Lee B. Harlen

Date of Award

3-1-2005

Document Type

Thesis

Degree Name

Master of Science in Astronautical Engineering

Department

Department of Aeronautics and Astronautics

First Advisor

Marina B. Ruggles-Wrenn, PhD

Abstract

Oxide/oxide ceramic matrix composites (CMCs) are being considered for applications such as jet engine combustion chambers and afterburner flaps. Nextel™ 720/A (N720/A), an oxide/oxide CMC with an alumina matrix and no interphase at the fiber-matrix interface, was developed specifically to provide improved long-term properties and performance at 1200°C. This study focused on experimental investigation of creep behavior of N720/A [0/90] at elevated temperatures in laboratory air and in 100% steam environment. Monotonic tensile tests to failure were performed at 23, 1200, and 1330°C. Ultimate tensile strength (UTS) values were established and monotonic stress-strain curves were produced. Creep-rupture tests at 1200°C and 1330°C were conducted in laboratory air and in steam environment to examine the combined effects of temperature and moisture exposure on creep resistance. Creep curves were generated and creep rates were evaluated for all test conditions. Effects of elevated temperature and steam environment on creep-rupture life were assessed. The N720/A CMC exhibited good creep resistance at 1200°C in laboratory air. Presence of steam degraded creep performance. At 1330°C, creep resistance was poor. Microscopy and fractography was used to examine specimen microstructure and fracture surfaces. Fiber fracture and pullout appeared to be the primary damage mechanisms. Based on the obtained results, N720/A is a candidate material for 1200°C applications in air environment. However, degrading effects of steam on creep performance cannot be neglected.

AFIT Designator

AFIT-GA-ENY-05-M05

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