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Type Krug, ME; Dunand, DC; Seidman, DN
  Publication Composition Profiles within Al3Li and Al3Sc/Al3Li Nanoscale Precipitates in Aluminum Volume Journal Article
Pages (down) 2008
  Abstract Applied Physics Letters  
  Corporate Author App. Phys. Let.  
Publisher 92  
Editor
  Summary Language 124107-1 - 124107-3 Series Editor Al; Sc; Li; Aluminum; Scandium; Lithium; Core-shell Precipitates; Al-Sc  
Abbreviated Series Title An Al–11.3Li–0.11Sc (at. %) alloy was double-aged to induce first Alpha'-Al3Sc and then delta'-Al3Li precipitates. Atom-probe tomography revealed both single-phase delta'-precipitates and core-shell alpha'/delta'-precipitates (with respective average radii of 16 and 27 nm, and respective volume fractions of 12 and 9%) conferring a high strength to the alloy. Although the delta'-shells contain little Sc (~0.027 at. %), the alpha'-cores have a high Li content, with an average composition of Al0.72(Sc0.17Li0.11). The Li concentrations within the delta'-phase and the Li interfacial excess at the delta'/alpha'-interface both exhibit wide precipitate-to-precipitate variations.
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no NU @ m-krug @ 10263
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Biswas, Aniruddha; Siegel, Donald J.; Seidman, David N. Simultaneous Segregation at Coherent and Semi-coherent Heterophase Interfaces Journal Article 2010 Physical Review Letters 105 7 076102-76103 Al-Cu Employing a combination of three-dimensional atom-probe tomography and first-principles calculations, significant qualitative and quantitative differences in solute segregation at coherent and semi-coherent interfaces bounding a single θ'-precipitate in an Al-Cu-based alloy are found. Qualitatively, localized segregation is observed at the semi-coherent interface, whereas delocalized behavior is present at the coherent facets. Quantitatively, segregation at the semi-coherent interface is a factor of two greater than at the coherent interface, resulting in a decrease in interfacial energy that is more than five times greater than that observed at the coherent facet. These observations illustrate unambiguously the strong couplings among interface structure, chemical composition, and energetics. no NU @ karnesky @ 10810
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Marquis, E. A.; Seidman, D. N.; Asta, M.; Woodward, C.; Ozolins, V. Mg Segregation at Al/Al[sub:3]Sc Heterophase Interfaces on an Atomic Scale: Experiments and Computations Journal Article 2003 Physical Review Letters 91 3 036101: 1-4 Al-Sc alloys total-energy calculations wave basis-set molecular-dynamics transition aluminum precipitation diffusion scandium metals Microscopic factors governing solute partitioning in ternary two-phase Al-Sc-Mg alloys are investigated combining three-dimensional-atom-probe (3DAP) miscroscopy measurements with first-principles computations. 3DAP is employed to measure composition profiles with subnanometer-scale resolution, leading to the identification of a large enhancement of Mg solute at the coherent alpha -Al/Al3Sc (fcc/L12) heterophase interface. First-principles calculations establish an equilibrium driving force for this interfacial segregation reflecting the nature of the interatomic interactions. Marquis, E. A. Sandia Natl Labs, Livermore, CA 94551 USA USAF, Res Lab, Mat & Mfg Directorate, Wright Patterson AFB, OH 45433 USA Northwestern Univ, Dept Mat Sci & Engn, Evanston, IL 60208 USA Univ Calif Los Angeles, Dept Mat Sci & Engn, Los Angeles, CA 90095 USA no NU @ karnesky @ 40
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van Dalen, Marsha E.; Dunand, David C.; Seidman, David N. Nanoscale Precipitation and Mechanical Properties of Al-0.06 at.% Sc Alloys Micro-Alloyed with Yb or Gd Journal Article 2006 Journal of Materials Science 41 23 7814-7823 Aluminum alloys; Precipitation; Nucleation; Three-dimensional atom-probe tomography; Rare earth elements; Al-Sc Dilute Al-0.06 at.% Sc alloys with micro-alloying additions of 50 at. ppm of Yb or Gd are studied with 3-D local-electrode atom-probe (LEAP) tomography for different aging times at 300C. Peak-aged alloys exhibit Al3(Sc1-xYbx) or Al3(Sc1-xGdx) precipitates (L12 structure) with a much higher number density (and therefore higher peak hardness) than a binary Al-0.06 at.% Sc alloy. The Al-Sc-Gd alloy exhibits a higher number density of precipitates with a smaller average radius than the Al-Sc-Yb alloy, leading to a higher hardness. In the Al-Sc-Gd alloy, only a small amount of the Sc is replaced by Gd in the Al3(Sc1-xGdx) precipitates, where x = 8.0%. By contrast, the hardness incubation time is significantly shorter in the Al-Sc-Yb alloy, due to the formation of Yb-rich Al3(Yb1-xScx) precipitates to which Sc subsequently diffuses, eventually forming Sc-rich Al3(Sc1-xYbx) precipitates. For both alloys, precipitate radii are found to be relatively stable up to 24 h of aging, although the concentration and distribution of the RE elements in the precipitates continues to evolve temporally. Similar to microhardness at ambient temperature, the creep resistance at 300C is significantly improved by RE microalloying of the binary Al-Sc alloy. no NU @ karnesky @ 767
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van Dalen, Marsha E.; Gyger, Thomas; Dunand, David C.; Seidman, David N. Effects of Yb and Zr microalloying additions on the microstructure and mechanical properties of dilute Al–Sc alloys Journal Article 2011 Acta Materialia 59 20 7615-7626 Aluminum alloys; Nucleation; Precipitation; Coarsening; Creep; Al-Sc 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. 1359-6454 no NU @ karnesky @ 11325
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Fuller, Christian B.; Seidman, David N. Temporal Evolution of the Nanostructure of Al(Sc,Zr) Alloys: Part II—Coarsening of Al[sub:3]Sc[sub:1-x]Zr[sub:x] Precipitates Journal Article 2005 Acta Materialia Acta Mater. 53 20 5415-5428 Al-Sc-Zr; Phase Transformations; nanostructure; Transmission electron microscopy (TEM), The coarsening behavior of four Al(Sc,Zr) alloys containing small volume fractions (< 0.01) of Al3(Sc1-xZrx) (L12) precipitates was investigated employing conventional transmission electron microscopy (CTEM) and high-resolution electron microscopy (HREM). The activation energies for diffusion-limited coarsening were obtained employing the Umantsev-Olson-Kuehmann-Voorhees (UOKV) model for multi-component alloys. The addition of Zr is shown to retard significantly the coarsening rate and stabilize precipitate morphologies. HREM of Al(Sc,Zr) alloys aged at 300C reveals Al3(Sc1-xZrx) precipitates with sharp facets parallel to {100} and {110} planes. Coarsening of Al-0.07 Sc-0.019 Zr at.%, Al-0.06 Sc-0.005 Zr at.%. and Al-0.09 Sc-0.047 Zr at.% alloys is shown to be controlled by volume diffusion of Zr atoms, while coarsening of Al-0.14 Sc-0.012 Zr et al. is controlled by volume diffusion of Sc atoms. no NU @ karnesky @ 235
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Fuller, Christian B.; Murray, Joanne L.; Seidman, David N. Temporal Evolution of the Nanostructure of Al(Sc,Zr) Alloys: Part I—Chemical Compositions of Al[sub:3](Sc[sub:1-x]Zr[sub:x]) Precipitates Journal Article 2005 Acta Materialia Acta Mater. 53 20 5401-5413 Al-Sc-Zr alloys; Precipitation; Microstructure; High-resolution electron microscopy; Three-dimensional atom-probe microscopy Atom-probe tomography (APT) and high-resolution transmission electron microscopy are used to study the chemical composition and nanostructural temporal evolution of Al3(Sc1-xZrx) precipitates in an Al-0.09 Sc-0.047 Zr at.% alloy aged at 300C. Concentration profiles, via APT, reveal that Sc and Zr partition to Al3(Sc1-xZrx) precipitates and Zr segregates concomitantly to the &#945;-Al/Al3(Sc1-xZrx) interface. The Zr concentration in the precipitates increases with increasing aging time, reaching a maximum value of 1.5 at.% at 576 h. The relative Gibbsian interfacial excess () of Zr, with respect to Al and Sc, reaches a maximum value of 1.240.62 atoms nm-2 after at 2412 h. The temporal evolution of Al3(Sc1-xZrx) precipitates is determined by measuring the time dependence of the depletion of the matrix supersaturation of Sc and Zr. The time dependency of the supersaturation of Zr does not follow the asymptotic t-1/3 law while that of Sc does, indicating that a quasi-stationary-state is not achieved for both Sc and Zr. no NU @ karnesky @ 172
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Knipling, Keith E.; Karnesky, Richard A.; Lee, Constance P.; Dunand, David C.; Seidman, David N. Precipitation Evolution in Al-0.1Sc, Al-0.1Zr, and Al-0.1Sc-0.1Zr (at.%) Alloys during Isochronal Aging Journal Article 2010 Acta Materialia 58 15 5184-5195 Aluminum alloys, Precipitation, Scandium, Zirconium, Atom-probe tomography; Al-Sc-Zr 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. no NU @ karnesky @ 10705
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Fuller, Christian B.; Seidman, David N.; Dunand, David C. Mechanical Properties of Al(Sc,Zr) Alloys at Ambient and Elevated Temperatures Journal Article 2003 Acta Materialia Acta Mater. 51 16 4803-4814 al-sc-zr alloys mechanical properties creep deformation mechanisms strengthened alloys threshold stress creep-properties al3sc microstructure particles additions evolution model sc This study investigates the mechanical properties of ternary Al(Sc,Zr) alloys containing 0.27–0.77 vol.% of Al3(Sc,Zr) precipitates with an average radius left angle bracketrright-pointing angle bracket=2&#8722;24 nm. Microhardness values at ambient temperature follow predictions of the Orowan dislocation bypass mechanism, with a transition to the precipitate shearing mechanism predicted for left angle bracketrright-pointing angle bracket larger than 2 nm. Addition of Zr to binary Al(Sc) alloys delays the onset and kinetics of over-aging at 350 and 375 °C, but has little influence on the magnitude of the peak microhardness. Creep deformation at 300 °C is characterized by a threshold stress, which increases with left angle bracketrright-pointing angle bracket in the range 2–9 nm, in agreement with prior results for binary Al(Sc) alloys and a recently developed general climb model considering elastic interactions between dislocations and coherent, misfitting precipitates. At constant left angle bracketrright-pointing angle bracket and precipitate volume fraction, Zr additions do not significantly improve the creep resistance of Al(Sc) alloys. Dunand, D. C. Northwestern Univ, Dept Mat Sci & Engn, 2220 Campus Dr, Evanston, IL 60208 USA Northwestern Univ, Dept Mat Sci & Engn, Evanston, IL 60208 USA no NU @ karnesky @ 224
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Marquis, Emmanuelle A.; Seidman, David N.; Dunand, David C. Effect of Mg Addition on the Creep and Yield Behavior of an Al–Sc Alloy Journal Article 2003 Acta Materialia Acta Mater. 51 16 4751-4760 Transmission electron microscopy; Aluminum alloys; Coarsening; Creep; Al3Sc precipitates; olid-solution alloys dislocation climb viscous glide deformation stress dependence particles fracture; Al-Sc The relationships between microstructure and strength were studied at room temperature and 300 °C in an Al–2 wt% Mg–0.2 wt% Sc alloy, containing Mg in solid-solution and Al3Sc (L12 structure) as nanosize precipitates. At room temperature, the yield strength is controlled by the superposition of solid-solution and precipitation strengthening. At 300 °C and at large applied stresses, the creep strength, which is characterized by a stress exponent of ~5, is significantly improved compared to binary Al–Sc alloys, and is independent of the size of the Al3Sc precipitates. At small applied stress, a threshold stress exists, increasing from 9% to 70% of the Orowan stress with increasing Al3Sc precipitate radius from 2 to 25 nm. An existing model based on a climb-controlled bypass mechanism is in semi-quantitative agreement with the precipitate radius dependence of the threshold stress. The model is, however, only valid for coherent precipitates, and the Al3Sc precipitates lose coherency for radii larger than 11 nm. For semi-coherent precipitates with radii greater than 15 nm, the threshold stress remains high, most likely because of the presence of interfacial misfit dislocations. Marquis, E. A. Sandia Natl Labs, Thin Film & Interface Dept, Livermore, CA 94550 USA Northwestern Univ, Dept Mat Sci & Engn, Evanston, IL 60208 USA no NU @ karnesky @ 212
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