Modeling Microstructural Evolution During Sintering In A Complexpowder Compact
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Modeling Microstructural Evolution During Sintering In A Complex Powder Compact Veena Tikare and Michael V. Braginsky, Sandia National Laboratory, Albuquerque, NM 87185-1411 ABSTRACT Sintering theory has been developed either as the application of complex diffusion mechanisms to a simple geometry or as the deformation and shrinkage of a continuum body. We present a model that can treat in detail both the evolution of microstructure and the sintering mechanisms, on the mesoscale, so that constitutive equations with detailed microstructural information can be generated. The model is capable of simulating vacancy diffusion by grain boundary diffusion, annihilation of vacancies at grain boundaries resulting in densification, and coarsening of the microstructural features. In this paper, we review the capabilities of this model and present a number of different problems that have been treated by the model. Finally, we discuss the limitations of this model. INTRODUCTION The theory of sintering has been developed primarily by considering sintering of simple geometry with varied and complex transport mechanisms. Most of the work treats the microstructural evolution of two or three particles during sintering in great detail. Some of the earliest and most rigorous analytical models of sintering were proposed in the 1950’s of two particles with different diffusion mechanisms [1]. This body of work considers driving forces, transport mechanisms, kinetic factors and geometry to give detailed information about the shapes of the particles and sintering rates during various stages of sintering. Almost 50 years later, current microstructural models of sintering [2] still consider a limited number of particles. One notable exception is the stereological model of sintering [3], which treats sintering as the evolution of a stereological construct. However, numerical implementations of this have not been possible. While today’s models give more accurate results, they fail, like their predecessors, to treat a macroscopic sintering piece – what is the shape change of, density distribution in, and stress state in a large body? We propose a model that can simulate the microstructural evolution during sintering of a powder compact comprised of hundreds of particles. Such a model can be used to bridge the gap between mesoscale and continuum models by generating constitutive equations describing the deformation and shrinkage of a sintering compact as a function of its microstructure, i.e. grain size distribution, pore size distribution, etc. The kinetic Monte Carlo model has been demonstrated to simulate a variety of microstructure evolution phenomena. We have adapted this model to simulate simple sintering of a powder compact. The different microstructural evolution processes that this model can simulate simultaneously are curvature driven grain growth, coarsening of pores by surface diffusion, vacancy formation at the pore surfaces, diffusion of these vacancy by grain boundary diffusion and finally annihilation of the vacancies at grain boun
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