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Marquis, E. A.; Seidman, D. N.; Asta, M.; Woodward, C.; Ozolins, V. |
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Mg Segregation at Al/Al[sub:3]Sc Heterophase Interfaces on an Atomic Scale: Experiments and Computations |
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Journal Article |
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2003 |
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Physical Review Letters |
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91 |
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3 |
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036101: 1-4 |
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Al-Sc alloys total-energy calculations wave basis-set molecular-dynamics transition aluminum precipitation diffusion scandium metals |
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Abbreviated Series Title |
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. |
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Series Issue |
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 |
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NU @ karnesky @ |
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40 |
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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 |
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Marquis, Emmanuelle A. |
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Microstructural Evolution and Strengthening Mechanisms in Al-Sc and Al-Mg-Sc Alloys |
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Book Whole |
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2002 |
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223 |
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Al-Sc |
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Al-Sc alloys are potential candidates for structural industrial applications because of their excellent mechanical properties due to the presence of small, coherent Al3Sc (L12 structure) precipitates that are formed during aging. Additional Mg alloying not only enhances the mechanical properties by solid-solution hardening but also provides corrosion resistance and better weldability. Understanding and controlling the microstructure, i.e. the temporal evolution of the Al3Sc precipitate morphologies and the effects of other alloying elements such as Mg, are critical for optimizing mechanical properties.
First, this research aims at describing the microstructural evolution of the Al3Sc precipitates during aging using transmission electron microscopies. The effects of Mg additions on precipitation are described using high-resolution transmission electron microscopy observations and three-dimensional atom-probe microscopy analyses.Results on Mg segregation, on the nanoscale level, at the coherent Al / Al3Sc interface are presented.
A second goal of this research is to understand the precipitation-strengthening parameters controlling optimal yield strength at room temperature and creep resistance at elevated temperature (0.6 Tm), the effects of precipitate size and volume fraction upon yield and creep strengths of dilute Al-Sc and Al-Mg-Sc alloys are studied. Room temperature strength is described in terms of precipitate shearing and Orowan dislocation looping. Creep threshold stresses are found to be about ten times lower than the yield stresses at 300°C, indicative of a climb-controlled bypass mechanism, which is modeled by extending existing dislocation-particle interaction models. |
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Northwestern University |
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Ph.D. thesis |
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NU @ karnesky @ |
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151 |
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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 |
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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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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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Acta Materialia |
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Acta Mater. |
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53 |
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15 |
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4259-4268 |
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Al3Sc precipitate; Morphology; Coarsening; Transmission electron microscopy; Atom-probe tomography; Al-Sc |
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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.; Dunand, David C. |
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Effect of Mg Addition on the Creep and Yield Behavior of an Al–Sc Alloy |
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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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4751-4760 |
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Transmission electron microscopy; Aluminum alloys; Coarsening; Creep; Al3Sc precipitates; olid-solution alloys dislocation climb viscous glide deformation stress dependence particles fracture; Al-Sc |
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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. |
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Marquis, E. A. Sandia Natl Labs, Thin Film & Interface Dept, Livermore, CA 94550 USA Northwestern Univ, Dept Mat Sci & Engn, Evanston, IL 60208 USA |
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NU @ karnesky @ |
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212 |
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Marquis, Emmanuelle A.; Seidman, David N.; Dunand, David C. |
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Precipitation Strengthening at Ambient and Elevated temperatures of Heat-Treatable Al(Sc) Alloys [Acta Materialia 50(16), pp. 4021–4035] |
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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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1 |
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285-287 |
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Al-Sc |
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In the final printed issue, the Publisher regrets to inform that the sequence of authors’ names given under the title on page 4021 was incorrect. The correct sequence is now shown above.
The Publisher also wishes to apologise for the poor quality reproduction of Fig. 1, Fig. 9 and Fig. 10, which are now reprinted correctly below: |
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NU @ karnesky @ |
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213 |
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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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NU @ karnesky @ |
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224 |
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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 |
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