Nonequilibrium Alloys in Systems with Positive Heat of Mixing

具有正混合热的系统中的非平衡合金

• 批准号: 0080361
• 负责人: En (Evan) Ma
• 金额: $ 36.19万
• 依托单位: Johns Hopkins University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2000
• 资助国家: 美国
• 起止时间: 2000-07-01 至 2003-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0080361&HistoricalAwards=false
• 关键词: Nonequilibrium; Alloys; Systems; Positive; Heat

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. ***

0080361 Ma这项研究着眼于在二元系统中产生的非平衡合金，表现出正的混合热。 它建立在最近的进展，了解这些阶段合金在固态使用机械铣削。几个未解决的基本问题，确定有关的结构和热力学性质的合金远离平衡。所研究的合金是通过使用共溅射技术的蒸气淬火制备的非晶相或高度过饱和的结晶固溶体。模型体系包括Ag-Ni、Cu-TA、Cu-Nb、Ag-Cu、Cu-Fe和Cu-Cr。 计划利用扩展X射线吸收精细结构（EXAFS）和X射线吸收近边结构（XANES）技术系统地研究局部原子级结构。短程聚类或订购的趋势和键长进行检查。 除了证明真正的原子级合金化，当地的环境信息将与热力学状态定量确定通过大量的量热表征的沉积箔。这项工作将确定相对于其他竞争对手形成的相稳定性的原因。还考虑了在同一系统中通过不同工艺路线获得的合金的相似性和差异性。 还将研究可能的分解和成分调节、对合金能量学和稳定性的影响，以及旋节分解与成核和生长的竞争机制。***