【作者】 王晓东；

【导师】 齐民； 董闯；

【作者基本信息】 大连理工大学 ， 材料学， 2003， 博士

【摘要】 非晶态材料是相对于传统的晶态材料而言的。主要包括氧化物玻璃，高分子聚合物，非晶态半导体以及金属玻璃，由于其结构的无序性而表现出的独特物理与化学特性，已成为凝聚态物理与新材料设计的前沿课题。 本文首先回顾了非晶合金的发展历史以及国内外的研究现状；总结了人们在非晶的形成能力，结构弛豫和晶化，以及结构模型方面的研究成果；并讨论了非晶合金在纳米复合方面的潜在应用和面临的问题。 非晶合金作为一种亚稳相，随着温度的升高，会发生一系列的结构演化，最终形成稳定的晶化相导致性能的恶化。因此，非晶的稳定性是决定非晶应用范围的重要因素之一。本文首先考察了低于Tg温度的退火、动载荷以及超强磁场对Zr₆₂Al₈Ni₁₃Cu₁₇非晶合金晶化过程的影响，分析非晶合金在特定条件下的稳定性变化。另一方面，根据组织遗传性原理，认为析出相必然保留着与母相的某些结构的特征，尤其在局域结构范围内。从团簇的角度，引入基于第一性原理的离散变分法理论，考察了非晶合金的稳定性与其团簇电子结构的关系；领先晶化相间的结构共性及其电子结构。然后在TiZrNi合金系中，分析了从准晶到Bergman相的结构变化规律和在zrTiAlCu，ZrTiAlNi合金中，析出相的结构随Ti／Zr比的变化规律，进一步证实这些合金相间的结构共性。 研究表明预弛豫和动载荷促进了该合金的晶化转变，而超强磁场则对之起到明显抑制作用。非晶稳定性很大程度取决于外界条件对临界晶核形成的影响，换句话说，即短程序范围内团簇的稳定性。 EXAFS的结果表明Zr-Ni，Zr-Cu非晶合金与其同成分的晶化相间存在相近的近邻原子排列。采用适合于团簇计算的离散变分Xα方法，讨论了Al及其它合金元素对这两类非晶合金稳定性的影响，发现非晶的稳定性与团簇内原子间的亲和力密切相关，稳定非晶的Fermi能级位于能隙处，基本满足Nagel-Tauc推论。 对Zr基大块非晶合金的常见晶化产物—准晶，fcc-Zr₂Ni或MgCu₂型相，tI-Zr₂Cu，hp-Zr₆Al₂Ni或hp-MgZn₂型相的团簇分析表明：这些合金相主要基于两种结构单元，二十面体和Gaskell多面体结构。fcc-Zr₂Ni，fcc-MgCu₂以及hp_MgZn₂型相中存在由双生二十面体堆垛的两壳层Bergman团簇；在tI-Zr₂Cu中，团簇转变为与二十面体相关的截角八面体堆垛结构；而在hp-Zr₆Al₂Ni中，以Zr原子为中心，存在五棱柱覆盖两个五棱锥的结构单元，若使得两个五棱锥相对倾转36°，其将会转变为二十面体结构，而以Ni，Al原子为中心则存在Gaskell多面体（三棱柱覆盖三个半八面体结构）。虽然这种结构类似于Gaskell提出的金属．类金属（T₃M型）非晶的局域结构单元，但具体的堆垛模式发生了改变。 根据Bergman团簇模型，同样采用离散变分Xα方法考察三种Bergman团簇的稳定性。电子结构的计算表明，三种团簇的态密度曲线和（100）晶面上电荷密度的分布反映出的fcc相和hp相的稳定性与实验结果基本一致。说明摘要（Abstract）这三种相的稳定性可以通过其中的Bergman团簇来反映。同时也证实了“要提高非晶形成能力，并不只是要提高液相的稳定性，而且要使得对应的晶体相失稳”的观点。 一定量的Fe可以促进TizrNi准晶向cF96相转变，而AI则促进其向hP（C14）相转变。在Zr64CuZsAls非晶中，用Ti置换Zr，随着Ti含量的增加，析出相为非晶加tl一ZrZCu，非晶加hp（C14），最终完全为hp（C14）相。在 Zr6oNiZoA12。非晶中，同样用Ti置换zr，so，oTi时析出相为非晶加hp一zr6A12Ni以及少量hp（e14），巧%Ti时为hp一zr6A12Ni与hP（C 14）相的混合。这种析出相的变化规律也进一步说明在这些合金相间存在结构的共性，反映了局域团簇的演化趋势。 合金中的团簇可以部分反映出块体材料的特性，展望未来，若以团簇作为合金化设计考虑的基元，通过控制团簇稳定存在的条件，选择不同特性的团簇组合，将会设计出具有不同特性的新型材料。更多还原

【Abstract】 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更多还原