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Plastic deformation in bulk metallic glasses characterized by nanoindentation creep.

机译：以纳米压痕蠕变为特征的块状金属玻璃的塑性变形。

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摘要

Plasticity and flow in metallic glasses (MGs) is believed to be the result of the activation of defects in the amorphous structure. These defects are regions of the glass, thought to be comprised of 10--100 atoms, which can undergo a localized rearrangement in response to a shear stress (tau) and are called shear transformation zones (STZs). This dissertation is an investigation strain rate-dependence of the hardness in three, Zr-based bulk metallic glasses (BMGs) to back out information about the STZs. The primary characterization technique is nanoindentation, which is capable of determining both the static materials properties, such as hardness and elastic modulus, as well as the time-dependent properties, which include information on the activation of flow defects. Other experimental techniques, such as differential scanning calorimetry and X-ray diffraction, were applied to measure the thermophysical properties of the BMGs. The low-stress activation energies (Delta G0*) for defect rearrangement are in the range 3.5--10 eV, and the stress-dependence of the activation energy is a power-law of the form DeltaG*(tau) ∼ taun , where n is measured to be in the range 1.5--2.0. From the measurements it is possible to estimate the volume of the STZ, O*, which has not been measured previously. , O* , is found to vary anywhere from 100--300 atomic volumes. In addition to the experiments conducted on the as-cast alloys for the three different Zr-Cu-Al compositions, similar tests were carried out on the same materials after they had been subjected to heat-treatment near the glass transition temperature. Not only are the characteristics of the STZs sensitive to the composition of the BMG, but they also exhibit substantial changes upon annealing; the quantities DeltaG0* and O* decrease by 10--30%. These latter results are in good agreement with expected trends and provide some insight into the relationship between the structure and dynamics in the MG.
机译：据信，金属玻璃（MGs）中的可塑性和流动是非晶态结构中缺陷激活的结果。这些缺陷是玻璃的区域，被认为由10--100个原子组成，可以响应剪切应力（tau）发生局部重排，称为玻璃化转变区（STZs）。本文研究了三种基于Zr的块状金属玻璃（BMG）的硬度与应变率的关系，以得出有关STZ的信息。主要的表征技术是纳米压痕，它能够确定静态材料的特性，例如硬度和弹性模量，以及随时间变化的特性，其中包括有关流动缺陷激活的信息。其他实验技术，例如差示扫描量热法和X射线衍射，也被用于测量BMG的热物理性质。用于缺陷重排的低应力活化能（Delta G0 *）在3.5--10 eV范围内，活化能的应力依赖性是DeltaG *（tau）〜taun形式的幂律，其中n的测量范围为1.5--2.0。根据测量结果，可以估算之前未测量的STZ的体积O *。 O *被发现在100--300原子体积范围内变化。除了在三种不同的Zr-Cu-Al组成的铸态合金上进行的实验之外，对相同的材料在接近玻璃化转变温度的条件下进行热处理后，还对它们进行了类似的测试。 STZ的特性不仅对BMG的成分敏感，而且在退火后它们也表现出很大的变化。 DeltaG0 *和O *的数量减少了10--30％。后者的结果与预期趋势非常吻合，并为MG中的结构和动力学之间的关系提供了一些见识。

著录项

  • 作者

    Puthoff, Jonathan B.;

  • 作者单位

    The University of Wisconsin - Madison.;

  • 授予单位 The University of Wisconsin - Madison.;
  • 学科 Engineering Materials Science.
  • 学位 Ph.D.
  • 年度 2009
  • 页码 200 p.
  • 总页数 200
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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