The barrier-free nanomultilayered structure via enthalpy-mediated phase separation in refractory high-entropy films

Patterned metal systems to periodically modulated nanomultilayered architectures, with crystalline and/or amorphous states, has acted as an effective strategy for tuning desirable mechanical properties. While the spontaneous assembly offers an effective and promising path for constructing nanomultilayers, in high-entropy alloys (HEA) how to trigger such a barrier-free route still faces challenges. In this paper, the enthalpy-difference-guided strategy, incorporating Pt, was employed to induce spinodal decomposition for the barrier-free nanomultilayer structure in refractory HEA systems. Aiming at exploring the elastic and chemical interactions, three HEA films with different degrees of size mismatch δ (Zr-Nb-Ta-Mo-W, Zr-Hf-Nb-Ta-Mo, Zr-Hf-Nb-Cr-Mo systems) were fabricated as model systems. Contributed by differences in ΔH_mix and δ , in each HEA film, certain-content Pt can trigger both spinodal decomposition and amorphization behavior, which lead to the barrier-free Pt-rich/Pt-lean nanomultilayers with different topological combinations: crystalline/crystalline and amorphous/amorphous. Compared to model HEAs, such barrier-free nanomultilayers can significantly improve the nanoindentation hardness. In HEA systems, tuning ΔH_mix and δ simultaneously can assist the further understanding of the structural arrangements and the progress on the barrier-free nanomultilayered configuration for superior mechanical properties.