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Crystal structure and nucleation behavior of (111) precipitates in an aluminum-3.9copper-0.5magnesium-0.5silver (wt. percent) alloy.

紀錄類型:	書目-語言資料,手稿 : Monograph/item
正題名/作者:	Crystal structure and nucleation behavior of (111) precipitates in an aluminum-3.9copper-0.5magnesium-0.5silver (wt. percent) alloy./
作者:	Chang, Yuan-Chang.
面頁冊數:	1 online resource (242 pages)
附註:	Source: Dissertation Abstracts International, Volume: 54-01, Section: B, page: 4310.
標題:	Materials science. -
電子資源:	click for full text (PQDT)

Crystal structure and nucleation behavior of (111) precipitates in an aluminum-3.9copper-0.5magnesium-0.5silver (wt. percent) alloy.
Chang, Yuan-Chang.

Crystal structure and nucleation behavior of (111) precipitates in an aluminum-3.9copper-0.5magnesium-0.5silver (wt. percent) alloy. - 1 online resource (242 pages)

Source: Dissertation Abstracts International, Volume: 54-01, Section: B, page: 4310.

Thesis (Ph.D.)--Carnegie Mellon University, 1992.

Includes bibliographical references

The crystal structure, stability and nucleation behavior of precipitates on $\{$111$\}$ habit planes (hereafter called $\{$111$\}$ precipitates) in an Al-3.9Cu-0.5Mg-0.5Ag (wt.%) alloy were studied by transmission electron microscopy (TEM) techniques, including selected-area diffraction (SAD), energy dispersive x-ray spectroscopy (EDS), high resolution TEM (HRTEM) and image simulations, and x-ray diffraction (XRD) analysis. The studies included early-stage precipitates formed by quenching and aging with or without cold-work as well as direct aging treatments and large well-developed precipitates formed by aging at temperatures up to the $\theta$ solvus.

Electronic reproduction.
Ann Arbor, Mich. :
ProQuest,
2018

Mode of access: World Wide Web

Subjects--Topical Terms:

557839
Materials science.
Index Terms--Genre/Form:

554714
Electronic books.

Crystal structure and nucleation behavior of (111) precipitates in an aluminum-3.9copper-0.5magnesium-0.5silver (wt. percent) alloy.
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100 1 $a Chang, Yuan-Chang. $3 1188511
245 1 0 $a Crystal structure and nucleation behavior of (111) precipitates in an aluminum-3.9copper-0.5magnesium-0.5silver (wt. percent) alloy.
264 0 $c 1992
300 $a 1 online resource (242 pages)
336 $a text $b txt $2 rdacontent
337 $a computer $b c $2 rdamedia
338 $a online resource $b cr $2 rdacarrier
500 $a Source: Dissertation Abstracts International, Volume: 54-01, Section: B, page: 4310.
500 $a Adviser: James M. Howe.
502 $a Thesis (Ph.D.)--Carnegie Mellon University, 1992.
504 $a Includes bibliographical references
520 $a The crystal structure, stability and nucleation behavior of precipitates on $\{$111$\}$ habit planes (hereafter called $\{$111$\}$ precipitates) in an Al-3.9Cu-0.5Mg-0.5Ag (wt.%) alloy were studied by transmission electron microscopy (TEM) techniques, including selected-area diffraction (SAD), energy dispersive x-ray spectroscopy (EDS), high resolution TEM (HRTEM) and image simulations, and x-ray diffraction (XRD) analysis. The studies included early-stage precipitates formed by quenching and aging with or without cold-work as well as direct aging treatments and large well-developed precipitates formed by aging at temperatures up to the $\theta$ solvus.
520 $a It was found that the $\{$111$\}$ precipitates form independent of previously precipitated G.P. zones. No evidence of a precursor phase was found by either TEM or HRTEM. These precipitates nucleate with a thickness of one unit-cell in terms of the orthorhombic $\Omega$ structure model (or $\theta$ structure rotates 45$\sp\circ$) with pure Al atoms in the precipitate structure adjacent to the $\{$111$\}$ matrix planes. Dislocations are not required during nucleation process. The $\{$111$\}$ precipitates could formed homogeneously in the matrix or heterogeneously at dislocations. However, the formation of the $\{$111$\}$ precipitates only possible when Mg atoms were associated in the nucleation mechanisms to reduce the activation free energy, the formation of this phase only can be heterogeneous nucleation.
520 $a It was shown that the $\{$111$\}$ precipitate is a $\{$111$\}\sb{\rm Al}$ variant of the $\theta$ phase previously designated as Vaughan II-type $\theta.$ Since the $\{$111$\}$ precipitate is one variant of $\theta$ phase and quenched-in defects do not promote precipitation of $\{$111$\}$ precipitates, it appears that the role of Mg + Ag on the precipitation process is mainly to influence the thermodynamic factor and then augment the nucleation rate. The mechanism is thought to be a catalytic reaction, where Mg is a catalyst which lowers the activation free energy by segregating to $\{$111$\}\sb{\rm Al}$/precipitate interfaces, while Ag acts to prevent formation of S phase (or G.P.B. zones) thereby leaving free Mg to stimulate nucleation of the $\{$111$\}$ precipitates instead of the metastable $\theta\sp\prime$ phase. The interaction of Mg + Ag in the precipitation process therefore appears to provide an alternative path for precipitation of the $\theta$ phase on the $\{$111$\}\sb{\rm Al}$ habit planes.
533 $a Electronic reproduction. $b Ann Arbor, Mich. : $c ProQuest, $d 2018
538 $a Mode of access: World Wide Web
650 4 $a Materials science. $3 557839
650 4 $a Engineering, Materials science. $3 1188512
655 7 $a Electronic books. $2 local $3 554714
690 $a 0794
690 $a 0743
710 2 $a ProQuest Information and Learning Co. $3 1178819
710 2 $a Carnegie Mellon University. $3 845406
856 4 0 $u http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=9312827 $z click for full text (PQDT)