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首页> 外文学位 >Microscale Mechanical Deformation Behaviors and Mechanisms in Bulk Metallic Glasses Investigated with Micropillar Compression Experiments.
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Microscale Mechanical Deformation Behaviors and Mechanisms in Bulk Metallic Glasses Investigated with Micropillar Compression Experiments.

机译：微柱压缩实验研究了大块金属玻璃的微观机械变形行为和机理。

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摘要

Over the past years of my PhD study, the focused-ion-beam (FIB) based microcompression experiment has been thoroughly investigated with respect to the small-scale deformation in metallic glasses. It was then utilized to explore the elastic and plastic deformation mechanisms in metallic glasses. To this end, micropillars with varying sample sizes and aspect ratios were fabricated by the FIB technique and subsequently compressed on a modified nanoindentation system.;An improved formula for the measurement of the Young's modulus was derived by adding a geometrical prefactor to the Sneddon's solution. Through the formula, geometry-independent Young's moduli were extracted from microcompression experiments, which are consistent with nanoindentation results. Furthermore, cyclic microcompression was developed, which revealed reversible inelastic deformation in the apparent elastic regime through high-frequency cyclic loading. The reversible inelastic deformation manifests as hysteric loops in cyclic microcompression and can be captured by the Kelvin-type viscoelastic model. The experimental results indicate that the free-volume zones behave essentially like supercooled liquids with an effective viscosity on the order of 1 x 108 Pas.;The microscopic yield strengths were first extracted with a formula derived based on the Mohr-Coulomb law to account for the geometrical effects from the tapered micropillar and the results showed a weak size effect on the yield strengths of a variety of metallic-glass alloys, which can be attributed to Weibull statistics. The nature of the yielding phenomenon was explored with the cyclic micro-compression approach. Through cyclic microcompression of a Zr-based metallic glass, it can be demonstrated that its yielding stress increases at higher applied stress rate but its yielding strain is kept at a constant of ~ 2%.;The room-temperature post-yielding deformation behavior of metallic glasses is characterized by flow serrations, which were found sample geometry dependent. The geometry effect is implicative of an intrinsic ductile to brittle transition mechanism in metallic glasses, which can be formulated using the principle of energy balance. As consistent with the findings from solid micropillars, a microscale hollow pillar experiment was devised to further understand the geometry dependence of shear banding, which showed enhanced shear-band stability with the decreasing thickness of the hollow micropillars.
机译：在我的博士研究的过去几年中，基于聚焦离子束（FIB）的微压缩实验已针对金属玻璃的小尺寸变形进行了彻底研究。然后，它被用于探索金属玻璃中的弹性和塑性变形机制。为此，通过FIB技术制造了具有不同样本大小和纵横比的微柱，然后将其压缩在改进的纳米压痕系统上;通过在Sneddon溶液中添加几何预因子得出了改进的杨氏模量测量公式。通过该公式，从微压缩实验中提取了与几何无关的杨氏模量，这与纳米压痕结果一致。此外，开发了循环微压缩，它通过高频循环载荷在表观弹性范围内揭示了可逆的非弹性变形。可逆的非弹性变形在循环微压缩中表现为磁滞回线，并且可以通过开尔文型粘弹性模型捕获。实验结果表明，自由体积区的行为基本类似于过冷液体，有效粘度约为1 x 108 Pas .;首先使用基于Mohr-Coulomb定律得出的公式提取微观屈服强度锥形微柱的几何效应和结果表明，尺寸变化对各种金属-玻璃合金的屈服强度具有微弱的影响，这可以归因于Weibull统计。利用循环微压缩方法探索了屈服现象的性质。通过Zr基金属玻璃的循环微压缩，可以证明在较高的施加应力速率下其屈服应力增加，但其屈服应变保持在〜2％的恒定值。金属玻璃的特征是流锯齿，这些锯齿与样品的几何形状有关。几何效应暗示着金属玻璃固有的韧性到脆性转变机制，可以使用能量平衡原理来表述。与实心微柱的发现一致，设计了一个微型空心柱实验以进一步了解剪切带的几何形状依赖性，该关系表明随着空心微柱厚度的减小，剪切带的稳定性增强。

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  • 作者

    Ye, Jianchao.;

  • 作者单位

    Hong Kong Polytechnic University (Hong Kong).;

  • 授予单位 Hong Kong Polytechnic University (Hong Kong).;
  • 学科 Engineering Materials Science.
  • 学位 Ph.D.
  • 年度 2011
  • 页码 180 p.
  • 总页数 180
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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