Date of Award

Spring 4-2016

Embargo Period

5-2-2018

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemical Engineering

Advisor(s)

Andy Gellman

Second Advisor

Jim Miller

Abstract

The high-temperature oxidation of multicomponent metal alloys involves complex kinetic processes that are not fully understood for many systems. As a result, prospective alloy compositions must typically be screened experimentally during the design of oxidation-resistant alloys. The comprehensiveness with which this can be done has conventionally been limited by the time required to prepare and test large numbers of single-composition alloy samples. This thesis describes the development, implementation, and assessment of a high-throughput methodology for studying the compositional dependence of alloy oxidation using composition spread alloy films (CSAFs), compact samples containing continuous, lateral gradients in composition. High-throughput analyses of the oxidation behavior of many different alloy compositions can be performed with a single CSAF by using spatially resolvable characterization techniques to probe different locations across its surface. We have used CSAFs to study the oxidation of aluminum-iron-nickel (Al-Fe-Ni) and aluminum-iron-nickel-chromium (Al-Fe-Ni-Cr) alloys. Given a minimum “critical Al concentration”, 𝑁Al∗, these alloys preferentially form a surface layer of Al2O3 upon initial exposure to an oxidizing environment, which provides substantial protection to the underlying metal against further oxidation. However, the value of 𝑁Al∗ can vary as a function of both multicomponent composition and the thermochemical identity of the oxidizing environment. By oxidizing CSAFs in dry or humid air at 427 °C, we have identified continuous boundaries through the Al-Fe-Ni and Al-Fe-Ni-Cr composition spaces where phenomenological transitions in oxidation behavior occur, including 𝑁Al∗ boundaries delineating the compositional limits for protective Al2O3 formation. The results demonstrate the potential of CSAF-based methods to screen with unprecedented detail the effects of composition on multicomponent alloy oxidation, and offer important fundamental insights into its mechanisms.

Available for download on Wednesday, May 02, 2018

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