Self-assembly of nanocrystalline@amorphous core-shell nanostructure in the TA19 alloy film to achieve high strength

Abstract

Improving the strength of alloy materials and simultaneously retaining high toughness are strongly desirable by various engineering applications. Nanocrystalline@amorphous dual-phase nanostructure consisting of nanocrystalline-cores encapsulated with amorphous-shells has been regarded as one of the most effective routes to achieve high strength yet high toughness, which may overcome the limitation of either single-phase nanocrystalline alloys or single-phase metallic glasses because of reverse Hall-Petch effect or shear-band deformation. Herein, nanocrystalline@amorphous core-shell nanostructure has been successfully assembled in the sputtered TA19 alloy film only by regulating bias voltages (Vb), and then Vb induced evolution of microstructure and mechanical property was further investigated by combined experiments of X-ray diffraction (XRD), atomic force microscope (AFM), scanning electron microscope (SEM), select area electron diffraction (SAED), transmission electron diffraction (TEM) and nanoindentation. The results show that the bombardment of energy ions can promote formation of amorphous zones in TA19 alloy film, successfully achieving ordered core-shell nanostructure at −120 V of Vb, while single-phase nanocrystalline occurs at Vb = −40 V and amorphous dominated structure appears at Vb = −200 V. Maximum hardness value of 11.2 GPa achieves at Vb = −120 V when the ordered core-shell nanostructure is formed with invisible shear bands around indenter, but more amorphous result in disappearance of core-shell nanostructure at Vb = −200 V, which worsens hardness, accompanying with presence of obvious shear bands around indenter. This novel core-shell-like structure succeeded in achieving high strength or hardness yet high toughness by providing strong resistance to hinder movements of both grains and shear bands due to large amount of nanocrystalline@amorphous interfaces. It is suggested that the Vb as a key factor controlling the core-shell-like structure of TA19 films, which may provide a new strategy to improve mechanical properties of alloy films.