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Type Karnesky, Richard A.; Meng, Liang; Seidman, David N.; Dunand, David C.
  Publication Mechanical Properties of a Heat-Treatable Al-Sc Alloy Reinforced with Al[sub:2]O[sub:3] Volume Book Chapter
Pages 2003
  Abstract Affordable Metal-Matrix Composites for High Performance Applications II  
  Corporate Author  
Publisher  
Editor
  Summary Language 215-224 Series Editor Aluminum alloys, Scandium, Alumina, Mechanical properties, Precipitation strengthening, Dispersoid strengthening, Threshold stress; Al-Sc  
Abbreviated Series Title The mechanical behavior of precipitation-strengthened Al-0.18 wt.% Sc alloys containing 30 vol.% Al2O3 dispersoids is studied at 25, 300 and 350°C. The effect of Al3Sc precipitate size is studied by varying aging treatments. Microhardness measurements show that both populations of particles (nanometer-sized Al3Sc precipitates and submicron-sized Al2O3 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 Al2O3 dispersoids or Al-30 vol.% Al2O3 without Al3Sc 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-Al2O3 alloys.
  Series Issue Northwestern University ISSN  
Medium
  Expedition TMS Notes Chicago  
Call Number Awadh B. Pandey, Kevin L. Kendig, John Lewandowski, and Sandeep R. Shah  
Contribution Id English  
Serial URL ISBN  
0-87339-557-3 Materials Science & Technology 2003 no NU @ karnesky @ 528
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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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Karnesky, Richard A.; Seidman, David N.; Dunand, David C. Creep of Al-Sc Microalloys with Rare-Earth Element Additions Journal Article 2006 Materials Science Forum Mater. Sci. Forum 519-521 1035-1040 Scandium, Rare-Earth Elements, Creep, Precipitation Strengthening; Al-Sc Cast and aged Al-Sc microalloys are creep-resistant to 300C, due to the blocking of dislocations by nanosize, coherent Al[sub:3]Sc (L1[sub:2]) 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. ICAA10 no NU @ karnesky @ 660
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Karnesky, Richard A.; van Dalen, Marsha E.; Dunand, David C.; Seidman, David N. Effects of Substituting Rare-Earth Elements for Scandium in a Precipitation-Strengthened Al 0.08 at.% Sc Alloy Journal Article 2006 Scripta Materialia Scripta Mater. 55 5 437-440 Aluminum alloys; Scandium; Rare-earth elements; Lanthanides, Precipitation strengthening; Local-Electrode Atom-Probe tomography; LEAP; Al-Sc The microhardness of Al-0.06 Sc-0.02 RE (at.%, with RE = Dy, Er, Gd, Sm, Y, or Yb) alloys is measured as a function of aging time at 300C. As compared to Al-0.08 Sc, the ternary alloys exhibit: (i) the same incubation time, except for Al-0.06 Sc-0.02 Yb which hardens much faster; (ii) the same or reduced peak microhardnesses (which are higher than for Al-0.06 Sc) and (iii) the same overaging behavior. All RE segregate to the core of Al[sub:3](Sc[sub:1-x]RE[sub:x]) precipitates. no NU @ karnesky @ 779
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Knipling, K. E.; Seidman, D. N.; Dunand, D. C. Ambient- and High- Temperature Mechanical Properties of Isochronally Aged Al-0.06Sc, Al-0.06 Zr, and Al-0.06Sc-0.06Zr Alloys (at.%) Journal Article 2011 Acta Materialia 59 3 943-954 Al-Sc; Aluminum alloys; Precipitation; Isochronal heat-treatments; Scandium; Zirconium Ambient- and high-temperature precipitation strengthening are investigated in Al0.06Sc, Al0.06Zr and Al0.06Sc0.06Zr (at.%) alloys. Following solidification, Sc is concentrated at the dendrite peripheries while Zr is segregated at the dendrite cores. During isochronal aging, precipitation of Al3Sc (L12) commences between 250 and 300 °C for Al0.06Sc, and reaches a 429 MPa peak microhardness at 325 °C. For Al0.06Zr, precipitation of Al3Zr (L12) first occurs between 400 and 425 °C and reaches a 295 MPa peak microhardness at 475 °C. A pronounced synergistic effect is observed when both Sc and Zr are present. Above 325 °C, Zr additions provide a secondary strength increase that is attributed to precipitation of Zr-enriched outer shells onto the Al3Sc precipitates, leading to a peak microhardness of 618 MPa at 400 °C for Al0.06Sc0.06Zr. Upon compressive creep deformation at 300400 °C, Al0.06Sc0.06Zr exhibits threshold stresses of 712 MPa; these values may be further improved by optimal heat-treatments. no NU @ karnesky @ 10884
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Knipling, K.E.; Dunand, D.C. Creep resistance of cast and aged Al-0.1Zr and Al-0.1Zr-0.1Ti (at.%) alloys at 300-400ºC Journal Article 2008 Scripta Materialia 59 4 387-390 Aluminum alloys; Creep; Precipitation strengthening; Titanium; Zirconium; Al-Zr 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. no NU @ jscott @ 1793 10370
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Knipling, K.E.; Dunand, D.C.; Seidman, D.N. Precipitation evolution in Al-Zr and Al-Zr-Ti alloys during aging at 450-600 C Journal Article 2008 Acta Materialia 56 6 1182-1195 Aluminum alloys; Zirconium; Titanium; Precipitation strengthening; Coarsening; Al-Zr 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. no NU @ karnesky @ 10274
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Knipling, K.E.; Dunand, D.C.; Seidman, D.N. Atom Probe Tomographic Studies of Precipitation in Al-0.1Zr-0.1Ti (at.%) Alloys Journal Article 2007 Microscopy and Microanalysis 13 06 503-516 atom probe tomography, Al[sub:3]Zr precipitates, local magnification, Al-Zr-Ti Atom probe tomography was utilized to measure directly the chemical compositions of Al3(Zr1−xTix) precipitates with a metastable L12 structure formed in Al-0.1Zr-0.1Ti (at.%) alloys upon aging at 375°C or 425°C. The alloys exhibit an inhomogeneous distribution of Al3(Zr1−xTix) precipitates, as a result of a nonuniform dendritic distribution of solute atoms after casting. At these aging temperatures, the Zr:Ti atomic ratio in the precipitates is about 10 and 5, respectively, indicating that Ti remains mainly in solid solution rather than partitioning to the Al3(Zr1−xTix) precipitates. This is interpreted as being due to the very small diffusivity of Ti in [alpha]-Al, consistent with prior studies on Al-Sc-Ti and Al-Sc-Zr alloys, where the slower diffusing Zr and Ti atoms make up a small fraction of the Al3(Sc1−xTix/Zrx) precipitates. Unlike those alloys, however, the present Al-Zr-Ti alloys exhibit no interfacial segregation of Ti at the matrix/precipitate heterophase interface, a result that may be affected by a significant disparity in the evaporation fields of the [alpha]-Al matrix and Al3(Zr1−xTix) precipitates and/or a lack of local thermodynamic equilibrium at the interface. no NU @ karnesky @ 10102
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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 α-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 α-Al. Ternary additions of Ti are also investigated, forming Al3(Zr,Ti) (L12) precipitates with a reduced lattice parameter mismatch with α-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 300−400°C exhibit a dislocation climb-controlled threshold stress, ca. 6−12 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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Knipling, Keith E.; Dunand, David C.; Seidman, David N. Precipitation evolution in Al-Zr and Al-Zr-Ti alloys during isothermal aging at 375-425 C Journal Article 2008 Acta Materialia Acta Mater. 56 1 114-127 Aluminum alloys, Zirconium, Titanium, Precipitation strengthening, Coarsening; Al-Zr-Ti; Al-Zr Formation of Al3Zr or Al3(Zr1Àx Tix) precipitates with a metastable L12 structure was investigated in conventionally solidified A10.1 Zr, Al0.2 Zr, Al0.1 Zr0.1 Ti, and Al0.2 Zr0.2 Ti (at.%) alloys aged isothermally at 375, 400, or 425 °C. Pronounced hardening results from nanometer-scale, spheroidal Al3Zr or Al3(Zr1ÀxTix) (L12) precipitates within solute-enriched dendrites. Interdendritic regions contain a significantly lower number density of coarser cauliflower-, rod- and plate-shaped precipitates with the L12 structure. Neither the magnitude of the peak-aged hardness, nor the subsequent loss in hardness due to overaging, is affected by ternary additions of Ti. After extended aging times (1600 h) at 425 °C, there is no difference in the mean precipitate radii of spheroidal Al3Zr or Al3(Zr1ÀxTix) precipitates, confirming that Ti additions do not improve the coarsening resistance. Comparison with prior coarsening studies on Al3Zr, and Al3(Zr1ÀxVx), Al3(Zr1ÀxTix) and Al3(Zr1ÀxÀyVxTiy) (L12) precipitates at 425 °C confirms the lack of an effect from ternary alloying additions. no NU @ karnesky @ 1909
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