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URN etd-1116109-202132
Author Yen-Huei Lai
Author's Email Address d953060006@student.nsysu.edu.tw
Statistics This thesis had been viewed 5355 times. Download 223 times.
Department Materials and Optoelectronic Science
Year 2009
Semester 1
Degree Ph.D.
Type of Document
Language English
Title Effects of Sample Size on Various Metallic Glass Micropillars in Microcompression
Date of Defense 2009-06-29
Page Count 204
Keyword
  • microcompression tests
  • sample size effect
  • metallic glass
  • Abstract Over the past decades, bulk metallic glasses (BMGs) have attracted extensive interests
    because of their unique properties such as good corrosion resistance, large elastic limit, as
    well as high strength and hardness. However, with the advent of micro-electro-mechanical
    systems (MEMS) and other microscaled devices, the fundamental properties of
    micrometer-sized BMGs have become increasingly more important. Thus, in this study, a
    methodology for performing uniaxial compression tests on BMGs having micron-sized
    dimensions is presented.
    Micropillar with diameters of 3.8, 1 and 0.7 μm are fabricated successfully from the
    Mg65Cu25Gd10 and Zr63.8Ni16.2Cu15Al5 BMGs using focus ion beam, and then tested in
    microcompression at room temperature and strain rates from 1 x 10-4 to 1 x 10-2 s-1.
    Microcompression tests on the Mg- and Zr-based BMG pillar samples have shown an
    obvious sample size effect, with the yield strength increasing with decreasing sample
    diameter. The strength increase can be rationalized by the Weibull statistics for brittle
    materials, and the Weibull moduli of the Mg- and Zr-based BMGs are estimated to be about
    35 and 60, respectively. The higher Weibull modulus of the Zr-based BMG is consistent with
    the more ductile nature of this system.
    In additions, high temperature microcompression tests are performed to investigate the
    deformation behavior of micron-sized Au49Ag5.5Pd2.3Cu26.9Si16.3 BMG pillar samples from
    room to their glass transition temperature (~400 K). For the 1 μm Au-based BMG pillars, a
    transition from inhomogeneous flow to homogeneous flow is clearly observed at or near the
    glass transition temperature. Specifically, the flow transition temperature is about 393 K atthe strain rate of 1 x 10-2 s-1.
    For the 3.8 μm Au-based BMG pillars, in order to investigate the homogeneous
    deformation behavior, microcompression tests are performed at 395.9-401.2 K. The strength
    is observed to decrease with increasing temperature and decreasing strain rate. Plastic flow
    behavior can be described by a shear transition zone model. The activation energy and the
    size of the basic flow unit are deduced and compared favorably with the theory.
    Advisory Committee
  • New-Jin Ho - chair
  • Liu-Win Chang - co-chair
  • Jinn-P. Chu - co-chair
  • Shian-Ching Jang - co-chair
  • Chih-Ching Huang - advisor
  • Files
  • etd-1116109-202132.pdf
  • indicate in-campus access immediately and off_campus access in a year
    Date of Submission 2009-11-16

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