Date of Award

3-23-2017

Document Type

Thesis

Degree Name

Master of Science

Department

Department of Aeronautics and Astronautics

First Advisor

Marina Ruggles-Wrenn, PhD.

Abstract

Hypersonic vehicles with narrow airfoils produce thin boundary layers and shock temperatures in excess of 2000 deg C, exceeding the operating limits of traditional aerospace materials. The use of ultra-high temperature ceramics (UHTCs) allows for operating temperatures far exceeding those of metallic alloys. One such UHTC is hafnium diboride (HfB2). Transition metal diborides generally experience significant oxidation degradation at elevated temperatures. The use of additives, such as silicon carbide (SiC) has been shown to reduce the oxidation of transition metal diborides. This research focused on the compressive creep of HfB2 with varying amounts of SiC in air at 1500 deg C. The existing test set-up was successfully modified to permit compression creep testing at higher stress (75-100 MPa) levels for longer durations (>66 h). Post-test microstructural examination revealed significant SiC-depleted layers in HfB2-SiC samples. Oxide layers in HfB2 samples subjected to 75 and 100 MPa compressive creep tests were significantly thinner than those observed under zero stress, suggesting that sustained compressive load may restrict oxidation.

AFIT Designator

AFIT-ENY-MS-17-M-243

DTIC Accession Number

AD1055313

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