Processing and Characterization of Multiphase Ceramic Composites

Multiphase ceramic composites structure design has advantages for many applications. It is not only an effective way of limiting grain growth which allows for fine-grain size superplasticity at elevated temperatures, but also a combination of various desirable properties can be obtained from different phases, which otherwise cannot be found in one single phase material. The goal of this research is to select, design and optimize multiphase ceramic systems for mainly two purposes: shape forming and inert matrix nuclear fuel. These ceramic composites feature the machinability of monazite (LaPO 4) due to weak interfacial bonding with other oxides, the superplasticity of 3 mol% tetragonal zirconia (3Y-TZP), and the high hardness and strength of Al2O3 and MgAl2O4. These materials were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Mechanical behavior at room temperature was characterized for the elastic modulus, hardness and fracture toughness. They were fabricated and demonstrated to have deformation rates in the superplastic range of at high temperatures and easy machinability at room temperature using conventional tools. An issue with conventional nuclear fuel, UO2, is its very low thermal conductivity that causes high central temperatures, which can lead to melting and cracking during reactor operation. The solution can be found in multiphase ceramic composites, by combining nuclear fuel particles in a heat conducting phase with high thermal conductivity and other phases that absorb fission byproducts while maintaining good radiation stability. In the current research, proposed multiphase ceramic composite materials were designed and radiation damage was characterized by scanning and transmission electron microscopy (TEM). Gold irradiation was used to represent the primary knock-on atoms damage caused by neutrons. Xenon irradiation was used to represent the fission product damage. Magnetoplumbite, was the most susceptible to radiation damage.