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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Mechanical Properties and Micro-Forming Ability of Au-Based Bulk Metallic Glasses

Tang, Chen-wei 10 July 2008 (has links)
The mechanical properties and micro-forming of the Au-based bulk metallic glasses are reported in this thesis. The original ingots were prepared by arc melting and induction melting. The Au49Ag5.5Pd2.3Cu26.9Si16.3 bulk metallic glasses with different diameters 2 and 3 mm were successfully fabricated by conventional copper mold casting in an inert atmosphere. By the observation of transmission electron microscopy diffraction pattern, there are crystalline phases among the amorphous matrix phase. The Au49Ag5.5Pd2.3Cu26.9Si16.3 bulk metallic glass shows the high glass forming ability and good thermal stability. By the Differential scanning calorimetry (DSC) results, the values of£G£Vx and £G£Vm are 50 and 21 K. And Trg, £^, and £^m values for the Au49Ag5.5Pd2.3Cu26.9Si16.3 bulk metallic glass (BMG) at the heating rate of 0.67 K/s are 0.619, 0.430 and 0.774, respectively. The mechanical properties of Au49Ag5.5Pd2.3Cu26.9Si16.3 in terms of compression testing are examined using an Instron 5582 universal testing machine. Room temperature compression tests are conducted on specimens with various strain rates. To know the size effect, the micro-pillars were made by using a focus ion beam (FIB) technique. The micro-pillars were under the tests of compression at different strain rates, compared with macro-scale 2 mm rod specimens. In contrast to the brittle fracture in a bulk sample, these micro-pillar specimens show significant plasticity. The morphology of compressed pillar samples indicates that the number of shear bands increased with the sample size and strain rates.

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