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Effects of Changes in Chemistry and Test Temperature on Deformation Behavior and Fatigue Properties of Al-Based Amorphous Alloys

Huang, Chun-Kuo
http://rave.ohiolink.edu/etdc/view?acc_num=case1301526672

Abstract Details

2011, Doctor of Philosophy, Case Western Reserve University, Materials Science and Engineering.
The extraordinary mechanical properties such as high strength, hardness, elasticity, and strength to density ratio, as well as good formability and shaping abilities make Al-based amorphous alloys good candidates for structural applications. In this dissertation, the effects of changes in chemical composition of Al-Gd-Ni-X (X= transition metals) were investigated. Three aspects of properties were examined: thermal stability, deformation behavior, and fatigue properties. Systematic additions of Fe and Co significantly improved Tg and Tx1 of the base Al87Gd6Ni7 amorphous alloy since Fe and Co exhibit a negative heat of mixing with Al. However, the value of (i.e. Tx - Tg) was not changed significantly over the range of alloying additions investigated. The deformation behavior of Al-Gd-Ni-X ribbons was determined by high temperature micro-hardness tests and dynamic mechanical analysis (DMA). Although these ribbons exhibited high hardness/viscosity at room temperature, a distinct reduction near their Tg was observed, with subsequent increases when the test temperature passed Tx. Such behavior and separate TEM analysis indicated that microstructural evolution occurred at this temperature. The deformation behavior also was studied by tensile tests at various temperatures. A transition from inhomogeneous flow to more homogeneous flow was obtained at low strain rates upon approaching Tg, while the deformation behavior at different strain rates and temperatures was captured in a deformation map. In addition, the fatigue performance was examined at both R= -1 and R= 0 conditions. It was demonstrated that the substitution for Al by Fe and Co additions increased the stress amplitude at the fatigue limit from 240 MPa for Al87Gd6Ni7 to 397 MPa for Al86Gd6Ni7Co1 when tested at R= -1. Conducting fatigue tests at R= 0 revealed that tensile mean stresses produced a detrimental effect on the fatigue performance, but not as great as that exhibited in commercial aluminum alloys. It also was demonstrated that the improvement of high cycle fatigue performance of higher alloyed glasses may be a result of their higher Tg, providing a lower value of the ratio of the test temperature to Tg. The importance of this was checked by conducting fatigue tests at lower test temperatures (i.e. different values of T/Tg). The increases in the Fe/Co level that produced improvements in the HCF behavior are partly attributed to the lower T/Tg present during fatigue testing of the highly alloyed ribbons.
John J. Lewandowski, PhD (Committee Chair)
Gary M. Michal, PhD (Committee Member)
David Schiraldi, PhD (Committee Member)
David Schwam, PhD (Committee Member)
Materials Science
Amorphous alloys; mechanical properties; fatigue of materials

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Citations

  • Huang, C.-K. (2011). Effects of Changes in Chemistry and Test Temperature on Deformation Behavior and Fatigue Properties of Al-Based Amorphous Alloys [Doctoral dissertation, Case Western Reserve University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=case1301526672

    APA Style (7th edition)

  • Huang, Chun-Kuo. Effects of Changes in Chemistry and Test Temperature on Deformation Behavior and Fatigue Properties of Al-Based Amorphous Alloys. 2011. Case Western Reserve University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=case1301526672.

    MLA Style (8th edition)

  • Huang, Chun-Kuo. "Effects of Changes in Chemistry and Test Temperature on Deformation Behavior and Fatigue Properties of Al-Based Amorphous Alloys." Doctoral dissertation, Case Western Reserve University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=case1301526672

    Chicago Manual of Style (17th edition)

case1301526672
603
© 2011, all rights reserved.
This open access ETD is published by Case Western Reserve University School of Graduate Studies and OhioLINK.