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A theoretical study of the HCP to omega martensitic phase transition in titanium

Trinkle, Dallas Rhea, III
http://rave.ohiolink.edu/etdc/view?acc_num=osu1070481734

Abstract Details

2003, Doctor of Philosophy, Ohio State University, Physics.
Under pressure, titanium transforms from the hexagonal-closed-packed (hcp) structure to the high pressure omega phase. This phase transition from hcp (alpha) to omega (omega) is martensitic: there is a macroscopic cell change, described by a strain tensor, coupled with microscopic internal relaxations of the unit cell, described by shuffle vectors. In addition, the transformation occurs directly and without diffusion. Despite this, the atomistic transformation was not known. Trace amounts (1 at.%) of oxygen impurities shut down the shock-induced transformation. Ab initio, tight-binding, and classical potential calculations model the hcp to omega transformation, and the effects of impurities on the transformation. A new pathway generation and sorting algorithm systematically searches through all possible pathways to find the most probable homogeneous mechanism. A new mechanism is found with a barrier 4 times lower than any other homogeneous mechanisms, even when nucleation effects are considered. Using molecular dynamics, the transformation from hcp to omega moves across the interphase boundary under pressure at a finite temperature. The interstitial impurities oxygen, nitrogen, carbon, and substitutional impurities aluminum and vanadium shift both the energy barrier between and the relative energies of alpha and omega; these changes explain the shutdown of the alpha to omega transformation by oxygen and aluminum. The final result is an atomistic understanding of the Ti alpha to omega transformation: moving from the homogeneous energy barrier to nucleation effects to finite temperature to the effect of impurities. This serves as a template for future studies of the atomistic mechanisms of other martensitic transformations.
John Wilkins (Advisor)
201 p.
Physics, Condensed Matter
martensitic; titanium; omega phase; atomistic mechanism; impurities; molecular dynamics; nucleation; solid-solid transformation

Recommended Citations

Citations

  • Trinkle, III, D. R. (2003). A theoretical study of the HCP to omega martensitic phase transition in titanium [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1070481734

    APA Style (7th edition)

  • Trinkle, III, Dallas. A theoretical study of the HCP to omega martensitic phase transition in titanium. 2003. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1070481734.

    MLA Style (8th edition)

  • Trinkle, III, Dallas. "A theoretical study of the HCP to omega martensitic phase transition in titanium." Doctoral dissertation, Ohio State University, 2003. http://rave.ohiolink.edu/etdc/view?acc_num=osu1070481734

    Chicago Manual of Style (17th edition)

osu1070481734
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© 2003, all rights reserved.
This open access ETD is published by The Ohio State University and OhioLINK.