Studies of Ultra High Temperature Ceramic Composite Components: Synthesis and Characterization of HfOxCy and Si Oxidation in Atomic Oxygen Containing Environments

Ultrahigh temperature ceramics (UHTC) are a class of materials being considered for reusable atmospheric re-entry vehicles, hypersonic flight vehicles and rocket propulsion [1, 2]. In these applications, the materials are subjected to high temperatures and extremely reactive and high flow environments (e.g. O, O2). Therefore, potential material candidates have to be mechanically, chemically and thermally stable. Currently no one material exists that have all the properties required for these applications therefore composites have to be developed. However, materials choices are limited [3]. While some candidates have proven to be more suitable than others, the underlying mechanisms by which they withstand the environment and offer protection are still not understood [4]. For other materials, the processing method and the resulting properties of the starting materials can be a major contributor to preventing or promoting some of the microscopic processes [1]. One part of the inability to find suitable materials can be attributed to the fact that most of the work has been application driven. Recent reports on the progress of research in this field indicate that only if fundamental knowledge of the behavior each material in different regimes is obtained in a systematic process, can a solution be developed. The first part of this work primarily focuses on the Hf-C system within the UHTC class of materials. It addresses the processing challenges in the synthesis of Hf-C based films such as oxygen dissolution, particulate and void formation, non-stoichiometric and non-uniform film formation. In Chapter II we explore the diffusion and reaction characteristics of these two elements through thermal treatment in an inert environment. In Chapter III, the formation of hafnium carbide (HfC) by pulsed laser deposition and the inherent technique parameters that need to be considered are addressed. The efficacy of thus deposited HfC as a protective coating is then explored. The original document contains color images.