Collaborative Research: Microscopic Mechanism of Surface Oxide Formation in Multi-Principal Element Alloys

Northwestern University, Evanston IL

Investigators

Abstract

NON-TECHNICAL SUMMARY Multi-principal element alloys (MPEAs) are compositionally complex alloys consisting of five or more elements in relatively equal proportions. Certain MPEAs have demonstrated superior mechanical properties (e.g., hardness, strength) unattainable from traditional alloys, making them ideal for high temperature applications (e.g., gas turbine blades and surface coatings for reentry vehicles). Incidentally, degradation by oxidation is a critical material challenge that must still be overcome to improve performance in such applications. Due to the complex compositional combinations, making oxidation resistant MPEAs is nontrivial. In this project, composition-processing-structure-property relationships for oxidation-resistant MPEAs are established through state-of-the-art experimental characterizations and computer simulations, guided by an artificial intelligence (AI) assisted innovative data-adaptive discovery strategy. Fundamentally, the oxidation mechanism¬ from the atomic to micro-meter scale is studied through both experimental discovery and machine learning embedded within a materials design and surface engineering framework. The results of this project enable an advanced materials paradigm for the discovery and creation of oxidation resistant MPEAs applicable for high temperature operations. TECHNICAL SUMMARY Multi-principal element alloys (MPEAs) are concentrated random solid-solutions typically consisting of five or more elements in significant proportions. While the remarkable mechanical properties (e.g., hardness, or strength) of certain MPEAs have encouraged their potential use for components operating at high temperatures such as those found in gas turbine blades or surface coatings for reentry vehicles. At the operation conditions for such components, degradation by oxidation remains a critical materials challenge. Consequently, during synthesis of oxidation resistant MPEAs, the versatility in elemental compositions for these complex alloys translates to an extensive range of possible oxidation products, many with poor resistance to the penetration of oxygen into the bulk alloy. To address this challenge and explore the associated enormous composition-processing-structure-property landscape, the oxidation mechanism¬ from atomic scale oxygen chemisorption to micro-meter oxide scale formation are studied by an innovative and experimentally validated data-guided adaptive approach. A surface engineering paradigm for the synthesis and processing of MPEAs with improved oxidation resistance are being developed. Central to the proposed framework are four research developments: (1) MPEA Concept Exploration; (2) Surface Engineering & Atomic Characterization; (3) Density Functional Theory Calculations; and (4) Adaptive Discovery. The results of this research are expected to have significant economic impact on society through innovations in surface-engineered MPEAs across a wide range of industries such as energy, hypersonic applications, defense and healthcare. This timely research lies within the domains of fundamental materials physics, predictive synthesis, and data science and offers unique collaborative and interdisciplinary research and training experiences for researchers across the fields of surface physics, material science, data analytics, and computational materials. Research is integrated with education through cross-university teaching and assessment, exchange-visits and co-advised student training coupled with technology innovation and entrepreneurial experiences. In this project, PIs also actively engage with programs for pre-college women and underrepresented minority students to encourage them to pursue STEM careers. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.