(Dr. Jack Lackey, advisor)
"Equipment and Process Development for Fabrication of Rhenium-Based Composites by CVI"
Most materials do not satisfy designers' requirements for advanced heat engines. While many metals are strong and tough at room temperature, their performance degrades at high temperatures. On the other hand, high temperature resistant ceramics do not have the mechanical toughness to stand up to the loads experienced in many modern machines. This problem can prevent the construction of an extremely high temperature heat engine or heat exchanger.
A material and a process were selected for that could withstand temperatures of 1200 C at moderate stress levels. This material should also have a high emissivity, low oxidation rate and be tough enough for use in an engine. The material is a laminated matrix composite composed of Nicalon Fibers. The matrix is load-bearing (as opposed to epoxies which do not carry a significant load). The matrix composition selected was alternating layers of rhenium and silicon carbide. Chemical Vapor Infiltration, or CVI was explored experimentally as a means for fabricating such a composite material. Theoretically, the successive matrix layers can delaminate from each other as a crack propagates and toughen the material considerably.
Several samples were made
and examined using a Scanning Electron Microscope (SEM) and Energy Dispersive
Spectroscopy (EDS). Rhenium was successfully deposited within carbon
and silicon carbide fiber preforms via CVI using ReCl5 as the reagent.