Medium-range structure and glass forming ability in Zr–Cu–Al bulk metallic glasses

Abstract Fluctuation electron microscopy experiments combined with hybrid reverse Monte Carlo modeling show a correlation between medium-range structure at the nanometer scale and glass forming ability in two Zr–Cu–Al bulk metallic glass (BMG) alloys. Both Zr 50 Cu 35 Al 15 and Zr 50 Cu 45 Al 5 exhibit two nanoscale structure types, one icosahedral and the other more crystal-like. In Zr 50 Cu 35 Al 15 , the poorer glass former, the crystal-like structure is more stable under annealing below the glass transition temperature, T g , than in Zr 50 Cu 45 Al 5 . Variable resolution fluctuation microscopy of the MRO clusters show that in Zr 50 Cu 35 Al 15 on sub- T g annealing, the crystal-like clusters shrink even as they grow more ordered, while icosahedral-like clusters grow. Overall, the results suggest that achieving better glass forming ability in this alloy system may depend more on destabilizing crystal-like structures than enhancing non-crystalline structures.