Characterization of the structure, stability, mechanical and electrochemical properties of metallic glasses

Resumen

Metallic glasses are often referred as glassy or amorphous alloys. They lack long-range order and microstructural defects that are characteristics in crystals, such as grain and phase boundaries and dislocations. These new materials have demonstrated very interesting structural and mechanical properties derived from their homogeneity in composition and the absence of grain boundaries. Structural, mechanical or chemical properties, among others, may be even superior to those observed in conventional metallic alloys, and therefore attracted great scientific and technological interest. In this thesis project three different families of metallic glasses were selected to achieve a better understanding of amorphous alloys. First, a Ce-based alloy has been used to analyze a polyamorphic transition upon application of pressure to a more densely packed structure. X-ray diffraction and inelastic x-ray scattering data show a polyamorphic transition in the 2-10 GPa range, and this transition presents a hysteresis cycle between both compression and decompression data. The effect of this transition on mechanical properties is then evaluated. Second, a family of Fe-based metallic glasses, or amorphous steels, was selected to study their mechanical and electrochemical properties as a function of the structure and composition. The composition of the base alloy was first modified by addition of Yttrium in different concentrations as microalloying element and the structure was changed by thermal annealing, forming intermediate crystal/amorphous composites, up to a complete crystallization state. Finally, an entirely new alloy for biocompatible purposes has been designed, synthesized, and characterized. The basic structural characterization of this new Zr-Ti based amorphous alloy shows that is possible to produce the amorphous state in an alloy that does not contain toxic or unhealthy elements.