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Time-resolved lattice measurements of shock-induced phase transitions in polycrystalline materials.

机译:时间分辨的晶格测量,用于测量多晶材料中的冲击诱导相变。

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摘要

The response of materials under extreme temperature and pressure conditions is a topic of great significance because of its relevance in astrophysics, geophysics, and inertial confinement fusion. In recent years, environments exceeding several hundred gigapascals in pressure have been produced in the laboratory via laser-based dynamic loading techniques. Shock-loading is of particular interest as the shock provides a fiducial for measuring time-dependent processes in the lattice such as phase transitions. Time-resolved x-ray diffraction is the only technique that offers an insight into these shock-induced processes at the relevant spatial (atomic) and temporal scales.;In this study, nanosecond resolution x-ray diffraction techniques were developed and implemented towards the study of shock-induced phase transitions in polycrystalline materials. More specifically, the capability of a focusing x-ray diffraction geometry in high-resolution in situ lattice measurements was demonstrated by probing shock-compressed Cu and amorphous metallic glass samples. In addition, simultaneous lattice and free surface velocity measurements of shock-compressed Mg in the ambient hexagonal close packed (hcp) and shock-induced body centered cubic (bcc) phases between 12 and 45 GPa were performed. These measurements revealed x-ray diffraction signals consistent with a compressed bcc lattice above a shock pressure of 26.2+/-1.3 GPa, thus capturing for the first time direct lattice evidence of a shock-induced hcp to bcc phase transition in Mg. Our measurement of the hcp-bcc phase boundary in Mg was found to be consistent with the calculated boundary from generalized pseudopotential theory in the pressure and temperature region intersected by the principal shock Hugoniot. Furthermore, the subnanosecond timescale of the phase transition implied by the shock-loading conditions was in agreement with the kinetics of a martensitic transformation. In conclusion, we report on the progress and future work towards time-resolved x-ray diffraction measurements probing solid-liquid phase transitions in high Z polycrystalline materials, specifically Bi.
机译:材料在极端温度和压力条件下的响应具有重要意义,因为它与天体物理学,地球物理学和惯性约束聚变有关。近年来,通过基于激光的动态加载技术在实验室中产生了超过数百吉帕的压力环境。冲击载荷特别受关注,因为冲击为测量晶格中随时间变化的过程(例如相变)提供了基准。时间分辨X射线衍射是唯一可洞察相关空间(原子)和时间尺度上这些激振过程的技术。在本研究中,纳秒分辨率X射线衍射技术已被开发并应用于多晶材料中冲击诱导的相变的研究。更具体地,通过探测冲击压缩的Cu和非晶态金属玻璃样品证明了在高分辨率原位晶格测量中聚焦x射线衍射几何学的能力。另外,在环境六方密堆积(hcp)和冲击诱发的体心立方(bcc)相之间的冲击压缩镁的12和45 GPa之间进行了同时晶格和自由表面速度测量。这些测量结果揭示了与高于26.2 +/- 1.3 GPa的冲击压力的压缩bcc晶格一致的x射线衍射信号,从而首次捕获了晶格中镁引起的hcp到bcc相激转变的直接晶格证据。发现我们在Mg中的hcp-bcc相界的测量结果与广义伪电势理论在主激波Hugoniot相交的压力和温度区域中所计算的边界相一致。此外,冲击载荷条件隐含的亚纳秒级时标与马氏体相变动力学是一致的。总之,我们报告了时间分辨的X射线衍射测量的进展和未来的工作,这些测量用于探测高Z多晶材料(特别是Bi)中的固液相转变。

著录项

  • 作者

    Milathianaki, Despina.;

  • 作者单位

    The University of Texas at Austin.;

  • 授予单位 The University of Texas at Austin.;
  • 学科 Chemistry, Polymer.;Engineering, Materials Science.;Physics, Fluid and Plasma.;Physics, Condensed Matter.
  • 学位 Ph.D.
  • 年度 2010
  • 页码 215 p.
  • 总页数 215
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 ;
  • 原文服务方 国家工程技术数字图书馆
  • 关键词

    ;

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