Competing microstructure and crystalline phase formation and their roles in glass formability: a molecular dynamics study

Glass formation is often considered as the transition from a liquid to a surviving non-crystalline phase when all crystallizations fail. What the competing microstructures and crystalline phases are and precisely how they affect the glass formation are important issues that need to be resolved. In this work, we report on a systematic investigation that addresses several aspects of the issues using molecular dynamics simulation. A binary hard sphere model with a purely repulsive interatomic interaction is adopted due to its fast crystallization rates and identifiable complex crystalline phases competing with glass formation. Various microstructure and crystalline phases are identified and their roles in affecting the glass formation are analyzed. Our results provide an independent confirmation that glass formation is a result of the competing phase formation where the times needed for either the crystal nucleation or initial growth of the crystal nucleus exceed the time scales for cooling a glass-forming liquid. The limiting times are critically determined by intrinsic material properties and vary in different systems. Mechanisms of atomic size effect on glass transition and the limitations in the existing theories of the atomic size effect on glass formability are discussed.