A research team has recently made significant progress in the field of self-assembled nanomultilayer film construction in high-entropy alloy (HEA) thin films. Their study, titled “The barrier-free nanomultilayered structure via enthalpy-mediated phase separation in refractory high-entropy films”, was published in Acta Materialia. The work systematically reveals a new thermodynamically driven route to spontaneously form nanomultilayer structures in multicomponent alloy systems, offering new theoretical support and design principles for advanced high-performance structural materials.

In conventional metallic systems, nanomultilayer films with periodic interfaces are typically fabricated through deposition techniques involving external control (e.g., shutter timing or substrate motion), which effectively enhance strength and durability. However, such methods are often limited in their applicability to complex alloy compositions due to their high dependence on process precision. This study introduces an innovative approach based on enthalpy-mediated phase separation, where the addition of Pt triggers spinodal decomposition in various refractory HEA films. This leads to the spontaneous formation of self-assembled nanomultilayer films, without the need for external layer-by-layer control. These multilayers exhibit clear interfaces and uniform morphologies, with diverse metastable topologies including crystalline/crystalline and amorphous/amorphous layer combinations.

The research focuses on three HEA systems with different degrees of atomic size mismatch (δ): Zr-Nb-Ta-Mo-W, Zr-Hf-Nb-Ta-Mo, and Zr-Hf-Nb-Cr-Mo. By fine-tuning the Pt content and its enthalpic interactions (ΔH_mix) with the matrix elements, the study induces the compositional separation between Pt-rich and Pt-lean regions, forming distinct nanolayers at the microscopic scale. Notably, in systems with sufficient ΔH_mix contrast and elastic strain contributions, such multilayers can spontaneously emerge with as little as ~3 at.% Pt addition, and demonstrate significant enhancement in mechanical hardness.

Furthermore, the study highlights that the structural state of each sublayer—whether crystalline or amorphous—is closely related to the alloy’s glass-forming ability (GFA), broadening the theoretical framework for metastable phase engineering in HEAs. Compared to conventional single-phase HEA films, the self-assembled nanomultilayer films exhibit superior hardness and structural stability in nanoindentation tests.

This work marks the first report of using enthalpy–elasticity coupling to spontaneously form nanomultilayers in multicomponent HEA systems, without relying on traditional layer-by-layer fabrication. It offers a promising pathway toward the development of next-generation structural materials with tunable architectures and superior mechanical performance.

Citation:
Xingjia He, Yu Zhang, Mao Wen*, JiLei Qi, Longpeng Wang, Kan Zhang*, Weitao Zheng,
“The barrier-free nanomultilayered structure via enthalpy-mediated phase separation in refractory high-entropy films”,
Acta Materialia, Vol. 267, 119729 (2024).
https://doi.org/10.1016/j.actamat.2024.119729