New insights into melt hydrogenation effects on glass-forming ability in a Zr-based bulk metallic glass

Notable improvements in the glass-forming ability (GFA) of Zr-based metallic glasses with melt hydrogenation have been reported in our previous studies. The effects of hydrogen on GFA are usually explained via short-range structural order, local symmetry, structural free-volume, and bonding character. To fundamentally understand why hydrogen enhances GFA, thermal analyses were carried out on a Zr55Cu30Ni5Al10 amorphous alloy to assess how hydrogen affected viscosity, fragility, critical cooling rate, and Gibbs free energy difference, ∆ G. Amorphous alloys subjected to melt hydrogenation were found to possess higher viscosity and lower fragility, indicating increased GFA. The critical cooling rate of hydrogenated alloy melts gradually decreased and the lowest critical cooling rate was 10 K/s when the alloy was fabricated in Ar + 10%H2. The liquid/solid ∆ G of melt‑hydrogenated alloy was significantly smaller than that of the equivalent non‑hydrogen alloy. From thermodynamic and dynamic perspectives, viscosity, fragility, critical cooling rate, and ∆ G demonstrated that melt hydrogenation improved these alloys' GFA and explained the present experimentally observed improvements in GFA.