The Optical and Mechanical Properties of Multiphase Ceramics.

摘要

Transparent crystalline ceramic applications range from commercial scratch resistant surfaces to impact resistant defense applications. However, large scale fabrication of transparent materials is limited to fabrication of flat geometries. Complex shapes such as domes must be machined from large bulk pieces that require expensive tooling and post processing before use. This research investigates routes for the fabrication of multiphase, shape formable (superplastic) ceramics that are transparent in the visible and infrared light spectrums. The presence of multiple phases typically leads to light scattering in ceramic composites. By selecting phases with similar indexes of refraction and reducing the grain size and porosity to well below the wavelength of visible light, light scattering sources can be reduced. This study evaluates reductions in scattering sources by (1) selection of materials, (2) processing fine starting materials, (3) varying the volumetric amounts of each phase, (4) minimizing grain growth by the presence of three phases and (5) achieving high densities by spark plasma sintering. The goal is to identify processing routes that will result in a fully transparent multiphase ceramics that can be superplastically formed at high temperatures but will demonstrate ultrahigh hardness and ultrahigh strength at room temperature.