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Marquis, Emmanuelle A.; Seidman, David N.; Dunand, David C. |
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Publication |
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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Abstract |
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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Abbreviated Series Title |
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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Series Issue |
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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Monachon, C.; Krug, M. E.; Seidman, D. N.; Dunand, D. C. |
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Chemically and Structurally Complex Nanoscale Core/Double-Shell Nanoscale Precipitates in an Al-Li-Sc-Yb Alloy |
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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-Sc |
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NU @ karnesky @ |
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10883 |
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Monachon, Christian; Dunand, David C.; Seidman, David N. |
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Atomic-Scale Characterization of Aluminum-Based Multishell Nanoparticles Created by Solid-State Synthesis |
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Journal Article |
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2010 |
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Small |
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6 |
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16 |
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1728-1731 |
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atom-probe tomography; core–shell precipitates; transmission electron microscopy; trialuminides; Al-Sc |
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Core/double-shell nanoparticles are produced by solid-state precipitation in an aluminum matrix and characterized by transmission electron microscopy and atom-probe tomography. By choosing three solute elements (Yb, Sc, Li) with substantially disparate diffusivities and by judiciously selecting aging temperatures to precipitate each element sequentially, nanoparticles are formed with three chemically distinct concentric Al3(Yb,Sc,Li) phases with radii of 1.6, 3.4, and 13.4 nm. |
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NU @ karnesky @ |
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10885 |
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Seidman, David N. |
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Three-Dimensional Atom-Probe Tomography: Advances and Applications |
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Journal Article |
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2007 |
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Annual Review of Materials Research |
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37 |
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127-158 |
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field-ion microscopy, time-of-flight mass spectrometry, laser-assisted LEAPTM tomography, α-Al/Al3Sc heterophase interfaces, Ni-Al-Cr alloys, Ni-Al-Cr-Re alloys, InAs nanowires |
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This review presents the historical temporal evolution of an atomprobe
tomograph (APT) from its genesis (1973) from field-ion microscope
images of individual tungsten atoms (1955). The capabilities
of modern APTs employing either electrical or laser pulsing are
discussed. The results of the application of APTs to specific materials
science problems are presented for research performed at Northwestern
University on the following problems: (a) the segregation
of Mg at α-Al/Al3Sc heterophase interfaces, (b) phase decomposition
in ternary Ni-Al-Cr and quaternary Ni-Al-Cr-Re alloys, and
(c) 3-D nanoscale composition mapping of an InAs semiconductor
nanowire whose growth was catalyzed by gold. These results demonstrate
that it is now possible to obtain highly quantitative information
from APT that can be compared with modeling, theory, simulations,
and/or first-principles calculations. |
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NU @ karnesky @ |
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1926 |
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Seidman, David N.; Marquis, Emmanuelle A.; Dunand, David C. |
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Precipitation Strengthening at Ambient and Elevated Temperatures of Heat-Treatable Al(Sc) Alloys |
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Journal Article |
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2002 |
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Acta Materialia |
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Acta Mater. |
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50 |
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16 |
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4021-4035 |
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Aluminum alloys; Scandium; Mechanical properties; Precipitation strengthening; Creep; Threshold stress; Al-Sc |
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Yield strength at ambient temperature and creep resistance between 225 and 300C were investigated in dilute Al(Sc) alloys containing coherent Al3Sc precipitates, which were grown by heat-treatments to radii in the range 1.49.6 nm. The dependence of the ambient-temperature yield stress on precipitate size is explained using classical precipitation strengthening theory, which predicts a transition from precipitate shearing to Orowan dislocation looping mechanisms at a precipitate radius of 2.1 nm, in good agreement with experimental data. At 300C creep threshold stresses are observed and found to be much lower than the yield stresses, indicative of a climb-controlled bypass mechanism. The threshold stress increases with increasing precipitate radius, in qualitative agreement with a climb model taking into account stiffness and lattice mismatches between matrix and precipitates [1]. |
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NU @ karnesky @ |
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618 |
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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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van Dalen, M.E.; Seidman, D.N.; Dunand, D.C. |
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Creep- and coarsening properties of Al-0.06 at.% Sc-0.06 at.% Ti at 300-450 °C |
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Journal Article |
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2008 |
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Acta Materialia |
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56 |
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16 |
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4369-4377 |
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Aluminum alloys; Nanostructure; Precipitation; Creep; Titanium; Al-Sc |
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Upon aging at 300-450 °C, nanosize, coherent Al3(Sc1-xTix) precipitates are formed in pure aluminum micro-alloyed with 0.06 at.% Sc and 0.06 at.% Ti. The outstanding coarsening resistance of these precipitates at these elevated temperatures (61-77% of the melting temperature of aluminum) is explained by the significantly smaller diffusivity of Ti in Al when compared to that of Sc in Al. Furthermore, this coarse-grained alloy exhibits good compressive creep resistance for a castable, heat-treatable aluminum alloy: the creep threshold stress varies from 17 MPa at 300 °C to 7 MPa at 425 °C, as expected if the climb bypass by dislocations of the mismatching precipitates is hindered by their elastic stress fields. |
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NU @ m-krug @ |
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10486 |
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van Dalen, Marsha E. |
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Microstructure and Creep Properties of Al-Sc Alloys Micro-alloyed with Lanthanides (Yb or Gd) and Transition Metals (Ti or Zr) |
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Book Whole |
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2007 |
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289 |
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Al-Sc |
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This thesis examines the effects of micro-alloying additions to Al-Sc alloys on the
microstructure, coarsening resistance and creep properties. The overarching goal of this research
is to develop castable, creep-resistant aluminum alloys which can be used at temperatures in
excess of 300°C. Successful high-temperature application of aluminum based alloys offers a
lower cost and lower weight alternative to other materials commonly used at high temperatures,
including titanium- and nickel-based alloys.
To this end, this aims to improve the properties of the Al alloys by adding various
alloying elements in small quantities, on the order of several hundred atomic parts per million, to
aluminum. The thesis begins by focusing on additions of Ti to Al-Sc. Ti is a slow diffuser in Al
[1], and it will be shown that it improves the coarsening kinetics of the precipitate phase at
300°C. Since these alloys are coarsening resistant, it is found that they can be aged and crept at
temperatures of up to 425°C. The properties displayed are similar to those of Al-Sc-Zr alloys
studied previously [2, 3].
The examination of Ti additions is followed by a study of the additions of lanthanide
elements. These elements are of interest since they are known to increase the lattice parameter of
the precipitate phase [4-8], which could potentially lead to improved creep resistance [9].
Initially, binary Al-Yb alloys are studied to obtain some fundamental knowledge of the behavior
of Yb in Al. Subsequent additions of Yb to Al-Sc result in improved creep resistance. A similar
improved creep resistance is observed for additions of Gd to Al-Sc.
Finally, this dissertation concludes with the study of Al-Sc-Yb-Zr alloys. Since the goal
of this research is to obtain a creep-resistant as well as coarsening resistant alloy, both a slow
diffusing element (Zr) and an element which improves the creep resistance (Yb) are added. The
quaternary alloys are found to maintain the creep resistance and coarsening resistance of the Al-
Sc-Yb and Al-Sc-Zr alloys, respectively, which points to opportunities for future research in this
area. |
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Northwestern University |
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Ph.D. thesis |
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NU @ karnesky @ |
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9848 |
| Permanent link to this record |
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van Dalen, Marsha E.; Dunand, David C.; Seidman, David N. |
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Precipitation Strengthening in Al (Sc,Ti) Alloys |
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Book Chapter |
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2003 |
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Affordable Metal-Matrix Composites for High Performance Applications II |
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195-201 |
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Al-Sc-Ti alloys; Precipitation hardening; Microstructure; Three-dimensional atom-probe microscopy |
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Three-dimensional atom probe (3DAP) and field-ion microscopies, together with microhardness measurements, are employed to analyze Al3(Sc1-xTix) precipitates in an Al-0.06at%Sc-0.06at.%Ti alloy aged at 300°C for different times. The field-ion microscope images show a relatively high number density of precipitates (estimated at (3±2)×1021ppt m-3) at the aging times analyzed. Concentration profiles obtained with 3DAP microscopy show that both Sc and Ti partition to these precipitates. While most of the Sc is contained in the precipitates, the Ti resides mainly in the matrix in solid solution. Consequently, the addition of Ti increases the hardness of this alloy only modestly over that of binary Al-Sc alloys. Additionally, the coherent Al3(Sc1-xTix) precipitates remain stable and coarsening-resistant up to aging times of at least 240 hr. at 300°C. |
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Northwestern University; Northwestern University |
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TMS |
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Chicago |
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English |
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0-87339-557-3 |
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Materials Science & Technology 2003 |
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NU @ karnesky @ |
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570 |
| Permanent link to this record |
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van Dalen, Marsha E.; Dunand, David C.; Seidman, David N. |
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Nanoscale Precipitation and Mechanical Properties of Al-0.06 at.% Sc Alloys Micro-Alloyed with Yb or Gd |
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Journal Article |
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2006 |
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Journal of Materials Science |
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41 |
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23 |
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7814-7823 |
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Aluminum alloys; Precipitation; Nucleation; Three-dimensional atom-probe tomography; Rare earth elements; Al-Sc |
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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. |
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NU @ karnesky @ |
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767 |
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