Hydrogen microalloying depresses the crystallization in metallic glass-forming liquids

Implementing hydrogen microalloying to metallic glasses can typically enhance their glass-forming ability, as proven in our recent experiments. With the aim of discerning the physical origins about this situation, we applied molecular dynamics simulations in this work to investigate the role of trace hydrogen additions on the temperature dependence of transport properties and atomic structure in both Zr-Cu and Ni-Al systems. Our results demonstrate that, while hydrogen alloying can indeed accelerate atomic dynamics, it paradoxically enhances the dynamic heterogeneity of metallic glass-forming liquids, and finally creates frustration against crystallization. By systematic scrutiny of the structural evolution during the dynamic arrest, the increased crystallization resistance of H-alloyed MGs should be attributed to both the formation of more solid-like order and the reservation of more liquid-like one upon the glass transition, forming a more disordered but geometrically stable amorphous structure. The current findings not only show how the glass-forming ability can be significantly improved in metallic glasses, but we also regard this understanding as a step forward to decoding the salient underlying mechanisms for the thermodynamics, kinetics and atomic structure of these materials.