Multiphysics Modeling for Predicting Microstructural Evolution of Powder Materials during Solid-state Sintering

Sudipta Biswas, Purdue University

Abstract

Sintering is a disruptive manufacturing technique which coalesces powder materials into solids by applying heat and pressure, leading to microstructural evolution with reduced surface area and improved density. Understanding the densification mechanism and grain growth kinetics during the powder compaction process is of immense importance in order to evaluate usability of the final material. The initial focus of this study is on capturing the microstructural changes as the powder particles compact into a polycrystalline structure. The phase field modeling approach has been adopted here to predict consolidation kinetics. A special emphasis is placed on modeling rigid body motion of particles during the mass transport process. Additional multiphysics aspects such as mechanical deformation, heat conduction, along with joule heating etc. have been considered in the model to extend its capability to capture different types of sintering. The current work uses finite element based MOOSE framework as the platform for model development. MOOSE’s vast finite element library, extensive solver and preexisting physics modules make multiphysics model development straightforward. A significant contribution in terms of enhancing and extending MOOSE’s capability to solve sintering problems has been made. As an outcome of the study, morphological changes in the material microstructure leading to consolidation and grain growth are observed and mechanisms behind the alterations are identified from the developed model. The model correctly predicts consolidation of powder particles during sintering because of two competing mechanisms - neck formation and grain growth. The simulations show that the material undergoes three distinctive stages during the sintering process – stage I where neck or grain boundary between two particles are formed; stage II in which neck length stabilizes and growth or shrinkage of individual particles initiates; and finally stage III with rapid grain growth leading to disappearance of one of the grains. At the initial stage, the densification is governed by the surface and grain boundary diffusion, while at the later stage bulk diffusion and grain boundary migration dominate. The driving forces corresponding to different mechanisms are found to be dependent on the radius of the particles, curvature at the neck location, surface energy, and grain boundary energy. In addition, variation in temperature is found to significantly influence the microstructure evolution by affecting the diffusivity and grain boundary mobility of the sintered material. It is observed that mechanical loading contributes to the deformation and shape change of the particles during the process. Furthermore, the inhomogeneity of the microstructure induces variations in microstructure of the final sintered product. Finally, the model is extended to evaluate material behavior during three dimensional powder compact and with multiple powder particles and the predictions from the model are qualitatively verified with experimental observations.

Degree

Ph.D.

Advisors

Okuniewski, Purdue University.

Subject Area

Materials science

COinS