Nonequilibrium Alloys in Systems with Positive Heat of Mixing

这项研究着眼于在二元体系中产生的非平衡合金，表现出正的混合热。它建立在了解使用机械球磨在固态中合金化这类相的最新进展的基础上。关于远离平衡生产的合金的结构和热力学性质，确定了几个尚未解决的基本问题。被研究的合金是通过共溅射技术通过蒸气淬火获得的非晶相或高过饱和晶态固溶体。模型体系包括Ag-Ni、铜-TA、铜-Nb、Ag-铜、铜-铁、铜-铬。该计划是利用扩展X射线吸收精细结构(EXAFS)和X射线近边吸收结构(XANES)技术系统地研究局域原子级结构。考察了短程聚集或有序倾向和键长。除了证明真正的原子水平的合金化，局部环境信息将与通过广泛的沉积箔的量热表征而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相稳定的原因。还考虑了在同一系统中通过不同的加工路线获得的合金的异同。可能的分解和成分调制，对合金能量学和稳定性的影响，以及调幅分解与形核和生长的竞争机制，也将被研究。***

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. ***