Impact of crystal lattice and alloy composition on formation and stability of amorphous high entropy metal composites under forced mechanical mixing

Recognizing the benefits of exploring the cocktail effect as one of the defining concepts of high-entropy alloys (HEAs), this study reviews emergent microstructures and functionalities in such compositionally complex systems using severe plastic deformation (SPD). High-pressure torsion (HPT), as an SPD technique, is used to enable the forced intermixing of chemically distinct HEAs and to create metastable compositional states that are inaccessible through equilibrium processing. In this work, the fcc CoCrFeMnNi Cantor alloy was mechanically mixed with the bcc HfNbTaTiZr alloy or the bcc HfNbTiVZr Senkov alloy to explore how cocktail-effect-driven interactions influence phase formation, thermal stability, and magnetic behavior. The forced mechanical mixing of the two HEAs produced distinct structural pathways depending on the chemistry of the refractory alloy. Although atomic-scale intermixing occurred in both systems, only the Ta-containing nanocomposite formed a ten-element amorphous interfacial phase, whereas substitution of Ta with V resulted in a highly defected nanocrystalline intermixed region. The ten-element amorphous phase remained stable during annealing at 680 °C despite extensive phase separation in the surrounding crystalline regions. In parallel, room-temperature ferromagnetism emerged in the otherwise paramagnetic Cantor alloy following severe plastic deformation and was further enhanced, in terms of contrast, by intermixing with the Ta-containing Senkov alloy. Subsequent annealing-induced cocktail-effect-driven phase separation, producing chemically distinct magnetic regions that further increased magnetic contrast, enhanced coercivity, and strengthened magnetic ordering at cryogenic temperatures. While HPT provides the non-equilibrium processing route that enables forced mechanical mixing, the primary objective of this work is to understand how cocktail-effect-driven chemical interactions govern interfacial phase formation, element-specific amorphization, phase stability, and the emergence of new functional behavior in chemically complex HEA nanocomposites.