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Lee, D.-H.; Hong, K.T.; Nam, S.W. |
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Intergraular fracture behavior of an Al-3at.%Mg solid solution alloy under the viscous glide creep condition |
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Journal Article |
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1991 |
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Abstract |
Scripta Metallurgica et Materialia |
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25 |
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4 |
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823-828 |
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NU @ karnesky @ |
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10279 |
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Lee, Z.; Witkin, D.B.; Radmilovic, V.; Lavernia, E.J.; Nutt, S.R. |
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Bimodal microstructure and deformation of cryomilled bulk nanocrystalline Al-7.5Mg alloy |
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Journal Article |
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2005 |
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Materials Science and Engineering: A |
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The Langdon Symposium: Flow and forming of Crystalline Materials |
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410-411 |
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462-467 |
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Nanocrystalline; Bimodal; Cryomilling; Aluminum; Deformation |
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The microstructure, mechanical properties and deformation response of bimodal structured nanocrystalline Al-7.5Mg alloy were investigated. Grain refinement was achieved by cryomilling of atomized Al-7.5Mg powders, and then cryomilled nanocrystalline powders blended with 15 and 30% unmilled coarse-grained powders were consolidated by hot isostatic pressing followed by extrusion to produce bulk nanocrystalline alloys. Bimodal bulk nanocrystalline Al-7.5Mg alloys, which were comprised of nanocrystalline grains separated by coarse-grain regions, show balanced mechanical properties of enhanced yield and ultimate strength and reasonable ductility and toughness compared to comparable conventional alloys and nanocrystalline metals. The investigation of tensile and hardness test suggests unusual deformation mechanisms and interactions between ductile coarse-grain bands and nanocrystalline regions. |
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NU @ karnesky @ |
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10321 |
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Witkin, D.; Lee, Z.; Rodriguez, R.; Nutt, S.; Lavernia, E. |
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Al-Mg alloy engineered with bimodal grain size for high strength and increased ductility |
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Journal Article |
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2003 |
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Scripta Materialia |
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49 |
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4 |
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297-302 |
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Aluminum alloys; Nanocrystalline materials; Mechanical properties |
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Al-7.5Mg powders were cryomilled, then consolidated and extruded to produce bulk nanostructured material. The extrusions had a tensile yield strength of 641 MPa and an ultimate strength of 847 MPa. Additional samples were prepared by combining cryomilled powder unmilled Al-7.5Mg, resulting in extrusions with high strength and increased ductility. |
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NU @ karnesky @ |
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10322 |
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Ye, J.; Han, B.Q.; Lee, Z.; Ahn, B.; Nutt, S.R.; Schoenung, J.M. |
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A tri-modal aluminum based composite with super-high strength |
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Journal Article |
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2005 |
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Scripta Materialia |
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53 |
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5 |
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481-486 |
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Metal matrix composites; Aluminum alloy; Cryomilling; Compression test; Nanocrystalline |
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A bulk composite with 10 wt.% B4C, 50 wt.% coarse-grained 5083 Al and the balance nanocrystalline 5083 Al was fabricated, using cryomilling and compaction. This tri-modal composite exhibited an extremely high yield strength (up to 1065 MPa) when tested under compressive load. The structure-property relationships are discussed. |
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NU @ karnesky @ |
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10328 |
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Lee, W.-S.; Chen, T.-H. |
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Mechanical and microstructural response of aluminum-scandium (Al-Sc) alloy as a function of strain rate and temperature |
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Journal Article |
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2009 |
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Materials Chemistry and Physics |
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113 |
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2-3 |
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734-745 |
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Al-Sc alloy; Strain rate sensitivity; Activation energy; Shearing; Dislocation; Precipitates |
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This study applies a compressive split Hopkinson bar to investigate the mechanical response, microstructural evolution and fracture characteristics of aluminum-scandium (Al-Sc) alloy at temperatures ranging from -100 °C to 300 °C and strain rates of 1.2 × 103 s-1, 3.2 × 103 s-1 and 5.8 × 103 s-1. The relationship between the dynamic mechanical behaviour of the Al-Sc alloy and its microstructural characteristics is explored. The fracture features and microstructural evolution are observed using scanning and transmission electron microscopy techniques. The stress-strain relationships indicate that the flow stress, work hardening rate and strain rate sensitivity increase with strain rate, but decrease with increasing temperature. Conversely, the activation volume and activation energy increase as the temperature increases or the strain rate decreases. Additionally, the fracture strain reduces with increasing strain rate and decreasing temperature. However, at room temperature under a low strain rate of 1.2 × 103 s-1 and at a high experimental temperature of 300 °C under all three tested strain rates, the specimens do not fracture, even under large strain deformations. The Zerilli-Armstrong fcc constitutive model is used to describe the plastic deformation behaviour of the Al-Sc alloy. Comparing the predicted flow stress values with the experimental values over all the considered strain rate and temperature conditions, the maximum error between the two sets of results is found to be less than 4%. SEM observations show that the specimens fracture predominantly as a result of a shearing mechanism. Moreover, the surfaces of the fractured specimens are characterised by transgranular dimpled features, which are indicative of a ductile fracture mode. Fine Al3Sc precipitates are found to be distributed in the matrix and at the grain boundaries. Finally, the TEM analysis results reveal that the dislocation density increases, but the dislocation cell size decreases, with increasing strain rate. However, a higher temperature causes the dislocation density to decrease, thereby increasing the dislocation cell size. |
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NU @ karnesky @ |
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10512 |
| Permanent link to this record |
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Lee, W.S.; Chen, T.H. |
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Effects of strain rate and temperature on dynamic mechanical behaviour and microstructural evolution in aluminium-scandium (Al-Sc) alloy |
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Journal Article |
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2008 |
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Materials Science and Technology |
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24 |
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10 |
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1271-1282 |
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AL-SC ALLOY; STRAIN RATE SENSITIVITY; ACTIVATION ENERGY; ADIABATIC SHEARING; DISLOCATION; AL3SC PRECIPITATES |
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The present study applies a compressive split Hopkinson bar to investigate the mechanical response, microstructural evolution and fracture characteristics of an aluminium-scandium (Al-Sc) alloy at temperatures ranging from − 100 to 300°C and strain rates of 1·2 × 103, 3·2×103 and 5·8 × 103 s−1. The relationship between the dynamic mechanical behaviour of the Al-Sc alloy and its microstructural characteristics is explored. The fracture features and microstructural evolution are observed using scanning and transmission electron microscopy techniques. The stress-strain relationships indicate that the flow stress, work hardening rate and strain rate sensitivity increase with increasing strain rate, but decrease with increasing temperature. Conversely, the activation volume and activation energy increase as the temperature increases or the strain rate decreases. Additionally, the fracture strain reduces with increasing strain rate and decreasing temperature. The Zerilli-Armstrong fcc constitutive model is used to describe the plastic deformation behaviour of the Al-Sc alloy, and the error between the predicted flow stress and the measured stress is found to be less than 5%. The fracture analysis results reveal that cracks initiate and propagate in the shear bands of the Al-Sc alloy specimens and are responsible for their ultimate failure. However, at room temperature, under a low strain rate of 1·2 × 103 s−1 and at a high experimental temperature of 300°C under all three tested strain rates, the specimens do not fracture, even under large strain deformations. Scanning electron microscopy observations show that the surfaces of the fractured specimens are characterised by transgranular dimpled features, which are indicative of ductile fracture. The depth and density of these dimples are significantly influenced by the strain rate and temperature. The transmission electron microscopy structural observations show the precipitation of Al3Sc particles in the matrix and at the grain boundaries. These particles suppress dislocation motion and result in a strengthening effect. The transmission electron microscopy analysis also reveals that the dislocation density increases, but the dislocation cell size decreases, with increasing strain rate for a constant level of strain. However, a higher temperature causes the dislocation density to decrease, thereby increasing the dislocation cell size. |
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NU @ m-krug @ |
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10531 |
| Permanent link to this record |
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Muraleedharan, K.; Balamuralikrishnan, R.; Das, N. |
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TEM and 3D atom probe characterization of DMS4 cast nickel-base superalloy |
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Journal Article |
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2009 |
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Journal of Materials Science |
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J. Mater. Sci. |
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44 |
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9 |
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2218-2225 |
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Cast nickel-base superalloys possess the required mechanical properties (creep resistance and stress rupture life) at elevated temperatures that make them suitable for turbine blades in aero-engines. The origin of these properties lies in the presence of a simple two phase [gamma]-[gamma]' microstructure (with cuboidal [gamma]' particles dispersed in a [gamma] matrix), in spite of the presence of several alloying elements. The cuboidal nature of the [gamma]' particles arises from an optimal misfit between the two phases, which is a function of the composition of [gamma] and [gamma]' phases. In addition, several microstructural issues arising out of the partitioning of the alloying elements influences directly the deformation mechanisms in the [gamma] and [gamma]', and therefore the mechanical properties of the alloy. In this article, we discuss how some of these microstructural issues have been investigated in DMS4, a cast single crystal superalloy, experimentally using TEM and 3DAP techniques. |
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NU @ karnesky @ |
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10534 |
| Permanent link to this record |
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Knipling, Keith E.; Karnesky, Richard A.; Lee, Constance P.; Dunand, David C.; Seidman, David N. |
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Precipitation Evolution in Al-0.1Sc, Al-0.1Zr, and Al-0.1Sc-0.1Zr (at.%) Alloys during Isochronal Aging |
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Journal Article |
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2010 |
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Acta Materialia |
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58 |
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15 |
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5184-5195 |
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Aluminum alloys, Precipitation, Scandium, Zirconium, Atom-probe tomography; Al-Sc-Zr |
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Precipitation strengthening is investigated in binary Al-0.1Sc, Al-0.1Zr, and ternary Al-0.1Sc-0.1Zr (at.%) alloys aged isochronally between 200 and 600 °C. A pronounced synergistic effect is observed when both Sc and Zr are present. Above 325 °C, where peak microhardness (670 MPa) occurs in the binary Al-Sc alloy due to Al[sub:3]Sc (L1[sub:2]) nanometer-scale precipitates, Zr additions result in a secondary increase in strength due to additional precipitation of Zr-enriched outer shells onto these precipitates. The ternary alloy reaches a peak microhardness of 780 MPa at 400 °C, delaying overaging by >100 °C compared with the binary Al-Sc alloy and increasing strength compared with the binary Al-Zr alloy (peak microhardness of 420 MPa at 425–450 °C). Compositions, radii, volume fractions, and number densities of the Al[sub:3](Sc[sub:1-x]Zr[sub:x]) precipitates are measured directly using atom-probe tomography. This information is used to quantify the observed strengthening increments, attributed to dislocation shearing of the Al[sub:3](Sc[sub:1-x]Zr[sub:x]) precipitates. |
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NU @ karnesky @ |
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10705 |
| Permanent link to this record |
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Zhou, F.; Lee, J.; Dallek, S.; Lavernia, E.J. |
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High grain size stability of nanocrystalline Al prepared by mechanical attrition |
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Journal Article |
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2001 |
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Journal of Materials Research |
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J. Mater. Res. |
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16 |
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12 |
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3451-3458 |
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Grain growth in nanocrystalline (nc) Al with a grain size of 26 nm produced by cryogenic mechanical milling was studied through x-ray diffraction, transmission electron microscopy, and differential scanning calorimetry. Grain growth kinetics resembled those of ball-milled nc Fe. For homologous temperatures (T/TM) of 0.61-0.83, the time exponent n from D1/n - D01/n = kt was 0.04-0.28, tending toward 0.5 as T/TM increased. Two grain-growth regimes were distinguished: below T/TM = 0.78 growth ceased at an approximate grain size of 50 nm while at higher temperatures, grain growth proceeded steadily to the submicrometer range. Grain growth over the range of temperatures studied cannot be explained in terms of a single thermally activated rate process. The observed high grain size stability was attributed primarily to impurity pinning drag associated with the grain growth process. |
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0884-2914 |
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NU @ karnesky @ 2757 |
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10753 |
| Permanent link to this record |
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Rogozhkin, S.; Ageev, V.; Aleev, A.; Zaluzhnyi, A.; Leont’eva-Smirnova, M.; Nikitin, A. |
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Tomographic atom-probe analysis of temperature-resistant 12%-chromium ferritic-martensitic steel EK-181 |
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Journal Article |
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2009 |
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The Physics of Metals and Metallography |
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108 |
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6 |
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579-585 |
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Abstract At present, the temperature-resistant steels with a rapid reduction of induced radioactivity appear to be a perspective structural material for new-generation nuclear and thermonuclear reactors. Special attention is paid to the nanostructural state of the elaborated materials. In this work, for the first time, there have been carried out tomographic atom-probe studies of the chromium ferritic-martensitic steel EK-181 (RUSFER EK-181) with 12% Cr. Spatial distributions of chemical elements in the investigated volumes of the material with an atomic resolution have been obtained. The dimensions of the investigated portions of the material are on the order of 10 × 10 × 30 nm3. There have been observed nanosized preprecipitates (nanoclusters), i.e., regions enriched in V, Cr, and N atoms, with characteristic sizes of about 3 nm. |
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NU @ karnesky @ |
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10767 |
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