arXiv subjects

Chad W. Sinclair

Publications and source records attributed to Chad W. Sinclair.

10 recordsLinked to original sources

arXiv2025

The influence of solute induced memory on interface migration

Interface migration governs microstructural evolution during phase transformations and grain growth thereby dictating those material properties that depend on microstructure. Recent work continues to highlight the rich range of behaviors exhibited by migrating interfaces and the complex connection between these behaviors and the underlying atomistic processes that determine coarse-grained interfacial mobility. For interfaces moving at low homologous temperatures and small driving forces, we show that significant non-Markovian effects can arise that invalidate commonly used analysis methods. Specifically, we demonstrate that solute can act as a source of such non-Markovian motion. In turn, we introduce a time-local (TCL) propagator approach to account for memory-dominated short and intermediate time interface dynamics. This approach extrapolates to the long time diffusive limit, enabling robust mobility estimates from simulation windows far shorter than those required to observe linear scaling directly. Comparison with solute-free boundaries validates the method and quantifies solute drag in the Cahn-Hillert sense, providing a route to extract drag coefficients and effective mobilities across a range of solute concentrations. Our results demonstrate that analysis including memory is essential for connecting atomistic simulations to continuum models and offer a practical framework for studying interface kinetics in systems with slow internal processes.

cond-mat.mtrl-sci↗

arXiv2022

Predicting the effect of strain path on the strain aging behaviour of Ultra-low carbon steel

A recently presented model is adapted to predict the effects of strain path change on the strain aging (bake hardening) behaviour of an ultra low carbon (ULC) steel. Samples pre-deformed by rolling were aged and then tested in uniaxial tension at 0, 45 and 90$^\circ$ degrees to the prior rolling direction. The results show that aging changes not only the yield strength of the material but also the work hardening rate. The increase in yield strength is interpreted to be dominated by a reduction in mobile dislocation density, this reflecting the classic ideas of Hahn and others. The change in work hardening behaviour is treated as arising from the different role played by solute `loaded' dislocations compared to dislocations generated by straining after aging.

cond-mat.mtrl-sci↗

arXiv2022

Exploring glassy dynamics with Markov state models from graph dynamical neural networks

Amorphous materials exhibit structural heterogeneities that relax only on long timescales. Using machine learning techniques, we construct a Markov state model (MSM) for model glass formers that coarse-grains the dynamics into a low-dimensional space, in which transitions occur with rates corresponding to the slowest modes of the system. The transition timescale between states is more than an order of magnitude larger than the conventional alpha-relaxation time, and reveals a fragile to strong crossover at the glass transition. The learned map of states assigned to the particles exhibits correlations of a few molecular diameters both at liquid and glassy temperatures. We show that the MSM effectively constructs a map of scaled excess Voronoi volume, and the free energy difference between the two states is given exactly by the entropy of the these distributions. These results resonate with classic free volume theories of the glass transition, singling out local packing fluctuations as the slowest relaxing features.

cond-mat.soft↗

arXiv2020

Carbon Diffusion in Concentrated Fe-C Glasses

By combining atomistic simulations with a detailed analysis of individual atomic hops, we show that the diffusion of carbon in a binary Fe-C glass exhibits strong (anti-)correlations and is largely determined by the local environment. Higher local carbon concentrations lead to slower atomic mobility. Our results help explain the increasing stability of Fe-C (and other similar metal-metalloid glasses) against crystallization with increasing carbon concentration.

cond-mat.mtrl-sci↗

arXiv2019

Controlling solid-liquid interfacial energy anisotropy through the isotropic liquid

Although the anisotropy of the solid-liquid interfacial free energy for most alloy systems is very small, it plays a crucial role in the growth rate, morphology and crystallographic growth direction of dendrites. Previous work posited a dendrite orientation transition via compositional additions. In this work we examine experimentally the change in dendrite growth behaviour in the Al-Sm (Samarium) system as a function of solute concentration and study its interfacial properties using molecular dynamics simulations. We observe a dendrite growth direction which changes from <100> to <110> as Sm content increases. The observed change in dendrite orientation is consistent with the simulation results for the variation of the interfacial free energy anisotropy and thus provides definitive confirmation of conjecture in previous works. In addition, our results provide physical insight into the atomic structural origin of the concentration dependent anisotropy, and deepens our fundamental understanding of solid-liquid interfaces in binary alloys.

cond-mat.mtrl-sci↗

arXiv2018

Atomistic Insights Into Cluster Strengthening in Aluminum Alloys

In certain naturally aged aluminum alloys, significant strengthening can be obtained due to the decomposition of a super-saturated solid solution into clusters. The origins of such strengthening remain unclear due to the challenge of differentiating solute cluster strengthening from solid solution or precipitate strengthening. To shed light on the origin of cluster strengthening in aluminum alloys, the interaction between the smallest possible type of clusters (i.e. dimers) and moving dislocations in a model Al-Mg alloy is studied using atomistic simulations. Additionally, theoretical models for both the parelastic and dielastic interactions between clusters and dislocations is used to identify which factor among order strengthening, elastic interaction, and change of stacking fault energy controls cluster strengthening. The comparison of the results from these models to that of the atomistic simulations show that in the case of Mg dimers, the strength of the strongest ones are dominated by the dielastic contribution through the change of stacking fault energy.

physics.comp-ph↗

arXiv2015

An Atomistic Study of Diffusion-Mediated Plasticity and Creep using Phase Field Crystal Methods

The nonequilibrium dynamics of diffusion-mediated plasticity and creep in materials subjected to constant load at high homologous temperatures is studied atomistically using Phase Field Crystal (PFC) methods. Creep stress and grain size exponents obtained for nanopolycrystalline systems, $m \simeq 1.02$ and $p \simeq 1.98$, respectively, closely match those expected for idealized diffusional Nabarro-Herring creep. These exponents are observed in the presence of significant stress-assisted diffusive grain boundary migration, indicating that Nabarro-Herring creep and stress-assisted boundary migration contribute in the same manner to the macroscopic constitutive relation. When plastic response is dislocation-mediated, power law stress exponents inferred from dislocation climb rates are found to increase monotonically from $m \simeq 3$, as expected for generic climb-mediated natural creep, to $m \simeq 5.8$ as the dislocation density $ρ_d$ is increased beyond typical experimental values. Stress exponents $m \gtrsim 3$ directly measured from simulations that include dislocation nucleation, climb, glide, and annihilation are attributed primarily to these large $ρ_d$ effects. Extrapolation to lower $ρ_d$ suggests that $m \simeq 4-4.5$ should be obtained from our PFC description at typical experimental $ρ_d$ values, which is consistent with expectations for power law creep via mixed climb and glide. The anomalously large stress exponents observed in our atomistic simulations at large $ρ_d$ may nonetheless be relevant to systems in which comparable densities are obtained locally within heterogeneous defect domains such as dislocation cell walls or tangles.

cond-mat.mtrl-sci↗

arXiv2014

Phase Field Crystal Modeling as a Unified Atomistic Approach to Defect Dynamics

Material properties controlled by evolving defect structures, such as mechanical response, often involve processes spanning many length and time scales which cannot be modeled using a single approach. We present a variety of new results that demonstrate the ability of phase field crystal (PFC) models to describe complex defect evolution phenomena on atomistic length scales and over long, diffusive time scales. Primary emphasis is given to the unification of conservative and non- conservative dislocation creation mechanisms in three-dimensional FCC and BCC materials. These include Frank-Read-type glide mechanisms involving closed dislocation loops or grain boundaries as well as Bardeen-Herring-type climb mechanisms involving precipitates, inclusions, and/or voids. Both source classes are naturally and simultaneously captured at the atomistic level by PFC de- scriptions, with arbitrarily complex defect configurations, types, and environments. An unexpected dipole-to-quadrupole source transformation is identified, as well as various new and complex geomet- rical features of loop nucleation via climb from spherical particles. Results for the strain required to nucleate a dislocation loop from such a particle are in agreement with analytic continuum theories. Other basic features of FCC and BCC dislocation structure and dynamics are also outlined, and initial results for dislocation-stacking fault tetrahedron interactions are presented. These findings together highlight various capabilities of the PFC approach as a coarse-grained atomistic tool for the study of three-dimensional crystal plasticity.

cond-mat.mtrl-sci↗

arXiv2013

A three-dimensional atomistic kinetic Monte Carlo study of dynamic solute-interface interaction

A three-dimensional atomistic Kinetic Monte Carlo model was developed and used to study the interaction between mobile solutes and a migrating interface. While the model was developed with a simplified energetic and topological description, it was also constructed to capture, in the absence of solute, the Burke-Turnbull model for interface migration and, in the presence of solutes, solute segregation to different types of interface sites. After parameterizing the model, simulations were performed to study the relationship between average interface velocity and imposed driving pressure for varying solute concentration and solute diffusivity. While the effect of solute concentration on solute drag pressure was found to be consistent with classical solute drag models, the effect of solute diffusivity was found to give a response not captured by either continuum or previously reported two-dimensional atomistic models. The dependence of maximum drag pressure on solute diffusivity was observed and attributed to the coupling between the structure of a migrating interface and the ability for solute to remain segregated to the interface.

cond-mat.mtrl-sci↗

arXiv2012

Defect stability in phase-field crystal models: Stacking faults and partial dislocations

The primary factors controlling defect stability in phase-field crystal (PFC) models are examined, with illustrative examples involving several existing variations of the model. Guidelines are presented for constructing models with stable defect structures that maintain high numerical efficiency. The general framework combines both long-range elastic fields and basic features of atomic-level core structures, with defect dynamics operable over diffusive time scales. Fundamental elements of the resulting defect physics are characterized for the case of fcc crystals. Stacking faults and split Shockley partial dislocations are stabilized for the first time within the PFC formalism, and various properties of associated defect structures are characterized. These include the dissociation width of perfect edge and screw dislocations, the effect of applied stresses on dissociation, Peierls strains for glide, and dynamic contraction of gliding pairs of partials. Our results in general are shown to compare favorably with continuum elastic theories and experimental findings.

cond-mat.mtrl-sci↗