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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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Abstract |
Materials Science and Engineering A |
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527 |
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15 |
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Summary Language |
3501-3509 |
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Dilute aluminum alloys, Scandium, Precipitation, Impurities, Atom Probe; Al-Sc |
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Abbreviated Series Title |
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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Biswas, Aniruddha; Siegel, Donald J.; Seidman, David N. |
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Simultaneous Segregation at Coherent and Semi-coherent Heterophase Interfaces |
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Journal Article |
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2010 |
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Physical Review Letters |
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105 |
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7 |
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076102-76103 |
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Al-Cu |
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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. |
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NU @ karnesky @ |
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10810 |
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Biswas, Aniruddha; Siegel, Donald J.; Wolverton, C.; Seidman, David N. |
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Segregation at [alpha]-Al/[theta]'-precipitate interfaces in Al-Cu alloys: Atom-probe tomographic experiments and first-principles calculations |
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Journal Article |
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2010 |
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Acta Materialia |
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Submitted |
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Al-Cu |
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Atom-probe tomography, transmission electron-microscopy, x-ray diffraction, and firstprinciples
calculations were employed to study the (i) compositional evolution of GPII-zones and
"!-precipitates, and (ii) solute segregation at !-Al/"!-interfaces in Al-4 wt. % Cu alloys. GPII
zones are observed for aging at 438 K for 8 h, whereas higher aging temperatures, 463 K for 8 h
and 533 K for 4 h, reveal only "!-precipitates. Most GPII-zones and "!-precipitates were found to
be Cu-deficient at the lower aging temperatures; only the high temperature treatment (533 K)
resulted in "! stoichiometries consistent with the expected Al2Cu equilibrium composition. For
alloys containing ca. 200 at. ppm Si we find evidence of Si partitioning to GPII-zones and "!-
precipitates. Significant Si segregation is observed at the coherent !-Al/"!-interface, with aging
at 533 K resulting in an interfacial Si concentration more than 11 times greater than in the Al
matrix. Importantly, the Si interfacial concentration profile undergoes a transition from
nonmonotonic to confined as the aging temperature is raised from 463 K to 533 K. Consistent
with these measurements, first-principles calculations predict a strong thermodynamic driving
force favoring Si partitioning at Cu sites in "!. Silicon segregation and partitioning to "!-
precipitates results in a decrease in interfacial free energy and concomitantly an increase in the
rate of precipitate nucleation. Our results suggest that Si catalyzes the early stages of
precipitation in these alloys, consistent with the higher precipitate number densities observed in
commercial Al-Cu-Si alloys. |
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NU @ karnesky @ |
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10811 |
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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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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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Fuller, Christian B. |
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Temporal Evolution of the Microstructures of Al(Sc,Zr) Alloys and Their Influences on Mechanical Properties |
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Book Whole |
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2003 |
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179 |
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Al-Sc |
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Al(Sc) alloys represent a new class of potential alloys for aerospace and automotive applications. These alloys have superior mechanical properties due to the presence of fine, coherent, unshearable Al3Sc precipitates, which form upon the decomposition of an supersaturated Al(Sc) solid-solution. Additions of Zr to Al(Sc) are found to improve alloy strength and coarsening resistance, but the operating mechanisms are not well understood.
In this thesis, the relationships between the mechanical and microstructural properties of Al(Sc,Zr) alloy are presented. Three-dimensional atom probe microscopy (3DAP) and conventional and high-resolution transmission electron microscopies (CTEM and HREM) are utilized to study the temporal evolution of Al3Sc1-xZrx (L12 structure) precipitates in dilute Al(Sc,Zr) alloys (precipitate volume fractions < 1%) aged between 300 and 375°C.
Concentration profiles, obtained with 3DAP, show Sc and Zr to partition to Al3Sc1-xZrx precipitates, and Zr to segregate near the Al/Al3Sc1-xZrx interface. CTEM and 3DAP are utilized to determine the temporal evolution of Al(Sc,Zr) alloys, which is discussed employing diffusion-limited coarsening theories. Zirconium additions are found to retard the precipitate coarsening kinetics and stabilize precipitate morphologies.
Mechanical properties of Al(Sc,Zr) alloys are investigated utilizing Vicker’s microhardness and creep. Deformation at ambient-temperature is explained by classic precipitation-strengthening mechanisms, where a transition between
precipitate shearing and Orowan looping is calculated to occur at an average precipitate radius, <r>, of 2-3 nm. Al(Sc,Zr) alloys deformed by creep at 300°C are found to exhibit a climb controlled threshold stress, which is shown to increase with <r>, in agreement with previous results in Al(Sc) alloys and a previous general climb model considering the interaction between dislocations and coherent misfitting precipitates. Finally, the effect 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 are investigated. The presence of the Al3Sc1-xZrx precipitates is found to improve the alloy strength, by pinning subgrain and grain boundaries, as shown by hardness, tensile, and fatigue measurements. |
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Northwestern University |
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Ph.D. thesis |
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NU @ karnesky @ |
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147 |
| Permanent link to this record |
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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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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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8-16 |
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Al-Sc-Zr alloys; Fatigue (materials); Mechanical properties; Aluminum alloys; Microstructural properties |
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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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Fuller, Christian B.; Murray, Joanne L.; Seidman, David N. |
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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 |
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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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20 |
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5401-5413 |
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Al-Sc-Zr alloys; Precipitation; Microstructure; High-resolution electron microscopy; Three-dimensional atom-probe microscopy |
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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 α-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. |
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NU @ karnesky @ |
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172 |
| Permanent link to this record |
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Fuller, Christian B.; Seidman, David N. |
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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 |
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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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20 |
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5415-5428 |
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Al-Sc-Zr; Phase Transformations; nanostructure; Transmission electron microscopy (TEM), |
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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. |
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NU @ karnesky @ |
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235 |
| Permanent link to this record |
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Fuller, Christian B.; Seidman, David N.; Dunand, David C. |
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Mechanical Properties of Al(Sc,Zr) Alloys at Ambient and Elevated Temperatures |
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Journal Article |
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2003 |
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Acta Materialia |
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Acta Mater. |
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51 |
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16 |
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4803-4814 |
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al-sc-zr alloys mechanical properties creep deformation mechanisms strengthened alloys threshold stress creep-properties al3sc microstructure particles additions evolution model sc |
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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=2−24 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. |
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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 |
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no |
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NU @ karnesky @ |
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224 |
| Permanent link to this record |
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Fuller, Christian B.; Seidman, David N.; Dunand, David C. |
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Structure-Property Relationships for Al(Sc,Zr) Alloys |
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Book Chapter |
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2003 |
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Hot Deformation of Aluminum Alloys III |
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531-540 |
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Al-Sc |
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TMS |
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Warrendale, PA |
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Zin, J.; Beaudoin, A.; Bieler, T. A.; Radhakrishnan, B. |
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NU @ karnesky @ |
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1907 |
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