Diffusion Kinetics in High-Entropy Alloys

High‐entropy alloys (HEAs) are near‐equimolar, multicomponent metallic systems distinguished by their high configurational entropy and complex atomic environments. Diffusion kinetics in HEAs governs phase stability, mechanical creep resistance and high‐temperature corrosion performance. Unlike conventional alloys, HEAs exhibit intricate interactions between multiple elements, lattice distortions and heterogeneous defect structures that collectively influence both volume and grain boundary transport. Key debates in the field concern the existence of a “sluggish diffusion” effect—whereby multicomponent entropy is proposed to retard atomic mobility—and the role of specific elemental combinations in modulating diffusion rates. A precise understanding of diffusion pathways, whether through vacancy‐mediated jumps, interstitial mechanisms or along grain boundaries, is essential for the rational design of HEAs for aerospace, power generation and nuclear applications. Advances in atomic‐scale characterisation and radiotracer techniques have begun to resolve long‐standing uncertainties about the interplay between local chemical disorder, free‐volume formation and temperature‐dependent diffusion coefficients.

Research from Nature Portfolio

Recent measurements of nickel grain boundary diffusion in model equiatomic HEAs demonstrate that an increased number of constituent elements does not inherently suppress boundary transport. Radiotracer analysis in CoCrFeNi and CoCrFeMnNi alloys has revealed non‐sluggish kinetics, with grain boundary energies rising markedly with temperature and varying according to the nature of added elements. High‐resolution in situ scanning transmission electron microscopy has provided direct visualisation of single‐atom random walks in a metal matrix, distinguishing volume diffusion from defect‐assisted migration and offering a template for analogous studies in multicomponent systems. Complementary investigations using positron spectroscopy and synchrotron X‐ray methods have quantified vacancy concentrations and heterogeneous lattice distortions in CoCrFeNi and CoCrFeMnNi alloys. These studies show enlarged free volumes in HEAs, facilitating vacancy‐mediated diffusion and underscoring the influence of specific element combinations on atomic mobility under quasi‐equilibrium heating.

Diffusion Kinetics in High-Entropy Alloys publication trend

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

Technical terms

High‐entropy alloy (HEA): A multicomponent metallic alloy with near‐equimolar composition and high configurational entropy.

Grain boundary diffusion: Atomic transport along interfaces between crystallites, often faster than through the lattice.

Tracer diffusion: Measurement of atomic mobility using isotopic or analytical markers to track individual species.

In situ STEM: Real‐time observation of atomic movements under an electron microscope at elevated temperatures.

Vacancy: A missing atom in the crystal lattice that enables neighbouring atoms to jump into the vacant site.

Configurational entropy: A thermodynamic quantity reflecting the number of possible atomic arrangements in an alloy.

Arrhenius dependence: Exponential relationship between diffusion rate and reciprocal temperature, often used to characterise activation energies.

References

1. Atomic scale volume and grain boundary diffusion elucidated by in situ STEM. Nature Communications (2023).
2. Anomalies in the short-range local environment and atomic diffusion in single crystalline equiatomic CrMnFeCoNi high-entropy alloy. Nano Research (2024).
3. Radioactive isotopes reveal a non sluggish kinetics of grain boundary diffusion in high entropy alloys. Scientific Reports (2017).
4. Investigation of sluggish diffusion in FCC Al0.25CoCrFeNi high-entropy alloy. Materials Research Letters (2021).
5. Element Effects on High-Entropy Alloy Vacancy and Heterogeneous Lattice Distortion Subjected to Quasi-equilibrium Heating. Scientific Reports (2019).
6. Reactive interdiffusion of an Al film and a CoCrFeNi high-entropy alloy. Materials & Design (2022).