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Fuller, Christian B.; Krause, Albert R.; Dunand, David C.; Seidman, David N. |
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Microstructure and Mechanical Properties of a 5754 Aluminum Alloy Modified by Sc and Zr Additions |
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Journal Article |
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2002 |
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Abstract |
Materials Science and Engineering A |
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Mater. Sci. Eng. A |
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338 |
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1-2 |
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Summary Language |
8-16 |
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Al-Sc-Zr alloys; Fatigue (materials); Mechanical properties; Aluminum alloys; Microstructural properties |
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Abbreviated Series Title |
The effects of various heat treatments upon the microstructure and mechanical properties of a rolled 5754 aluminum alloy modified with 0.23 wt.% Sc and 0.22 wt.% Zr were investigated. Grain size, as well as precipitate size, type, and morphology were observed by optical and transmission electron microscopies. Two populations of the Al3Sc1-xZrx phase were present: (i) large incoherent precipitates formed during solidification and hot-rolling; and (ii) fine coherent precipitates formed from secondary precipitation, which improved alloy strength, as shown by hardness, tensile, and fatigue measurements. Aging, however, also produced two types of grain-boundary precipitates, Al6Mn and -Al3Mg2, which contributed to poorer fatigue behavior and reduced ductility. |
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NU @ karnesky @ |
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526 |
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Harada, Y.; Dunand, D.C. |
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Microstructure of Al[sub:3]Sc with Ternary Transition-Metal Additions |
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Journal Article |
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2002 |
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Materials Science and Engineering A |
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Mater. Sci. Eng. A |
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329-331 |
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686-695 |
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L12-trialuminides; Microstructure; Lattice parameter; Microhardness; Al-Sc |
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The microstructure of binary Al3Sc and ternary Al3(Sc1-yXy), where X is one of the transition metals from Group IIIA (Y), IVA (Ti, Zr or Hf) or VA (V, Nb or Ta), was investigated as a function of alloying element concentration for 0.1y0.75. Alloys with Group IIIA and IVA additions exhibited a single L12 solid-solution phase with some Kirkendall porosity. At the highest concentration studied, a second phase precipitated with the D019 (Y), D022 (Ti) or D023 (Zr and Hf) structure. Conversely, alloys with Group VA additions exhibited both the L12 trialuminide phase and a dendritic trialuminide second phase with D022 structure for all concentrations studied. The solubility limit in the ternary L12-type Al3(Sc1-yXy) phase was high for Group IIIA and IVA metals (almost 12.5 at.% or y=0.5), and much lower for Group VA metals (from about 1.8 at.% or y=0.07 for Ta to about 2.7 at.% or y=0.11 for V). Similarly, the solubility limit of Sc in the non-L12 phases decreases from the Group IIIA trialuminide to the Group VA trialuminides. The lattice parameter of the L12 solid-solution decreased linearly with increasing concentration of Group IVA and VA metals, but increased linearly with concentration of Y (Group IIIA). This linear concentration dependence of the lattice parameter is found to correlate with the atomic size mismatch between Sc and the transition metal. The microhardness of the L12 solid-solution increased linearly with increasing concentration of ternary elements. The concentration dependence of hardness is strongest for Group VA metals and weakest for Group IVA metals, for which a correlation is found with the concentration dependence of lattice parameter. |
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NU @ karnesky @ |
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543 |
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Karnesky, Richard A.; van Dalen, Marsha E.; Dunand, David C.; Seidman, David N. |
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Effects of Substituting Rare-Earth Elements for Scandium in a Precipitation-Strengthened Al 0.08 at.% Sc Alloy |
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Journal Article |
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2006 |
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Scripta Materialia |
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Scripta Mater. |
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55 |
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5 |
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437-440 |
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Aluminum alloys; Scandium; Rare-earth elements; Lanthanides, Precipitation strengthening; Local-Electrode Atom-Probe tomography; LEAP; Al-Sc |
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The microhardness of Al-0.06 Sc-0.02 RE (at.%, with RE = Dy, Er, Gd, Sm, Y, or Yb) alloys is measured as a function of aging time at 300C. As compared to Al-0.08 Sc, the ternary alloys exhibit: (i) the same incubation time, except for Al-0.06 Sc-0.02 Yb which hardens much faster; (ii) the same or reduced peak microhardnesses (which are higher than for Al-0.06 Sc) and (iii) the same overaging behavior. All RE segregate to the core of Al[sub:3](Sc[sub:1-x]RE[sub:x]) precipitates. |
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NU @ karnesky @ |
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779 |
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Beeri, Ofer; Dunand, David C.; Seidman, David N. |
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Role of Impurities on Precipitation Kinetics of Dilute Al-Sc alloys |
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Journal Article |
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2010 |
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Materials Science and Engineering A |
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527 |
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15 |
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3501-3509 |
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Dilute aluminum alloys, Scandium, Precipitation, Impurities, Atom Probe; Al-Sc |
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High purity (HP) aluminum and commercial purity (CP) aluminum (major impurities: ~250
at. ppm Si and ~130 at. ppm Fe) are alloyed with ~250 to ~1100 at. ppm Sc and ~50 at. ppm
RE (RE = La, Ce, Pr, or Nd). The alloys are homogenized at 640 C and aged at 300 C. The
precipitation kinetics, basic mechanical properties, and microstructure are studied using AC
electrical conductivity, microhardness measurements, scanning electron microscopy in
conjunction with energy dispersive x-ray spectroscopy, and atom-probe tomography,
respectively. The Fe and RE elements form micrometer-scale diameter Al~3(Fe,RE) primary
precipitates, which have no effect on the mechanical properties. Silicon accelerates the
precipitation kinetics of nanometer-scale diameter Al3Sc precipitates, increasing their number
density, thereby resulting in a higher microhardness values for CP aluminum than the HP
aluminum having the same Sc concentration. Additionally, the Sc equilibrium solubility in
the -Al matrix is estimated and Orowan's strengthening mechanism is confirmed for the
Al3Sc precipitates. |
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NU @ karnesky @ |
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10742 |
| Permanent link to this record |
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Krug, Matthew E.; Dunand, David C.; Seidman, David N. |
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Effects of Li additions on precipitation-strengthened Al-Sc and Al-Sc-Yb 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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1700-1715 |
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aluminium alloys, atom-probe field-ion microscopy (AP-FIM), rare earth, nanostructure, precipitation; Al-Sc |
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Two Al-Sc based alloys (Al-0.12 Sc and Al-0.042 Sc-0.009 Yb, at. %) and their counterparts with
Li-additions (Al-2.9 Li-0.11 Sc and Al-5.53 Li-0.048 Sc-0.009 Yb, at. %) are aged at 325 °C. For
both base alloys, the addition of Li results in greater peak hardness from incorporation of Li in the
L12-structured alpha'–Al3(Sc,Li) and alpha'–Al3(Sc,Li,Yb) precipitates, and a concomitant increase in
number density and volume fraction of the precipitates and a reduction in their mean radius. These
changes result from a combination of (i) an increase in the driving force for precipitate nucleation
due to Li, (ii) a decrease in the elastic energy of the coherent misfitting precipitates from a decrease
in their lattice parameter mismatch due to their Li content, and (iii) a decrease in the interfacial free
energy, as determined from measurements of relative Gibbsian interfacial excess of Li. In Al-2.9 Li-
0.11 Sc (at. %), the Li content of the precipitates drops from 9.1 at. % in the peak-aged state (8 h) to
5.7 at. % in the overaged state (1536 h). As a result, the precipitate volume fraction decreases from
0.56% at peak-age to 0.45% at 1536 h. In Al-5.53 Li-0.048 Sc-0.009 Yb (at. %), the relatively
limited Li concentration produces only a small increase in Vickers microhardness from precipitation
of metastable delta'–Al3Li upon a second aging at 170 °C following the primary aging at 325 °C. |
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NU @ karnesky @ |
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10984 |
| Permanent link to this record |
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Knipling, K. E.; Seidman, D. N.; Dunand, D. C. |
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Ambient- and High- Temperature Mechanical Properties of Isochronally Aged Al-0.06Sc, Al-0.06 Zr, and Al-0.06Sc-0.06Zr Alloys (at.%) |
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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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3 |
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943-954 |
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Al-Sc; Aluminum alloys; Precipitation; Isochronal heat-treatments; Scandium; Zirconium |
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Ambient- and high-temperature precipitation strengthening are investigated in Al–0.06Sc, Al–0.06Zr and Al–0.06Sc–0.06Zr (at.%) alloys. Following solidification, Sc is concentrated at the dendrite peripheries while Zr is segregated at the dendrite cores. During isochronal aging, precipitation of Al3Sc (L12) commences between 250 and 300 °C for Al–0.06Sc, and reaches a 429 MPa peak microhardness at 325 °C. For Al–0.06Zr, precipitation of Al3Zr (L12) first occurs between 400 and 425 °C and reaches a 295 MPa peak microhardness at 475 °C. A pronounced synergistic effect is observed when both Sc and Zr are present. Above 325 °C, Zr additions provide a secondary strength increase that is attributed to precipitation of Zr-enriched outer shells onto the Al3Sc precipitates, leading to a peak microhardness of 618 MPa at 400 °C for Al–0.06Sc–0.06Zr. Upon compressive creep deformation at 300–400 °C, Al–0.06Sc–0.06Zr exhibits threshold stresses of 7–12 MPa; these values may be further improved by optimal heat-treatments. |
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NU @ karnesky @ |
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10884 |
| Permanent link to this record |
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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 |
| Permanent link to this record |
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Krug, M.E.; Werber, A.; Dunand, D.C.; Seidman, D.N. |
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Core-shell nanoscale precipitates in Al-0.06 at.% Sc microalloyed with Tb, Ho, Tm or Lu |
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Journal Article |
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2010 |
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Acta Materialia |
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Acta Mater. |
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58 |
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1 |
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134-145 |
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Rare earth; Precipitation; Microhardness; Atom-probe field-ion microscopy (AP-FIM); Aluminum alloys; Al-Sc |
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The age-hardening response at 300 C of Al-0.06Sc-0.02RE (at.%, with RE = Tb, Ho, Tm or Lu) is found to be similar to that of binary Al-0.08Sc (at.%), except that a shorter incubation period for hardening is observed, which is associated with nanoscale RE-rich Al-3(RE1-xScx) precipitates. In addition, Al-0.06Sc-0.02Tb (at.%) has a much lower peak microhardness than that of Al-0.08Sc (at.%) due to the small solubility of Tb in alpha-Al(Sc). Peak-age hardening occurs after 24 h. and is associated with a high number density of nanoscale Sc-rich Al-3(Sc1-xREx) precipitates. Analysis by three-dimensional local-electrode atom-probe tomography shows that x increases with increasing atomic number, and that the REs partition to the core of the precipitates. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. |
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[Krug, Matthew E.; Werber, Alexandra; Dunand, David C.; Seidman, David N.] Northwestern Univ, Evanston, IL 60208 USA, Email: m-krug@northwestern.edu |
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Pergamon-Elsevier Science Ltd |
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English |
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1359-6454 |
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ISI:000272405600015 |
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NU @ m-krug @ |
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10807 |
| Permanent link to this record |
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van Dalen, Marsha E.; Karnesky, Richard A.; Cabotaje, Joseph R.; Dunand, David C.; Seidman, David N. |
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Erbium and Ytterbium Solubilities and Diffusivities in Aluminum as Determined by Nanoscale Characterization of Precipitates |
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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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4081-4089 |
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Aluminum alloys; Rare-earth elements; Diffusion; Precipitation; Coarsening; Al-Er; Al-Yb |
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Binary aluminum alloys with 0.03-0.06 at.% RE (RE = Yb or Er) were aged to produce coherent, nanosize Al[sub:3]RE precipitates in an [alpha]-Al matrix. The temporal evolution of precipitate radii and matrix concentrations at 300 °C are measured by transmission electron microscopy and localelectrode atom-probe tomography, respectively. The temporal dependence of the matrix concentration of each RE is utilized to determine its solubility in Al. The solubility as well as the coarsening rate constants are used to determine the diffusivity of each RE in [alpha]-Al and the [alpha]-Al/Al[sub:3]RE interfacial free energies at 300 °C. When compared to Sc, both Yb and Er exhibit smaller solubilities but larger diffusivities in [alpha]-Al and larger [alpha]-Al/Al[sub:3]RE interfacial energies. |
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NU @ karnesky @ |
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10598 |
| Permanent link to this record |
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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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