Design and Discovery of Compositionally Complex Alloys that Include High Corrosion Resistance

Abstract

The novel compositionally complex alloy (CCA) design space provides opportunities to improve corrosion resistance through design of passive films based on alloy composition and structure. The passive films are designed for thermodynamic stability as well as to provide corrosion protection by regulating charge transfer and transport processes operative during corrosion as well as by providing self-healing capability. Film protectivity can be obtained from single passivating element formation, passivity “helper” elements, secondary passivators, as well as other second and third element effects. Oxides can form congruently or enrich in certain elements and be depleted in others. The wide range of possible alloying combinations and resultant oxide compositions for a given design space necessitates efficient alloy selection for experimental synthesis and characterization of down-selected choices with high potential for good corrosion resistance. A design process for Al-Co-Cr-Fe-Mn-Mo-Ni-containing CCAs providing testable strategies for effective incorporation of corrosion-influencing elements in the oxide is introduced. Guidelines for elemental selection for protection by passive oxides, compositional optimization, and microstructural refinement are discussed.