Nonequilibrium Alloys in Systems with Positive Heat of Mixing

[00:80361]这项研究着眼于在二元系统中产生的非平衡合金，它们表现出正的混合热。它建立在最近的进展，了解这些相合金在固态使用机械铣削。几个未解决的基本问题，确定了有关结构和热力学性质的合金生产远离平衡。要研究的合金是非晶相或高度过饱和的结晶固溶体，通过气相淬火采用共溅射技术制备。模型体系包括Ag-Ni、Cu-TA、Cu-Nb、Ag-Cu、Cu-Fe和Cu-Cr。该计划是利用扩展x射线吸收精细结构（EXAFS）和x射线吸收近边缘结构（XANES）技术系统地研究局部原子水平结构。研究了短程聚类或有序趋势和键长。除了证明真正的原子级合金化之外，局部环境信息将与通过沉积箔的广泛量热表征定量确定的热力学状态相关联。这项工作将确定相对于其他竞争对手形成的阶段稳定的原因。在同一体系中，通过不同的工艺路线获得合金的异同。可能的分解和成分调节，对合金能量学和稳定性的影响，以及独立分解与成核和生长的竞争机制，也将被检查。＊＊＊

0080361MaThis research looks at nonequilibrium alloys created in binary systems exhibiting a positive heat of mixing. It builds on recent progress in understanding such phases alloyed in the solid state using mechanical milling. Several unresolved fundamental issues are identified regarding the structural and thermodynamic nature of alloys produced far from equilibrium. The alloys to be studied are amorphous phases or highly supersaturated crystalline solid solutions prepared through vapor quenching using a co-sputtering technique. The model systems include Ag-Ni, Cu-TA, Cu-Nb, Ag-Cu, Cu-Fe, and Cu-Cr. The plan is to systematically study the local atomic-level structure using Extended X-ray Absorption Fine Structure (EXAFS) and X-ray Absorption Near Edge Structure (XANES) techniques. Short-range clustering or ordering tendencies and bond lengths are examined. In addition to proving true atomic-level alloying, local environment information will be correlated with the thermodynamic states quantitatively determined through extensive calorimetric characterizations of the deposited foils. %%%This work will identify the reasons for the stability of the phases formed relative to other competitors. The similarities and differences for alloys obtained in the same system through different processing routes are also considered. Possible decomposition and compositional modulations, effects on alloy energetics and stability, as well as competing mechanisms of spinodal decomposition versus nucleation and growth, will also be examined. ***