Structural Evolution, Chemical Order, and Crystallization of Metallic Liquids and Glasses

Download or read book Structural Evolution, Chemical Order, and Crystallization of Metallic Liquids and Glasses written by Mark Lyell Johnson and published by . This book was released on 2015 with total page 291 pages. Available in PDF, EPUB and Kindle. Book excerpt: Over the last 60 years, bulk metallic glasses have emerged as a new class of materials with highly desirable material properties. Their high strength, high elasticity, and corrosion resistance are attractive properties for viable commercial products. At its core, material properties are directly related to the underlying microstructure. By understanding the structural and chemical order in the liquid and undercooled liquid and their relationship to thermophysical properties such as viscosity, a greater understanding of bulk metallic glass formation can be achieved. In this dissertation, electrostatic levitation techniques are used to study the liquid in a containerless environment using a combination of X-ray and neutron scattering techniques. An X-ray diffraction study of liquid and glass Ni-Nb(-Ta) alloys reveals that an acceleration in the rate of structural ordering must take place near the glass transition, providing the framework for a structural description of fragility. X-ray diffraction and thermophysical property measurements of Zr-Ni binary alloys further characterize the structural connection to viscosity, and reveal signatures of chemical ordering in the liquid. By combining X-ray and neutron scattering measurements, the topological and chemical order in Zr80Pt20 and Zr77Rh23 liquids is characterized. Very different chemical order is found between these alloys, despite their remarkable similarity in topological order. Due to this structural similarity, a new metastable phase is predicted and later identified emerging from a deeply supercooled Zr77Rh23 liquid. Zr77Rh23 is found to have many metastable crystallization pathways, which are further characterized here. Through simultaneous wide-angle and small-angle X-ray scattering, the devitrification behavior of a bulk metallic glass (Vitreloy 105) is investigated and is found to decompose into two distinct compositions during crystallization. By understanding crystallization pathways in good glass-forming alloys, a better understanding of glass formation and its connections to structural and thermophysical properties can be achieved.