Diffraction contrast from spherically symmetrical coherency strains

Ashby, Michael F.; Brown, L. M.

doi:10.1080/14786436308207338

Cited by 639 publications

(56 citation statements)

References 12 publications

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“…Figure 5(c) is a complementary bright-field micrograph to that of Figure 5(b), recorded under two-beam conditions. The characteristic Ashby-Brown [54] strain contrast surrounding the Al 3 Zr (L1 2 ) precipitates indicates that they are coherent with a-Al. It is the small, coherent, high number density Al 3 Zr (L1 2 ) precipitates within the dendrites that are responsible for the marked precipitation-hardening response of Al-0.19Zr presented in Figure 3.…”

Section: Electron Microscopymentioning

confidence: 99%

Nucleation and Precipitation Strengthening in Dilute Al-Ti and Al-Zr Alloys

Knipling

Dunand

Seidman

2007

Metall Mater Trans A

178

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Two conventionally solidified Al-0.2Ti alloys (with 0.18 and 0.22 at. pct Ti) exhibit no hardening after aging up to 3200 hours at 375°C or 425°C. This is due to the absence of Al 3 Ti precipitation, as confirmed by electron microscopy and electrical conductivity measurements. By contrast, an Al-0.2Zr alloy (with 0.19 at. pct Zr) displays strong age hardening at both temperatures due to precipitation of Al 3 Zr (L1 2 ) within Zr-enriched dendritic regions. This discrepancy between the two alloys is explained within the context of the equilibrium phase diagrams: (1) the disparity in solid and liquid solubilities of Ti in a-Al is much greater than that of Zr in a-Al; and (2) the relatively small liquid solubility of Ti in a-Al limits the amount of solute retained in solid solution during solidification, while the comparatively high solid solubility reduces the supersaturation effecting precipitation during post-solidification aging. The lattice parameter mismatch of Al 3 Ti (L1 2 ) with a-Al is also larger than that of Al 3 Zr (L1 2 ), further hindering nucleation of Al 3 Ti. Classical nucleation theory indicates that the minimum solute supersaturation required to overcome the elastic strain energy of Al 3 Ti nuclei cannot be obtained during conventional solidification of Al-Ti alloys (unlike for Al-Zr alloys), thus explaining the absence of Al 3 Ti precipitation and the presence of Al 3 Zr precipitation.

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Section: Electron Microscopymentioning

confidence: 99%

Nucleation and Precipitation Strengthening in Dilute Al-Ti and Al-Zr Alloys

Knipling

Dunand

Seidman

2007

Metall Mater Trans A

178

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“…In particular the XTEM image shows extended defects, which appear to be H-platelets. These platelets show Ashby-Brown contrast [117], corroborating that they act as strain centers. The damaged zone ranges from a depth of 375 nm to 500 nm.…”

Section: Growth Kinetics Of Hydrogen Plateletsmentioning

confidence: 58%

“…An analysis of the defects above the implantation damage zone at even higher magnification (not shown) revealed the point-like nature of these strain defects (vacancies or interstitials clusters). Upon annealing, higher resolution XTEM showed that these defects develop Ashby-Brown contrast [117]. That indicates, that these defects are equal in nature to the defects found in the tail region of the implantation zone (figure 5-8), i. e. dislocation loops, but smaller in size.…”

Section: Microstructure Of the Implantation Zonementioning

confidence: 88%

“…Analysis of the image reveals a 0.29 µm broad densely damaged region starting at a depth of 1.32 µm, followed by a broad tail region of less dense damage. The tail region of the implanted zone is composed of some dislocation loops (12-20 nm diameter) or rounded strain centres showing Ashby-Brown contrast [117], indicating that defects are strain centers, likely to result from the growth of small defects clusters into dislocation loops. The detailed nature of these loops (vacancy or interstitial) was not determined.…”

Section: Microstructure Of the Implantation Zonementioning

confidence: 99%

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On the Mechanisms of Hydrogen Implantation Induced Silicon Surface Layer Cleavage

Höchbauer

2001

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ZusammenfassungDer sogenannte "Ion-Cut", ein Schichtabspaltungsprozess mittels WasserstoffIonenimplantation und darauffolgender Probenerwärmung ist eine effektive, vielseitige und ökonomische Methode, um Siliziumschichten mit einer Dicke von nur einigen Nanometern von einem Siliziumsubstrat auf andere Materialien zu transferieren. Somit ermöglicht der Ion-Cut die Produktion von Siliziumschichen auf isolierenden Materalien ("silicon-on-insulator" (SOI) AbstractThe "Ion-Cut", a layer splitting process by hydrogen ion implantation and subsequent annealing is a versatile and efficient technique of transferring thin silicon surface layers from bulk substrates onto other substrates, thus enabling the production of silicon-oninsulator (SOI) materials. Cleavage is induced by the coalescence of the highly pressurized sub-surface H 2 -gas bubbles, which form upon thermal annealing. A fundamental understanding of the basic mechanisms on how the cutting process occurs is still unclear, inhibiting further optimization of the Ion-Cut process. This work elucidates the physical mechanisms behind the Ion-Cut process in hydrogen-implanted silicon. The investigation of the cleavage process reveals the cut to be largely controlled by the lattice damage, generated by the hydrogen ion irradiation process, and its effects on the local stress field and the fracture toughness within the implantation zone rather than by the depth of maximum H-concentration. Furthermore, this work elucidates the different kinetics in the H-complex formations in silicon crystals with different conductivity types, and examines the mechanically induced damage accumulation caused by the crack propagation through the silicon sample in the splitting step of the Ion-Cut process. Additionally, the influence of boron pre-implantation on the Ion-Cut in hydrogen implanted silicon is investigated. These studies reveal, that both, the atomic interaction between the boron implant and the hydrogen implant and the shift of the Fermi level due to the electrical activation of the implanted boron have a tremendous enhancing effect on the Ion-Cut process.

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“…In a series of studies of microstructural evolution during the very early stages of ageing in Al-10 mass% Mg alloy aged 550 h at room temperature, [19][20][21][22] further detailed evidence was found of a modulated structure with Ashby-Brown contrast, 23) which was aligned along the h100i . This structure was observed to develop into spherical GP zones having the superlattice reflections of the L1 2 structure after a further 12 years ageing.…”

Section: Effects Of Natural Ageing On Precipitation Sequencesmentioning

confidence: 99%

Characterisation of Precipitate Microstructures of Natural and Artificial Ageing in Al-Mg(-Ag) Alloys

Kubota¹

2005

Mater. Trans.

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In order to improve fundamental understanding of the ageing behaviour in Al-Mg(-Ag) alloys, the effects of trace additions of Ag on the precipitate microstructures of the Al-Mg alloys aged at temperature range 20 and 90 C was examined. The fine-scale and uniformly distributed spheroidal precipitate particles were formed in the ternary Al-10Mg-0.5Ag (mass%) alloy during the natural ageing process of periods of 16 months, while no precipitate particles were observed in the binary Al-10 mass% Mg alloy under the same ageing conditions. These fine scale, spheroidal precipitate particles observed in the ternary Al-10Mg-0.5Ag (mass%) alloy were identified as the 00 phase which has the ordered L1 2 structure with the lattice parameter of a ¼ 0:408 nm. The orientation relationship between the 00 phase and the aluminium matrix was of the form: ð100Þ L12 k ð100Þ , ½001 L12 k ½001 . The spheroidal precipitate particles having the ordered L1 2 structure in the Ag-modified alloys were unstable when the specimen was aged at 90 C. The plate-like precipitate particles were formed in binary alloys aged from 30 days at 90 C. The plate-like particles had habit planes of f100g , and were identified as the 0 phase which is consistent with the metastable 0 phase (Al 3 Mg 2 , a ¼ 1:002 nm, c ¼ 1:636 nm) in Al-Mg alloys.

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Diffraction contrast from spherically symmetrical coherency strains

Cited by 639 publications

References 12 publications

Nucleation and Precipitation Strengthening in Dilute Al-Ti and Al-Zr Alloys

Nucleation and Precipitation Strengthening in Dilute Al-Ti and Al-Zr Alloys

On the Mechanisms of Hydrogen Implantation Induced Silicon Surface Layer Cleavage

Characterisation of Precipitate Microstructures of Natural and Artificial Ageing in Al-Mg(-Ag) Alloys

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