Controlling particle orientation during forming.

摘要

Particle orientation is a microstructural feature that can significantly impact the properties of a fired ceramic. For example, Patwardhan and Cannon showed that particle orientation occurring during tape casting affects dimensional control due to the influence that particle shape has on sintering kinetics. The particle orientation was caused by the complex shear state that occurs during tape casting. This dissertation examined the relationship between shear state and the resulting particle orientation and its influence on selected properties of the body.;The first step towards this was the determination of the shear state during tape casting. Based on measured geometries and rheologies, computational fluid dynamics (CFD) simulations were performed which predicted shear rates throughout the geometry. The simulations predicted that for slurries exhibiting power-law shear thinning behavior, shear rate is higher near the doctor blade and the slurry is not only sheared between the doctor blade and substrate but also into the slurry reservoir and behind the doctor blade.;Tape casting was performed on the compositions that were characterized for the determination of shear state. Casting parameters such as doctor blade gap and casting velocity were varied to alter the shear profile in the system. These samples were then analyzed to determine the particle orientation and texture in various regions throughout the tapes.;An optical texture measurement technique based on the birefringence of green bodies was developed to address the need for highly sensitive measurements capable of detecting small variations in green texture. Results given by this technique were found to be consistent with measurements performed by XRD. Experimental samples were analyzed and localized texture measurements were found to follow shear profiles predicted by the CFD simulations.;Elastic moduli of fired samples exhibiting a range of textures were measured to reveal effects of particle orientation on fired properties. The texture of the bodies was found to distinctly affect the elastic moduli of the bodies.;These findings demonstrate that varying tape casting parameters can be used to control texture induced into a tape cast body. This ability could be applied as a strategy to tailor properties to optimize bodies for specific applications.