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Since the discovery of metallic glass formation by ultra-rapid melt quenching at Caltech in 1959, it was thought that metallic glasses can be processed only as very thin ribbons or fine powders, due to the required high cooling rate, and that they are not stable above the glass transition temperature. This has severely limited the technological applications of metallic glasses which combine unique and desirable properties. Also, bulk glass forming metallic alloys have long been desired to improve our scientific knowledge of nucleation, crystal growth and other properties of undercooled metallic melts.
After the discovery of solid state amorphization in early eighties, there were several years of paused research on metallic glass formation by melt quenching. At the end of the last decade, a Japanese group in Sendai discovered new metallic systems, which require substantially lower cooling rates for glass formation than previous systems and which have high thermal stability above their glass transition temperature.
As a major contribution to a new era of metallic glasses, this thesis extended the formation and the thermal stability of metallic glasses to the extent that many potential uses of metallic glasses have come to the brink of reality. For the first time, the art of metallic glass making has become as easy as a single step alloy preparation using conventional metallurgical processing. The production of the larger bulk metallic glass specimens is limited only by the scale of equipment in our laboratory and not by limitations arising from the glass forming ability of the particular alloy. These new developments presented throughout this thesis may not only extend the applications of metallic glasses but they also allow us to study the properties of highly undercooled metallic melts which are very important in phenomena such as nucleation and crystal growth.
The thesis starts with an introductory chapter describing the art and science of metallic glasses prior to this work. Then, a critical review of the current knowledge of thermodynamics and kinetics of glass formation is given in chapter 2. In chapter 3, an example of a highly processable metallic glass alloy, [...], is presented along with its preparation methods. Its general characteristics which distinguish it from conventional metallic glasses are emphasized. This particular glassy alloy, [...], belongs to an exceptionally large family of excellent glass forming metallic systems, which were developed in the course of this thesis research. In chapter 4, various forms of heterogeneous nucleation,--an important phenomena in glass formation--are discussed with reference to several glass forming alloys. Finally, conditions for bulk glass formation are proposed in view of our current theoretical knowledge and experimental observations. Difficulties in attaining these conditions are also discussed and suggestions are made for finding other bulk glass forming alloys
