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Karnesky, Richard A.; Seidman, David N.; Dunand, David C. |
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Publication |
Creep of Al-Sc Microalloys with Rare-Earth Element Additions |
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Journal Article |
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2006 |
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Abstract |
Materials Science Forum |
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Corporate Author |
Mater. Sci. Forum |
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519-521 |
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Summary Language |
1035-1040 |
Series Editor |
Scandium, Rare-Earth Elements, Creep, Precipitation Strengthening; Al-Sc |
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Abbreviated Series Title |
Cast and aged Al-Sc microalloys are creep-resistant to 300C, due to the blocking of dislocations by nanosize, coherent Al3Sc (L12) precipitates. Rare-earth elements substitute for Sc in these precipitates, leading to a higher number density of smaller precipitates, which have a greater lattice-parameter mismatch with Al than in the Al-Sc binary microalloy. This leads
to an improvement in both ambient temperature microhardness and high temperature creep. Creep threshold stresses of Al-Sc-RE (RE = Y, Dy, or Er) at 300C; are higher than for Al-Sc and Al-Sc-M (M = Mg, Ti, or Zr) microalloys. This is in agreement with a dislocation climb model that includes the elastic stress fields of the precipitates. |
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ICAA10 |
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NU @ karnesky @ |
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660 |
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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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Journal Article |
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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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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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Knipling, K.E.; Dunand, D.C. |
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Creep resistance of cast and aged Al-0.1Zr and Al-0.1Zr-0.1Ti (at.%) alloys at 300-400ºC |
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Journal Article |
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2008 |
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Scripta Materialia |
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59 |
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4 |
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387-390 |
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Aluminum alloys; Creep; Precipitation strengthening; Titanium; Zirconium; Al-Zr |
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Cast and aged Al-0.1Zr and Al-0.1Zr-0.1Ti (at.%) alloys, upon compressive creep deformation at 300-400ºC, exhibit threshold stresses attributable to climb-controlled bypass of coherent Al3Zr and Al3(Zr1-xTix) precipitates. Al-0.1Zr-0.1Ti exhibits a smaller threshold stress than Al-0.1Zr, which is attributed principally to a reduced lattice parameter mismatch between the Al3(Zr1-xTix) precipitates and the matrix. The present alloys are less creep resistant than Al-Sc and Al-Sc-Zr/Ti alloys with similar precipitate radii and volume fractions. |
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NU @ jscott @ 1793 |
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10370 |
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Harada, Y.; Dunand, D.C. |
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Microstructure of Al[sub:3]Sc with ternary rare-earth additions |
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Journal Article |
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2009 |
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Intermetallics |
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1-2 |
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17-24 |
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Al-Sc; Trialuminides; Rare-earth intermetallics; Solid-solution hardening; Microstructure; Diffraction |
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The microstructure of ternary L1[sub:2]-Al[sub:3](Sc[sub:1-y]RE[sub:y]) intermetallics, where RE is one of the rare-earth elements selected from five light (La, Ce, Nd, Sm or Eu) or two heavy lanthanoids (Yb or Lu), was investigated as a function of RE concentration for 0.02 <= y <= 0.75. Alloys with light RE show two phases: L1[sub:2]-Al[sub:3](Sc,RE) and D0[sub:19]-Al[sub:3](RE,Sc) (or C11[sub:b]-Al[sub:4](Eu,Sc)). Alloys with heavy RE exhibit a single L1[sub:2]-Al[sub:3](Sc,RE) phase. The maximum RE solubility in the L1[sub:2] phase is very low (<0.4 at.%) for La, Ce, Nd and Eu, low (3.2 at.%) for Sm and complete solid-solution for Yb and Lu. Both lattice parameter and hardness of the L1[sub:2]-Al[sub:3](Sc,RE) phases increase linearly with Sm, Yb or Lu concentration, and the magnitude of both effects correlates with the atomic size mismatch between Sc and RE. |
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NU @ karnesky @ |
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10536 |
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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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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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Knipling, K.E.; Dunand, D.C.; Seidman, D.N. |
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Precipitation evolution in Al-Zr and Al-Zr-Ti alloys during aging at 450-600 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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6 |
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1182-1195 |
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Aluminum alloys; Zirconium; Titanium; Precipitation strengthening; Coarsening; Al-Zr |
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The transformation of Al3Zr (L12) and Al3(Zr1-xTix) (L12) precipitates to their respective equilibrium D023 structures is investigated in conventionally solidified Al-0.1Zr and Al-0.1Zr-0.1Ti (at.%) alloys aged isothermally at 500 [degree sign]C or aged isochronally in the range 300-600 [degree sign]C. Titanium additions delay neither coarsening of the metastable L12 precipitates nor their transformation to the D023 structure. Both alloys overage at the same rate at or above 500 [degree sign]C, during which spheroidal L12 precipitates transform to disk-shaped D023 precipitates at ca. 200 nm in diameter and 50 nm in thickness, exhibiting a cube-on-cube orientation relationship with the [alpha]-Al matrix. The transformation occurs heterogeneously on dislocations because of a large lattice parameter mismatch of the D023 phase with [alpha]-Al. The transformation is very sluggish and even at 575 [degree sign]C coherent L12 precipitates can remain untransformed. Mechanisms of microstructural coarsening and strengthening are discussed with respect to the micrometer-scale dendritic distribution of precipitates. |
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NU @ karnesky @ |
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10274 |
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Knipling, Keith E.; Dunand, David C.; Seidman, David N. |
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Criteria for Developing Castable, Creep-Resistant Aluminum-Based Alloys–A Review |
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Journal Article |
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2006 |
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Zeitschrift für Metallkunde |
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Z. Metallkd |
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97 |
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3 |
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246-265 |
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Aluminum alloys; Trialuminides; Precipitation strengthening; Creep; Al-Sc |
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We describe four criteria for the selection of alloying elements capable of producing castable,
precipitation-strengthened Al alloys with high-temperature stability and strength: these alloying
elements must (i) be capable of forming a suitable strengthening phase, (ii) show low solid solubility
in Al, (iii) showlow diffusivity in Al, and (iv) retain the ability for the alloy to be conventionally
solidified. With regard to criterion (i), we consider those systems forming Al3Mtrialuminide compounds
with a cubic L12 crystal structure, which are structurally analogous to Ni3Al (
0) in the
Ni-based superalloys. Eight elements, clustered in the same region of the periodic table, fulfill
criterion (i): the first Group 3 transition metal (Sc), the three Group 4 transition metals (Ti, Zr, Hf)
and the four latest rare-earth elements (Er, Tm, Yb, Lu). Based on a review of the existing literature,
these elements are discussed in terms of criteria (ii) and (iii), which satisfy the need for a
dispersion in Al with slow coarsening kinetics, and criteria (iv), which is discussed based on the
binary phase diagrams. |
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NU @ karnesky @ |
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236 |
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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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