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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
OSTIDOI

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

Nanocrystal-enabled solid state bonding

Holm, Elizabeth A.; Puskar, J.D.; Reece, Mark R.; Tikare, Veena T.

In this project, we performed a preliminary set of sintering experiments to examine nanocrystal-enabled diffusion bonding (NEDB) in Ag-on-Ag and Cu-on-Cu using Ag nanoparticles. The experimental test matrix included the effects of material system, temperature, pressure, and particle size. The nanoparticle compacts were bonded between plates using a customized hot press, tested in shear, and examined post mortem using microscopy techniques. NEDB was found to be a feasible mechanism for low-temperature, low-pressure, solid-state bonding of like materials, creating bonded interfaces that were able to support substantial loads. The maximum supported shear strength varied substantially within sample cohorts due to variation in bonded area; however, systematic variation with fabrication conditions was also observed. Mesoscale sintering simulations were performed in order to understand whether sintering models can aid in understanding the NEDB process. A pressure-assisted sintering model was incorporated into the SPPARKS kinetic Monte Carlo sintering code. Results reproduce most of the qualitative behavior observed in experiments, indicating that simulation can augment experiments during the development of the NEDB process. Because NEDB offers a promising route to low-temperature, low-pressure, solid-state bonding, we recommend further research and development with a goal of devising new NEDB bonding processes to support Sandia's customers.

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TYPE SAND Report YEAR 2010
OSTIDOI

Multi-physics microstructural simulation of sintering

Tikare, Veena T.

Simulating the detailed evolution of microstructure at the mesoscale is increasingly being addressed by a number of methods. Discrete element modeling and Potts kinetic Monte Carlo have achieved success in capturing different aspects of sintering well. Discrete element cannot treat the details of neck formation and other shape evolution, especially when considering particles of arbitrary shapes. Potts kMC treats the micorstructural evolution very well, but cannot incorporate complex stress states that form especially during differential sintering. A model that is capable of simulating microstructural evolution during sintering at the mesoscale and can incorporate differential stresses is being developed. This multi-physics model that can treat both interfacial energies and the inter-particle stresses will be introduced. It will be applied to simulate microstructural evolution while resolving individual particles and the stresses that develop between them due to local shrinkage. Results will be presented and the future development of this model will be discussed.

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TYPE Conference YEAR 2010
OSTI

Crossing the mesoscale no-mans land via parallel kinetic Monte Carlo

Plimpton, Steven J.; Battaile, Corbett C.; Chandross, M.; Holm, Elizabeth A.; Thompson, Aidan P.; Tikare, Veena T.; Webb, Edmund B.; Zhou, Xiaowang Z.

The kinetic Monte Carlo method and its variants are powerful tools for modeling materials at the mesoscale, meaning at length and time scales in between the atomic and continuum. We have completed a 3 year LDRD project with the goal of developing a parallel kinetic Monte Carlo capability and applying it to materials modeling problems of interest to Sandia. In this report we give an overview of the methods and algorithms developed, and describe our new open-source code called SPPARKS, for Stochastic Parallel PARticle Kinetic Simulator. We also highlight the development of several Monte Carlo models in SPPARKS for specific materials modeling applications, including grain growth, bubble formation, diffusion in nanoporous materials, defect formation in erbium hydrides, and surface growth and evolution.

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TYPE SAND Report YEAR 2009
OSTIDOI
Results 51–100 of 116
Results 51–100 of 116