Date of Award

3-21-2019

Document Type

Thesis

Degree Name

Master of Science in Materials Science

Department

Department of Aeronautics and Astronautics

First Advisor

Marina B. Ruggles-Wrenn, PhD

Abstract

A recent study evaluated tensile stress-strain and tensile creep behavior of an oxide-oxide composite (Nextel™720/alumina) with laser-drilled effusion holes at 1200°C. It was determined that the presence of laser-drilled holes degraded the mechanical properties and performance of the CMC as a result of damage caused to the composite microstructure by the laser drilling process. Based on these results, the present effort sought to assess the effects of diamond-drilled holes on the mechanical behavior of this CMC. Tensile properties of the N720/A composite at 1200°C in laboratory air were unaffected by the presence of an array of 17 diamond-drilled effusion holes. Notably, examination of the composite microstructure did not reveal any damage caused by the drilling process. The diamond-drilled specimens exhibited similar degradation to creep lifetimes as laser-drilled specimens for creep tests between 46-150 MPa in air, but contrary to unnotched and laser-drilled specimens, saw minimal degradation to creep lifetimes due to steam. These results were attributed to a change in dominant damage mechanism that caused minimum creep rates in air to exceed those in steam. Further experiments and analysis are needed to explore the damage mechanism at play in specimens with diamond-drilled effusion holes.

AFIT Designator

AFIT-ENY-MS-19-M-218

DTIC Accession Number

AD1076360

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