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Chao, Paul; Karnesky, Richard A. |
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Hydrogen Isotope trapping in Al-Cu binary alloys |
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Journal Article |
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2016 |
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Materials Science & Engineering A |
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Mater Sci Eng A |
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658 |
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422-428 |
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Age-hardening, Aluminium alloys, Al-Cu, Hydrogen diffusion and trapping, Hydrogen desorption |
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Abbreviated Series Title |
The trapping mechanisms for hydrogen isotopes in Al-X Cu (0.0 at. % < X < 3.5 at. %) alloys were investigated using thermal desorption spectroscopy (TDS), electrical conductivity, and differential scanning calorimetry. Constant heating rate TDS was used to determine microstructural trap energies and occupancies. In addition to the trapping states in pure Al reported in the literature (interstitial lattice sites, dislocations, and vacancies), a trap site due to Al-Cu intermetallic precipitates is observed. The binding energy of this precipitate trap is (18 ± 3) kJ∙mol-1 (0.19 ± 0.03 eV). Typical occupancy of this trap is high; for Al-2.6 at. % Cu (a Cu composition comparable to that in AA2219) charged at 200 °C with 130 MPa D2 for 68 days, there is ca. there is 3.15x10-7 mol D bound to the precipitate trap per mol of Al, accounting for a third of the D in the charged sample. |
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NU @ karnesky @ |
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11513 |
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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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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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Krug, Matthew E. |
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Microstructural Evolution and Mechanical Properties in Al-Sc Alloys With Li and Rare Earth Additions |
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Book Whole |
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2011 |
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372 |
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Al-Sc, Al-Li, Al-Li-Sc, rare earth, LEAP, atom probe |
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Aluminum-scandium alloys have excellent mechanical properties at ambient and elevated temperatures due to the presence of coherent, nano-scale, L12-ordered Al3Sc precipitates. In this thesis, a variety of Al-Sc alloys with additions of Li and RE elements, primarily Yb, are studied. An addition of ytterbium reduces the cost of Al-Sc alloys by replacing some of the more-expensive Sc. Lithium is a unique alloying addition to Al-Sc alloys, because it has significant solubility in both the matrix and precipitate phases. Lithium also provides solid solution strengthening, and a large strengthening increment on aging through the formation of Al3Li precipitates. The effects of these alloying additions on Al-Sc alloys are investigated in detail, and discussed in the context of physical models linking the microstructure to measured mechanical properties.
The alloys undergo a variety of aging treatments between 170 – 450 °C, producing a range of precipitate distributions. Their aging response is assessed using Vickers microhardness to monitor ambient-temperature strength, and electrical conductivity to monitor the progress of the precipitation reaction. The alloys are creep-tested in compression at 300 °C, and exhibit threshold stresses, below which no measurable creep occurs. Detailed microstructural investigations rely primarily on local electrode atom probe tomography, as well as transmission electron microscopy. The volume fractions, number densities, and chemical compositions of precipitates are measured at the nano-scale, and their size and spatial distributions are quantitatively determined.
Compared to binary Al-Sc alloys, Al-Li-Sc and Al-Li-Sc-Yb alloys contain a finer distribution of Al3(Sc1-x-yLixYby) precipitates at a greater number density and volume fraction, as well as solid-solution strengthening in the Al(Li) matrix, all of which lead to a greater peak strength at ambient-temperature. Because partitioning of Li to the precipitates results in a smaller lattice parameter mismatch with the matrix, a Li addition is detrimental to the elevated temperature strength of Al-Sc alloys, but this effect is mitigated if additions of both Li and Yb are made. A model for threshold stresses at elevated temperature semi-quantitatively captures experimentally-observed trends in threshold stress data in Al-Sc-X alloys. Dislocation dynamics simulations on directly-measured precipitate arrangements lead to a rule for superposition of strength contributions from dissolved solutes, α′–Al3(Li,Sc,Yb) precipitates, and δ′–Al3Li precipitates. |
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Northwestern University |
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Ph.D. thesis |
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English |
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NU @ m-krug @ |
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11430 |
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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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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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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 |
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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 |
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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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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 |
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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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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 |
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