Nanoheterogeneous ZrTa metallic glass thin films with high strength and toughness

Abstract

This study investigated the mechanical behavior of ZrxTa1−x (x = 21–79 at%) thin films and nanolayered films of ZrTa with modulated composition as model systems to gain insight into the hardness and toughness of metallic glasses and metallic glass nanocomposites. The monolithic films exhibit two primary microstructures, namely, a fully amorphous form (Zr = 35–70at%.) and an amorphous-crystalline composite (21–30 at% Zr). The amorphous films show a monotonic hardness variation with composition over a wide range of 5.5 – 9 GPa. The partial crystallization of the films results in a further jump in hardness, as opposed to the general trend of softening upon crystallization. The emergence of the crystalline phase also improves the ductility of the films, as verified by nanoindentation-based fracture toughness measurements. The indentation pile-up exhibits several shear bands in the fully amorphous films, replaced by a featureless pile-up zone for the case of Zr25Ta75, further verifying the superior toughness of the composite. The second part of the analysis pursued obtaining a similar toughening through fully amorphous nanolayered films of Zr35Ta65 / Zr70Ta30. The results indicate that these films provide a balanced combination of high hardness and enhanced ductility, providing an alternative route to the development of tough metallic glass coatings.