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Investigating the Stability of the α/ω Dual Phase Microstructure in Shock Impacted Zr

Low, Thaddeus Song En
http://rave.ohiolink.edu/etdc/view?acc_num=osu1524178270425181

Abstract Details

2018, Doctor of Philosophy, Ohio State University, Materials Science and Engineering.
Under high pressure, Zr undergoes a transformation from its ambient equilibrium hexagonal close packed α phase to a simple hexagonal ω phase. Subsequent unloading to ambient conditions does not see a full reversal to the α phase, but rather a retention of significant ω. The thermal stability of the ω phase was investigated via in-situ synchrotron X-ray diffraction analysis of the isothermal annealing of Zr samples shocked to 8 and 10.5 GPa at temperatures 443, 463, 483, and 503 K. The phase volume fractions were tracked quantitatively and the dislocation densities were tracked semi-quantitatively. Trends included a rapid initial (transient) transformation rate from ω→α followed by a plateau to a new metastable state with lesser retained ω (asymptotically stable). Samples shocked to a higher peak pressure experienced relatively higher transformation rates and extent of transformation. A significant reduction in dislocation densities in the ω phase was observed prior to initiation of an earnest reverse transformation, leading to the hypothesis that the ω→α transformation from is being hindered by defects in the ω phase. Additional electron backscatter diffraction analysis of the samples affirmed the expected (0001)α || (10-11)ω and [10-10]α || [11-2-3]ω orientation relationship is maintained during the nucleation and growth of the α phase during annealing. In an effort to build on the hypothesis from the experimental studies, this work also presents a temperature dependent model that couples the removal of dislocations in the ω phase and the reverse transformation via a barrier energy that is associated with the free energy of remaining dislocations. The reduction of dislocations in the ω phase occur as a sum of glide and climb controlled processes, both of which dictate the transient and asymptotic behavior of the annealing process respectively. Furthermore, a single crystal plasticity framework is introduced as a venue toward future work on the reverse transformation. The model incorporates phase transformation, slip, twinning and an equation of state for Ti in order to model dynamic deformation and shock wave propagation. The model is able to serve as a basis toward future work and was part of my contribution toward a VUMAT user subroutine implementation in Abaqus.
Stephen Niezgoda (Advisor)
Glenn Daehn (Committee Member)
Maryam Ghazisaeidi (Committee Member)
Ralf Bundschuh (Committee Member)
151 p.
Materials Science
omega; zirconium; stability; model; shock; in-situ; annealing;

Recommended Citations

Citations

  • Low, T. S. E. (2018). Investigating the Stability of the α/ω Dual Phase Microstructure in Shock Impacted Zr [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1524178270425181

    APA Style (7th edition)

  • Low, Thaddeus Song En. Investigating the Stability of the α/ω Dual Phase Microstructure in Shock Impacted Zr. 2018. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1524178270425181.

    MLA Style (8th edition)

  • Low, Thaddeus Song En. "Investigating the Stability of the α/ω Dual Phase Microstructure in Shock Impacted Zr." Doctoral dissertation, Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1524178270425181

    Chicago Manual of Style (17th edition)

osu1524178270425181
356
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This open access ETD is published by The Ohio State University and OhioLINK.