Machine-learned accelerated discovery of oxidation-resistant NiCoCrAl high-entropy alloys

TL;DR

This paper uses data-driven analysis to uncover new oxidation resistance trends in NiCoCrAl high-entropy alloys, revealing temperature-dependent protection mechanisms and the effects of dopants, leading to the identification of promising new alloy compositions.

Contribution

It provides novel insights into oxidation behavior of NiCoCrAl HEAs across temperatures and demonstrates the effectiveness of Hf and Y doping, advancing alloy design for high-temperature applications.

Findings

Temperature-dependent transition between alumina- and chromia-dominated protection.

Cr-rich low-Al alloys perform best at 850°C, challenging previous assumptions.

Hf reduces oxidation rate most significantly, Y is effective mainly in NiCo-lean alloys.

Abstract

The development of oxidation-resistant high-entropy alloy (HEA) bond coats is restricted by the limited understanding of how multi-principal element interactions govern scale formation across temperatures. This study uncovers new oxidation trends in NiCoCrAl HEAs using a data-driven analysis of high-fidelity experimental oxidation data. The results reveal a clear temperature-dependent transition between alumina- and chromia-dominated protection, identifying the compositional regimes where alloys rich in Al dominate at $\ge1150$ {\deg}C, mixed Al-Cr chemistries are optimal at intermediate temperatures, and, unexpectedly, Cr-rich low-Al alloys perform best at 850 {\deg}C-challenging the assumption that high Al is universally required. The effects of Hf and Y are shown to be strongly composition-dependent with Hf producing the largest global reduction in oxidation rate, while Y becomes effective primarily in NiCo-lean alloys. Y-Hf co-doping offers consistent improvement but exhibits site-saturation behavior. These insights identify new high-performing HEA bond-coat families, including $\mathrm{Ni_{17}Co_{23}Cr_{30}Al_{30}}$ as a substitute for conventional mutlilayer thermal barrier coatings.