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Lagow, B.W.; Robertson, I.M.; Jouiad, M.; Lassila, D.H.; Lee, T.C.; Birnbaum, H.K. |
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Observation of dislocation dynamics in the electron microscope |
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Journal Article |
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2001 |
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Abstract |
Materials Science And Engineering A |
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Mater. Sci. Eng. A |
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309-310 |
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Summary Language  |
445-450 |
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Deformation experiments performed in situ in the transmission electron microscope have led to an increased understanding of dislocation dynamics. To illustrate the capability of this technique two examples will be presented. In the first example, the processes of work hardening in Mo at room temperature will be presented. These studies have improved our understanding of dislocation mobility, dislocation generation, and dislocation-obstacle interactions. Zn the second example, the interaction of matrix dislocations with grain boundaries will be described. From such studies predictive criteria for slip transfer through grain boundaries have been developed. |
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0921-5093 |
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WOS:000169044600089 |
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NU @ m-krug @ |
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10533 |
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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 |
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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 |
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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 |
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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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Lee, Woei-Shyan; Chen, Tao-Hsing; Lin, Chi-Feng; Chen, Ming-Shiang |
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Impact deformation behaviour and dislocation substructure of Al-Sc alloy |
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Journal Article |
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2010 |
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Journal of Alloys and Compounds |
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493 |
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1-2 |
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580-589 |
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Al-Sc alloy; Strain rate sensitivity; Activation volume; Adiabatic shear band; Dislocation; Precipitates |
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This paper employs a compressive split-Hopkinson pressure bar to investigate the impact deformation behaviour of Al-Sc alloy under high strain rates of 1.2103s-1, 3.2103s-1 and 5.8103s-1, respectively, and temperatures of -100C, 25C and 300C. It is shown that for a constant temperature, the flow stress, work hardening rate and strain rate sensitivity increase with increasing strain rate, while the activation volume decreases. Conversely, for a constant strain rate, the flow stress, work hardening rate and strain rate sensitivity decrease with increasing temperature, while the activation volume increases. It is found that the impact deformation behaviour of Al-Sc alloy can be accurately described using the Zerilli-Armstrong constitutive equation. Optical microscopy (OM) observations reveal that the specimens fail principally as the result of an adiabatic shearing mechanism. Furthermore, scanning electron microscopy (SEM) observations show that the fracture surfaces are characterised by a dimple-like structure, which indicates a ductile failure mode. Transmission electron microscopy (TEM) observations indicate that the dislocation density and cell size are related to the strain rate, flow stress and temperature. Finally, the TEM observations suggest that the strengthening effect observed in the deformed Al-Sc alloy is the result of Al3Sc precipitates within the matrix and at the grain boundaries, which suppress dislocation motion and prompt an increase in the work hardening stress. |
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0925-8388 |
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NU @ karnesky @ |
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10784 |
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Lee, Woei-Shyan; Chen, Tao-Hsing; Lin, Chi-Feng; Lu, Ging-Ting |
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Adiabatic Shearing Localisation in High Strain Rate Deformation of Al-Sc Alloy |
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Journal Article |
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2010 |
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Materials Transactions |
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51 |
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7 |
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1216-1221 |
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aluminium-scandium alloy, strain rate sensitivity, adiabatic shearing, precipitates |
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Aluminium-scandium (Al-Sc) alloy is subjected to shear deformation at high strain rates ranging from 3.0×105 s−1 to 6.2×105 s−1 using a compressive-type split-Hopkinson pressure bar (SHPB). The effects of the strain rate on the shear stress, adiabatic shear band characteristics, and fracture features of the Al-Sc alloy are systematically examined. The results show that both the shear stress and the strain rate sensitivity increase with an increasing strain rate. In addition, it is shown that an adiabatic shear band is formed within the deformed specimens for all values of the strain rate. As the strain rate is increased, the width of the shear band decreases, but the microhardness increases. Moreover, the distortion angle and the magnitude of the local shear strain near the shear band both increase with an increasing strain rate. At a strain rate of 3.0×105 s−1, the fracture surface is characterised by multiple transgranular clearage fractures. However, for strain rates greater than 4.4×105 s−1, the fracture surface has a transgranular dimple-like characteristic, and thus it is inferred that the ductility of the Al-Sc alloy improves with an increasing strain rate. |
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NU @ karnesky @ |
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10917 |
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Rogozhkin, S.V.; Aleev, A.A.; Zaluzhnyi, A.G.; Nikitin, A.A.; Iskandarov, N.A.; Vladimirov, P.; Lindau, R.; Möslang, A. |
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Atom probe characterization of nano-scaled features in irradiated ODS Eurofer steel |
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Journal Article |
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2011 |
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Journal of Nuclear Materials |
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409 |
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2 |
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94-99 |
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ODS steel; ODS Eurofer; clusters; irradiation; fast neutron |
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Our previous investigations of unirradiated ODS Eurofer by tomographic atom probe (TAP) revealed numerous nano-scaled features (nanoclusters) enriched in vanadium, yttrium and oxygen. In this work the effect of neutron irradiation on nanostructure behaviour of ODS Eurofer (9%-CrWVTa) was investigated. The irradiation was performed in the research reactor BOR-60 (Dimitrovgrad, Russia) where materials were irradiated at 330°S to 32 dpa. TAP studies were performed on the needles prepared from parts of broken Charpy specimens. For all specimens except one, which was tested at 500°C, the Charpy tests were performed at temperatures not exceeding the irradiation temperature. A high number density 2÷4×1024 m-3 of ultra fine 1-3 nm diameter nanoclusters enriched in yttrium, oxygen, manganese and chromium was observed in the as-irradiated state. The composition of detected clusters differs from that for unirradiated ODS Eurofer. It was observed in this work that after neutron irradiation vanadium atoms had left the clusters, moving from the core into solid solution. The concentrations of yttrium and oxygen in the matrix, as it was detected, increase several times under irradiation. In the samples tested at 500°C both the number density of clusters and the yttrium concentration in the matrix decrease by a factor of two. |
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0022-3115 |
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NU @ karnesky @ |
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10946 |
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Aleev, A.A.; Iskandarov, N.A.; Klimenkov, M.; Lindau, R.; Möslang, A.; Nikitin, A.A.; Rogozhkin, S.V.; Vladimirov, P.; Zaluzhnyi, A.G. |
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Investigation of oxide particles in unirradiated ODS Eurofer by tomographic atom probe |
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Journal Article |
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2011 |
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Journal of Nuclear Materials |
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409 |
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2 |
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65-71 |
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Ods; atom probe tomography; precipitation |
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Oxide dispersion strengthened steels possess better high-temperature creep and radiation resistance than conventionally produced ferritic/martensitic steels. This behavior is mainly caused by the presence of highly dispersed and extremely stable oxide particles with diameters of a few nanometers. In this work the nanostructure of ODS Eurofer steel was investigated by means of tomographic atom probe and correlations with recent TEM and SANS studies were derived. The present investigation revealed nanoscaled clusters of typically 2 nm diameter containing not only yttrium and oxygen but also vanadium and nitrogen. Moreover, concentration of vanadium in particles was found to be higher than that of yttrium, which indicates the importance of these elements in cluster formation. The estimated average cluster number density is about 2×1024 m-3. These enriched zones might be evidently attributed to precursors of the larger precipitates observed by TEM. This conclusion is also supported by the similarities of the chemical composition inside enriched zones seen in both atomic probe and TEM data. |
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0022-3115 |
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NU @ karnesky @ |
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10951 |
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Michler, Thorsten; Lee, Yongwon; Gangloff, Richard P.; Naumann, Joerg |
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Influence of macro segregation on hydrogen environment embrittlement of SUS 316L stainless steel |
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Journal Article |
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2009 |
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International Journal of Hydrogen Energy |
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34 |
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7 |
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3201-3209 |
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Hydrogen embrittlement; Austenitic stainless steel; Macro segregation; Nickel |
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The objective of this work is to identify microstructural variables that lead to the large scatter of the relative resistance of 316 grade stainless steels to hydrogen environment embrittlement. In slow displacement rate tensile testing, two almost identical (by nominal chemical composition) heats of SUS 316L austenitic stainless steel showed significantly different susceptibilities to HEE cracking. Upon straining, drawn bar showed a string-like duplex microstructure consisting of [alpha]'-martensite and [gamma]-austenite, whereas rolled plate exhibited a highly regular layered [alpha]'-[gamma] structure caused by measured gradients in local Ni content (9.5-13 wt%). Both martensite and austenite are intrinsically susceptible to HEE. However, due to Ni macro segregation and microstructural heterogeneity, fast H-diffusion in martensite layers supported a 10 times faster H-enhanced crack growth rate and thus reduced tensile reduction in area. Nickel segregation is thus a primary cause of the high degree of variability in H2 cracking resistance for different product forms of 316 stainless steel. |
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0360-3199 |
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NU @ karnesky @ |
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10957 |
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