during various manufacturing and material processing techniques. Solidification characteristics and the microstructures formed during the process dictate the properties and performance of the materials. Hence, understanding how the process conditions relate to various mic...

To improve the economics of commercial light water reactors, increased understanding of UO2 nuclear fuel with the high burnup structure (HBS) is required in both steady-state and transient conditions. Here, a phase-field model of the fission gas bubble microstructure in nuclear fuel is developed based on the Kim-Kim-Suzuki (KKS) formulation and imp...

In light water nuclear reactors, waterside corrosion of the cladding material leads to the production of hydrogen, a fraction of which is picked up by the zirconium cladding and precipitates into brittle hydride particles. These nanoscale hydride particles aggregate into mesoscale hydride clusters. The principal stacking direction of the nanoscale...

A fundamental understanding of lanthanide transport in metallic fuels is critical for high fidelity modeling of the fuel-cladding chemical interaction (FCCI) phenomenon, which can lead to the formation of brittle intermetallic compounds and premature failure of the cladding. Here we report a combined ab initio density functional theory (DFT) and ki...

The phase-field method has been established as a de facto standard for simulating the microstructural evolution of materials. In quantitative modeling the assessment and compilation of thermodynamic/kinetic data is largely dominated by the CALPHAD approach, which has produced a large set of experimentally and computationally generated Gibbs free en...

The contribution of the author Pierre-Clément A. Simon has been added to the CRediT authorship contribution statement: Pierre-Clément A. Simon: Conceptualization, Methodology, Software, Validation, Visualization, Writing - original draft, Writing - review & editing.

Understanding the interactions of noble gases with metals is of fundamental importance for the design of radiation-resistant structural materials for fission and fusion nuclear reactors. Here we present a unified theory for describing the energetics of He, Ne, Ar, and Kr bubbles in bcc metals in group 5B (V, Nb, Ta), 6B (Cr, Mo, W) and 8B (Fe). Our...

Uranium silicide (U3Si2) is a concept explored as a potential alternative to UO2 fuel used in light water reactors (LWRs) since it may improve accident tolerance and economics due to its higher thermal conductivity and increased uranium density. U3Si2 has been previously used in research reactors in the form of dispersion fuel which operates at low...

The phase-field method has been established as a de facto standard for simulating the microstructural evolution of materials. In quantitative modeling the assessment and compilation of thermodynamic/kinetic data is largely dominated by the CALPHAD approach, which has produced a large set of experimentally and computationally generated Gibbs free en...

Efficient solution via Newton’s method of nonlinear systems of equations requires an accurate representation of the Jacobian, corresponding to the derivatives of the component residual equations with respect to the degrees of freedom. In practice these systems of equations often arise from spatial discretization of partial differential equations us...

Introducing elastic energy in the phase field method has been shown to influence interfacial energy, depending on the elastic interpolation scheme. This study investigates the impact of the elastic energy when using a grand potential-based phase field method, comparing the result of Khachaturyan’s strain interpolation scheme (KHS) and Voight-Taylor...

U3Si2 is a potential accident-tolerant fuel that shows promise due to its high thermal conductivity and higher uranium density relative to UO2. However, its swelling and fission gas release behavior in light water reactor (LWR) conditions is relatively unknown. To provide mechanistic insight and determine parameters for engineering-scale fuel perfo...

Deformation twinning is one of the major deformation mechanisms in crystals, which plays an important role in determining the mechanical properties of metals and alloys. One of the important issues to understand twinning mechanisms is the determination of the deformation path. However, due to a lack of theoretical tools, a fundamental relationship...

Uranium-zirconium alloy fuels are candidates for advanced sodium cooled fast reactors due to their high uranium density, high thermal conductivity, inherent safety and ability to incorporate minor actinides into the fuel. Unlike traditional ceramic UO2 fuel, U–Zr alloys swell rapidly and substantially, but the actual mechanistic process of swelling...

The kinetics of oxidation is examined using a phase-field model of electrochemistry when the oxide film is smaller than the Debye length. As a test of the model, the phase-field approach recovers the results of classical Wagner diffusion-controlled oxide growth when the interfacial mobility of the oxide-metal interface is large and the films are mu...

As a signature of symmetry-breaking processes, the generation and annihilation of topological defects (domain walls, strings, etc.) are of great interest in condensed matter physics and cosmology. Here we propose a distinctive self-organization process through phase transitions, in which all the generated topological defects are dimension-ality red...

Microstructure is a controlling factor in the behavior of sintered materials. This work presents a quantitative phase field model of thermal sintering that predicts the evolution of the microstructure by capturing the sintering stress, GB/vacancy interactions, non-uniform diffusion, and grain coarsening without introducing a separate rigid body mot...

Scientific communities struggle with the challenge of effectively and efficiently sharing content and data. An online portal provides a valuable space for scientific communities to discuss challenges and collate scientific results. Examples of such portals include the Micromagnetic Modeling Group (μMAG) [1], the Interatomic Potentials Repository (I...

Mesoscale modeling and simulation approaches provide a bridge from atomic-scale methods to the macroscale. The phase field (PF) method has emerged as a powerful and popular tool for mesoscale simulation of microstructure evolution, and its use is growing at an ever-increasing rate. While initial research using the PF method focused on model develop...

We studied surface corrosion effects on Zr and UN using first-principles density functional theory-based calculations. We focused on the energetics of Zr (1000), UN (100) and UN (110) surfaces, exposed to water and oxygen. Average distance between the terminating UN (100) surface and bulk increases due to the presence of additional oxygen content,...

A phase-field model of fission gas bubble evolution was developed and applied to gain an improved understanding of the microstructure-level processes leading to fission gas release from nuclear fuel, and to inform engineering-scale fission gas release models. The phase-field model accounts for multiple fuel grains and fission gas bubbles and tracks...

The structural hierarchy exhibited by materials on more than one length scale can play a major part in determining bulk material properties. Understanding the hierarchical structure can lead to new materials with physical properties tailored for specific applications. We have used a combined experimental and phase-field modeling approach to explore...

We have examined the influence of spontaneous nano-patterning on the placement of InAs quantum dots (QDs) on (Al)GaAs surfaces using an experimental-computational approach. Both atomically flat and mounded surfaces, generated via a surface instability induced by the Ehrlich-Schwoebel barrier, are employed as templates for the subsequent deposition...

We have developed a mesoscale model to calculate the degradation of the effective thermal conductivity in irradiated U-Mo alloys caused by the fission-induced gas bubbles and recrystallization. The phase-field approach is employed to generate the grain microstructures of U-7Mo fuels with intra- and inter-granular gas bubbles. Based on the phase-fie...

The Center for Predictive Integrated Structural Materials Science (PRISMS Center) is creating a unique framework for accelerated predictive materials science and rapid insertion of the latest scientific knowledge into next-generation ICME tools. There are three key elements of this framework. The first is a suite of high-performance, open-source in...

Grand-potential-based phase-field model for multiple phases, grains, and chemical components is derived from a grand-potential functional. Due to the grand-potential formulation, the chemical energy does not contribute to the interfacial energy between phases, simplifying parametrization and decoupling interface thickness from interfacial energy, w...

The phase field (PF) method provides a valuable means of predicting radiation induced microstructure evolution of domains ranging roughly from 100 nm to 100 microns in size and for lengths of time ranging from microseconds to years, depending on the rate of diffusion. In this work we summarize how to apply the PF method to modeling radiation damage...

Dislocation dynamics simulations were used to predict the strengthening of a commercial magnesium alloy, AZ91, due to β-Mg17Al12 formed in the continuous precipitation mode. The precipitate distributions used in simulations were determined based on experimental characterization of the sizes, shapes, and number densities of the precipitates for 10-h...

Phase-field modeling is a microstructure-level simulation technique often used in the Integrated Computational Materials Engineering (ICME) approach to materials design. To perform quantitatively accurate phase-field simulations for this application, potential sources of error in model parameters such as interfacial energy must be fully understood....

We report on a combined computational and experimental examination of coherent precipitation in a MgNd alloy, a prototypical Mg-rare earth alloy. Three-dimensional phase field simulations are conducted to predict the composition and morphology of precipitates, a unique family of hierarchically ordered phases that are metastable in a wide Nd concent...

We present a novel phase-field model development capability in the open source MOOSE finite element framework. This facility is based on the 'modular free energy' approach in which the phase-field equations are implemented in a general form that is logically separated from model-specific data such as the thermodynamic free energy density and mobili...

We present a novel phase-field model development capability in the open source MOOSE finite element framework. This facility is based on the 'modular free energy' approach in which the phase-field equations are implemented in a general form that is logically separated from model-specific data such as the thermodynamic free energy density and mobili...

High-operating-temperature direct ink writing (HOT-DIW) of mesoscale architectures that are composed of eutectic silver chloride-potassium chloride. The molten ink undergoes directional solidification upon printing on a cold substrate. The lamellar spacing of the printed features can be varied between approximately 100 nm and 2 µm, enabling the man...

div class="title">Understanding of Inverse Coarsening of γ' precipitates in Ni-base Superalloys - Volume 22 Issue S3 - Subhashish Meher, Larry K. Aagesen, Laura J. Carroll, Mark C. Carroll, Tresa M. Pollock

3D mesostructured AgCl-KCl photonic crystals emerge from colloidal templating of eutectic solidification. Solvent removal of the KCl phase results in a mesostructured AgCl inverse opal. The 3D-template-induced confinement leads to the emergence of a complex microstructure. The 3D mesostructured eutectic photonic crystals have a large stop band rang...

Three-dimensional phase-field simulations of GaN growth by selective area epitaxy were performed. The model includes a crystallographic-orientation-dependent deposition rate and arbitrarily complex mask geometries. The orientation-dependent deposition rate can be determined from experimental measurements of the relative growth rates of low-index cr...

GaN/InGaN nanostructures have numerous potential electronic and opto-electronic applications, such as energy-selective contacts for hot carrier solar cells and light-emitting diodes. A joint experimental and computational approach has been developed to understand the properties of GaN/InGaN nanostructures grown by selective area epitaxy (see the ar...

Porosity in linear autogenous laser welds of 304L stainless steel has been investigated using micro computed tomography to reveal defect content in fifty-four welds made with varying delivered power, travel speed and focal lens. Trends associated with porosity size and frequencies are shown and interfacial measures are employed to provide quantitat...

We investigated the origin of broad luminescence observed from an array of site-controlled InGaN nanodots grown by selective area epitaxy (SAE). Epitaxially grown site-controlled nanodots with lateral dimensions <50nm and an array density of 10(10)cm(-2) have been studied. During the nanoscale SAE, incorporation of adatoms from the SiO2 mask has gr...

Porosity resulting from linear autogenous laser-welds of 304L stainless steel are non-destructively examined and digitally reproduced by means of micro-computed tomography. These digitized microstructures are then imported into a finite element framework in which the pores are surrounded by an idealized, homogenized geometry, and exposed to a plast...

Quantum dot (QD) superlattices have been proposed for improving solar cell efficiency by providing intermediate energy bands to allow sub-bandgap photon absorption. Although photocurrent enhancement from QD solar cells has been demonstrated, QD cells exhibit lower open-circuit voltages and efficiencies than the GaAs reference cells, presumably due...

Arrays of semiconductor quantum dots grown by selective area epitaxy, a process in which the size and position of the dots is determined by a lithographically patterned mask, can have a high degree of uniformity in both size and position. However, non-uniformity in the initial stages of growth causes broadening of the energy states of GaN/InGaN het...

Standing-edge joints made by a continuous-wave Nd:YAG laser are examined in 304L stainless steel to advance understanding of the linkage between processing and microstructure in high-rate solidification events. Microcomputed tomography combined with traditional metallography has provided qualitative and quantitative characterization of welds in thi...

A variety of edge joints utilizing a continuous wave Nd:YAG laser have been produced and examined in a 304-L stainless steel to advance fundamental understanding of the linkage between processing and resultant microstructure in high-rate solidification events. Acquisition of three-dimensional reconstructions via micro-computed tomography combined w...

Fluid flow within the dendritic structure at the solid–liquid interface in nickel-based superalloys has been studied in two directionally solidified alloy systems. Millimeter-scale, three-dimensional (3D) datasets of dendritic structure have been collected by serial sectioning, and the reconstructed mushy zones have been used as domains for fluid-f...

The morphology of a rod embedded in a matrix undergoing pinching by interfacial-energy-driven bulk diffusion is determined near the point of pinching. We find a self-similar solution that gives a unique temporal power law and interfacial shape prior to pinching and self-similar solutions after pinching. The theory is compared to experiments that em...

The evolution of the solid–liquid interface in an Al–Cu dendritic microstructure is predicted using a phase-field model and compared to experimental data. The interfacial velocities are measured during isothermal coarsening using in situ X-ray tomographic microscopy. Good qualitative agreement is found between experimental and simulated velocities....

As rodlike domains pinch off owing to Rayleigh instabilities, a finite-time singularity occurs as the interfacial curvature at the point of pinch-off becomes infinite. The dynamics controlling the interface become independent of initial conditions and, in some cases, the interface attains a universal shape. Such behaviour occurs in the pinching of...

Convection during directional solidification can cause defects such as freckles and misoriented grains. To gain a better understanding of conditions associated with the onset of convective instabilities, flow was investigated using three-dimensional (3D) computational fluid dynamics simulations in an experimentally obtained dendritic network. A ser...

Phase-field models are used to simulate dendritic microstructures during solidification and coarsening of metallic alloys. Equiaxed dendrites in a Cu-Ni alloy are simulated during rapid solidification and coarsening. The morphology of the solid-liquid interface is characterized using Interface Shape Distributions. The interface's topology is quanti...

Transformation of broadband emission of oxygen defects in the carcass of ZnO-inverted opal into a multiple-mode amplified spontaneous emission band has been observed in the spectral interval of a photonic bandgap upon increasing excitation intensity. The mode structure has been assigned to amplification of emission coupled to resonance modes of the...

Colloidal photonic crystals were grown using a vertical deposition method. The effect of colloidal concentration and deposition rate on crystalline quality and domain size was studied by means of response surface design. The crystalline quality was assessed using the optical reflectance. The results show that a strong negative correlation exists be...

Photoluminescence spectra of the ZnO carcass of inverted opal have been examined in the conditions of the strong lightto-structure interaction achieved by matching the photonic bandgaps of these photonic crystals to different parts of the ZnO emission spectrum. Developing the bands of enhanced spontaneous emission associated with both the emission...

A change of up to 40% of the relative transmission at the photonic bandgap edge has been observed in photoconductive inverted ZnO opals under ultraviolet laser irradiation. This effect has been related to the irradiation-stimulated change of the refraction index of the photonic crystal. The desorption (chemosorption) of oxygen molecules on the surf...

Three-dimensional photonic crystals (PhCs) provide materials for the production of highly efficient light sources. In this respect, the channelling and suppression of the spontaneous emission (SE) due to the anisotropic nature of the photonic band gap (PBG), and band-edge stimulated emission, have been demonstrated. Various attempts have been repor...

X‐ray absorption spectroscopy technique is used to study copper‐doped ZnO thin films, prepared by pulsed‐laser deposition. The samples with various doping levels are examined. It is found that the samples contain metallic clusters with the sizes ⩽ 2 nm as well as Cu ¹⁺ and Cu ²⁺ states. The Cu ¹⁺ states exist as stable oxide clusters, while the Cu...