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Suh,Dong-Woo; Lee, Sang-Yong; Lee, Kyong-Hwan; Lim, Su-Keun; Oh, Kyu Hwan |
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Microstructural evolution of Al–Zn–Mg–Cu–(Sc) alloy during hot extrusion and heat treatments |
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Journal Article |
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2004 |
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Journal of Materials Processing Technology |
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155-156 |
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1330-1336 |
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Scandium; Microstructure; Recovery; Recrystallization |
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Abbreviated Series Title |
The microstructural evolution during hot extrusion and post heat treatment was investigated for two kind of Al–Zn–Mg–Cu–(Sc) alloy and AA7075. The microstructure of as-extruded bar is mainly comprised of recovered structure for all alloys, however, different restoration processes are observed during post heat treatment. For AA7075 and S1, which contains 0.1% Sc with relatively higher Zn and Cu content than S2, recovery still proceeds during the heat treatment, while the recrystallization becomes main restoration process during the heat treatment for S2.
The differences in abnormal grain growth and hardening behavior between S1, AA7075 and S2 during the heat treatment are discussed in connection with the restoration processes and resultant microstructures. |
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NU @ karnesky @ |
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622 |
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Lee, Woei-Shyan; Chen, Tao-Hsing |
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Rate-dependent deformation and dislocation substructure of Al–Sc alloy |
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Journal Article |
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2006 |
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Scripta Materialia |
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Scripta Mater. |
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54 |
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8 |
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1463-1468 |
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Al–Sc alloy; Strain rate effect; Activation volume; Dislocation |
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High strength aluminum–scandium (Al–Sc) alloy is impacted at strain rates ranging from 1.2 × 103 s−1 to 5.8 × 103 s−1 at room temperature. The deformation behaviour of Al–Sc alloy is highly dependent on the strain rate. A higher strain rate increases the dislocation density, thereby reducing the size of the dislocation cells. |
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NU @ karnesky @ |
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653 |
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Lee, Thomas C. M. |
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ON ALGORITHMS FOR ORDINARY LEAST SQUARES REGRESSION SPLINE FITTING: A COMPARATIVE STUDY |
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Journal Article |
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2002 |
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Journal of Statistical Computation and Simulation |
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72 |
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8 |
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647-663 |
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Bivariate smoothing; Generalized cross-validation; Genetic algorithms; Regression spline; Stepwise selection |
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Regression spline smoothing is a popular approach for conducting nonparametric regression. An important issue
associated with it is the choice of a ‘‘theoretically best’’ set of knots. Different statistical model selection
methods, such as Akaike’s information criterion and generalized cross-validation, have been applied to derive
different ‘‘theoretically best’’ sets of knots. Typically these best knot sets are defined implicitly as the optimizers
of some objective functions. Hence another equally important issue concerning regression spline smoothing is
how to optimize such objective functions. In this article different numerical algorithms that are designed for
carrying out such optimization problems are compared by means of a simulation study. Both the univariate and
bivariate smoothing settings will be considered. Based on the simulation results, recommendations for choosing a
suitable optimization algorithm under various settings will be provided. |
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NU @ karnesky @ |
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860 |
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Chi, E. J.; Shim, J. Y.; Baik, H. K.; Lee, S. M. |
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Fabrication of amorphous-carbon-nitride field emitters |
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Journal Article |
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1997 |
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Applied Physics Letters |
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Appl. Phys. Lett. |
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71 |
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324-326 |
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Field Emission; Field emitters; Eutectic silicon; Electric currents; Carbon; Electron affinities |
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o improve siliconfield emitters, an amorphous-carbon-nitride (a-CN) coating was applied by helical resonator plasma-enhanced chemical vapor deposition. By this process, a-CN was very uniformly coated on silicon tips without any damage. Microstructural and electrical investigation of the silicon and a-CN coated field emitters were performed. a-CN coating lowered turn-on voltage and increased emission current. Negative electron affinity of carbon nitride is suggested for enhancing emission current. |
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NU @ karnesky @ |
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2540 |
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Lee, S.-W.; Yeh, J.-W. |
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Superplasticity of 5083 alloys with Zr and Mn additions produced by reciprocating extrusion |
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Journal Article |
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2007 |
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Materials Science and Engineering: A |
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460-461 |
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409-419 |
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Aluminum alloys; Extrusion; Superplasticity |
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In this study, 5083 aluminum alloys modified with grain refiner, 0.25% Zr and 0.46% Mn, were processed by reciprocating extrusion to yield high-strain-rate superplasticity above 400 [degree sign]C and superior room-temperature mechanical properties. Without any prior homogenization treatment, 10 extrusion passes could give the cast billets an equiaxed grain structure with a grain size of about 4.5 [mu]m and a subgrain size about 0.2 [mu]m, and a uniform distribution of fine inclusions and dispersoids in the matrix. The fine-grained structure was stable up to 525 [degree sign]C, giving the alloy a high-strain-rate and low-stress superplasticity over a wide operating temperature of 400-500 [degree sign]C. In the tensile test at 500 [degree sign]C, a maximum elongation of 1013% and a low flow stress of 7.7 MPa at 5 x 10-2 s-1 were achieved. The apparent and true activation energies for low temperatures (300-400 [degree sign]C) without high-strain-rate superplasticity were 220.6 and 208 kJ/mol, respectively, whereas those at high temperatures (400-500 [degree sign]C) were 88.4 and 98.7 kJ/mol, respectively. Further analysis confirms that grain boundary sliding is the dominant mechanism over the high-strain-rate region from 1 x 10-2 to 5 x 10-1 s-1 at 500 [degree sign]C, and power-law breakdown mechanism occurs over the strain rate from 5 x 10-4 to 1 x 10-2 s-1 at 300 [degree sign]C. The high-strain-rate superplasticity was more strongly enhanced by Zr addition than addition of Cr and Mn. Two enhancing mechanisms for the maximum superplastic elongation and the optimum strain rate are proposed. This study concludes that the effectiveness of Zr is caused by the fineness and the coherency of Zr-rich dispersoids in the matrix. |
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NU @ karnesky @ |
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9637 |
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Tewari, S.N.; Vijayakumar, M.; Lee, J.E.; Curreri, P.A. |
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Solutal partition coefficients in nickel-based superalloy PWA-1480 |
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Journal Article |
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1991 |
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Materials Science and Engineering A |
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141 |
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1 |
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97-102 |
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Solutal profiles in dendritic single-crystal specimens of PWA-1480 nickel-base superalloy, which were directionally solidified and quenched, were examined on several transverse cross-sections to obtain the partition coefficients. Similar to their nickel-base binaries, the partition coefficients of tantalum, titanium, and aluminum were found to be less than unity; those of tungsten and cobalt were greater than unity. The partition coefficients were temperature independent in the range 1584-1608 K. The contribution of solid-state diffusion to microsegregation was observed to be negligible. |
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NU @ karnesky @ |
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9820 |
| Permanent link to this record |
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Lee, B.C.; Park, J.K. |
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Effect of the addition of Ag on the strengthening of Al3Li phase in Al-Li single crystals |
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Journal Article |
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1998 |
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Acta Materialia |
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46 |
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12 |
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4181-4187 |
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The variation of the critical resolved shear stress as a function of aging condition has been measured in ternary Al-~(1.9-2.0) wt% Li-~0.4 wt% Ag single crystals and has been analyzed using the same version of order-hardening theory as in our previous work in binary single crystals. The result showed that the antiphase boundary energy of the Al3Li lattice on {111} definitively increases from about 0.118 J/m2 in binary crystals to 0.128+/-0.012 J/m2 in ternary crystals, in good agreement with the analysis of the transition behavior from shearing to looping and of the dislocation pair spacings. A strong segregation tendency of Ag into the Al3Li lattice is believed to be responsible for this increment. Our previous result of [gamma]apb (0.118+/-0.006 J/m2) in binary crystals is, although unlikely from the recent suggestion of Nembach, the best value one can obtain from the recent knowledge of order-hardening theory. This is slightly larger than that (about 0.100 J/m2) obtained from the analysis of the transition from shearing to looping and somewhat larger than the result (about 0.085 J/m2) of the first-principles calculation. Three factors are discussed as principal causes of a possibility of an overestimation of [gamma]apb on applying order-hardening theory. |
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NU @ karnesky @ |
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9941 |
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Kim, Y.-C.; Adusumilli, P.; Lauhon, L.J.; Seidman, D.N.; Jung, S.-Y.; Lee, H.-D.; Alvis, R.L.; Ulfig, R.M.; Olson, J.D. |
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Three-dimensional atomic-scale mapping of Pd in Ni[sub:1 - x]Pd[sub:x]Si/Si(100) thin films |
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Journal Article |
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2007 |
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Applied Physics Letters |
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Appl. Phys. Lett. |
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91 |
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11 |
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113106:1-3 |
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annealing; interface roughness; nickel compounds; palladium compounds; rapid thermal processing; semiconductor-metal boundaries |
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Atom-probe tomography was utilized to map the three-dimensional distribution of Pd atoms in nickel monosilicide thin films on Si(100). A solid-solution Ni0.95Pd0.05 film on a Si(100) substrate was subjected to rapid thermal processing plus steady-state annealing to simulate the thermal processing experienced by NiSi source and drain contacts in standard complementary metal-oxide-semiconductor processes. Pd is found to segregate at the (Ni0.95Pd0.05)Si/Si(100) heterophase interface, which may provide a previously unrecognized contribution to monosilicide stabilization. The silicide-Si heterophase interface was reconstructed in three dimensions on an atomic scale and its chemical roughness was evaluated. |
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NU @ karnesky @ |
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9944 |
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Han, B.Q.; Lee, Z.; Witkin, D.; Nutt, S.; Lavernia, E.J. |
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Deformation behavior of bimodal nanostructured 5083 Al alloys |
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Journal Article |
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2005 |
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Metallurgical And Materials Transactions A-Physical Metallurgy And Materials Science |
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Metall. Mater. Trans. A-Phys. Metall. Mater. Sci. |
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36a |
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4 |
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957-965 |
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Cryomilled 5083 At alloys blended with volume fractions of 15, 30, and 50 pct unmilled 5083 At were produced by consolidation of a mixture of cryomilled 5083 At and Unmilled 5083 A] powders. A bimodal grain size was achieved in the as-extruded alloys in which nanostructured regions had a grain size of 200 nm and coarse-grained regions had a grain size of I µm. Compression loading in the longitudinal direction resulted in elastic-perfectly plastic deformation behavior. An enhanced tensile elongation associated with the occurrence of a Luders band was observed in the bimodal alloys. As the volume fraction of coarse grains was increased, tensile ductility increased and strength decreased. Enhanced tensile ductility was attributed to the occurrence of crack bridging as well as delamination between nanostructured and coarse-grained regions during plastic deformation. |
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Univ Calif Davis, Dept Chem Engn & Mat Sci, Davis, CA 95616 USA, Email: bqhan@ucdavis.edu |
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Minerals Metals Materials Soc |
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English |
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1073-5623 |
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ISI:000227914900007 |
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NU @ karnesky @ |
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10025 |
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Park, J.H.; Lee, Y.S.; Nam, W.J.; Park, K.T. |
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Comparison of compressive deformation of ultrafine-grained 5083 Al alloy at 77 and 298 K |
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Journal Article |
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2005 |
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Metallurgical And Materials Transactions A-Physical Metallurgy And Materials Science |
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Metall. Mater. Trans. A-Phys. Metall. Mater. Sci. |
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36a |
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5 |
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1365-1368 |
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The compression behaviors of well-annealed coarse-grained (CG) and ultrafine-grained (UFG) 5083 Al alloys at 77 and 298 K were compared. For the CG alloy, stage II and III strain hardening were dominant at 77 and 298 K, respectively, depending on the completeness of dislocation cell formation. The UFG alloy exhibited the elastic-near perfectly plastic behavior without distinctive dislocation cell formation at both temperatures. For both alloys, the flow stress at 77 K was much higher than that at 298 K. |
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Hanbat Natl Univ, Div Adv Mat Sci & Engn, Taejon 305719, South Korea, Email: ktpark@hanbat.ac.kr |
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Minerals Metals Materials Soc |
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English |
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1073-5623 |
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ISI:000228797500029 |
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NU @ karnesky @ |
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10027 |
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