High-Temperature Oxidation Behavior of High-Entropy Alloys

High-entropy alloys (HEAs) represent a class of multi-principal-element metallic materials that derive remarkable thermal stability and oxidation resistance from their core effects, including high mixing entropy, sluggish diffusion and severe lattice distortion. When exposed to elevated temperatures, HEAs develop oxide scales—composite films of metal-oxygen compounds—that govern long-term performance in oxidising environments. The initial stage of oxidation is controlled by thermodynamic affinities and atomic size differences among constituent elements, leading to preferential oxide formation. Over time, diffusion processes and redox potentials drive compositional inversions within the scale, inducing transitions from rapid, transient growth to protective, parabolic kinetics. Refractory HEAs, incorporating high-melting-point elements such as Cr, Ta and Mo, form specialised oxide phases—for example CrTaO4-based layers—that dramatically slow further oxidation. Advanced characterisation techniques, including in situ atom-probe tomography, transmission electron microscopy and spectroscopic methods, have elucidated the atomic-scale mechanisms underpinning alloy-scale interactions. These insights enable the predictive design of HEAs for critical applications in aerospace, power generation and chemical processing, where materials must withstand temperatures above 800 °C with minimal mass gain and maintained mechanical integrity.

Research from Nature Portfolio

Recent studies have deconvoluted the speciated oxide growth mechanisms in model equiatomic HEAs, revealing that early oxidation follows atomic-size ordering but is later dominated by redox potentials. In situ atom-probe tomography, transmission electron microscopy and X-ray absorption near-edge structure analyses have tracked the evolution of oxide film structure and composition, demonstrating an inversion in metallic distributions within the scale and paving the way for chemistry-driven alloy design with enhanced oxidation resistance. Complementary long-duration isothermal oxidation experiments on refractory HEAs at 1,000–1,100 °C for up to 200 hours have shown that dense CrTaO4-rich oxide layers, often with dispersed alumina and chromia inclusions, shift mass-gain behaviour from exponential to parabolic regimes. The formation of a continuous CrTaO4-based scale at higher temperatures yields one of the lowest reported oxidation rates among RHEAs, highlighting the importance of oxide phase selection in achieving durable high-temperature performance.

High-Temperature Oxidation Behavior of High-Entropy Alloys publication trend

The graph below shows the total number of articles in high-temperature oxidation behavior of high-entropy alloys across all publications each year (not limited to Nature Index journals).

Technical terms

High-Entropy Alloy (HEA): A metallic material composed of five or more principal elements in near-equiatomic proportions, leading to high configurational entropy and unique properties.

Oxide Scale: A surface layer of metal-oxygen compounds that forms on alloys during high-temperature exposure and governs corrosion resistance.

Parabolic Oxidation Kinetics: A rate law in which mass gain due to oxidation is proportional to the square root of exposure time, indicative of diffusion-controlled scale growth.

Refractory Alloy: A material containing high-melting-point elements that retains strength and resists degradation at temperatures typically above 1,000 °C.

Cocktail Effect: The synergistic enhancement of material properties in HEAs arising from complex multi-element interactions beyond simple additive effects.

References

1. Mechanistic understanding of speciated oxide growth in high entropy alloys. Nature Communications (2024).
2. Unveiling the oxidation mechanism of CrTaTiMo refractory medium-entropy alloys: A synergy of density functional theory and ab initio molecular dynamics. Materials & Design (2024).
3. An oxidation resistant refractory high entropy alloy protected by CrTaO4-based oxide. Scientific Reports (2019).
4. High-Temperature Oxidation in Dry and Humid Atmospheres of the Equiatomic CrMnFeCoNi and CrCoNi High- and Medium-Entropy Alloys. High Temperature Corrosion of Materials (2020).
5. Alloying effect on the oxidation behavior of a ductile Al0.5Cr0.25Nb0.5Ta0.5Ti1.5 refractory high-entropy alloy. Materials Today Advances (2020).