Date of Award

3-2006

Document Type

Thesis

Degree Name

Master of Science

Department

Department of Aeronautics and Astronautics

First Advisor

Marina B. Ruggles-Wrenn, PhD

Abstract

The compressive creep behavior of a N610/monazite/alumina composite was investigated in this work. The composite consists of a porous alumina matrix reinforced with NextelTM610 fibers coated with monazite in a symmetric cross-ply (0°/90°/0°/90°)s orientation. Compressive stress-strain behavior was investigated as well. The addition of monazite coating resulted in ~ 35% loss in compressive strength at 900°C and in ~45% loss in compressive strength at 1100°C. Compressive creep behavior was examined at 900 and 1100°C for creep stresses ranging from 50 to 95 MPa. Primary and secondary creep regimes were observed at both temperatures. Minimum creep rate was reached in all tests. At 900°C both monazite containing and control specimens produced creep strains ≤ 0.05. Conversely, at 1100°C creep strains were significant, approaching 9%, with monazite containing specimens accumulating larger creep strains at a given stress than the control samples. Creep strain rates were on the order of 10-7 s-1. Creep run-out, defined as 100 h at creep stress, was achieved in all tests. The residual strength and modulus of specimens that achieved run-out at 1100°C were characterized. Composite microstructure, as well as damage and failure mechanisms were investigated. Furthermore, effects of variation in microstructure on mechanical response were examined. While differences in processing and consequently the composite microstructure did not have a significant effect on tensile response of the CMC, effects on the compressive properties were dramatic.

AFIT Designator

AFIT-GAE-ENY-06-M17

DTIC Accession Number

ADA451284

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