Identification Of G-Phase In Aged Cast CF 8 Type Stainless Steel

1985 ◽  
Vol 43 ◽  
pp. 328-329 ◽  
Author(s):  
J. Bentley ◽  
M. K. Miller ◽  
S. S. Brenner ◽  
J. A. Spitznagel
Keyword(s):  
Stainless Steel ◽  
Nuclear Reactors ◽  
Analytical Electron Microscopy ◽  
Atom Probe ◽  
Duplex Structure ◽  
Primary Coolant ◽  
Probe Field ◽  
Aged Material ◽  
Type Stainless Steel ◽  
Analytical Electron

The microstructure of as-cast and aged CF 8 type stainless steel, used for the primary coolant pipes in pressurized light-water nuclear reactors, is being studied by analytical electron microscopy (AEM) and atom probe field-ion microscopy (APFIM). The phase transformations of the ferrite (∼19 vol % of the duplex structure) that occur after aging at 673 K for 7500 h are described by Miller et al. The present work deals with the identification of G-phase (prototype compound Ni16Ti6Si7) observed in the ferrite of aged material.In FIM images the precipitates had bright contrast, appeared roughly spherical, were ∼10 nm in diameter, and were present at a concentration of ∼1023 m-3. Atom probe selected area microchemical analyses of the central portion of five precipitates revealed that they were alloy silicides, Table 1.

scholarly journals Thermal Aging Of Primary Coolant Pipe Steel

1985 ◽  
Vol 43 ◽  
pp. 326-327 ◽  
Author(s):  
M. K. Miller ◽  
J. Bentley ◽  
S. S. Brenner ◽  
J. A. Spitznagel
Keyword(s):  
Stainless Steel ◽  
Thermal Aging ◽  
Nuclear Reactor ◽  
Cooling Water ◽  
Atom Probe ◽  
Primary Coolant ◽  
Probe Field ◽  
Pressurized Water ◽  
Type Stainless Steel

The long term mechanical integrity of the pipes used to carry the primary cooling water in a pressurized water nuclear reactor is of the utmost importance for safe operation. A combined atom probe field-ion microscopy (APFIM) and transmission electron microscopy (TEM) study was performed to characterize the microstructure of this cast stainless steel and to determine the changes that occur during long-term low-temperature thermal aging.The material used in this investigation was a commercial CF 8 type stainless steel with a bulk chemical composition as given in Table 1. The steel was examined in the as-cast, unaged condition and also after aging for 7500 h at 673K. This temperature is 100K higher than the normal service temperature and was chosen to accelerate the microstructural changes that may occur during service. As these pipes are external to the reactor they are not exposed to any significant radiation that may influence the aging behavior.

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.

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.

Understanding complex phase chemistry in a Ni-base superalloy: A combined AEM/APFIM approach

1990 ◽  
Vol 48 (4) ◽  
pp. 208-209
Author(s):  
M.G. Burke ◽  
M.K. Miller
Keyword(s):  
Elevated Temperatures ◽  
Bulk Composition ◽  
Analytical Electron Microscopy ◽  
Atom Probe ◽  
Treatment Schedule ◽  
Alloy 718 ◽  
Microstructural Stability ◽  
Probe Field ◽  
Analytical Electron ◽  
Base Superalloy

Alloy 718 is a Nb-modified Ni-base superalloy widely-used for gas turbine and related applications which require microstructural stability and good mechanical properties at elevated temperatures (≈ 650°C). In order to achieve the desired properties, the alloy is given a multi-step thermal treatment during which a complex multiphase microstructure is developed. The primary strengthening phases in this alloy are DO22-ordered γ" and Ll2-ordered γ'. A variety of other phases such as Laves, MC-type carbides, and δ (Ni3Nb) have been observed in this material. In this study, the techniques of analytical electron microscopy (AEM) and atom probe field-ion microscopy (APFIM) have been successfully applied to characterize the microstructure of Alloy 718.The nominal bulk composition of the material examined in this investigation is listed in Table 1 together with the heat treatment schedule. Specimens for AEM characterization were examined in a Philips EM400T analytical electron microscope operated at 120kV and equipped with a Link LZ5/AN10-85S analyzer system.

3d Mapping Of Light-Element Segregation In 316 Stainless Steel By Atom Probe

1999 ◽  
Vol 5 (S2) ◽  
pp. 116-117
Author(s):  
T. F. Kelly ◽  
D. J. Larson ◽  
M. K. Miller ◽  
J. E. Flinn
Keyword(s):  
Stainless Steel ◽  
Light Element ◽  
Hot Extrusion ◽  
Atom Probe ◽  
Nitrogen Gas ◽  
Probe Field ◽  
Tramp Element ◽  
316 Stainless Steel ◽  
Oxygen Gas ◽  
Counting Statistics

A vanadium-bearing variant of 316 stainless steel that was rapid solidification processed (RSP) by gas atomization and hot extrusion of the powder (10:1 extrusion ratio at 900°C) has been studied previously by conventional atom probe field ion microscopy (APFIM). The mechanical properties of this steel were markedly improved by RSP and aging (600°C for 1000 hours). High nitrogen (0.45 at% (0.2 wt%)) and oxygen (0.16 at% (0.05 wt%)) contents were intentionally introduced by melting under 80% nitrogen/20% oxygen gas and atomizing in nitrogen gas. A nominal boron concentration of 0.04 at% (0.01 wt%)) is present as a tramp element. As a result, a large number density (˜ 2 × 1021 m-3) of 25 nm plate-like vanadium-rich nitrides precipitate during aging of the alloy and these precipitates contribute a major portion of the strengthening. Previous efforts to locate the oxygen in the structure using APFIM were inconclusive largely due to poor counting statistics.

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