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Isheim, Dieter; Kolli, R. Prakash; Fine, Morris E.; Seidman, David N. |
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An atom-probe tomographic study of the temporal evolution of the nanostructure of Fe-Cu based high-strength low-carbon steels |
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2006 |
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Scripta Materialia |
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Scripta Mater. |
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55 |
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35-40 |
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Precipitation strengthening; Interfacial segregation; Ferritic steels; Nanostructure; Temporal evolution; LEAP |
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A three-dimensional (3D) knowledge of the atomic-scale structure is necessary for improving the design and understanding of modern materials with complex microstructures, such as high-performance steels. Local-electrode atom-probe tomography is used to obtain atom-by-atom 3D reconstructions to characterize three versions of a copper, nickel, manganese, and aluminum bearing high-strength low-carbon steel, which achieve their high tensile yield strength, up to 1170 MPa (170 ksi), from the formation of nanometer-radius copper rich precipitates. The temporal evolution of these precipitates is followed at 500 |
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NU @ p-kolli @ |
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790 |
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Kolli, R. Prakash |
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Kinetics of nanoscale Cu-rich precipitates in a multicomponent concentrated steel |
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Book Whole |
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2007 |
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320 |
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Kinetics; Cu; precipitate; steel |
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The kinetics of nanoscale Cu-rich precipitates of multicomponent concentrated steels has been investigated utilizing primarily APT and supplemented with a synchrotron radiation experiment, first-principles calculations, Thermo-Calc study, and CTEM (at the longest aging time). Results on mechanical properties and microstructure at a greater length scale are also presented. The studied steels, NUCu-170 and NUCu-140-x, are HSLC steels, and are primarily strengthened by nanoscale Cu-rich precipitates. NUCu-170 contains 1.82 at. % Cu, whereas NUCu-140-x contains nominally ca. 1.15 at. % Cu. This study focused on a 900 °C solutionizing treatment followed by isothermal aging at 500 °C between 0.25 and 1024 h for NUCu-170 and NUCu-140-1, and aging at 550 °C between 0.25 and 4 h for NUCu-140-3. In addition, a double aging treatment of 550 °C aging followed by 200 °C for 2 h was investigated for NUCu-140-3. |
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Ph.D. thesis |
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Northwestern University |
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NU @ m-krug @ |
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10472 |
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Kolli, R. Prakash Kolli; Wojes, Ryan M.; Zaucha, Stephanie; Seidman, David N. |
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A subnanoscale study of the nucleation, growth, and coarsening kinetics of Cu-rich precipitates in a multicomponent Fe–Cu based steel |
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Journal Article |
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2008 |
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International Journal of Materials Research |
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Int. J. Mater. Res. |
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05 |
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513-527 |
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Nucleation; Growth; Coarsening; Fe-Cu alloy; Atom-probe tomography |
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The nucleation, growth, and coarsening kinetics of Cu-rich precipitates in a multicomponent Fe–Cu based steel, containing 1.17 at.% Cu, aged at 500°C for up to 1024 h are investigated. The temporal evolution of the precipitate, heterophase interface, matrix compositions and precipitate morphology are presented. Coarsening temporal exponents are determined for mean radius, [R(t)], number density, NV(t), and supersaturations, and are compared to the Lifshitz–Slyzov–Wagner model for coarsening, modified for multicomponent alloys by Umantsev and Olson. The experimental results indicate that the alloy does not strictly follow Umantsev–Olson model behavior. Additionally, we compare the results to an investigation of a similar multicomponent steel containing 1.82 at.% Cu and to results in the literature. Furthermore, we present a Thermo-Calc determined phase diagram. |
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NU @ p-kolli @ |
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10374 |
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Kolli, R. Prakash; Mao, Zugang; Keane, D. T.; Seidman, David N. |
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Identification of a Ni0.5(Al0.5-xMnx) B2 Phase at the Heterophase Interfaces of Cu-rich Precipitates in an a-Fe Matrix |
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Journal Article |
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2007 |
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Applied Physics Letters |
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Accepted |
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A phase with the stoichiometry Ni0.5(Al0.5-xMnx) is observed at heterophase interfaces of Cu-rich
precipitates in an α-Fe matrix, utilizing atom-probe tomography. First-principles calculations are
utilized to determine the substitutional energies, yielding E Mn →Ni = 0.916 eV atom-1 and
E Mn →Al = −0.016 eV atom-1, indicating that the manganese atoms prefer substituting at Al sub-
lattice sites instead of Ni-sites. A synchrotron radiation experiment demonstrates that the
identified phase possesses the B2 structure. |
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NU @ karnesky @ |
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9945 |
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Kolli, R. Prakash; Seidman, D.N. |
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The temporal evolution of the decomposition of a concentrated multicomponent Fe-Cu-based steel |
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Journal Article |
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2008 |
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Acta Materialia |
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56 |
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9 |
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2073-2088 |
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Coarsening; Fe-Cu alloy; Phase separation; Atom-probe tomography; Interfacial segregation |
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The nucleation (to a limited extent), growth and coarsening behavior of Cu-rich precipitates in a concentrated multicomponent Fe-Cu-based steel aged at 500 °C from 0.25 to 1024 h is investigated. The temporal evolution of the precipitates, heterophase interfaces, matrix compositions and precipitate morphologies are presented. With increasing time, Cu partitions to the precipitates, Ni, Al and Mn partition to the interfacial region, whereas Fe and Si partition to the matrix. Coarsening time exponents are determined for the mean radius, <R(t)>, number density, NV(t), and supersaturations, which are compared to the Lifshitz-Slyzov-Wagner (LSW) model for coarsening, modified for concentrated multicomponent alloys by Umantsev and Olson (UO). The experimental results indicate that the alloy does not strictly follow UO model behavior. Additionally, we delineate the formation of a Ni-Al-Mn shell with a stoichiometric ratio of 0.51:0.41:0.08 at 1024 h, which reduces the interfacial free energy between the precipitates and the matrix. |
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NU @ p-kolli @ |
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10373 |
| Permanent link to this record |
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Kolli, R. Prakash; Seidman, David N. |
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Comparison of Compositional and Morphological Atom-Probe Tomography Analyses for a Multicomponent Fe-Cu Steel |
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Journal Article |
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2007 |
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Microscopy & Microanalysis |
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Microsc. Microanal. |
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13 |
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4 |
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272-284 |
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precipitate morphology, concentration profiles, atom-probe tomography, maximum separation distance, envelope method, proxigram, Fu-Cu steel, high-strength low-carbon ~HSLC! steel |
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A multicomponent Fe-Cu based steel is studied using atom-probe tomography. The precipitates are identified using two different methodologies and subsequent morphological and compositional results are compared. The precipitates are first identified using a maximum separation distance algorithm, the envelope method, and then by a concentration threshold method, an isoconcentration surface. We discuss in detail the proper selection of the parameters needed to delineate precipitates utilizing both methods. The results of the two methods exhibit a difference of 44 identified precipitates, which can be attributed to differences in the basis of both methods and the sensitivity of our results to user-prescribed parameters. The morphology of the precipitates, characterized by four different precipitate radii and precipitate size distribution functions ~PSDs!, are compared and evaluated. A variation of less than ;8% is found between the different radii. Two types of concentration profiles are compared, giving qualitatively similar results. Both profiles show Cu-rich precipitates containing Fe with elevated concentrations of Ni, Al, and Mn near the heterophase interfaces. There are, however, quantitative disagreements due to differences in the basic foundations of the two analysis methods. |
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no |
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NU @ karnesky @ |
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713 |
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Kolli, R. Prakash; Seidman, David N. |
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Asymmetric Chemical Composition Profiles of Nanoscale Precipitates in a Multi-component Alloy Studied by 3-D Atom-Probe Tomography |
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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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Submitted |
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3-D atom-probe tomography, Fe-Cu steels, phase transformations, heterogeneous segregation, precipitation |
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Compositional profiles of precipitates in a multi-component Fe-Cu steel are obtained by 3-D
local-electrode atom-probe (LEAP) tomography. Adjacent Cu-rich and Ni-Al-Mn rich regions in
the 1-hour aged alloy evolve temporally into a Cu-rich precipitate core enveloped by a Ni-Al-Mn
(0.42:0.49:0.09) enriched spherical-shell in the 1024-hour aged alloy. The compositions of the
shells are demonstrated, for the first time, to be asymmetric. We propose this results from
precipitation of Cu-rich precipitates followed by heterogeneous nucleation of Ni-Al-Mn on them
and subsequent diffusional growth. |
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PDF removed at request of author |
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NU @ karnesky @ |
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773 |
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Kolli, R. Prakash; Seidman, David N. |
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The temporal evolution of the decomposition of a concentrated multicomponent Fe-Cu based steel |
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Manuscript |
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NU @ m-krug @ |
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9834 |
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Kolli, R.P.; Mao, Z.; Seidman, D.N.; Keane, D.T. |
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Identification of a Ni[sub:0.5](Al[sub:0.5 - x]Mn[sub:x]) B2 phase at the heterophase interfaces of Cu-rich precipitates in an alpha-Fe matrix |
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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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24 |
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241903-3 |
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ab initio calculations; aluminium alloys; manganese alloys; nickel alloys; precipitation; stoichiometry; surface segregation |
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A phase with the stoichiometry Ni0.5(Al0.5−xMnx) is observed at heterophase interfaces of Cu-rich precipitates in an alpha-Fe matrix, utilizing atom-probe tomography. First-principles calculations are utilized to determine the substitutional energies, yielding EMn-->Ni=0.916 eV atom−1 and EMn-->Al=−0.016 eV atom−1 indicating that the manganese atoms prefer substituting at Al sublattice sites instead of Ni sites. A synchrotron radiation experiment demonstrates that the identified phase possesses the B2 structure. |
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NU @ karnesky @ |
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10170 |
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Kolli, R.Prakash; Seidman, David N. |
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Coarsening kinetics of Cu-rich precipitates in a concentrated multicomponent Fe–Cu based steel |
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Journal Article |
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2011 |
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International Journal of Materials Research (formerly Zeitschrift fuer Metallkunde) |
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102 |
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1115-1124 |
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Coarsening, Phase separation, Fe-Cu alloys, Atom-probe tomography, Precipitation |
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The coarsening kinetics of Cu-rich precipitates in a concentrated multicomponent Fe–Cu based steel, containing 1.12 at.% Cu, aged at 550 °C or at 550 °C plus 2 h at 200 °C is investigated. The temporal evolution of the precipitates, heterophase interfaces, and α-Fe matrix compositions and precipitate morphology are presented. Coarsening time exponents are determined for the mean radius, <R(t)>, and number density, NV(t), and compared to the Lifshitz–Slyzov–Wagner model for coarsening, modified for concentrated multicomponent alloys by Umantsev–Olson. The experimental results indicate that <R(t)> and NV(t) are in reasonable agreement with Umantsev–Olson model behavior. Additionally, we compare the results to earlier investigations of similar concentrated multicomponent steels containing 1.82 at.% Cu and 1.17 at.% Cu, aged at 500 °C. |
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1862-5282 |
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NU @ karnesky @ 2186 |
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11293 |
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