Crystallization of zirconium palladium copper and zirconium nickel copper metallic glass

One interesting aspect of metallic glasses is the numerous instances of the deviation of the phase selection from the amorphous state to thermodynamically stable phases during the crystallization process. Their devitrification pathways allow us to study the relationship between the original amorphous structure and their crystalline counter parts. Among the various factors of phase selections, size and electronic effects have been most extensively studied. Elucidating the phase selection process of a glassy alloy will be helpful to fill in the puzzle of the changes from disordered to ordered structures. In this thesis, Two model Zr2PdxCu(1-x) and Zr2NixCu(1-x) (x = 0, 0.25, 0.5, 0.75 and 1) glassy systems were investigated since: (1) All of the samples can be made into a homogenous metallic glass; (2) The atomic radii differ from Pd to Cu is by 11%, while Ni has nearly the identical atomic size compare to Cu. Moreover, Pd and Ni differ by only one valence electron from Cu. Thus, these systems are ideal to test the idea of the effects of electronic structure and size factors; (3) The small number of components in these pseudo binary systems readily lend themselves to theoretical modeling.;Using high temperature X-ray diffraction (HTXRD) and thermal analysis, topological, size, electronic, bond and chemical distribution factors on crystallization selections in Zr2PdxCu(1-x) and Zr2 NixCu(1-x) metallic glass have been explored. All Zr2PdxCu(1-x) compositions share the same C11b phase with different pathways of meta-stable, icosahedral quasicrystalline phase (i-phase), and C16 phase formations. The quasicrystal phase formation is topologically related to the increasing icosahedral short range order (SRO) with Pd content in Zr 2PdxCu(1-x) system. Meta-stable C16 phase is competitive with C11b phase at x = 0.5, which is dominated by electronic structure rather than size effects. Cu-rich and Ni-rich compositions in Zr2NixCu(1-x) trend to divitrify to C11b or C16 phases respectively. In the proposed pseudo binary phase diagram, the domain of C16, C11b and co-existence phases are mainly related with the topology in the amorphous structure and formation enthalpies of crystalline phases.