A discrete lattice plane analysis of the interfacial energy of coherent F.C.C.: H.C.P. interfaces and its application to the nucleation of γ in AlAg alloys

Ramanujan, R.V.; Lee, J.K.; Aaronson, H.I.

doi:10.1016/0956-7151(92)90056-k

Cited by 25 publications

(12 citation statements)

References 30 publications

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“…(b) HAADF-STEM image of θ ′ phase with Ag on one interface. for the γ ′ (AlAg 2 ) phase, having the lowest interfacial energy [19]. The semi-coherent interfaces are less well resolved along the [001] zone, ( Fig.…”

Section: Semi-coherent θ ′ -Al Interfacesmentioning

confidence: 99%

“…Calculations of the interface energies for the Al-θ ′ coherent precipitate-matrix interfaces have provided values 1 ranging from 156 mJ.m −2 using molecular dynamics [22] to 190 mJ.m −2 for some first-principles calculations [23]. Discrete lattice plane method calculations for coherent γ ′ -Al {111} interfaces estimated a much lower energy of 6.5 mJ.m −2 , with facets on other planes in the range 6.3-7.1 mJ.m −2 [19]. Wetting of the {001} θ ′ -Al coherent interface would therefore reduce the interfacial energy with the matrix by replacing the higher energy θ ′ -Al interface with a Ag-Al interface.…”

Section: Silver Segregation To θ ′ -Al Interfacesmentioning

confidence: 99%

“…The edge of the θ ′ precipitate is jagged, with the adhering Ag bi-layer having facets that alternate between (111) and (111) planes. It is notable that these are preferred habit planes for the γ ′ (AlAg 2 ) phase, having the lowest interfacial energy [19]. The semi-coherent interfaces are less well resolved along the [001] zone, (Fig.…”

Section: Semi-coherent θ ′ -Al Interfacesmentioning

confidence: 99%

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Silver segregation to θ′ (Al2Cu)–Al interfaces in Al–Cu–Ag alloys

2012

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θ ′ (Al 2 Cu) precipitates in Al-Cu-Ag alloys were examined using high angle annular dark field scanning transmission electron microscopy (HAADF-STEM). The precipitates nucleated on dislocation loops on which assemblies of γ ′ (AlAg 2 ) precipitates were present. These dislocation loops were enriched in silver prior to θ ′ precipitation. Coherent, planar interfaces between the aluminium matrix and θ ′ precipitates were decorated by a layer of silver of two atomic layers in thickness. It is proposed that this layer lowers the chemical component of the Al-θ ′ interfacial energy. The lateral growth of the θ ′ precipitates was accompanied by the extension of this silver bi-layer, resulting in the loss of silver from neighbouring γ ′ precipitates and contributing to the deterioration of the γ ′ precipitate assemblies. Pre-printSilver segregation to θ ′ -Al interfaces in Al-Cu-Ag alloys J.M.Rosalie & L. Bourgeois forms with {111} habit instead of {100} and displays remarkable coarsening resistance. Drift corrected energy dispersive x-ray analysis [7] and 3D atom probe studies [8] have shown that Ag and Mg both segregate to the Ω-Al matrix interface. The Ω phase has a distinctive interface structure, with a bilayer of Ag atoms at the coherent interface with the matrix [9]. Density functional theory calculations indicated while substitution of either Mg or Ag alone was energetically unfavourable, a combination of both elements provided a lower-energy interface [10].Recent work has shown that compositional changes at the θ ′ -matrix interface occur in other alloys. Silicon was found to segregate to the coherent {100} interfaces of the θ ′ phase in Al-Cu-Si alloys, substituting for Cu sites in the precipitate [11]. It has also been demonstrated that the interface composition and structure of θ ′ in binary Al-Cu differs substantially from the bulk structure, with additional Cu atoms occupying octahedral interstices in the precipitate [12]. Despite these studies a detailed understanding of precipitate-matrix interfaces has yet to be developed in the majority of Al alloys.Aluminium-copper-silver (Al-Cu-Ag) alloys are ideal for studying the effect of a third element on the precipitation of the θ ′ phase. Unlike many ternary systems (e.g. Al-Cu-Mg) the Al-rich region of the phase field contains only binary phases [13], eliminating the complexities associated with competing ternary phase precipitation. The interatomic spacing in pure Ag also corresponds very closely to that of pure Al, and substantial additions of silver have little effect on the lattice parameter of Al [14,15]. Solute misfit can therefore be regarded as minimal, and solute-induced strain can be largely neglected. In addition, the chemical affinity between Ag and Cu atoms is weak and the strong co-clustering behaviour exhibited by systems such as Al-Si-Mg is not observed.Early studies on Al-Cu-Ag alloys established that for compositions of ∼1at.%(Ag,Cu) both γ ′ (AlAg 2 ) and θ ′ precipitates were formed [16] and it been shown that both phases can form on disloc...

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Section: Semi-coherent θ ′ -Al Interfacesmentioning

confidence: 99%

Section: Silver Segregation To θ ′ -Al Interfacesmentioning

confidence: 99%

Section: Semi-coherent θ ′ -Al Interfacesmentioning

confidence: 99%

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Silver segregation to θ′ (Al2Cu)–Al interfaces in Al–Cu–Ag alloys

2012

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“…[12,14] Compared with the FCC/BCC and HCP/BCC systems, the HCP/FCC system has attracted much less attention. Ramanujan and co-workers [15,16] proposed a discrete lattice plane model to analyze the composition profile and surface energy between HCP and FCC structures in an Al-Ag alloy. Using the atomic site correspondence concept, Howe [17] considered that both the martensitic transformation and diffusion-controlled phase transformation could lead to the formation of surface relief in the FCC to HCP transformation.…”

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confidence: 99%

Crystallography of the Simple HCP/FCC System

Zhang

Chen

Ren

et al. 2008

Metall Mater Trans A

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The edge-to-edge matching model has been used to predict the orientation relationships (ORs) between crystals that have simple hexagonal-close-packed (HCP) and face-centered-cubic (FCC) structures. Using the critical values for the interatomic spacing misfit along the matching directions and the d-value mismatch between matching planes, a total of seven ORs have been predicted for the most common HCP/FCC metallic systems. However, the ORs that appear more frequently in a particular system depend on the type of matching directions and the interatomic spacing misfit along these directions together with the d-value mismatch between the matching planes. The latter two are related to the lattice parameters of both phases. For example, in the Al/Ag 2 Al system, three ORs have been predicted.

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“…The low volumetric strain for the precipitation of the γ ′ phase, together with the coherent broad faces and low estimates for the interfacial energy [9], would suggest that precipitation should proceed readily. However, silver-rich Guinier-Preston zones are known to survive 120 h of ageing at 160 o C [3], indicating that significant solute remains in the matrix rather than partitioning to the γ ′ phase.…”

Section: Introductionmentioning

confidence: 99%

Precipitate assemblies formed on dislocation loops in aluminium-silver alloys

Rosalie

Bourgeois

Muddle

2009

Philosophical Magazine

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A detailed study of the precipitation of the γ ′ (AlAg 2 ) phase in undeformed aluminium-silver alloys has been conducted. Several previously unreported features were observed, including the formation of discrete three-dimensional assemblies comprised of 5-7 precipitates on faulted dislocation loops. The precipitates assemblies adopted a morphology approximating a tetrahedral bipyramidal assembly. The bounding defect of the stacking fault was found to control both the nucleation of additional precipitates which was responsible for the formation of the assembly structure and also the growth characteristics of individual precipitates with these assemblies.

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A discrete lattice plane analysis of the interfacial energy of coherent F.C.C.: H.C.P. interfaces and its application to the nucleation of γ in AlAg alloys

Cited by 25 publications

References 30 publications

Silver segregation to θ′ (Al2Cu)–Al interfaces in Al–Cu–Ag alloys

Silver segregation to θ′ (Al2Cu)–Al interfaces in Al–Cu–Ag alloys

Crystallography of the Simple HCP/FCC System

Precipitate assemblies formed on dislocation loops in aluminium-silver alloys

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