Date of Award

3-22-2012

Document Type

Thesis

Degree Name

Master of Science

Department

Department of Aeronautics and Astronautics

First Advisor

Marina B. Ruggles-Wrenn, PhD.

Abstract

Structural aerospace components require materials to have superior long-term mechanical properties that can withstand severe environmental conditions, such as high temperatures, high pressures and moisture, whilst enduring the loads they are designed for. Ceramic-matrix composites (CMCs) are capable of maintaining excellent strength and creep resistance at high temperatures, which make them attractive candidate materials for aerospace applications, particularly in propulsion. Silicon Carbide (SiC) ceramic fibers have been used as constituent materials in CMCs, although oxidation of the SiC to SiO2 has been a known degredation mechanism. Recently developed near stoichiometric SiC fibers have shown significant improvements in thermochemical stability; however performance of the new fibers at elevated temperatures in steam environments has not been studied thoroughly. The objective of this thesis is to investigate creep of near stoichiometric SiC fiber tows at elevated temperatures in air and in steam environments. The creep response of Hi-Nicalon™-S SiC fiber tows was investigated at 800°C and 1100°C in laboratory air and in steam environments. The creep stresses ranged from 76 MPa to 1560 MPa. Creep run-out was defined as 100 h at creep stress. The presence of steam significantly degraded the creep performance of the fiber tows both at 800°C and at 1100°C. The creep lifetimes of the Hi-Nicalon™-S SiC fiber tows were reduced by approximately an order of magnitude due to steam.

AFIT Designator

AFIT-GMS-ENY-12-M03

DTIC Accession Number

ADA558297

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