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Fuller, Christian B.; Seidman, David N.; Dunand, David C. |
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Creep Properties of Coarse-Grained Al(Sc) Alloys at 300°C |
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Journal Article |
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1999 |
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Abstract |
Scripta Materialia |
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Scripta Mater. |
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40 |
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6 |
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691-696 |
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Al-Sc |
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NU @ karnesky @ |
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527 |
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Harada, Y.; Dunand, D.C. |
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Creep Properties of Al[sub:3]Sc and Al[sub:3](Sc, X) Intermetallics |
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Journal Article |
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2000 |
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Acta Materialia |
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Acta Mater. |
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48 |
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13 |
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3477-3487 |
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Journal Article; Aluminum compounds, Mechanical properties; Scandium compounds, Mechanical properties; Intermetallics, Mechanical properties; Titanium, Alloying additive; Yttrium, Alloying additive; Zirconium, Alloying additive; Hafnium, Alloying additive; Creep (materials), Alloying effects; Dislocation mobility, Deformation effects; Al-Sc; mechanical properties creep intermetallic compounds bulk diffusion scandium microstructure high-temperature creep l12 trialuminides self-diffusion behavior fracture films al3ti compression chromium aluminum |
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A systematic creep study was undertaken for the binary intermetallic Al sub 3 Sc and the ternary single-phase intermetallic Al sub 3 (Sc sub 0.74 X sub 0.26 ), where X is one of the transition-metals Ti, Y, Zr or Hf. Creep tests were conducted in the temperature range from 673-1200K under a constant compressive stress ranging from 30-300 MPa. The binary Al sub 3 Sc exhibits a stress exponent of 4.4-4.9 indicative of creep controlled by climb of dislocations. The activation energy for creep of Al sub 3 Sc was 128plus/minus6 kJ/mol, close to that for self-diffusion for pure aluminum, in agreement with the Cu sub 3 Au rule, indicating that diffusion on the Al-sublattice is controlling. Ternary Al sub 3 (Sc sub 0.74 X sub 0.26 ) exhibits a decrease in creep rate by about one order of magnitude for Zr and Hf and by about two orders of magnitude for Ti and Y. For all ternary alloys, a stress exponent of 3.9-5.5 was observed, indicative of dislocation creep. Activation energies for creep of 202plus/minus8 kJ/mol were found, showing that ternary substitution for scandium with transition metals affects diffusion on the Al sublattice. |
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Northwestern University (Evanston); Ministry of International Trade and Industry (Japan) |
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1359-6454 |
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37 ref., Photomicrographs, Graphs, Numerical Data |
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NU @ karnesky @ |
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544 |
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Harada, Y.; Dunand, D.C. |
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Microstructure and Creep Properties of Al[sub:3]Sc with Ternary Transition Metal Additions |
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Book Chapter |
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2001 |
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The 7th International Conference on Creep and Fatigue at Elevated Temperature (Creep VII) |
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219-226 |
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Al-Sc |
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Japan Society of Mechanical Engineers |
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NU @ karnesky @ |
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1904 |
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Marquis, E. A.; Seidman, D. N. |
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Nanoscale Structural Evolution of Al[sub:3]Sc Precipitates in Al(Sc) Alloys |
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Journal Article |
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2001 |
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Acta Materialia |
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Acta Mater. |
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49 |
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11 |
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1909-1919 |
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aluminum scandium transmission electron microscopy (tem) phase transformations microstructure al-sc alloys creep-properties nucleation scandium aluminum intermetallics kinetics growth energy; Al-Sc |
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Precipitation of the Al3Sc (L12) phase in aluminum alloys, containing 0.1, 0.2 or 0.3 wt% Sc, is studied with conventional transmission and high-resolution (HREM) electron microscopies. The exact morphologies of the Al3Sc precipitates were determined for the first time by HREM, in Al–0.1 wt% Sc and Al–0.3 wt% Sc alloys. The experimentally determined equilibrium shape of the Al3Sc precipitates, at 300°C and 0.3 wt% Sc, has 26 facets, which are the 6 {100} (cube), 12 {110} (rhombic dodecahedron), and 8 {111} (octahedron) planes, a Great Rhombicuboctahedron. This equilibrium morphology had been predicted by first principles calculations of the pertinent interfacial energies. The coarsening kinetics obey the (time)1/3 kinetic law of Lifshitz–Slyozov–Wagner theory and they yield an activation energy for diffusion, 164±9 kJ/mol, that is in agreement with the values obtained from tracer diffusion measurements of Sc in Al and first principles calculations, which implies diffusion-controlled coarsening. |
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Seidman, D. N. Northwestern Univ, Dept Mat Sci & Engn, 2225 N 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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568 |
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Marquis, E. A.; Seidman, D. N. |
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A Subnanoscale Study of Segregation at Al/Al[sub:3]Sc Interfaces |
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Journal Article |
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2002 |
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Microscopy and Microanalysis |
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8 |
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S2 |
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1100-1101 |
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Al-Sc |
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NU @ karnesky @ |
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1905 |
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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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Marquis, E. A.; Seidman, D. N.; Dunand, D. C. |
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Creep of Precipitation-Strengthened Al(Sc) Alloys |
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Book Chapter |
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2002 |
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Creep Deformation: Fundamentals and Applications |
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299-308 |
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Al-Sc |
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TMS |
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Warrendale, PA |
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Mishra, Rajiv S.; Earthman, James C.; ;Raj, Sai V. |
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0873395158 |
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refbase @ user |
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1384 |
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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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Marquis, Emmanuelle A.; Dunand, David C. |
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Model for Creep Threshold Stress in Precipitation-Strengthened Alloys with Coherent Particles |
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Journal Article |
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2002 |
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Scripta Materialia |
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Scripta Mater. |
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47 |
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8 |
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503-508 |
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creep threshold stress precipitation strengthening aluminum alloys dislocation mobility al(sc) alloys al3sc; Al-Sc |
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The general climb model for creep threshold stress for dislocations interacting with incoherent particles is modified for the case of coherent precipitates, by taking into account elastic interactions between matrix dislocations and particles due to particle/matrix stiffness and lattice mismatches. The model is in qualitative agreement with experimental data for the Al–Sc system. |
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Dunand, D. C. Northwestern Univ, Dept Mat Sci & Engn, MLSB 1123,2225 N 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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569 |
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Harada, Y.; Dunand, D.C. |
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Microstructure of Al[sub:3]Sc with Ternary Transition-Metal 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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329-331 |
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686-695 |
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L12-trialuminides; Microstructure; Lattice parameter; Microhardness; Al-Sc |
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The microstructure of binary Al3Sc and ternary Al3(Sc1-yXy), where X is one of the transition metals from Group IIIA (Y), IVA (Ti, Zr or Hf) or VA (V, Nb or Ta), was investigated as a function of alloying element concentration for 0.1y0.75. Alloys with Group IIIA and IVA additions exhibited a single L12 solid-solution phase with some Kirkendall porosity. At the highest concentration studied, a second phase precipitated with the D019 (Y), D022 (Ti) or D023 (Zr and Hf) structure. Conversely, alloys with Group VA additions exhibited both the L12 trialuminide phase and a dendritic trialuminide second phase with D022 structure for all concentrations studied. The solubility limit in the ternary L12-type Al3(Sc1-yXy) phase was high for Group IIIA and IVA metals (almost 12.5 at.% or y=0.5), and much lower for Group VA metals (from about 1.8 at.% or y=0.07 for Ta to about 2.7 at.% or y=0.11 for V). Similarly, the solubility limit of Sc in the non-L12 phases decreases from the Group IIIA trialuminide to the Group VA trialuminides. The lattice parameter of the L12 solid-solution decreased linearly with increasing concentration of Group IVA and VA metals, but increased linearly with concentration of Y (Group IIIA). This linear concentration dependence of the lattice parameter is found to correlate with the atomic size mismatch between Sc and the transition metal. The microhardness of the L12 solid-solution increased linearly with increasing concentration of ternary elements. The concentration dependence of hardness is strongest for Group VA metals and weakest for Group IVA metals, for which a correlation is found with the concentration dependence of lattice parameter. |
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