Date of Award

2024-05-01

Degree Name

Doctor of Philosophy

Department

Materials Science And Engineering

Advisor(s)

SK Varma

Abstract

High entropy alloys (HEA) differ from traditional alloying systems because five elements are mixed in equi-atomic proportions, as opposed to having one main principal element. As a result of exploring this new method of alloying, it was found that high entropy alloys demonstrate exceptional mechanical properties, an example being oxidation resistance, and are capable of enduring elevated temperatures. Seeing the potential that this new area of interest contains, studies involving a combination of elements to form various HEA have been performed. Most refractory metals are body-centered cubic and possess extremely high melting temperatures, so they are regularly considered when designing high entropy alloys. However, the main goal of this investigation is to characterize and study the oxidation behavior of a high entropy alloying system that is comprised of only non-body centered cubic elements. The two alloys of interest are Al-Cu-Ni-Mn (Non Si Alloy) and Al-Cu-Ni-Mn-Si (Si Alloy). Each element that was selected for the HEA did not occupy a body centered cubic crystal structure and did possess a relatively high melting temperature. During this investigation the main objective was to microstructurally characterize each alloy in the as received condition and subject each alloy to different oxidation experiments. Exposing each HEA toelevated temperatures, 600oC and 1000oC, led to the study of their static and cyclic oxidation behavior. For static oxidation experiments, each alloy was held for a time duration of 24 hours, 48 hours, and 72 hours at 600oC and 1000oC. For cyclic oxidation experiments, each alloy was exposed to heating for a 24 hour time period and then remained cooled for 24 hours, and this process was repeated until the heating time equaled 1 full week. After experimentation the next objective was to identify microstructural features, characterize the oxide layer, and analyze the interface between the bulk microstructure and the oxidation layer. This characterization was done by using transmission electron microscopy (TEM), x-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) to identify microstructural characteristics in the as received and oxidized condition.

Language

en

Provenance

Received from ProQuest

File Size

114 p.

File Format

application/pdf

Rights Holder

Mckenna Mae Lin Hitter

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