On the validity of simple precipitate size measurements by small-angle scattering in metallic systems

Deschamps, A.; Geuser, F. de

doi:10.1107/s0021889811003049

Cited by 91 publications

(77 citation statements)

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“…The cluster size was characterized using a self-consistent Guinier approximation [16]. The average cluster size is equal to the Guinier radius (R g ) when the size distribution of the clusters features a dispersion of 0.2 [16]. The uncertainty on the Guinier radius was calculated from the error associated with the slope of the linear Guinier fit.…”

Section: Introductionmentioning

confidence: 99%

“…The scattering spectra at the solutionizing temperature was used for background subtraction, and the absolute intensity, I, was normalized using glassy carbon as a secondary standard [15]. The cluster size was characterized using a self-consistent Guinier approximation [16]. The average cluster size is equal to the Guinier radius (R g ) when the size distribution of the clusters features a dispersion of 0.2 [16].…”

Section: Introductionmentioning

confidence: 99%

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Early cluster formation during rapid cooling of an Al–Cu–Mg alloy: In situ small-angle X-ray scattering

et al. 2015

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a b s t r a c tThe formation of Cu-Mg clusters in an Al-Cu-Mg aluminum alloy is observed by small-angle X-ray scattering during cooling. Cooling rates are choosen to mimic the different conditions obtained at the surface and in the center of large forgings. Clusters of 0.45 nm start to form at 250°C. Their volume fraction depends strongly on the cooling rate and the amount of excess vacancies. The difference in cluster kinetics explains the difference in rapid hardening across large forgings.Ó 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.Age-hardenable Al-Cu-Mg alloys are widely used for aerospace and engineering applications owing to their high specific strength and good corrosion resistance. Their age hardening response is characterized by two distinct stages. The first stage is defined by a fast initial increase in strength, which is known as rapid hardening. It was shown by 3D atom probe tomography (APT) and small-angle X-ray scattering (SAXS) experiments that the rapid hardening is associated with the formation of Cu-Mg clusters [1][2][3][4]. The second rise to peak hardness is generally ascribed to the formation of the equilibrium S phase (Al 2 CuMg) [4,5].For industrial applications, the Al-Cu-Mg alloys are commonly processed as large components such as forgings or plates. The mechanical properties are tailored by the age-hardening treatment, which also involves a quenching step. Thermal gradients decrease from the surface to the center and give rise to residual stresses (RS) [6]. The magnitude of the as-quenched RS can be very high and even exceed the as-quenched strength of the materials [6,7]. In the case of Al-Zn-Mg-Cu alloys, the high as-quenched RS are caused by the formation of fine hardening precipitates that form during quenching of large components and thereby increase the yield strength of the material [8,9].In order to predict the RS formation in industrial components during quench, the changes of the nanostructure during cooling conditions close to industrial practice needs to be characterized as they highly impact the yield strength and thus the internal stress generation. Further, the influence of excess vacancies on precipitation during cooling needs to be explored. This can be done by adapting the cooling rates at high temperature, which influence the excess vacancy concentration due to annihilation on defects.SAXS is a useful tool to monitor precipitation phenomena during fast time and temperature changes given that a sufficiently high electron density contrast between the precipitate and matrix exists [4,8,10]. SAXS provides the means to collect information on the size and volume fraction of the precipitates that can then be directly compared to predictions of thermodynamic-based precipitation models [11,12]. These models can be coupled with macroscopic finite-element RS simulations to better predict the residual stress formation during the processing of industrial components [9,13] as part of through-process modeling.This work investigates the Cu-Mg cluster ...

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Early cluster formation during rapid cooling of an Al–Cu–Mg alloy: In situ small-angle X-ray scattering

et al. 2015

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“…Thus, this technique provides quantitative and statistically reliable results including average precipitate size, volume fraction, number density and, potentially, precipitate size distribution (PSD). The application of SAXS for measuring the sizes of nanoscale precipitates in a range of metallic systems is well established, especially on binary and ternary systems [10][11][12][13][14]. Most previous studies of precipitation phenomena in aluminium alloys by SAXS have been conducted on precipitationhardened wrought alloys analogues, such as Al-Cu and Al-Mg-Si.…”

Section: Introductionmentioning

confidence: 99%

Characterising precipitate evolution in multi-component cast aluminium alloys using small-angle X-ray scattering

Wang

McCartney

et al. 2017

Journal of Alloys and Compounds

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The version presented here may differ from the published version or from the version of record. If you wish to cite this item you are advised to consult the publisher's version. Please see the repository url above for details on accessing the published version and note that access may require a subscription. AbstractAluminium alloys can be strengthened significantly by nano-scale precipitates that restrict dislocation movement. In this study, the evolution of inhomogenously distributed trialuminide precipitates in two multi-component alloys was characterised by synchrotron small-angle Xray scattering (SAXS). The appropriate selection of reference sample and data treatment required to successfully characterise a low volume fraction of precipitates in multi-component alloys via SAXS was investigated. The resulting SAXS study allowed the analysis of statistically significant numbers of precipitates (billions) as compared to electron microscopy (hundreds). Two cast aluminium alloys with different volume fractions of Al3ZrxV1-x precipitates were studied. Data analysis was conducted using direct evaluation methods on SAXS spectra and the results compared with those from transmission electron microscopy (TEM). Precipitates were found to attain a spherical structure with homogeneous chemical composition. Precipitate evolution was quantified, including size, size distribution, volume fraction and number density. The results provide evidence that these multi-component alloys have a short nucleation stage, with coarsening dominating precipitate size. The coarsening rate constant was calculated and compared to similar precipitate behaviour.2

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“…15 Structural information, such as Guinier radius (R g ) and scattering invariant (Q), were extracted from the scattering data by using a modelindependent analysis as performed by Deschamps and de Geuser. 16,17 The average particle size was estimated using a self-consistent Guinier approximation. 16 The uncertainty of the Guinier radius was calculated from the error associated with the slope of the linear Guinier fit.…”

mentioning

confidence: 99%

“…16,17 The average particle size was estimated using a self-consistent Guinier approximation. 16 The uncertainty of the Guinier radius was calculated from the error associated with the slope of the linear Guinier fit. The volume fractions of the two phases were obtained from the scattering invariant, which corresponds to the integral of the Kratky plot from 0 to infinity.…”

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confidence: 99%

Early precipitation during cooling of an Al-Zn-Mg-Cu alloy revealed by in situ small angle X-ray scattering

Schloth

Wagner

Fife

et al. 2014

Applied Physics Letters

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Early subnanometre cluster formation during quenching of a high-strength AA7449 aluminium alloy was investigated using in situ small angle X-ray scattering. Fast quench cooling was obtained by using a laser-based heating system. The size and number density of homogeneous nucleated clusters were found to be strongly dependent on the cooling rate, while the volume fraction of cluster formation is independent of the cooling rate. Heterogeneous larger precipitation starts at higher temperatures in volume fractions that depend on the cooling rate. V C 2014 AIP Publishing LLC. The fabrication of aluminium alloys involves a number of thermomechanical steps such as solute-heat treatment followed by fast cooling, i.e., quenching. It is well known that the cooling rate influences the homogeneous and heterogeneous formation of precipitates and that the effect of these differences on the mechanical properties cannot be removed by additional aging. The typical precipitation sequence of the equilibrium g phase (Mg(Zn,Cu,Al) 2 ) in the Al-Zn-Mg(-Cu) system is: GPZ ! g 0 ! g. 1 Early studies by Lendvai and L€ offler on Al-Zn-Mg alloys report that vacancy-rich clusters (VRC), acting as nucleation sites for Guinier Preston zones (GPZ), can form during the cooling from the solutionizing temperature. 2,3 The number of VRCs strongly depends on the quench parameters influencing the excess vacancies in the structure. Clusters formed by only a few atoms 4 have been identified using 3D atom probe. Despite their small size, the clusters are effective in increasing the yield strength of the material. 5 In addition to the VRCs, heterogeneous precipitation of the equilibrium g phase occurs at higher temperatures. 1 It is therefore not surprising that when producing thick Al alloy plates, the resultant precipitation size, density, and volume fraction are expected to differ across the plate because of the difference in cooling rates. The latter creates residual stresses at as quenched temper that are reduced by stress relief. The remaining residual stresses at final temper may lead to machining distortions. To investigate the influence of precipitation on residual stresses, thermomechanical models linking solid-state transformations to the final stress distribution have to be developed. Such simulation schemes need input on size, density, and volume fraction of precipitation as function of cooling rates that can only be provided by experimentation.Small angle X-ray scattering (SAXS) has proven to be a useful tool for the investigation of precipitation phenomena. 6 SAXS is a well established technique for investigating clusters with high contrast in atomic number with respect to the matrix. SAXS has been used extensively to study precipitation phenomena in Al alloys ex situ and also in situ during aging. [6][7][8] Providing information on the size and volume fraction of the precipitates, SAXS validated thermodynamic-based precipitation model predictions 7,9 of the effect of aging on precipitation. There is however no information to be gathered...

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On the validity of simple precipitate size measurements by small-angle scattering in metallic systems

Cited by 91 publications

References 42 publications

Early cluster formation during rapid cooling of an Al–Cu–Mg alloy: In situ small-angle X-ray scattering

Early cluster formation during rapid cooling of an Al–Cu–Mg alloy: In situ small-angle X-ray scattering

Characterising precipitate evolution in multi-component cast aluminium alloys using small-angle X-ray scattering

Early precipitation during cooling of an Al-Zn-Mg-Cu alloy revealed by in situ small angle X-ray scattering

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