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Molecular dynamics study of microstr...

Odunuga, Samson Olusikunanu.

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Molecular dynamics study of microstructural evolution in alloys subjected to severe plastic deformation.

紀錄類型:	書目-語言資料,印刷品 : Monograph/item
正題名/作者:	Molecular dynamics study of microstructural evolution in alloys subjected to severe plastic deformation./
作者:	Odunuga, Samson Olusikunanu.
面頁冊數:	167 p.
附註:	Adviser: Robert S. Averback.
Contained By:	Dissertation Abstracts International68-11B.
標題:	Engineering, Materials Science. -
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=3290338
ISBN:	9780549341284

Molecular dynamics study of microstructural evolution in alloys subjected to severe plastic deformation.
Odunuga, Samson Olusikunanu.

Molecular dynamics study of microstructural evolution in alloys subjected to severe plastic deformation. - 167 p.

Adviser: Robert S. Averback.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2007.

In this thesis, molecular dynamics simulations have been employed to study the microstructural evolution of immiscible binary alloys subjected to severe plastic deformation at various temperatures. The effect of various alloy properties on the deformation process was examined, including the heat of mixing, lattice mismatch, and relative differences in the shear modulus of the pure phases. At low temperatures, as long as dislocations glide homogeneously through the solid, the microstructures evolve towards nearly random solid solutions, regardless of both the amplitude of the heat of mixing and the lattice mismatch. At elevated temperatures, partially decomposed steady states are stabilized, as a result from the dynamical competition between forced mixing and thermally activated atomic motions. The latter events cannot be accounted for simply by thermally activated vacancy jumps, but instead appear to be correlated with dislocation glides. It is demonstrated that the steady states that are stabilized at low temperature are unique whereas at high temperatures, the final states appear to depend on the initial state, although steady states in these systems were not obtained.

ISBN: 9780549341284Subjects--Topical Terms:

1017759
Engineering, Materials Science.

Molecular dynamics study of microstructural evolution in alloys subjected to severe plastic deformation.
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245 1 0 $a Molecular dynamics study of microstructural evolution in alloys subjected to severe plastic deformation.
300 $a 167 p.
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500 $a Source: Dissertation Abstracts International, Volume: 68-11, Section: B, page: 7603.
502 $a Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2007.
520 $a In this thesis, molecular dynamics simulations have been employed to study the microstructural evolution of immiscible binary alloys subjected to severe plastic deformation at various temperatures. The effect of various alloy properties on the deformation process was examined, including the heat of mixing, lattice mismatch, and relative differences in the shear modulus of the pure phases. At low temperatures, as long as dislocations glide homogeneously through the solid, the microstructures evolve towards nearly random solid solutions, regardless of both the amplitude of the heat of mixing and the lattice mismatch. At elevated temperatures, partially decomposed steady states are stabilized, as a result from the dynamical competition between forced mixing and thermally activated atomic motions. The latter events cannot be accounted for simply by thermally activated vacancy jumps, but instead appear to be correlated with dislocation glides. It is demonstrated that the steady states that are stabilized at low temperature are unique whereas at high temperatures, the final states appear to depend on the initial state, although steady states in these systems were not obtained.
520 $a The atomic transport resulting from plastic deformation has been analyzed in new depths by tracking the evolution of pair of marker atoms. This analysis has proved to be a powerful tool in identifying the deformation mechanisms, including the glide of leading and trailing partial dislocations, and vacancy assisted atomic jumps during deformation, as well as quantifying the relative contributions of these mechanisms. It is found that the glide of dislocations plays a more important role than previously thought in accommodating plastic deformation in nanocrystalline alloys. A new property of the atomic mixing by plastic deformation that has been uncovered is that the effective diffusion coefficient increases, nearly linearly, with the separation distance of pairs of atoms. This superdiffusive mixing is revealed by monitoring the relative displacement of atoms as a function of the separation distance. This result can be tested experimentally by measuring the rate of dissolution of precipitates during deformation. This finding also provides a direct rationalization for the stabilization of compositional patterns when thermal diffusion and forced mixing compete.
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