Y.H. Liu

Characterization of nanoscale mechanical heterogeneity in a metallic glass by dynamic force microscopy.

We report nanoscale mechanical heterogeneity of a metallic glass characterized by dynamic force microscopy. Apparent energy dissipation with a variation of ~12%, originating from nonuniform distribution of local viscoelasticity, was observed. The correlation length of the heterogeneity was measured to be ~2.5 nm, consistent with the dimension of shear transformation zones for plastic flow. This study provides the first experimental evidence on the nanoscale viscoelastic heterogeneity in metallic glasses and may fill the gap between atomic models and macroscopic glass properties.

Structural origins of Johari-Goldstein relaxation in a metallic glass

Johari-Goldstein or β relaxation, persisting down to glassy state from a supercooled liquid, is a universal phenomenon of glassy dynamics. Nevertheless, the underlying micromechanisms leading to the relaxation are still in debate despite great efforts devoted to this problem for decades. Here we report experimental evidence on the structural origins of Johari-Goldstein relaxation in an ultra-quenched metallic glass. The measured activation energy of the relaxation (~26 times of the product of gas constant and glass transition temperature) is consistent with the dynamic characteristics of Johari-Goldstein relaxation. Synchrotron X-ray investigations demonstrate that the relaxation originates from short-range collective rearrangements of large solvent atoms, which can be realized by local cooperative bonding switch. Our observations provide experimental insights into the atomic mechanisms of Johari-Goldstein relaxation and will be helpful in understanding the low-temperature dynamics and properties of metallic glasses.

Excellent capability in degrading azo dyes by MgZn-based metallic glass powders

The lack of new functional applications for metallic glasses hampers further development of these fascinating materials. In this letter, we report for the first time that the MgZn-based metallic glass powders have excellent functional ability in degrading azo dyes which are typical organic water pollutants. Their azo dye degradation efficiency is about 1000 times higher than that of commercial crystalline Fe powders, and 20 times higher than the Mg-Zn alloy crystalline counterparts. The high Zn content in the amorphous Mg-based alloy enables a greater corrosion resistance in water and higher reaction efficiency with azo dye compared to crystalline Mg. Even under complex environmental conditions, the MgZn-based metallic glass powders retain high reaction efficiency. Our work opens up a new opportunity for functional applications of metallic glasses.

Correlation between structural relaxation and shear transformation zone volume of a bulk metallic glass

The effect of structural relaxation on shear transformation zones (STZs) in a Zr70Ni16Cu6Al8 glassy alloy is evaluated. Upon annealing, the measured STZ size dramatically decreases with moderate augment of mass density caused by the increase of icosahedra short-range orders. The greater atomic packing density gives rise to involvement of lesser atoms in the formation of STZs and thereby degradation of ductility. This study demonstrates that STZ volume is a key parameter reflecting the intrinsic relationship between atomic structure and mechanical properties of metallic glasses.

Deformation behavior of metallic glass thin films

We report room-temperature deformation behavior of damage-free metallic glass films characterized by nanoindentation and atomic force microscopy. The glass films with thicknesses ranging from 5u2009μm down to ∼60u2009nm plastically deform by shear bands when subjected to both spherical and sharp Berkovich indenters. Importantly, we found that gallium contamination from focus ion beam (FIB) milling significantly suppresses shear band formation, indicating that the absence of shear bands in FIB milled samples may be caused by gallium irradiation damage, rather than sample size effect. Finite element simulation reveals that a high stress gradient at the film/substrate interface promotes the plastic deformation of the thin films but does not give rise to significant strain inhomogeneity.