Glass Formability and Diffusion Mechanisms in Bulk Metallic Glasses and Supercooled Liquids

摘要

Three properties of bulk metallic glasses were investigated: (1) atomic motions; (2) characteristics of bonding and electronic states; (3) fracture. Atomic motion in glassy PdNiCuP was investigated by NMR over a wide temperature range from below the glass transition temperature Tg to above the liquidus temperature Tliq. This study reveals the temperature in the supercooled liquid region, below which motions of different elements begin to diverge. It sheds light on the nature of the crossover temperature Tc proposed by mode coupling theory. Also, hopping was shown to persist below Tg. The electronic states of various metallic glasses were studied by NMR including CuZrAl, Ce-based, and Y-based alloys. Results established some correlation between the glass forming ability and the characteristics of electronic states. This sheds light on the structure and formation of metallic glasses. Finally, we studied the fracture surfaces of various bulk metallic glasses including the brittle Mg-based bulk metallic glass. We established a clear correlation between the fracture toughness and plastic process zone size for various glasses. The results indicate that the fracture in brittle metallic glassy materials might also proceed through the local softening mechanism but at different length scales.