| The current class of amorphous Fe-based alloys, also referred to as amorphous steels, possess some outstanding physical properties, including high specific strength, elastic modulus, and excellent corrosion resistance, as well as maintaining fairly low cost. However, thermally-induced embrittlement and insufficient overall ductility are detrimental factors that prohibit amorphous steels from being widely used as structural materials for civilian and military applications. Also, the desire to continuously enlarge the physical size of amorphous alloys, which requires significant improvement of the glass formability, is another hurdle that requires more scientific understanding in order to promote their future application. Consequently, obtaining systematic and detailed characterizations of amorphous alloys from structural and electronic aspects are important for future improvements in their development. In this research, two directions are focused on in characterizing these effects. First, studying the crystallization processes can help gain insight as to the alloy's overall stability. Measuring formation kinetics of crystalline phases that result and the atomic segregation mechanisms associated with devitrification can be employed to interpret the factors contributing to the glass formability. Second, examining the electronic and atomic structures in the vitrified state can assist in determining effects associated with bonding strength and electronic interactions among the various elements, which can be correlated with glass formability and the alloy's fracture behavior when key elements are added to bring the alloy through the ductile-to-brittle transition. The characterization methods utilized in this research involve the complementary studies of crystallization sequences, phase identification, growth kinetics, chemical and structural analyses, as well as the atomic and electronic structure examination in the vitrified state of the alloys. Differential thermal analysis (DTA), X-ray diffraction (XRD), three-dimensional atom probe (3DAP), and conventional and analytical transmission electron microscopy (TEM) are employed to carry out these studies. Detailed investigation on the atomic and electronic structure in the undercooled amorphous region of the alloys is implemented with XRD, and electron energy loss spectroscopy (EELS). |
