Electronic structure and nanoindentation properties of electrochemical hydrogen-charged Zr-based metallic glasses

Abstract

Zr55Cu30Ni5Al10 metallic glasses were treated by an electrochemical hydrogen- (H-)charging method. Samples with different H content were obtained by changing the H-charging current density and charging time. X-ray diffraction, nanoindentation, X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy, and positron annihilation experiments were used to investigate amorphous structure, nanomechanical properties, electronic structure, and positron annihilation behavior of Zr55Cu30Ni5Al10 metallic glasses after electrochemical hydrogenation treatment. The results showed that the diffraction angle corresponding to the diffuse scattering peak gradually moved to a low angle with increased H content. At the same time, the hardness and elastic modulus of the MG were significantly increased with increased H-charging content. When the H content was high, the sawtooth rheological phenomenon disappeared in the load displacement curve of the MG during nanoindentation. XPS narrow spectrum analysis showed that the Zr-3d peak in samples shifted to higher binding energies, while the other elements shifted toward lower binding energy, indicating that H addition led to the transfer of valence electrons from Zr-3d to the Zr–H bond state, resulting in hardening. Three lifetime components are observed in the uncharged and charged sample, indicating the presence of three size ranges of open volume sites. After electrochemical hydrogen charging it causes a significant decrease in the size (lifetime) of the three open volume defects, indicating that the hydrogen occupies those sites. With the increase of hydrogen content, the concentration (intensity) of the first two open volume defects gradually decreases, while the third open volume defect gradually enhances, indicating that hydrogen atom mainly occupies the first two open volume defects. Positron annihilation experiments showed that H addition reduced the average annihilation lifetime of positron vacancies in these MGs, but no new defects were produced.