arXiv subjects

Mark R. Daymond

Publications and source records attributed to Mark R. Daymond.

5 recordsLinked to original sources

arXiv2026

Anomalous bulk dealloying below the parting limit

Dealloying has been extensively studied both as a corrosion degradation mechanism in structural materials, including those used in nuclear, aerospace, or marine environments, and as a versatile method to fabricate porous materials for catalysts and other functional applications. Classical dealloying theory in aqueous environments predicts a critical reactive-element concentration (parting limit) for continuous selective dissolution at temperatures where bulk diffusion does not dominate; this threshold is commonly reported around 50~60 at.%. Yet recent studies show that molten salt environments can generate extensive bulk dealloying below this threshold. Despite the importance of this anomalous dealloying behavior in many energy systems and electrochemical applications, its fundamental origin remains elusive. Here, we address this critical gap, revealing a grain boundary (GB)-assisted bulk dealloying mechanism. Using three-dimensional (3D) reconstruction of the dealloyed regions correlated with crystallographic and elemental analyses, we directly map the 3D GB-void architecture and reveal that diffusion-induced recrystallization (DIR) generates a high-density GB network, which then promotes molten-salt infiltration and can drive bulk dealloying far-below the conventionally reported parting limit, producing a distinctive morphology reminiscent of discontinuous precipitation (DP). Understanding this dynamic GB-void interplay is crucial for the prediction and control of dealloying in complex electrochemical environments.

cond-mat.mtrl-sci↗

arXiv2021

Interstitialcy-based reordering kinetics of Ni$_3$Al precipitates in irradiated Ni-based super alloys

Neutron irradiation tends to promote disorder in ordered alloys through the action of the thermal spikes that it generates, while simultaneously introducing point defects and defect clusters. As they migrate, these point defects will promote reordering of the alloys, acting against irradiation-induced disordering. In this study, classical molecular dynamics and a highly parallel accelerated sampling method are used to study the reordering kinetics of Ni$_3$Al under the diffusion of self-interstitial atoms (SIA). By monitoring the order parameter and potential energy from atomistic simulations, we show that the SIA acts as a reordering agent in Ni$_3$Al. A mean-field rate theory model of the interstitialcy-based reordering kinetics is introduced, which reproduces simulation data and predicts reordering at temperatures as low as 500 K.

cond-mat.mtrl-sci↗

arXiv2021

Deep Learning and Crystal Plasticity: A Preconditioning Approach for Accurate Orientation Evolution Prediction

Efficient and precise prediction of plasticity by data-driven models relies on appropriate data preparation and a well-designed model. Here we introduce an unsupervised machine learning-based data preparation method to maximize the trainability of crystal orientation evolution data during deformation. For Taylor model crystal plasticity data, the preconditioning procedure improves the test score of an artificial neural network from 0.831 to 0.999, while decreasing the training iterations by an order of magnitude. The efficacy of the approach was further improved with a recurrent neural network. Electron backscattered (EBSD) lab measurements of crystal rotation during rolling were compared with the results of the surrogate model, and despite error introduced by Taylor model simplifying assumptions, very reasonable agreement between the surrogate model and experiment was observed. Our method is foundational for further data-driven studies, enabling the efficient and precise prediction of texture evolution from experimental and simulated crystal plasticity results.

cond-mat.mtrl-sci↗

arXiv2020

Effect of He on the Order-Disorder Transition in Ni3Al under Irradiation

The order-disorder transition in Ni-Al alloys under irradiation represents an interplay between various re-ordering processes and disordering due to thermal spikes generated by incident high energy particles. Typically, ordering in enabled by diffusion of thermally-generated vacancies, and can only take place at temperatures where they are mobile and in sufficiently high concentration. Here, in-situ transmission electron micrographs reveal that the presence of He, usually considered to be a deleterious immiscible atom in this material, promotes reordering in Ni3Al at temperatures where vacancies are not effective ordering agents. A rate-theory model is presented, that quantitatively explains this behavior, based on parameters extracted from atomistic simulations. These calculations show that the V2He complex is an effective agent through its high stability and mobility. It is surmised that immiscible atoms may stabilize reordering agents in other materials undergoing driven processes, and preserve ordered phases at temperature where the driven processes would otherwise lead to disorder.

cond-mat.mtrl-sci↗

arXiv2019

Primary damage production in the presence of extended defects and growth of vacancy-type dislocation loops in hcp zirconium

Production rates in long-term predictive radiation damage accumulation models are generally considered independent of the material's microstructure for reactor components. In this study, the effect of pre-existing microstructural elements on primary damage production in alpha-Zr -- and vice-versa -- is assessed by molecular dynamics (MD) simulations. a-type dislocation loops, c-component dislocation loops and a tilt grain boundary (GB) were considered. Primary damage production is reduced in the presence of all these microstructural elements, and clustering behavior is dependent on the microstructure. Collision cascades do not cause a-type loop growth or shrinkage, but they cause c-component loop shrinkage. Cascades in the presence of the GBs produce more vacancies than interstitials. This result, as well as other theoretical, MD and experimental evidence, confirm that vacancy loops will grow in the vacancy supersaturated environment near GBs. Distinct temperature-dependent growth regimes are identified. Also, MD reveals cascade-induced events where a-type vacancy loops are absorbed by GBs. Fe segregation at the loops inhibits this cascade-induced absorption.

cond-mat.mtrl-sci↗