Title page for etd-0611112-081034


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URN etd-0611112-081034
Author Hao-Jan Pei
Author's Email Address No Public.
Statistics This thesis had been viewed 5338 times. Download 406 times.
Department Materials and Optoelectronic Science
Year 2011
Semester 2
Degree Ph.D.
Type of Document
Language English
Title Tensile Response of Amorphous/Nanocrystalline ZrCu/Cu Multilayered Thin Films
Date of Defense 2012-06-06
Page Count 223
Keyword
  • tensile testing
  • sputtering processes
  • multilayered thin films
  • nanocrystalline
  • amorphous
  • rule of mixtures
  • graded interfaces
  • Abstract In this research, the amorphous/nanocrystalline ZrCu/Cu multilayered thin films with various conditions such as individual layer thickness, total layer thickness, and interface type have been successfully fabricated by the multi-gun sputtering processes. To investigate the mechanical properties and deformation behaviors of substrate-supported ZrCu/Cu multilayered thin films, these films deposited on the Cu or polyimide foils were prepared for tensile testing.
    Firstly, the tensile behaviors of the monolithic ZrCu thin film metallic glass and the ZrCu/Cu multilayered thin films deposited on the pure Cu foils are systematically examined. The extracted tensile modulus and strength of the 1-μm-thick multilayered thin films are in good agreement with the theoretical iso-strain rule of mixture prediction. The extracted 2-μm-thick multilayered film data are lower, but can be corrected back by considering the actual intact cross-sectional area during the tensile loading. Moreover, the current results reveal that the ZrCu/Cu multilayered coating exhibit much better tensile performance than the monolithic ZrCu coating. It indicates that the amorphous/nanocrystalline multilayered thin film structure can certainly enhance the mechanical properties of monolithic thin film metallic glasses under tension.
    Secondly, for the further investigation of tensile response, the polyimide-supported amorphous/nanocrystalline ZrCu/Cu multilayered thin films with various individual layer thicknesses from 10 to 100 nm were prepared. The relatively soft, smooth, and flexible polyimide foils as the substrates in this experiment can undergo sufficient deformation under In this research, the amorphous/nanocrystalline ZrCu/Cu multilayered thin films with various conditions such as individual layer thickness, total layer thickness, and interface type have been successfully fabricated by the multi-gun sputtering processes. To investigate the mechanical properties and deformation behaviors of substrate-supported ZrCu/Cu multilayered thin films, these films deposited on the Cu or polyimide foils were prepared for tensile testing.
    Firstly, the tensile behaviors of the monolithic ZrCu thin film metallic glass and the ZrCu/Cu multilayered thin films deposited on the pure Cu foils are systematically examined. The extracted tensile modulus and strength of the 1-μm-thick multilayered thin films are in good agreement with the theoretical iso-strain rule of mixture prediction. The extracted 2-μm-thick multilayered film data are lower, but can be corrected back by considering the actual intact cross-sectional area during the tensile loading. Moreover, the current results reveal that the ZrCu/Cu multilayered coating exhibit much better tensile performance than the monolithic ZrCu coating. It indicates that the amorphous/nanocrystalline multilayered thin film structure can certainly enhance the mechanical properties of monolithic thin film metallic glasses under tension.
    Secondly, for the further investigation of tensile response, the polyimide-supported amorphous/nanocrystalline ZrCu/Cu multilayered thin films with various individual layer thicknesses from 10 to 100 nm were prepared. The relatively soft, smooth, and flexible polyimide foils as the substrates in this experiment can undergo sufficient deformation under tension. The modulus and strength of the multilayered thin film are again demonstrated to be consistent with the theoretical iso-strain rule of mixture values. As the individual layer thickness decreases from 100 to 10 nm, the Young’s moduli are only varied slightly. However, the maximum tensile stress exhibits a highest value for the 25 nm layer thickness. The higher crack spacing, or the lower crack density, of this 25 nm multilayer film leads to the highest strength.
    Thirdly, to avoid the stress and strain incompatibility owing to the mismatch of elastic modulus and strength levels from the connected amorphous/nanocrystalline layers, the Cu-supported amorphous/nanocrystalline ZrCu/Cu multilayered thin films with sharp and graded interfaces were successfully sputtered and examined by tensile testing. The extracted tensile properties of the multilayered films can be compared with the predicted values based on the two-phase and three-phase iso-strain rule of mixture model. The multilayered films with graded interfaces, each about 50 nm thick, consistently exhibit higher tensile strength and elongation. This can be rationalized by the reduced stress and strain incompatibility along the interfaces.
    Advisory Committee
  • L. W. Chang - chair
  • S. R. Jian - co-chair
  • K. C. Hsieh - co-chair
  • P. W. Kao - co-chair
  • J. C. Huang - advisor
  • Files
  • etd-0611112-081034.pdf
  • Indicate in-campus at 2 year and off-campus access at 2 year.
    Date of Submission 2012-06-11

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