Degree Type

Thesis

Date of Award

1-1-2005

Degree Name

Master of Science

Department

Materials Science and Engineering

Major

Materials Science and Engineering

Abstract

Surface undulations known as rumpling have been shown to develop at the surface of bond coats used in advanced thermal barrier coating systems. Rumpling can result in cracking and eventual spallation of the top coat. Many mechanisms to explain rumpling have been proposed, and among them is a martensitic transformation. High-temperature x-ray diffraction, differential scanning calorimetry and potentiometry were used to investigate the nature of the martensitic transformation in bulk platinum-modified nickel aluminides. It was found that the martensitic transformation has strong time dependence and can form over a range of temperatures. Cyclic oxidation experiments were performed on the bulk alloys to investigate the effect of the martensitic transformation on surface rumpling. It was found that the occurrence of rumpling was associated with the martensitic transformation. The degree of rumpling was found to increase with an increasing number of cycles and was independent of the heating and cooling rates used. The thickness of the oxide layer at the surface of the samples had a significant impact on the amplitude of the resulting undulations, with amplitude increasing with increasing oxide-layer thickness. Rumpling was also observed in an alloy based on the [Gamma]-[Gamma'] region of the nickel-aluminum-platinum phase diagram. Rumpling in this alloy was found to occur during isothermal oxidation and is associated with a subsurface layer containing a platinum-rich phase known as [Alpha]. Rumpling in both alloy systems may be explained by creep deformation of a weakened subsurface layer in response to the compressive stresses in the thermally grown oxide layer.

DOI

https://doi.org/10.31274/rtd-20200616-118

Copyright Owner

Benjamin Joseph Zimmerman

Language

en

OCLC Number

63192807

File Format

application/pdf

File Size

105 pages

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