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Marquis, Emmanelle A.; Seidman, David N |
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Coarsening Kinetics of Nanoscale Al[sub:3]Sc Precipitates in an Al-Mg-Sc Alloy |
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Journal Article |
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2005 |
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Abstract |
Acta Materialia |
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Acta Mater. |
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53 |
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15 |
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Summary Language |
4259-4268 |
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Al3Sc precipitate; Morphology; Coarsening; Transmission electron microscopy; Atom-probe tomography; Al-Sc |
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Abbreviated Series Title |
The effects of Mg alloying on the temporal evolution of Al3Sc (L12 structure) nanoscale precipitates are investigated, focusing on the morphology and coarsening kinetics of Al3Sc precipitates in an Al2.2 Mg0.12 Sc at.% alloy aged between 300 and 400 C. Approximately spheroidal precipitates are obtained after aging at 300 C and irregular morphologies are observed at 400 C. The coarsening behavior is studied using conventional and high-resolution transmission electron microscopies to obtain the temporal evolution of the precipitate radius, and atom-probe tomography is employed to measure the Sc concentration in the α-matrix. The coarsening kinetics are analyzed using a coarsening model developed by Kuehmann and Voorhees for ternary systems [Kuehmann CJ, Voorhees PW. Metall Mater Trans A 1996;27:937]. Values of the interfacial free energy and diffusion coefficient for Sc diffusion in this AlMgSc alloy at 300 C are independently calculated, and are in good agreement with the calculated value of interfacial free energy [Asta M, Ozolins V, Woodward C. JOM 2001;53:16] and the experimental diffusivity obtained for the AlSc system [previous termMarquisnext term EA, previous termSeidmannext term DN. Acta Mater 2001;49:1909; previous termMarquisnext term EA. Ph.D. Thesis. Materials Science and Engineering Department, Northwestern University, 2002; Fujikawa SI. Defect Diffusion Forum 1997;143147:115]. |
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NU @ karnesky @ |
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202 |
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Marquis, Emmanuelle A.; Seidman, David N.; Asta, Mark; Woodward, Christopher |
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Composition Evolution of Nanoscale Al[sub:3]Sc Precipitates in an Al-Mg-Sc Alloy: Experiments and Computations |
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Journal Article |
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2006 |
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Acta Materialia |
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Acta Mater. |
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54 |
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1 |
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119-130 |
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Atom-probe tomography; Ab initio calculations; Al3Sc precipitates; Mg segregation; Coherent heterophase interface; Al-Sc |
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Controlling the distribution of chemical constituents within complex, structurally heterogeneous systems represents one of the fundamental challenges of alloy design. We demonstrate how the combination of recent developments in sophisticated experimental high resolution characterization techniques and ab initio theoretical methods provide the basis for a detailed level of understanding of the microscopic factors governing compositional distributions in metallic alloys. In a study of the partitioning of Mg in two-phase ternary AlScMg alloys by atom-probe tomography, we identify a large Mg concentration enhancement at the coherent α-Al/Al3Sc heterophase interface with a relative Gibbsian interfacial excess of Mg with respect to Al and Sc, Click to view the MathML source, equal to 1.9 0.5 atom nm−2. The corresponding calculated value of Click to view the MathML source is not, vert, similar1.2 atom nm−2. Theoretical ab initio investigations establish an equilibrium driving force for Mg interfacial segregation that is primarily chemical in nature and reflects the strength of the MgSc interactions in an Al-rich alloy. |
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NU @ karnesky @ |
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260 |
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Knipling, Keith E.; Karnesky, Richard A.; Lee, Constance P.; Dunand, David C.; Seidman, David N. |
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Precipitation Evolution in Al-0.1Sc, Al-0.1Zr, and Al-0.1Sc-0.1Zr (at.%) Alloys during Isochronal Aging |
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Journal Article |
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2010 |
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Acta Materialia |
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58 |
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15 |
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5184-5195 |
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Aluminum alloys, Precipitation, Scandium, Zirconium, Atom-probe tomography; Al-Sc-Zr |
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Precipitation strengthening is investigated in binary Al-0.1Sc, Al-0.1Zr, and ternary Al-0.1Sc-0.1Zr (at.%) alloys aged isochronally between 200 and 600 °C. A pronounced synergistic effect is observed when both Sc and Zr are present. Above 325 °C, where peak microhardness (670 MPa) occurs in the binary Al-Sc alloy due to Al[sub:3]Sc (L1[sub:2]) nanometer-scale precipitates, Zr additions result in a secondary increase in strength due to additional precipitation of Zr-enriched outer shells onto these precipitates. The ternary alloy reaches a peak microhardness of 780 MPa at 400 °C, delaying overaging by >100 °C compared with the binary Al-Sc alloy and increasing strength compared with the binary Al-Zr alloy (peak microhardness of 420 MPa at 425–450 °C). Compositions, radii, volume fractions, and number densities of the Al[sub:3](Sc[sub:1-x]Zr[sub:x]) precipitates are measured directly using atom-probe tomography. This information is used to quantify the observed strengthening increments, attributed to dislocation shearing of the Al[sub:3](Sc[sub:1-x]Zr[sub:x]) precipitates. |
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NU @ karnesky @ |
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10705 |
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Vo, Nhon Q.; Dunand, David C.; Seidman, David N. |
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Atom probe tomographic study of a friction-stir-processed Al-Mg-Sc alloy |
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Journal Article |
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2012 |
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Acta Materialia |
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In Press |
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Al-Mg-Sc alloy; Friction-stir process; Atom probe tomography; Strengthening |
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The microstructure of a twin-roll-cast Al-4.5Mg-0.28Sc at.% alloy after friction-stir processing, performed at two tool rotational rates, was investigated by atom probe tomography. Outside the stir zone, the peak-aged alloy contains a high number density (~8.0 × 1023 m-3) of ~1.5 nm radius Al3Sc (L12) precipitates with a minor Mg content, providing an increase of ~600 MPa in the Vickers microhardness. In the stir zone of the sample processed at 400 rpm rotational rate, the microhardness increase is mainly due to grain refinement, rather than precipitate strengthening, because the Al3Sc precipitates, with spherical lobed cuboids and platelet-like morphology, grow and coarsen to a 10-20 nm radius. The Sc supersaturation across the stir-processed zone has a concentration gradient, which is higher on the retreating side and lower on the advancing side of the friction-stir tool. Hence, after aging at 290 °C for 22 h, the microhardness increase within the stir zone also displays a gradient due to precipitate strengthening with varying precipitate volume fractions. In the stir zone for the sample processed at 325 rpm rotational rate, the microhardness increase is also predominantly due to grain refinement, as coarse Al3Sc precipitates form heterogeneously at grain boundaries with a platelet-like morphology. The hardness remains unchanged after a 290 °C aging treatment. This is because the Al3Sc precipitates are highly heterogeneously distributed due to a combination of a small Sc supersaturation (0.05 at.%) in the matrix, the existence of dislocations, and a large area per unit volume of grain boundaries (~4-6 × 106 m-1). |
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1359-6454 |
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NU @ karnesky @ |
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11400 |
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van Dalen, M. E.; Dunand, D. C.; Seidman, D. N. |
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Effects of Ti Additions on the Nanostructure and Creep Properties of Precipitation-Strengthened Al-Sc Alloys |
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Journal Article |
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2005 |
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Acta Materialia |
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Acta Mater. |
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53 |
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15 |
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4225-4235 |
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Aluminum alloys; Precipitation; Coarsening; Three-dimensional atom-probe tomography; Creep; Al-Sc |
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Three-dimensional atom-probe tomography, transmission electron microscopy and microhardness were used to investigate the temporal evolution of nanosize, coherent Al3(Sc1−xTix) precipitates (L12 structure) in a coarse-grained Al0.06at.%Sc0.06at.%Ti alloy aged between 300 and 450 C. At 300 C, most scandium atoms partition within one day to the precipitates, whereas titanium atoms, even after 64 days of aging, remain predominantly in solid solution in the matrix, resulting in precipitates with average composition Al3(Sc0.94Ti0.06). While titanium is very effective at retarding the coarsening kinetics of the precipitates, the low levels of titanium substitution result in only modest hardness increases over the binary Al0.06at.%Sc alloy. When crept at 300 C, the peak-aged alloy exhibits a threshold stress, which when normalized by the Orowan stress, increases with increasing radius, as predicted by a recent model considering elastic interactions between dislocations and coherent precipitates, and as previously observed in AlScZr alloys. |
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NU @ vandalen @ |
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201 |
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van Dalen, Marsha E.; Gyger, Thomas; Dunand, David C.; Seidman, David N. |
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Effects of Yb and Zr microalloying additions on the microstructure and mechanical properties of dilute Al–Sc alloys |
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Journal Article |
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2011 |
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Acta Materialia |
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59 |
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20 |
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7615-7626 |
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Aluminum alloys; Nucleation; Precipitation; Coarsening; Creep; Al-Sc |
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It is known that Zr and Yb partition to the Al3Sc precipitates created during aging when microalloyed separately in dilute binary Al–Sc alloys. Addition of Zr delays precipitate coarsening, thereby improving the coarsening resistance of the ternary Al-Sc-Zr alloys. Addition of Yb increases the resistance against dislocation climb, thereby improving the creep resistances of the ternary Al-Sc-Yb alloys. A combination of microhardness, creep, and atom probe tomography measurements provide evidence that these effects of Zr and Yb additions are cumulative in quaternary dilute Al–Sc–Yb–Zr alloys: Yb increases their creep resistance at 300 °C compared with ternary Al–Sc–Zr alloys and Zr improves their coarsening resistance at 300 °C compared with ternary Al–Sc–Yb alloys. Additionally, excellent coarsening resistance is observed at 350 and 375 °C. |
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1359-6454 |
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NU @ karnesky @ |
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11325 |
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Karnesky, Richard A.; Dunand, David C.; Seidman, David N. |
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Evolution of Nanoscale Precipitates in Al Microalloyed with Sc and Er |
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Journal Article |
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2009 |
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Acta Materialia |
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Acta Mater. |
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57 |
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14 |
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4022-4031 |
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Aluminum alloys; Rare-earth elements; Scandium; Precipitation; Coarsening; Al-Sc-Er |
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The coarsening kinetics of nanoscale, coherent Al[sub:3](Sc[sub:1-x]Er[sub:x]) precipitates in [alpha]–Al during aging of a supersaturated Al–0.06 Sc–0.02 Er (at.%) alloy at 300 °C are studied using transmission electron microscopy and local-electrode atom-probe tomography. Erbium and Sc segregate at the precipitate core and shell, respectively. The matrix supersaturations of Er and Sc, as well as the mean precipitate radius and number density evolve in approximate agreement with coarsening models, allowing the determination of the matrix/precipitate interfacial free energy and solute diffusivities. At 300 °C, the [alpha]–Al/Al[sub:3](Sc[sub:1-x]Er[sub:x]) interfacial free energy due to Sc is about twice as large as for [alpha]–Al/Al[sub:3]Sc. The diffusivity of Er in the ternary alloy is about three orders of magnitude smaller than that of Er in binary Al–0.045 at.% Er and about two orders of magnitude smaller than the diffusivity of Sc in binary Al–Sc. The measured Sc diffusivity is consistent with literature values. |
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NU @ karnesky @ |
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10599 |
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Harada, Y.; Dunand, D.C. |
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Creep Properties of Al[sub:3]Sc and Al[sub:3](Sc, X) Intermetallics |
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Journal Article |
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2000 |
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Acta Materialia |
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Acta Mater. |
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48 |
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13 |
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3477-3487 |
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Journal Article; Aluminum compounds, Mechanical properties; Scandium compounds, Mechanical properties; Intermetallics, Mechanical properties; Titanium, Alloying additive; Yttrium, Alloying additive; Zirconium, Alloying additive; Hafnium, Alloying additive; Creep (materials), Alloying effects; Dislocation mobility, Deformation effects; Al-Sc; mechanical properties creep intermetallic compounds bulk diffusion scandium microstructure high-temperature creep l12 trialuminides self-diffusion behavior fracture films al3ti compression chromium aluminum |
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A systematic creep study was undertaken for the binary intermetallic Al sub 3 Sc and the ternary single-phase intermetallic Al sub 3 (Sc sub 0.74 X sub 0.26 ), where X is one of the transition-metals Ti, Y, Zr or Hf. Creep tests were conducted in the temperature range from 673-1200K under a constant compressive stress ranging from 30-300 MPa. The binary Al sub 3 Sc exhibits a stress exponent of 4.4-4.9 indicative of creep controlled by climb of dislocations. The activation energy for creep of Al sub 3 Sc was 128plus/minus6 kJ/mol, close to that for self-diffusion for pure aluminum, in agreement with the Cu sub 3 Au rule, indicating that diffusion on the Al-sublattice is controlling. Ternary Al sub 3 (Sc sub 0.74 X sub 0.26 ) exhibits a decrease in creep rate by about one order of magnitude for Zr and Hf and by about two orders of magnitude for Ti and Y. For all ternary alloys, a stress exponent of 3.9-5.5 was observed, indicative of dislocation creep. Activation energies for creep of 202plus/minus8 kJ/mol were found, showing that ternary substitution for scandium with transition metals affects diffusion on the Al sublattice. |
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Northwestern University (Evanston); Ministry of International Trade and Industry (Japan) |
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English |
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1359-6454 |
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37 ref., Photomicrographs, Graphs, Numerical Data |
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NU @ karnesky @ |
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544 |
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Marquis, E. A.; Seidman, D. N. |
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Nanoscale Structural Evolution of Al[sub:3]Sc Precipitates in Al(Sc) Alloys |
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Journal Article |
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2001 |
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Acta Materialia |
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Acta Mater. |
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49 |
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11 |
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1909-1919 |
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aluminum scandium transmission electron microscopy (tem) phase transformations microstructure al-sc alloys creep-properties nucleation scandium aluminum intermetallics kinetics growth energy; Al-Sc |
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Precipitation of the Al3Sc (L12) phase in aluminum alloys, containing 0.1, 0.2 or 0.3 wt% Sc, is studied with conventional transmission and high-resolution (HREM) electron microscopies. The exact morphologies of the Al3Sc precipitates were determined for the first time by HREM, in Al–0.1 wt% Sc and Al–0.3 wt% Sc alloys. The experimentally determined equilibrium shape of the Al3Sc precipitates, at 300°C and 0.3 wt% Sc, has 26 facets, which are the 6 {100} (cube), 12 {110} (rhombic dodecahedron), and 8 {111} (octahedron) planes, a Great Rhombicuboctahedron. This equilibrium morphology had been predicted by first principles calculations of the pertinent interfacial energies. The coarsening kinetics obey the (time)1/3 kinetic law of Lifshitz–Slyozov–Wagner theory and they yield an activation energy for diffusion, 164±9 kJ/mol, that is in agreement with the values obtained from tracer diffusion measurements of Sc in Al and first principles calculations, which implies diffusion-controlled coarsening. |
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Seidman, D. N. Northwestern Univ, Dept Mat Sci & Engn, 2225 N Campus Dr, Evanston, IL 60208 USA Northwestern Univ, Dept Mat Sci & Engn, Evanston, IL 60208 USA |
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NU @ karnesky @ |
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568 |
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Mao, Z.; Chen, W.; Seidman, D.N.; Wolverton, C. |
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First-principles study of the nucleation and stability of ordered precipitates in ternary Al-Sc-Li alloys |
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Journal Article |
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2011 |
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Acta Materialia |
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59 |
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3012-3023 |
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Al-Sc-Li; First principles; Interfacial energy; Core/shell structures; Site substitution |
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First-principles density functional calculations are used to study the nucleation and stability of L12-ordered precipitates in Al-Sc-Li alloys. For dilute Al alloys, there are three possible ordered L12 precipitates: Al3Sc, Al3Li and an Al3Sc/Al3Li core/shell structure. To calculate the nucleation behavior, information about bulk thermodynamics (both static total energies and vibrational free energies), interfacial energetics and coherency strain is required. The study finds the following: (1) the coherency strain energies for forming coherent interfaces between Al/Al3Sc, Al/Al3Li and Al3Sc/Al3Li are relatively small, owing to the small atomic size mismatches in these systems; (2) the sublattice site preferences of Sc and Li are calculated, and it is demonstrated that Sc and Li share the same sublattice sites in both Al3Sc(L12) and Al3Li(L12), in agreement with recent experimental results; (3) the calculated solubilities of Sc and Li in [alpha]-Al alloys are in good agreement with experimental values and, for Sc, agree well with prior first-principles results; (4) the interfacial energies for Al/Al3Sc, Al/Al3Li and Al3Sc/Al3Li for (1 0 0), (1 1 0) and (1 1 1) interfaces are calculated: the values of the Al/Al3Sc interfacial energies are significantly larger than those of the Al/Al3Li and Al3Sc/Al3Li interfaces; (5) combining the bulk and interfacial energies yields the nucleation barriers and critical radii for Al3Sc and Al3Li precipitates; and (6) the energetic stability of the Al3Sc/Al3Li core/shell structure is compared with individual Al3Sc and Al3Li nuclei, and the range of precipitate sizes for which the core/shell structure is energetically favored is determined quantitatively. |
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1359-6454 |
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NU @ karnesky @ |
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11034 |
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