Glass Stability and Kinetic Analysis of Iron-Metalloid Bulk Metallic Glass

Multicomponent Fe-based bulk metallic glasses (BMGs) with a combination of excellent properties such as good soft magnetic properties, high strength, high hardness, and high corrosion resistance have attracted increasing attention both from a basic science research standpoint and due to their industrial application potential. However, many of the elemental additions which lead to the easiest glass formation are expensive. The identification of alloys composed of abundant and inexpensive elements that still retain excellent properties would promote applications for engineering and industry. In short, the development of the Fe-based BMG without any glass-forming metal elements and with high glass forming ability is desired.;This study shows that the thermal stability of the Fe-based alloys can be improved beyond a simple rule of mixtures prediction by utilizing a well-balance multi-metalloid approach. The kinetics aspect of glass-forming ability is studied experimentally for Fe-B-Si-P alloys. The systematic variation in alloy composition gives access to differences in phase selection and the final dimensions of glass formation. Two alloys, representing the best glass-forming composition and the poorest glass-forming composition, were studied in terms of their stability to crystallization, solidification microstructure evolution and thermal history. The utility of the wedge-casting technique is developed to examine bulk glass-forming alloys by combining multiple temperature profiles of the quenching melt with a measurement-based kinetic analysis of the phase selection competition and critical cooling rate conditions. Based upon direct thermal measurement, microstructural analysis and kinetic modeling, it was found that both representative alloys show a board spectrum of solidification microstructures which include a critical cooling rate range. The kinetic competition in the formation of certain phases can enhance or detract from the final dimension of bulk glass formation of the representative alloys. Practical strategies in crystallization kinetics analysis and microstructure control are developed to extend the knowledge of phase competition leading to successful synthesis of BMGs. Low cost Fe-metalloid BMGs will provide a great advantage for the transition to commercial applications when material cost is a critical issue.