High-throughput Screening of Alloy Oxidation Across Al-Fe-Ni and Al-Fe-Ni-Cr Composition Space
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.