The resolution of G. P. zones in AlZn and AlZnMg

Gerstenberg, Kurt; Gerold, V.

doi:10.1002/crat.2170200116

Cited by 9 publications

(5 citation statements)

References 7 publications

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“…In some cases, like Al-Zn, [3][4][5] the average precipitate radius was found to increase continuously during dissolution, whereas in other systems, like Al-Li, 6 it decreased. A tentative explanation for the increasing radius in Al-Zn has been given in terms of a Zn-rich shell surrounding the precipitates which dissolves by diffusion.…”

Section: Introductionmentioning

confidence: 95%

Dissolution of precipitates heated above the solubility line: A Monte Carlo simulation

1997

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The use of precipitate hardened alloys at high temperatures is often limited by the thermal stability of the precipitates. To improve the understanding of precipitate dissolution after a rapid increase of temperature, we used computer simulation to study a binary A -5 at. % B model alloy. The system consisted of A and B atoms on a quadratic lattice with nearest-neighbor attractive interactions between like atoms. The dynamics was provided by a single vacancy moving across the lattice by exchanges with neighboring atoms. The evolution of the precipitates was studied as a function of time at various temperatures T a , starting from a given initial configuration, which was prepared by ''annealing'' a random mixture of A and B atoms at a low temperature inside the miscibility gap of the alloy. Depending on the new temperature T a , different processes were observed. For T a inside the miscibility gap, the precipitates stayed compact and dissolved partially at first, but afterwards their average size increased again by a coarsening process. For T a outside the miscibility gap, but below the critical temperature T c , the precipitates stayed compact and dissolved completely by evaporation of atoms from their surfaces. Above T c , they decomposed rapidly into many smaller particles in a process that resembles an explosion. A theoretical description of these various processes, based on a phase field model, is presented.

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Section: Introductionmentioning

confidence: 95%

Dissolution of precipitates heated above the solubility line: A Monte Carlo simulation

1997

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“…The dissolution processes of metastable phases, such as the dissolution of GP zones in A1--Cu, AI-Zn binary alloys have been called reversion (Dehlinger & Knapp, 1952;Merz, 1966;Gerstenberg & Gerold, 1985). For AI-Zn binary alloys, it has been shown that the miscibility gap for GP zones (Gerold, 1961;Sato & Kojima, 1979;Satyanatayana, 1981) explains the reversion phenomena very well (Wendrock & LOftier, 1981;Okuda, Osamura, Hashizume & Amemiya, 1988;Truong, Wendrock & LOftier, 1991), although there are still arguments on the rate-determining process (Gerstenberg & Gerold, 1985).…”

Section: Introductionmentioning

confidence: 99%

“…For AI-Zn binary alloys, it has been shown that the miscibility gap for GP zones (Gerold, 1961;Sato & Kojima, 1979;Satyanatayana, 1981) explains the reversion phenomena very well (Wendrock & LOftier, 1981;Okuda, Osamura, Hashizume & Amemiya, 1988;Truong, Wendrock & LOftier, 1991), although there are still arguments on the rate-determining process (Gerstenberg & Gerold, 1985). In previous investigations (Okuda, Osamura, Hashizume & Amemiya, 1988;Okuda, Osamura, Amemiya & Hashizume, 1989), we have examined the reversion processes of rather large (2.5-4.5 nm Guinier radius) GP zones in AI-Zn alloys and found that the reversion process is well understood as a dissolution process under a local metastable equilibrium.…”

Section: Introductionmentioning

confidence: 99%

Partial Reversion of Small GP Zones in an Al–Zn Binary Alloy

Okuda¹,

Tanaka²,

Osamura³

et al. 1997

J Appl Cryst

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The reversion process of very small Guinier-Preston (GP) zones in A1-Zn binary alloys has been studied by time-resolved synchrotron-radiation small-angle X-ray scattering (SR-SAXS) measurements. Al-15at.% Zn alloys with GP zones of 1.0 to 1.3 nm in radius formed by aging at 274K were up-quenched up to 463K. During reversion, the Guinier radius increased rapidly while the integrated intensity decreased. This rapid increase of the radius was completely different from what was found during the reversion of larger GP zones above the miscibility gap. It is concluded that a process of simultaneous dissolution and coarsening has been observed.

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“…A detailed analysis of several alloys with 12 to 18 mol-% Zn has confirmed that the deviation is less than 5 K (Ref.32). Extrapolation of the critical scattering I c above T m (after subtraction of other contributions in order to obtain the temperature dependence as predicted by Cook et al •• Ref.33) on a linear plot of T/l c vs. T yields the temperatures of the coherent spinodal (Ref.29) shown in Fig.4.In-beam reversion of small GPZs formed at room temperature in Al-2.73 mol-% Zn has been studied at temperatures between 70 and 130°C (Ref 34)…”

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confidence: 96%

“…but the higher the temperature the earlier it increases again, as the formation of another metastable phase called~' sets in.Osamura et al (Ref.35) who have studied reversion of GPZs formed at 313 K in Al-6.8 mol-% Zn using synchrotron radiation exclude diffusion-controlled dissolution of GPZs on the basis of numerical estimates of the relaxation times at the different inversion temperatures (but with a constant diffusion coefficient). In both studies (Refs 34,35),. the Guinier radius increases slightly upon reversion as initially, the smallest zones dissolve first.…”

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confidence: 97%