Date of Award

3-13-2007

Document Type

Thesis

Degree Name

Master of Science in Aeronautical Engineering

Department

Department of Aeronautics and Astronautics

First Advisor

Marina B. Ruggles-Wrenn, PhD

Abstract

This research investigated the creep behavior of an N720/Al203 composite. The composite consists of a porous alumina matrix reinforced with laminated, woven mullite/alumina fibers (NextelTM 720). This ceramic matrix composite (CMC) has no fiber coating and relies on the porous matrix for flaw tolerance. The tensile stress-strain behavior was investigated and the tensile properties measured in the 800-1100 °C temperature range. Tensile creep behavior was examined at 1000 and 1100 °C in laboratory air and in steam environment. In air creep stress was 150 MPa. In steam creep stresses ranged from 100 to 160 MPa. Primary and secondary creep, but no tertiary creep, were observed in all tests. Minimum creep rate was reached in all tests. Creep rates accelerated with increasing temperature and creep stress. The presence of steam further increased creep rates. At 1000 °C creep run-out, defined as 100 hours at creep stress, was achieved in all tests. At 1100 °C run-out was achieved at 150 MPa in laboratory air, but only at 100 MPa in steam. The residual strength and modulus of all specimens that achieved run-out were characterized. At 1100 °C in the presence of steam, creep performance deteriorated rapidly with increasing creep stress. Composite microstructure, as well as damage and failure mechanisms, were explored.

AFIT Designator

AFIT-GAE-ENY-07-M04

DTIC Accession Number

ADA468294

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