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首页> 外文学位 >Mechanism for gamma-precipitation in aluminum-silver alloys and self-assembly of polyelectrolytes: Modeling of complex layered materials.
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Mechanism for gamma-precipitation in aluminum-silver alloys and self-assembly of polyelectrolytes: Modeling of complex layered materials.

机译：铝-银合金中γ沉淀的机理和聚电解质的自组装：复杂层状材料的建模。

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摘要

In fcc Al, stacking fault energy (SFE) is high at ∼150 mJ/m 2, inhibiting stacking fault (SF) formation and dislocation motion. Yet hcp precipitates form rapidly in Al-rich face centered cubic (fcc) Al-Ag, even as the energy difference DeltaEhcp-fcc between hcp and fcc solid solution increases with Ag content. Using ab initio methods, based on electron density functional theory (DFT), I have calculated SFE versus distance of a Ag (111) plane from intrinsic (isf), extrinsic (esf) and twin (tsf) defects. I have found that Ag solute adjacent to (111) shear planes greatly reduces the ideal shear strength in fcc Al-Ag solid solution. Now with an inhomogeneous distribution of solute, SF formation is favorable, especially when a Tungsten-Carbide-like structure of alternating AlAg hcp decorates defects. I have found that solute position relative to defect plane, i.e. lattice symmetry, combined with favorable solute mixing, i.e. alloy chemistry, significantly lower SFE. My results indicate that commonly quoted arguments relating gammaesf ∼ gammaisf ∼ 2gamma tsf ∼ DeltaEhcp-fcc hold only in cases that maintain symmetry of the underlying Bravais lattice, such as elemental metals and homogeneous solid-solution. I then provide a generalization of the relation that is applicable to more realistic systems. I show that this defect/solute-mediated, low energy pathway provides a local mechanism in inhomogeneous solid solutions for rapid hcp precipitation as observed in Al-rich fcc Al-Ag. I have used approximate unit cells with DFT calculation to estimate hcp precipitate/fcc interface energy in Al-Ag and found that classical nucleation theory in combination with dendritic growth of secondary, nucleating edge structures gives √t increase in hcp precipitate width-to-thickness aspect ratio with time t. My aspect-ratio model is the first theory of which I am aware that accurately predicts an increasing aspect ratio for Al-Ag hcp precipitates, as observed.
机译：在fcc Al中，堆垛层错能（SFE）约为150 mJ / m 2，抑制了堆垛层错（SF）的形成和位错运动。即使在hcp和fcc固溶体之间的能量差DeltaEhcp-fcc随着Ag含量的增加，hcp沉淀也会在富铝的面心立方（fcc）Al-Ag中迅速形成。使用从头算的方法，根据电子密度泛函理论（DFT），我计算了SFE对Ag（111）平面与固有（isf），非本征（esf）和孪晶（tsf）缺陷的距离。我发现与（111）剪切平面相邻的Ag溶质大大降低了fcc Al-Ag固溶体中的理想剪切强度。现在，由于溶质分布不均匀，SF形成是有利的，特别是当交替交替的AlAg hcp的类似碳化钨的结构装饰缺陷时。我发现相对于缺陷平面的溶质位置，即晶格对称性，与有利的溶质混合，即合金化学性质相结合，显着降低了SFE。我的结果表明，仅在保持基本Bravais晶格对称的情况下，例如元素金属和均质固溶体，与gammaesf〜gammaisf〜2gamma tsf〜DeltaEhcp-fcc有关的引证论点才成立。然后，我提供了适用于更实际系统的关系的概括。我表明，这种缺陷/溶质介导的低能途径在不均匀的固溶体中提供了一种局部机制，可以在富铝fcc Al-Ag中观察到快速hcp沉淀。我已经使用近似单位晶胞通过DFT计算来估计Al-Ag中的hcp沉淀/ fcc界面能，发现经典成核理论与次级成核边缘结构的树枝状生长相结合，使hcp沉淀的宽度-厚度增加√t长宽比随时间t我所知的长宽比模型是我所知道的第一个理论，该理论准确地预测了Al-Ag hcp沉淀物的长宽比增加。

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  • 作者

    Finkenstadt, Daniel Kris.;

  • 作者单位

    University of Illinois at Urbana-Champaign.;

  • 授予单位 University of Illinois at Urbana-Champaign.;
  • 学科 Physics Condensed Matter.; Engineering Materials Science.
  • 学位 Ph.D.
  • 年度 2005
  • 页码 131 p.
  • 总页数 131
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 工程材料学;
  • 关键词

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