Stability And Cluster Models Of Zr-based Bulk Amorphous Alloys

Amorphous materials, counterpart to traditional crystalline materials, mainly include oxide glasses, macromolecule polymers, semiconductors in amorphous state and metallic glasses. Having unique physical and chemical properties due to their disorder structures, the investigation on such materials has been becoming the forefront of condensed physics and design to new materials.In the introduction, the development and present status of amorphous alloys have been reviewed first. Then certain known results were summarized, capping glass-forming ability, structural relaxation and devitrification, as well as the structural models on the amorphous. Additionally, we prospected the potential applications of amorphous alloys as nano-composites with high mechanical properties and high magnetic properties, respectively.As a metastable phase, the structure of amorphous evolves into stable phases with the increasing of temperature, resulting in the properties of amorphous deteriorated eventually. Therefore, the stability of amorphous is one of the important factors confining their practical applications. On the one hand, we studied the effect of sub-Tg pre-relaxation, dynamic load and super high magnetic field on the stability of amorphous alloy with nominal composition of ZreiAlgNiisCun, and analyzed the reasons for the change of stability under each certain condition. On the other hand, we thought that there should exist common structural characteristics between the precipitates and their mother phase according to structural transmission, especially keeping in the local structure region. From the clusters of view, we sought the relations between the stability of amorphous and their internal clusters, the structural similarity in clusters of the primary phases and their electronic structures by discrete variational method based on the first-principles theory. Finally, We investigated the structural evolutions from quasicrystal to Bergman phases in TiZrNi system and in ZrTiAlCu, ZrTiAINi alloys with change in content between Zr and Ti, which further confirmed that there exists structural community among such phases.The investigation showed that the pre-relaxation and dynamic load promote the ujatallization while super high magnetic field delays this process seriously. The stability of amorphous to some extent is affected by external conditions on the formation of critical nucleus, namely, the clusters in the short-range order.The results of EXAFS indicated that there exist similar nearest coordination of atoms in the Zr-Ni, Zr-Cu amorphous alloys and their crystalline with same compositions, By using discrete variational method, being suitable for the calculation of clusters, the effect of Al and other elements on the stability of such two kinds of amorphous has been studied. The results demonstrated that thein (Abstract)stability of amorphous is related to the atomic affinity in the clusters and reflected by the Fermi level lying at the energy gap, in coincidence with the Nagel-Tauc conjecture.The devitrification products of Zr-based BAA are usually some of quasicrystals, fcc-Zr2Ni, fcc-MgCu2 type, ll-Zr2Cu, hp-Zr6ANi or hp-MgZn2 type phases. Structural analysis showed that icosahedron and Gaskell polyhedron are mainly two kinds of building blocks of them. The two-shell Bergman clusters stacked by dual-icosahedra exist in fccZNi, fcc-MgCu2 and hp-MgZn2 type phases. In tlZCu, the cluster transforms into truncated octahedron distorted by icosahedron slightly. But in hp-Zr6ANi, the polyhedron centered by Zr is composed of a pentagonal prism capped by two pentagonal pyramids, which can also be derived from an icosahedron when rotating two opposite pentagonal pyramids by 36 degree relatively. If Al or Ni being regarded as the center, the Gaskell polyhedron, trigonal prism capped by three half octahedra, can be obtained. Although such structure is similar to the local units pointed out by Gaskell for Metal-Metalloid alloys, the packing mode in the phases is different.Based on Bergman clusters, and using discrete var...