Date of Award

6-2006

Document Type

Thesis

Degree Name

Master of Science

Department

Department of Aeronautics and Astronautics

First Advisor

Marina B. Ruggles-Wrenn, PhD

Abstract

Aerospace applications require materials capable of maintaining superior mechanical properties while operating at high temperatures and oxidizing environments. Nextel™ 720/A (N720/A), an oxide/oxide ceramic matrix composite (CMC) with a porous alumina matrix was developed specifically to provide improved long-term properties and performance at 1200°C. This research evaluated the creep behavior of N720/A with a ±45° fiber orientation at 1200°C in: laboratory air, steam, and argon environments. Creep-rupture tests at the creep stress levels of: 45, 40, 35, and 15 MPa were conducted in each environment.
The ultimate tensile strength of N720/A with ±45° fiber orientation was 55 MPa, the elastic modulus (E) was 45 GPa, and failure strain was 0.265%. The creep-rupture results showed a decrease in creep life with increasing creep stress. The material was found to perform best in air, followed by steam, and then argon. Prior to this effort, N720/A was believed to perform best in non-oxidizing environments such as argon. Tests at stress levels ≤ 35 MPa revealed good creep resistance achieving a run out of 100 h in all test environments at 1200°C. Fracture surface observations with a Scanning Electron Microscope showed a correlation between coordinated fiber bundle failure and increased creep life. A qualitative spectral analysis provided evidence of silicon species migration from the mullite phase of the fiber to the matrix in each environment, but increasingly so in steam and argon.

AFIT Designator

AFIT-GAE-ENY-06-J15

DTIC Accession Number

ADA453971

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