arXiv subjects

Peter Hatton

Publications and source records attributed to Peter Hatton.

6 recordsLinked to original sources

arXiv2026

Vacancy Diffusion Across FeCrAl Alloy Composition Space for Accident-Tolerant Fuel Cladding

Iron-chromium-aluminium (FeCrAl) alloys are leading candidates for accident-tolerant fuel cladding in light-water reactors, where their superior high-temperature oxidation resistance promises to extend coping times during loss-of-coolant accidents. The in-reactor lifetime of cladding is ultimately governed by radiation-induced microstructural evolution of which point defect transport is the dominant mechanism, however, this remains poorly understood. Here, we use a species-resolved kinetic Monte Carlo (KMC) model for vacancy diffusion in FeCrAl, parameterised by linear surrogate models trained on a database of migration barriers generated through the Hop-Decorate workflow. By sampling compositions spanning the Fe-rich to Cr-rich range of the Fe-Cr-Al system, we map how the local chemical environment controls vacancy hopping and hence macroscopic diffusivity. We find that increasing the Cr content in the alloy progressively decreases global diffusivity of vacancies even though activation energies stay relatively constant. This implies that the higher the Fe content in the alloy, the faster vacancies diffuse, thereby increasing annihilation events with fast-moving interstitials, potentially reducing irradiation induced defects and increasing radiation tolerance. Conversely, we find that Cr-rich alloy compositions stand out with a markedly elevated activation energy and significantly slower diffusion, orders of magnitude lower at accident-relevant temperatures. This indicates suppressed vacancy mobility in Cr-rich $\alpha'$ phases which are known to form under irradiation.

cond-mat.mtrl-sci↗

arXiv2026

Reduced-Order Modelling of Defect Transport using Surrogate Kinetics: Application to U$_x$Pu$_ {1-x}$N

Defect transport in chemically disordered materials is a difficult phenomenon to model since migration energetics depend strongly on the local chemical environment, producing a distribution of transition barriers that cannot be exhaustively enumerated. Here, we develop a reduced-order approach to modelling defect diffusion in compositionally complex materials using environment-dependent surrogate kinetics. Migration energetics for actinide vacancies, nitride vacancies, and actinide-nitride divacancies in U$_x$Pu$_{1-x}$N are generated using the Hop-Decorate workflow across thousands of chemical configurations. These data are distilled into compact surrogate functions that predict migration barriers and energy differences from simple descriptors based on local coordination counts. The surrogate models reproduce the atomistic dataset with low error and enable efficient evaluation of migration rates during lattice kinetic Monte Carlo simulations. Long-time diffusivities computed across temperature and composition reveal strongly non-linear behaviour arising from two dominant mechanisms: species-controlled migration on the actinide sublattice and environment-dependent trapping on the nitride sublattice. Although demonstrated for U$_x$Pu$_{1-x}$N the framework provides a general and computationally efficient approach for modelling defect transport in chemically disordered materials and for integrating atomistic kinetics into higher-scale simulations.

cond-mat.mtrl-sci↗

arXiv2025

Grain Boundary Anisotropy and Its Influence on Helium Bubble Nucleation, Growth, and Decohesion in Polycrystalline Iron

The accumulation of helium bubbles at grain boundaries (GBs) critically degrades the mechanical integrity of structural materials in nuclear reactors. While GBs act as sinks for radiation-induced defects, their inherent structural anisotropy leads to complex helium bubble evolution behaviors that remain poorly understood. This work integrates accelerated molecular dynamics simulations and a novel atomic-scale metric, the flexibility volume (V_f), to establish the interplay between GB character, helium segregation, and bubble growth mechanisms in body-centered cubic iron. We demonstrate that V_f, which incorporates both local atomic volume and vibrational properties, qualitatively predicts deformation propensity. Our results reveal that the atomic-scale segregation energy landscape dictates initial helium clustering and subsequent bubble morphology, with low-energy channels in tilt {\Sigma}5 boundary facilitating one-dimensional migration while isolated deep traps in twist {\Sigma}13 boundary promote larger, rounder bubble morphology. Critically, besides gradual bubble growth via trap mutation mechanism, we identify two distinct stress-relief mechanisms: loop punching in anisotropic tilt {\Sigma}5 boundary and interfacial decohesion in twist {\Sigma}11 boundary, with the dominant pathway determined by the interplay between bubble morphology and local mechanical softness. This study establishes a fundamental connection between GB crystallographic and energetical anisotropy and helium bubble evolution, providing critical insights for designing radiation-tolerant microstructures.

cond-mat.mtrl-sci↗

arXiv2025

Hop-Decorate: An Automated Atomistic Workflow for Generating Defect Transport Data in Chemically Complex Materials

Chemically complex materials (CCMs) exhibit extraordinary functional properties but pose significant challenges for atomistic modeling due to their vast configurational heterogeneity. We introduce Hop-Decorate (HopDec), a high-throughput, Python-based atomistic workflow that automates the generation of defect transport data in CCMs. HopDec integrates accelerated molecular dynamics with a novel redecoration algorithm to efficiently sample migration pathways across chemically diverse local environments. The method constructs a defect-state graph in which transitions are associated with distributions of kinetic and thermodynamic parameters, enabling direct input into kinetic Monte Carlo and other mesoscale models. We demonstrate HopDec's capabilities through applications to a Cu-Ni alloy and the spinel oxide (Fe,Ni)Cr2O4, revealing simple predictive relationships in the former and complex migration behaviors driven by cation disorder in the latter. These results highlight HopDec's ability to extract physically meaningful trends and support reduced-order or machine-learned models of defect kinetics, bridging atomic-scale simulations and mesoscale predictions in complex material systems.

cond-mat.mtrl-sci↗

arXiv2024

Changes in Dislocation Punching Behavior Due to Hydrogen-Seeded Helium Bubble Growth in Tungsten

The accumulation of gas atoms in tungsten is a topic of long-standing interest to the plasma-facing materials community due the metal's use as a divertor material in some tokamak fusion reactors. The nucleation and growth of He/H gas bubbles (along with their isotopes) can result from impinging fluxes of these gases which give rise to damage at the W divertor surface. The inclusion of He or H in W has been studied extensively by the community, finding that He bubbles modify the surface through periodic dislocation punching and bursting mechanisms while H bubbles impact the metal through plastic-strain induced material failure. However, the mechanisms which are present during the combined flux of both He and H is not well-studied atomistically. Motivated by this, an atomistic modeling study is conducted using molecular dynamics to assess the behavior of mixed concentration He:H bubbles in W. We find that the introduction of H into a growing He bubble results in a dramatic change in the nature and presence of dislocation loops which are typically generated via dislocation punching in over-pressurized He bubbles. Most notably, at high H concentrations, there is a switchover in energetic favorability from glissile 1/2$<$111$>$ dislocations to sessile $<$100$>$ dislocations. This thermodynamic crossover could imply a significant reduction in W surface morphology changes than with pure He bubbles and, additionally, we show this to have implications on the trapping of H in the bubbles and their associated dislocations.

cond-mat.mtrl-sci↗

arXiv2018

Proposal for a micromagnetic standard problem for materials with Dzyaloshinskii-Moriya interaction

Understanding the role of the Dzyaloshinskii-Moriya interaction (DMI) for the formation of helimagnetic order, as well as the emergence of skyrmions in magnetic systems that lack inversion symmetry, has found increasing interest due to the significant potential for novel spin based technologies. Candidate materials to host skyrmions include those belonging to the B20 group such as FeGe, known for stabilising Bloch-like skyrmions, interfacial systems such as cobalt multilayers or Pd/Fe bilayers on top of Ir(111), known for stabilising N\'eel-like skyrmions, and, recently, alloys with a crystallographic symmetry where anti-skyrmions are stabilised. Micromagnetic simulations have become a standard approach to aid the design and optimisation of spintronic and magnetic nanodevices and are also applied to the modelling of device applications which make use of skyrmions. Several public domain micromagnetic simulation packages such as OOMMF, MuMax3 and Fidimag already offer implementations of different DMI terms. It is therefore highly desirable to propose a so-called micromagnetic standard problem that would allow one to benchmark and test the different software packages in a similar way as is done for ferromagnetic materials without DMI. Here, we provide a sequence of well-defined and increasingly complex computational problems for magnetic materials with DMI. Our test problems include 1D, 2D and 3D domains, spin wave dynamics in the presence of DMI, and validation of the analytical and numerical solutions including uniform magnetisation, edge tilting, spin waves and skyrmion formation. This set of problems can be used by developers and users of new micromagnetic simulation codes for testing and validation and hence establishing scientific credibility.

cond-mat.other↗