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Type Marquis, Emmanuelle A.
  Publication Microstructural Evolution and Strengthening Mechanisms in Al-Sc and Al-Mg-Sc Alloys Volume (down) Book Whole
Pages 2002
  Abstract  
  Corporate Author  
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Editor
  Summary Language 223 Series Editor Al-Sc  
Abbreviated Series Title 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.
  Series Issue ISSN Northwestern University  
Medium Ph.D. thesis
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no NU @ karnesky @ 151
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van Dalen, Marsha E. Microstructure and Creep Properties of Al-Sc Alloys Micro-alloyed with Lanthanides (Yb or Gd) and Transition Metals (Ti or Zr) Book Whole 2007 289 Al-Sc 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. Northwestern University Ph.D. thesis no NU @ karnesky @ 9848
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Fuller, Christian B. Temporal Evolution of the Microstructures of Al(Sc,Zr) Alloys and Their Influences on Mechanical Properties Book Whole 2003 179 Al-Sc 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 Vickerís 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. Northwestern University Ph.D. thesis no NU @ karnesky @ 147
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Biswas, Aniruddha; Siegel, Donald J.; Wolverton, C.; Seidman, David N. Segregation at [alpha]-Al/[theta]'-precipitate interfaces in Al-Cu alloys: Atom-probe tomographic experiments and first-principles calculations Journal Article 2010 Acta Materialia Submitted Al-Cu 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. no NU @ karnesky @ 10811
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Monachon, C.; Krug, M. E.; Seidman, D. N.; Dunand, D. C. Chemically and Structurally Complex Nanoscale Core/Double-Shell Nanoscale Precipitates in an Al-Li-Sc-Yb Alloy Journal Article 2010 Acta Materialia Submitted Al-Sc no NU @ karnesky @ 10883
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Karnesky, Richard A.; Seidman, David N Criteria for Consistent Steady-State Coarsening Journal Article 2007 Scripta Materialia Scripta Mater. In Preparation Al-Sc no NU @ karnesky @ 1912
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Knipling, Keith E Development of a Nanoscale Precipitation-Strengthened Creep-Resistant Aluminum Alloy Containing Trialuminide Precipitates Book Whole 2006 230 Al-Zr This research is toward developing a castable and heat-treatable precipitation-strengthened aluminum alloy exhibiting coarsening- and creep resistance at temperatures exceeding 400°C. Criteria for selecting alloying elements capable of producing such an alloy are established. Those systems forming Al3M trialuminide compounds with a cubic L12 crystal structure are favored, and based on a review of the existing literature, these are assessed in terms of solid-solubility and diffusivity in &#945;-Al (satisfying the need for slow coarsening kinetics), and castability (which is discussed based on the binary phase diagrams). The first Group 3 element, Sc, and the second Group 4 element, Zr, are shown to be most promising. These expectations are confirmed by an initial study on the Al-Ti system, which demonstrates that conventionally-solidified alloys are not capable of precipitation strengthening. The Al-Zr system, by contrast, exhibits precipitation of nanometer-scale Al3Zr (L12) producing pronounced precipitation hardening when aged at 375, 400, or 425°C. The Al3Zr precipitates are coarsening resistant and have the metastable L12 structure up to 500°C, a result of very sluggish diffusion of Zr in &#945;-Al. Ternary additions of Ti are also investigated, forming Al3(Zr,Ti) (L12) precipitates with a reduced lattice parameter mismatch with &#945;-Al, potentially improving the coarsening resistance. The composition of Al3(Zr,Ti) precipitates formed at 375 or 425°C are measured directly using 3-D atom-probe tomography. At these temperatures, the Zr:Ti atomic ratio in the precipitates is about 10 and 5, respectively, indicating that most of the available Ti fails to partition to the Al3(Zr,Ti) phase. This is consistent with prior studies on Al-Sc alloys, where the slower-diffusing ternary solute species make up a small fraction of the Al3Sc-based precipitates. Despite the confirmed presence of Ti, Al3(Zr,Ti) precipitates exhibit no improvement in terms of coarsening resistance compared to binary Al3Zr. Mechanical properties of the Al-Zr and Al-Zr-Ti alloys are investigated utilizing Vickers microhardness and creep. The alloys deformed by creep at 300&#8722;400°C exhibit a dislocation climb-controlled threshold stress, ca. 6&#8722;12 MPa. The binary Al-Zr and ternary Al-Zr-Ti alloys behave similarly under ambient- and high temperature loading, consistent with the similar microstructures of the two alloys. Ph.D. thesis Northwestern University no NU @ keith.knipling @ 1785
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Karnesky, Richard A.; Meng, Liang; Seidman, David N.; Dunand, David C. Mechanical Properties of a Heat-Treatable Al-Sc Alloy Reinforced with Al[sub:2]O[sub:3] Book Chapter 2003 Affordable Metal-Matrix Composites for High Performance Applications II 215-224 Aluminum alloys, Scandium, Alumina, Mechanical properties, Precipitation strengthening, Dispersoid strengthening, Threshold stress; Al-Sc The mechanical behavior of precipitation-strengthened Al-0.18 wt.% Sc alloys containing 30 vol.% Al[sub:2]O[sub:3] dispersoids is studied at 25, 300 and 350°C. The effect of Al[sub:3]Sc precipitate size is studied by varying aging treatments. Microhardness measurements show that both populations of particles (nanometer-sized Al[sub:3]Sc precipitates and submicron-sized Al[sub:2]O[sub:3] dispersoids) contribute to strength at ambient temperature. At elevated temperature, a threshold stress is observed, indicative of interactions between matrix dislocations and the particles. The threshold stress is significantly higher than either Al-0.18 wt.% Sc alloys without Al[sub:2]O[sub:3] dispersoids or Al-30 vol.% Al[sub:2]O[sub:3] without Al[sub:3]Sc precipitates. This indicates that strengthening is occurring at both length scales and in a nonlinear manner, as the reinforced alloy exhibits strength higher than the sum of the strengths of Al-Sc and Al-Al[sub:2]O[sub:3] alloys. Northwestern University TMS Chicago Awadh B. Pandey, Kevin L. Kendig, John Lewandowski, and Sandeep R. Shah English 0-87339-557-3 Materials Science & Technology 2003 no NU @ karnesky @ 528
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Fuller, Christian B.; Seidman, David N.; Dunand, David C. Structure-Property Relationships for Al(Sc,Zr) Alloys Book Chapter 2003 Hot Deformation of Aluminum Alloys III 531-540 Al-Sc TMS Warrendale, PA Zin, J.; Beaudoin, A.; Bieler, T. A.; Radhakrishnan, B. no NU @ karnesky @ 1907
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Marquis, E. A.; Seidman, D. N; Dunand, D. C. Microstructural, and Creep Properties of an Al-2 Mg-0.2 Sc (wt.%) Alloy Book Chapter 2003 Hot Deformation of Aluminum Alloys III 177-184 Al-Sc TMS Warrendale, PA Zin, J.; Beaudoin, A.; Bieler, T. A.; Radhakrishnan, B. no NU @ karnesky @ 1906
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