Tribological Behavior of High-Entropy Alloys

High-entropy alloys (HEAs) have emerged as a transformative class of materials for wear-critical applications, combining multiple principal elements in near-equimolar ratios to stabilise simple solid-solution phases. Their tribological performance is governed by an interplay of hardness, ductility and surface chemistry, which can be tuned through composition, microstructure and processing. Distinctive features such as dual-phase architectures, nanoscale precipitates and dynamic surface reactions confer adaptive resistance to abrasive, adhesive and oxidative wear. Under sliding contact, many HEAs form protective tribo-oxide or nanocomposite glaze layers that arrest material removal and reduce friction. Grain-boundary engineering, inverse Hall-Petch behaviour and self-lubricating inclusions further modulate subsurface deformation and crack initiation. Temperature-dependent studies reveal that certain HEAs maintain low wear rates and stable friction coefficients from ambient conditions to several hundred degrees Celsius, making them suitable for aerospace, power generation and heavy-machinery components. Progress in bulk consolidation, thin-film deposition and composite design has broadened the practical deployment of HEAs in industrial tribological systems.

Research from Nature Portfolio

Recent studies have demonstrated a reactive wear protection strategy whereby an equiatomic TiNbZr–Ag alloy develops an in situ oxide-metal nanocomposite layer during sliding. The surface layer, combining amorphous and crystalline oxide domains, exhibits yield strengths above 2 GPa and accommodates homogeneous deformation to 20 percent strain, reducing wear by an order of magnitude. Another foundational work on a CoCrFeMnNi HEA has revealed inverse Hall-Petch behaviour: grain refinement under ultra-high vacuum leads to a super-nanocrystalline near-surface layer with remarkably low friction coefficients (~0.3) and wear rates (~10⁻⁶ mm³ N⁻¹ m⁻¹). Dynamic amorphisation in the subsurface layer and the formation of an ultra-nanocrystalline oxide-free film underpin this exceptional tribological performance.

Tribological Behavior of High-Entropy Alloys publication trend

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

Technical terms

High-entropy alloy: An alloy comprising five or more principal elements in near-equimolar proportions that stabilise simple solid-solution phases.

Wear rate: The volumetric material loss per unit load and sliding distance, typically expressed in mm³ N⁻¹ m⁻¹.

Coefficient of friction: The ratio of tangential force to normal load during sliding contact, indicating ease of relative motion.

Inverse Hall-Petch effect: A phenomenon in which further grain refinement below a critical size leads to softening rather than hardening.

Reactive wear protection: A strategy where surface reactions during sliding form a mechanically robust and deformable nanocomposite oxide layer.

Glaze layer: A dense, often nanocrystalline or amorphous tribo-oxide film formed on a sliding surface that reduces wear and friction.

Nanohierarchical architecture: A multiscale microstructure combining different grain sizes or phases at the nanoscale to distribute and dissipate frictional stresses.

References

1. Remarkable Wear Resistance in a Complex Concentrated Alloy with Nanohierarchical Architecture and Composition Undulation. Research (2023).
2. Reactive wear protection through strong and deformable oxide nanocomposite surfaces. Nature Communications (2021).
3. Evidence of Inverse Hall-Petch Behavior and Low Friction and Wear in High Entropy Alloys. Scientific Reports (2020).
4. Wear-resistant CrCoNi nanocrystalline film via friction-driven surface segregation. Acta Materialia (2024).
5. Excellent tribological performance at elevated temperatures and associated mechanisms of novel AlCoCrFeNi-MoS2 solid self-lubricating composite. Tribology International (2023).