Design Strategies for Improving the Oxidation Resistance of Multi-Principal Element Alloys

Since the early 1940’s, nickel-based superalloys (SA) have been the cornerstone of hightemperature structural alloys due to their unique yield strength, creep life, and oxidation re-sistance when subject to harsh environments exceeding 1000 °C. While they have withstoodthe increasing operation temperatures seen in turbine engines with use of intricate coolingand coatings, they have reached their core metallurgical limit. As engineering componentsrequire the ability to operated past 1000 °C, new alloys must be developed to replace thetraditional SAs. Multi-principal Element Alloys (MPEAS) are a new innovative class ofmaterials which generally contain at least 4 major alloying additions exceeding 10 At. % ofthe overall composition and exist in the central portions of the ternary phase diagram.The high entropy of mixing within the materials is said to suppress the formation of deleterioustopologically close packed (TCP) phases and stabilize simple microstructures while allowingfor heavy alloying to generate significant solid solution strengthening, slowed diffusivities,and highly tailorable microstructures. Not only are these materials useful for their potentialreplacement of SAs, but they also provide a framework for understanding the fundamentalstructure – property relationships of non-dilute alloys. This research has shown that new ageMPEAs are able to compete with traditional SAs in terms of oxidation resistance as well ascompressive strength. Several new High Entropy Superalloy (HESAs) were developed usingthe CALPHAD approach, particularly to study the impact of microstructure and chemistryon high temperature oxidation behavior. The volume fraction and precipitate size were foundto have a significant impact on scale formation and the resulting parabolic oxidation rates ofthese alloys. While these studies and those it compares to make use of arc-melting for syn-thesizing small quantities of new materials, it was determined that the abnormally large andtextured grain structure from the as-cast materials, even after homogenization, contributedgreatly to increased oxidation variability. The use of hot thermomechanical processing wasemployed and stable processing conditions were determined for HESA processing in gramquantities. The refined microstructures led to reduced variability in the thermogravimetric(TGA) results and also a total decrease in parabolic oxidation rates. Finally, the oxida-tion behavior of a newly developed, alumina forming, HESA and an ODS variant were fullycharacterized from 900 to 1200 °C.

Grantor dc:publisher

University of Alabama Libraries

Year dc:date.issued

2024

Author dc:creator

• Pavel, Michael

Advisor dc:contributor.advisor

• Weaver, Mark

Contributors dc:contributor

• Kubacki, Gregory
• Monroe, Charles
• Thompson, Gregory
• Schneider, Judy

Statement dc:rights

• All rights reserved by the author unless otherwise indicated.

Language dc:language.iso

en_US, English

Dc Identifier Other

1050345

OAI identifier oai:identifier

oai:ir.ua.edu:123456789/13786