Origin and Influence of Pre-Existing Segregation on Radiation-Induced Segregation In Austenitic Stainless Steels

1998 ◽  
Vol 540 ◽  
Author(s):  
E. A. Kenik ◽  
J. T. Busby ◽  
M. K. Miller ◽  
A. M. Thuvander ◽  
G. Was
Keyword(s):  
Electron Microscopy ◽  
Grain Boundaries ◽  
Stainless Steels ◽  
Analytical Electron Microscopy ◽  
Austenitic Stainless Steels ◽  
Atom Probe ◽  
Molecular Ions ◽  
Probe Field ◽  
Analytical Electron ◽  
Radiation Induced

AbstractThe pre-existing segregation at grain boundaries in two austenitic stainless steels has been investigated by atom probe field ion microscopy and analytical electron microscopy. In addition, the effect of radiation-induced segregation on the near-grain-boundary composition has been studied by analytical electron microscopy. Pre-existing enrichment of Cr, Mo, B, C and P and depletion of Fe and Ni near grain boundaries has been observed. Significant affinity between Mo and N in both alloys is indicated by the detection of MoN2+` molecular ions during field evaporation. The pre-existing segregation is modified by radiation-induced segregation resulting in Ni and Si enrichment near the boundary as well as depletion of chromium adjacent to the boundary resulting in a “W-shaped” Cr profile.

scholarly journals Radiation-induced segregation in austenitic stainless steels

1991 ◽  
Vol 49 ◽  
pp. 556-557
Author(s):  
E. A. Kenik ◽  
K. Hojou
Keyword(s):  
Stainless Steels ◽  
Analytical Electron Microscopy ◽  
Austenitic Stainless Steels ◽  
Test Facility ◽  
X Ray ◽  
Analytical Electron ◽  
Radiation Induced ◽  
Analysis System ◽  
Property Changes ◽  
Composition Fluctuations

Radiation-induced segregation (RIS) is driven by fluxes of point defects to sinks. RIS can induce composition fluctuations in irradiated stainless steels, which can result in microstructural and property changes, including precipitation, austenite instability, strengthening, embrittlement, and irradiation-assisted sensitization and stress corrosion cracking. Analytical electron microscopy (AEM) provides a powerful technique to study such segregation. RIS in several irradiated stainless steels has been investigated. AEM was performed in a Philips EM400T/FEG equipped with an EDAX 9100/70 analysis system. The specimens were neutron irradiated to 15 displacements per atom (dpa) at 520 ° C in the Fast Flux Test Facility (FFTF) and were only mildly radioactive (<50/μCi = 1.85 MBq), thus permitting high spatial resolution X-ray microanalysis to be employed. Typical acquisitions were performed for 100 s in the STEM mode with <2-nm-diam probes containing >0.5 nA current. Subtraction of “in-hole” spectra from the measured spectra corrected for both the normal “in-hole” counts and those associated with the radioactivity of the specimen.

scholarly journals Application of Analytical Electron Microscopy to design of creep-resistant advanced austenitic stainless steels

1987 ◽  
Vol 45 ◽  
pp. 226-227
Author(s):  
P.J. Maziasz
Keyword(s):  
Electron Microscopy ◽  
Stainless Steels ◽  
Power Plants ◽  
Fine Particles ◽  
Analytical Electron Microscopy ◽  
Austenitic Stainless Steels ◽  
High Brightness ◽  
Aisi Type ◽  
Analytical Electron ◽  
Insight Into

Analytical electron microscopy (AEM) has been used for the last ten years to study precipitation produced in reactor-irradiated austenitic stainless steels, such as AISI type 316. These studies have provided the insight to design irradiation resistant steels based on control of precipitiation. More recently, similar insight into precipitation effects in steels allowed the design of advanced austenitics that also exhibit outstanding thermal creep resistance at 700°C. These steels have direct application for superheater/ reheater tubing materials that will withstand higher temperatures and stresses in advanced steam cycle fossil power plants.Fine particles (<10 nm in diam) on extraction replicas have been studied by AEM using a high brightness electron source to provide sufficient probe currents for reliable analyses. These studies allowed alloy compositional modifications to be selected that produced stable, fine precipitates for creep strength.

Precipitation at α/γ interfaces in duplex stainless steel

1992 ◽  
Vol 50 (1) ◽  
pp. 60-61
Author(s):  
M.G. Burke ◽  
E.A. Kenik
Keyword(s):  
Electron Microscopy ◽  
Stainless Steel ◽  
Grain Boundaries ◽  
Duplex Stainless Steel ◽  
Stainless Steels ◽  
Analytical Electron Microscopy ◽  
Nuclear Industry ◽  
Temperature Range ◽  
Α Phase ◽  
Analytical Electron

Duplex (austenite/ferrite) stainless steels are used in a variety of applications in the nuclear industry, particularly for coolant pipes, valves and pumps. These materials may become embrittled after prolonged ageing in the temperature range ∼350 - 550°C due to precipitation of G-phase, an FCC-based Ni silicide, and the formation of a Cr-rich α' phase in the ferrite. In addition to the intragranular G-phase precipitates, preferential precipitation of other phases is often observed at grain boundaries, particularly α/γ interfaces. In this examination, the precipitates formed in a Nb-containing duplex stainless steel have been identified using analytical electron microscopy.

The Application of Analytical Electron Microscopy to Improving the Sensitization Resistance of Type 304 Stainless Steels

1985 ◽  
Vol 62 ◽  
Author(s):  
H. S. Betrabet ◽  
W. A. T. Clark
Keyword(s):  
Electron Microscopy ◽  
Stainless Steels ◽  
Volume Diffusion ◽  
Discontinuous Precipitation ◽  
Analytical Electron Microscopy ◽  
Austenitic Stainless Steels ◽  
Analytical Electron ◽  
Type 304 ◽  
Kinetics Of ◽  
Apparent Conflict

ABSTRACTThe sensitization resistance of austenitic stainless steels can be improved by replacing some of the C with N. Electrochemical potentionkinetic reactivation (EPR) tests indicate that this is effective up to ∼0.16 wt.%N, but that above this level sensitization is enhanced. Thermodynamic calculations indicate that N should continue to reduce sensitization up to at least 0.25 wt.%N, as it retards the growth kinetics of Cr carbides. Analytical electron microscopy was used to investigate this apparent conflict and showed that, while N did decrease the volume diffusion coefficient of Cr beyond 0.16 wt.%, an increase in the amount of discontinuous precipitation of carbides with increasing N was responsible for the sensitization at higher N levels.

Comparison Of Thermally- And Irradiation-Induced Grain Boundary Segregation In Austenitic Stainless Steels

1991 ◽  
Vol 238 ◽  
Author(s):  
Edward A. Kenik
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Stainless Steels ◽  
Analytical Electron Microscopy ◽  
Boundary Segregation ◽  
Austenitic Stainless Steels ◽  
Chromium Depletion ◽  
Thermal Sensitization ◽  
The Matrix ◽  
Radiation Induced

ABSTRACTSegregation at grain boundaries in austenitic stainless steels sensitized by either thermal annealing or irradiation was studied by analytical electron microscopy. Characterization of grain boundary compositions in both types of materials was performed by high spatial resolution (≥2 nm) X-ray microanalysis. Whereas similar chromium depletion is observed in both processes, there are differences in the behavior of the other alloying elements and in the mechanisms responsible for the segregation. In thermal sensitization, the nickel/iron ratio and the silicon level observed at grain boundaries are similar to those for the matrix. In cases where little or no precipitation occurs, co-segregation of phosphorus, chromium, and molybdenum occurs at boundaries and interfaces. For radiation sensitization, radiation-induced segregation (RIS) results in enrichment of nickel, silicon, and, in certain cases, phosphorus and in depletion of iron at grain boundaries. There appears to be some synergism between segregation of nickel and silicon, which increases the magnitude of RIS effects. Grain boundary precipitation is often observed in both thermally- and irradiation-sensitized materials. However, the nature and origins of the two types of precipitation are different. The formation of chromium-enriched grain boundary carbides is the cause of the chromium depletion in thermal sensitization. In contrast, the precipitates produced by irradiation are enriched in nickel and silicon and depleted in chromium relative to the matrix and therefore are the result of RIS. Results for thermal- and radiation-induced segregation in manganese-stabilized austenites are compared to that for nickel-stabilized austenites.

scholarly journals Combined Atom-Probe and Electron Microscopy Characterization of Fine Scale Structures in Aged Primary Coolant Pipe Stainless Steel

1986 ◽  
Vol 82 ◽  
Author(s):  
J. Bentley ◽  
M. K. Miller
Keyword(s):  
Electron Microscopy ◽  
Analytical Electron Microscopy ◽  
Atom Probe ◽  
Primary Coolant ◽  
Probe Field ◽  
Α Phase ◽  
Complementary Nature ◽  
Microscopy Characterization

ABSTRACTThe capabilities and complementary nature of atom probe field-ion microscopy (APFIM) and analytical electron microscopy (AEM) for the characterization of finescale microstructures are illustrated by examination of the changes that occur after long term thermal aging of cast CF 8 and CF 8M duplex stainless steels. In material aged at 300 or 400°C for up to 70,000 h, the ferrite had spinodally decomposed into a modulated fine-scaled interconnected network consisting of an iron-rich α′ phase and a chromium-enriched α phase with periodicities of between 2 and 9 nm. G-phase precipitates 2 to 10 nm in diameter were also observed in the ferrite at concentrations of more than 1021 m−3. The reported degradation in mechanical properties is most likely a consequence of the spinodal decomposition in the ferrite.

SHaRE: Collaborative materials science research

1988 ◽  
Vol 46 ◽  
pp. 804-805
Author(s):  
Edward A. Kenik ◽  
Karren L. More
Keyword(s):  
Electron Microscope ◽  
Materials Science ◽  
Analytical Electron Microscopy ◽  
Science Research ◽  
Atom Probe ◽  
Probe Field ◽  
Transmission Electron ◽  
Wide Range ◽  
Analytical Electron ◽  
Electron Microscopes

The Shared Research Equipment (SHaRE) Program provides access to the wide range of advanced equipment and techniques available in the Metals and Ceramics Division of ORNL to researchers from universities, industry, and other national laboratories. All SHaRE projects are collaborative in nature and address materials science problems in areas of mutual interest to the internal and external collaborators. While all facilities in the Metals and Ceramics Division are available under SHaRE, there is a strong emphasis on analytical electron microscopy (AEM), based on state-of-the-art facilities, techniques, and recognized expertise in the Division. The microscopy facilities include four analytical electron microscopes (one 300 kV, one 200 kV, and two 120 kV instruments), a conventional transmission electron microscope with a low field polepiece for examination of ferromagnetic materials, a high voltage (1 MV) electron microscope with a number of in situ capabilities, and a variety of EM support facilities. An atom probe field-ion microscope provides microstructural and elemental characterization at atomic resolution.

High Spatial Resolution X-ray Microanalysis of Radiation-Induced Segregation in Proton-Irradiated Stainless Steels

1999 ◽  
Vol 589 ◽  
Author(s):  
E.A. Kenik ◽  
J.T. Busby ◽  
G.S. Was
Keyword(s):  
Grain Boundaries ◽  
Analytical Electron Microscopy ◽  
Scanning Transmission Electron Microscope ◽  
Transmission Electron ◽  
Analytical Electron ◽  
Scanning Transmission ◽  
Spatial Redistribution ◽  
Radiation Induced ◽  
Composition Profiles ◽  
Compositional Changes

AbstractThe spatial redistribution of alloying elements and impurities near grain boundaries in several stainless steel alloys arising from non-equilibrium processes have been measured by analytical electron microscopy (AEM) in a field emission scanning transmission electron microscope. Radiation-induced segregation (RIS) has been shown to result in significant compositional changes at point defects sinks, such as grain boundaries. The influence of irradiation dose and temperature, alloy composition, prior heat treatment, and post-irradiation annealing on the grain boundary composition profiles have been investigated. Understanding the importance of these microchemical changes relative to the radiation-induced microstructural change in irradiation-assisted stress corrosion cracking (IASCC) of the irradiated materials is the primary goal of this study.

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