Controlled synthesis of nanostructured glassy and crystalline high entropy alloy films

High entropy alloy (HEA) based thin films have been attracting increasing research interest recently because of their unique mechanical/physical properties. However, the physical mechanisms that govern the formation of the atomic structure in HEA thin films are not clear yet. In this work, we synthesized a series of FeCoNiNb_0.5 HEA thin films via direct current magnetron sputtering with carefully controlled processing parameters. Through a systematical study by x-ray diffraction and transmission electron microscopy, we demonstrated that the atomic structure of the HEA thin films of the same composition could exhibit different nanostructures and metastable phases, including amorphous and metastable crystalline phases. In addition, we also developed a physical model which sheds quantitative insights into the thermodynamics and kinetics for the phase selection in our HEA thin films. Our current work could pave a way for a controlled synthesis of a variety of nanostructured chemically complex alloy thin films for future structural and functional applications.