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首页> 外文学位 >Nanometer-scale investigation of compositional and structural evolution during crystallization of melt-spun Co84Nb10B6 metallic glass.
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Nanometer-scale investigation of compositional and structural evolution during crystallization of melt-spun Co84Nb10B6 metallic glass.

机译：熔融纺制Co84Nb10B6金属玻璃结晶过程中组成和结构演变的纳米级研究。

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摘要

Nanocrystalline materials are increasingly showing progress in the quest to control the properties of a solid. As the building blocks of matter approach sizes on the order of 100 nanometers or less, nearly every physical property of the material is altered. One class of nanocrystalline material that has received considerable attention in recent decades and especially in the last several years is that of the metallic glass. This research project was performed in order to obtain a better understanding of the formation of nanocrystalline structure in a Co-based metallic glass.; Ribbons of a Co84Nb10B6 metallic glass were rapidly quenched by the melt spinning technique. Field Ion Microscopy (FIM), Atom Probe Field Ion Microscopy (APFIM) and Transmission Electron Microscopy (TEM) were applied to study the micro-structural and nanocompositional changes of Co84Nb10B6 due to annealing.; The as-quenched metallic glass was determined to be amorphous by FIM and APFIM. Subsequent annealing at various temperatures and times produced specimens in different stages of phase separation and nanocrystallinity. Crystal nuclei in specimens annealed for one hour at 500, 550, and 600 C were constant in size (4 nm) but increased in number density with increasing temperature. Annealing at 700 C for one hour produced a fully crystalline, three-phase material. The phases consist of a nanocrystalline boride phase, a nanocrystalline Co3Nb phase, both with average grain sizes of 20–50 nm, and a relatively pure cobalt matrix. The various phases exhibited significantly different field evaporation and imaging behavior in the FIM.; Prior to this work, it was hypothesized that boron atoms segregating to grain boundaries played a role in limiting the grain growth of this nanocrystalline material. The composition fluctuations across several grain boundaries were analyzed and there was no evidence of boron accumulation. The results of this work suggest another mechanism must be keeping the grains of this material in a nanocrystalline state. Such a hypothesis is presented at the conclusion of this work.
机译：纳米晶体材料在控制固体性质方面日益显示出进步。当物质的构造块接近100纳米或更小的尺寸时，几乎每种材料的物理特性都会发生变化。在最近几十年中，尤其是在最近几年中，引起人们广泛关注的一类纳米晶体材料是金属玻璃。进行该研究项目是为了更好地理解钴基金属玻璃中纳米晶体结构的形成。通过熔融纺丝技术将Co 84 Nb 10 B 6 金属玻璃带快速淬火。利用场离子显微镜（FIM），原子探针场离子显微镜（APFIM）和透射电子显微镜（TEM）研究Co 84 Nb 10 的微观结构和纳米组成变化。 sub> B 6 由于退火。通过FIM和APFIM确定淬火后的金属玻璃为非晶态。随后在不同的温度和时间进行退火，在相分离和纳米结晶度的不同阶段产生了样品。在500、550和600°C退火1小时的样品中的晶核大小不变（4 nm），但是随着温度的升高晶核数目增加。在700°C退火一小时，产生了一种完全结晶的三相材料。这些相包括纳米晶硼化物相，纳米晶Co 3 Nb相（均具有20–50 nm的平均晶粒尺寸）和相对纯的钴基质。在FIM中，各个阶段表现出明显不同的场蒸发和成像行为。在这项工作之前，假设硼原子偏析到晶界上起限制这种纳米晶体材料晶粒生长的作用。分析了跨几个晶界的成分波动，没有硼积累的迹象。这项工作的结果表明，另一种机制必须使这种材料的晶粒保持纳米晶态。在这项工作结束时提出了这样的假设。

著录项

  • 作者

    Lusby, Thomas Alan.;

  • 作者单位

    The Johns Hopkins University.;

  • 授予单位 The Johns Hopkins University.;
  • 学科 Engineering Materials Science.
  • 学位 Ph.D.
  • 年度 2000
  • 页码 134 p.
  • 总页数 134
  • 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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