Date of Award

3-26-2015

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Department of Aeronautics and Astronautics

First Advisor

Marina B. Ruggles-Wrenn, PhD.

Abstract

With a melting point in excess of 3000°C and a high density, ultra-high temperature ceramics (UHTCs) are a candidate material for hypersonic flight vehicles, atmospheric re-entry vehicles, and rocket propulsion systems. When ceramics are under consideration as a structural material, creep is an important design criterion and a life-limiting condition. However, the characterization of mechanical behavior at temperatures in excess of 1300°C has many challenges to overcome. Of utmost importance is the selection of materials for test fixtures. Materials selected must maintain their structural integrity, not cause chemical degradation of the test material, and not interfere with the acquisition of data at required temperatures in extreme environments over long durations. In this work, the thermo-chemical compatibility of hafnium diboride (HfB2) UHTC with other high temperature materials was investigated. The findings enabled the development and construction of a mechanical testing facility capable of reaching 1700°C in air. Platinum foil proved unstable in the presence of HfB2 at 1500°C, while yttrium aluminum garnet and alumina were demonstrated to successfully perform as test fixture materials inside the test chamber. The results of this research represent a significant contribution towards the use of UHTCs in extreme environments associated with hypersonic flight and atmospheric re-entry.

AFIT Designator

AFIT-ENY-DS-15-M-259

DTIC Accession Number

ADA616260

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