Bridging the gap between high-entropy alloys and metallic glasses: Control over disorder and mechanical properties of coatings

High-entropy alloys (HEAs) and high-entropy metallic glasses (HEMGs) represent two intensively researched classes of materials with high technological interest for applications as functional coatings with high strength, hardness, toughness, and corrosion resistance. The distinctive structural difference between single-phase crystalline solid solutions for HEAs and liquid-like disorder for HEMGs generates a seemingly insuperable contrast. In this work, we demonstrate that we can deliberately choose between crystalline or glassy properties by introducing structural disorder in HfMoNbTiZr thin films of identical composition. Using pulsed laser deposition (PLD) at different growth conditions, we reproducibly tune the structure of HfMoNbTiZr coatings from crystalline to fully amorphous. We show that the level of disorder has a profound impact on the mechanical properties of the coatings using the hardness derived from nanoindentation measurements as an example. While the hardness of polycrystalline HfMoNbTiZr layers already exceeds the single-phase bulk value, the amorphous HfMoNbTiZr is even clearly harder, demonstrating a distinctive improvement with introducing disorder. Our findings bridge the two seemingly different concepts of HEAs and HEMGs and demonstrate that structural disorder is not a given material property. Instead, disorder can serve as a useful design parameter for customizing the properties of functional coatings.