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Hybrid models for the simulation of microstructural evolution influenced by coupled, multiple physical processes

Tikare, Veena T.; Hernandez, Efrain H.; Madison, Jonathan D.; Winchester, Benjamin M.

Most materials microstructural evolution processes progress with multiple processes occurring simultaneously. In this work, we have concentrated on the processes that are active in nuclear materials, in particular, nuclear fuels. These processes are coarsening, nucleation, differential diffusion, phase transformation, radiation-induced defect formation and swelling, often with temperature gradients present. All these couple and contribute to evolution that is unique to nuclear fuels and materials. Hybrid model that combines elements from the Potts Monte Carlo, phase-field models and others have been developed to address these multiple physical processes. These models are described and applied to several processes in this report. An important feature of the models developed are that they are coded as applications within SPPARKS, a Sandiadeveloped framework for simulation at the mesoscale of microstructural evolution processes by kinetic Monte Carlo methods. This makes these codes readily accessible and adaptable for future applications.

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TYPE SAND Report YEAR 2013
DOIOSTI

A model for simulation of coupled microstructural and compositional evolution

Ceramic Engineering and Science Proceedings

Tikare, Veena T.; Homer, Eric H.; Holm, Elizabeth A.

The formation, transport and segregation of components in nuclear fuels fundamentally control their behavior, performance, longevity and safety. Most nuclear fuels enter service with a uniform composition consisting of a single phase with two or three components. Fission products form introducing more components. The segregation and transport of the components is complicated by the underlying microstructure consisting of grains, pores, bubbles and more, which is evolving during service. As they evolve, components and microstructural features interact such that composition affects microstructure and vice versa. The ability to predict compositional and microstructural evolution in 3D as a function of burn-up would greatly improve the ability to design safe, high burn-up nuclear fuels. We present a model that combines elements of Potts Monte Carlo, MC, and the phase-field model to treat coupled microstructural- compositional evolution. The evolution process demonstrated is grain growth and diffusion in a two-phase system. The hybrid model uses an equation of state, EOS, based on the microstructural state and composition. The microstructural portion uses the traditional MC EOS and the compositional portion uses the phase-field EOS: (Formula Presented) Ev is the bulk free energy of each site i and J is the neighbor interaction energy between neighboring sites i and j. The last term is the compositional interfacial energy as defined in the traditional phase-field model. The coupled microstructure-composition fields evolve by minimizing the free energy in a path dependent manner. An application of this modeling framework demonstrates the expected microstructural and phase coarsening, which is controlled by long-range diffusion.

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TYPE Conference YEAR 2013
OSTIScopus

On sintering stress in complex powder compacts

Journal of the American Ceramic Society

Cardona, Cristina G.; Tikare, Veena T.; Patterson, Burton R.; Olevsky, Eugene

Microstructural evolution during sintering can be simulated using the Potts kinetic Monte Carlo model. This model simulates detailed evolution of the powder particles, pore shapes, neck growth, and other microstructural features with sufficient resolution over a sufficiently large compact so that interfacial energies and curvatures of a statistically representative sample of surfaces in a complex compact can be obtained from the simulations. In this work, we present a technique based on measuring curvature of surfaces to obtain sintering stress of sintering powder compacts with arbitrarily complex geometries of powder size and powder shape distributions. The method is applied to three distinct powder compacts with very different sintering behavior to obtain sintering stress for each of these cases. The sintering stress for the three simulated cases were distinct and dependent on the geometric microstructural details of the powder compacts. © 2012 The American Ceramic Society.

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TYPE Journal Article YEAR 2012
ScopusOSTI
Results 51–75 of 120
Results 51–75 of 120