Proton Irradiation Induced Grain Boundary Segregation in Austenitic Stainless Steels

1994 ◽  
Vol 373 ◽  
Author(s):  
D.L. Damcott ◽  
G.S. Was ◽  
S.M. Bruemmer
Keyword(s):  
Grain Boundary ◽  
Proton Irradiation ◽  
Boundary Segregation ◽  
Reactor Core ◽  
Austenitic Stainless Steels ◽  
Sharp Decrease ◽  
Diffusion Parameters ◽  
Core Components ◽  
Radiation Induced ◽  
Higher Temperature

AbstractRadiation induced segregation (RIS) has been implicated as a mechanism for irradiationassisted stress corrosion cracking (IASCC) in reactor core components. Proton irradiation has been shown to be useful in creating grain boundary chemistries similar to those found in neutron and charged particle irradiated materials for accelerated testing of IASCC susceptibility. This work quantifies grain boundary RIS as a function of proton irradiation dose (0.1-3.0 dpa), temperature (200°−600°C), and alloy composition (20Cr-9Ni, 24Cr-19Ni, and xCr-24Ni, x=16, 20,24). Auger electron spectroscopy revealed Cr depletion and Ni enrichment under all irradiation conditions. As a function of dose, the degree of segregation increased rapidly to near saturation prior to 1 dpa, with a boundary composition of 12.1 at.% Cr and 36.0 at.% Ni at 1 dpa. Segregation peaked at approximately 500°C with 13.0 at.% Cr and 38.6 at.% Ni at the grain boundary at 0.5 dpa; very little segregation was observed at or below 300°C or at 600°C. The trends in segregation as a function of dose agreed well with the Perks' model predictions with the exception of the measurement at 600°C, which showed the sharp decrease in segregation predicted for a higher temperature (700°C-800°C). For alloys containing constant bulk Cr but varying Ni, the Perks' model agreed well with the observed segregation trend; however, for alloys containing constant bulk Ni and varying Cr, agreement was achieved only through the use of composition dependent diffusion parameters.

Influence of Initial Grain Boundary Composition on the Evolution of Radiation-Induced Segregation Profiles

1998 ◽  
Vol 540 ◽  
Author(s):  
J.T. Busby ◽  
G.S. Was ◽  
S.M. Bruemmer ◽  
D. J. Edwards ◽  
E.A. Kenik
Keyword(s):  
Grain Boundary ◽  
Stainless Steels ◽  
Boundary Segregation ◽  
Reactor Core ◽  
Austenitic Stainless Steels ◽  
Central Peak ◽  
Boundary Composition ◽  
Radiation Induced ◽  
The Impact ◽  
Profile Development

AbstractRadiation-induced segregation (RIS) has been identified as a potential contributor to irradiation-assisted stress corrosion cracking (IASCC) of austenitic stainless steels in reactor core components. The occurrence of grain boundary segregation prior to irradiation influences both the shape and magnitude of RIS profile development during subsequent irradiation. In an effort to better understand the impact of this pre-irradiation enrichment on RIS profile development, the evolution of grain boundary Cr segregation profiles with irradiation dose has been characterized. Commercial purity and high-purity austenitic stainless steels with different initial levels of grain boundary Cr have been irradiated with neutrons (at 275°C) or protons (at 360-400°C) to doses up to ∼5 dpa. Grain boundary composition profiles were measured before and after irradiation using scanning transmission electron microscopy with energy dispersive xray spectroscopy (STEM-EDS). The initial enrichment of Cr is shown to delay radiation-induced Cr depletion and produce a “W-shaped” profile at low irradiation doses. Further irradiation causes the central peak of the W to decrease, eventually resulting in the classical “V-shaped” depletion profile. Possible mechanisms for the pre-irradiation enrichment and its evolution into a “W-shaped” profile will be discussed.

Refinement of Irradiation and Analysis Techniques for Radiation-Induced Segregation

1996 ◽  
Vol 439 ◽  
Author(s):  
T. R. Allen ◽  
J. M. Cookson ◽  
D. L. Damcott ◽  
G. S. Was
Keyword(s):  
Grain Boundary ◽  
Reactor Core ◽  
Beam Current ◽  
304 Stainless Steel ◽  
Boundary Concentration ◽  
Ultra High Purity ◽  
Potential Contributor ◽  
Core Components ◽  
Radiation Induced ◽  
Boundary Chemistry

AbstractRadiation-induced segregation (RIS) has been implicated as a potential contributor to irradiation assisted stress corrosion cracking in light water reactor core components. To better understand changes to grain boundary chemistry during irradiation, RIS was measured in ultra-high purity (UHP) 304 stainless steel using Auger electron spectroscopy (AES). Variations in measured grain boundary concentration, both within a sample and between samples, are reduced by refinements in both the radiation and the AES techniques. These refinements include improvements in temperature control, uniformity of sample-to-sample dose, grain boundary acceptance criteria, amount of intergranular fracture, and amount of beam current used in analysis. AES measurements on samples irradiated at 400°C to 1.0 dpa show how implementing the technique refinements reduces the variability in the measured concentrations. Additionally, measurements from regions of ductile tearing in samples irradiated to 0.1 and 1.0 dpa at 400°C, to 1.0 dpa at 200°C, and from unirradiated samples show that sensitivity factors must be determined to obtain the most accurate measurement of grain boundary composition.

scholarly journals Radiation-Induced Grain Boundary Segregation in Austenitic Stainless Steels

1994 ◽  
Vol 373 ◽  
Author(s):  
S. M. Bruemmer ◽  
L. A. Charlot ◽  
J. S. Vetrano ◽  
E. P. Simonen
Keyword(s):  
Grain Boundary ◽  
Stainless Steels ◽  
Boundary Segregation ◽  
Austenitic Stainless Steels ◽  
Impurity Segregation ◽  
Interfacial Concentration ◽  
Radiation Induced ◽  
Compositional Changes ◽  
Temperature Equilibrium ◽  
Impurity Elements

AbstractRadiation-induced segregation (RIS) to grain boundaries in Fe-Ni-Cr-Si stainless alloys has been measured as a function of irradiation temperature and dose. Heavyion irradiation was used to produce damage levels from 1 to 20 displacements per atom (dpa) at temperatures from 175 to 550°C. Measured Fe, Ni, and Cr segregation increased sharply with irradiation dose (from 0 to 5 dpa) and temperature (from 175 to about 350°C). However, grain boundary concentrations did not change significantly as dose or temperatures were further increased. Although interfacial compositions were similar, the width of radiation-induced enrichment or depletion profiles increased consistently with increasing dose or temperature. Impurity segregation (Si and P) was also measured, but only Si enrichment appeared to be radiation-induced. Grain boundary Si peaked at levels approaching 8 at% after irradiation doses to 10 dpa at an intermediate temperature of 325°C. No evidence of grain boundary silicide precipitation was detected after irradiation at any temperature. Equilibrium segregation of P was measured in the high-P alloys, but interfacial concentration did not increase with irradiation exposure. Comparisons to reported RIS in neutronirradiated stainless steels revealed similar grain boundary compositional changes for both major alloying and impurity elements.

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.

The Measurement of Light Element Segregation Using EDS and EELS

1998 ◽  
Vol 4 (S2) ◽  
pp. 772-773
Author(s):  
J.T. Busby ◽  
E.A. Kenik ◽  
G.S. Was
Keyword(s):  
Grain Boundaries ◽  
Nuclear Reactor ◽  
Reactor Core ◽  
Light Element ◽  
Free Surfaces ◽  
Spatial Redistribution ◽  
Core Components ◽  
Radiation Induced ◽  
Potential Interactions ◽  
Impurity Elements

Radiation-induced segregation (RIS) is the spatial redistribution of elements at defect sinks such as grain boundaries and free surfaces during irradiation. This phenomenon has been studied in a wide variety of alloys and has been linked to irradiation-assisted stress corrosion cracking (IASCC) of nuclear reactor core components. However, several recent studies have shown that Cr and Mo can be enriched to significant levels at grain boundaries prior to irradiation as a result of heat treatment. Segregation of this type may delay the onset of radiation-induced Cr depletion at the grain boundary, thus reducing IASCC susceptibility. Unfortunately, existing models of segregation phenomena do not correctly describe the physical processes and therefore are grossly inaccurate in predicting pre-existing segregation and subsequent redistribution during irradiation. Disagreement between existing models and measurement has been linked to potential interactions between the major alloying elements and lighter impurity elements such as S, P, and B.

Influence of Phosphorus Grain Boundary Segregation on Fracture Behaviour of Iron-Base Alloys

2007 ◽  
Vol 567-568 ◽  
pp. 33-38
Author(s):  
Jozef Janovec ◽  
Jaroslav Pokluda ◽  
Pavel Lejček
Keyword(s):  
Grain Boundary ◽  
Intergranular Fracture ◽  
Stainless Steels ◽  
Structural Changes ◽  
Fracture Behaviour ◽  
Boundary Segregation ◽  
Austenitic Stainless Steels ◽  
Grain Boundary Segregation ◽  
Boundary Concentration ◽  
Factors Influencing

Chemical and structural changes at the grain boundaries were investigated to quantify their influence on fracture behaviour of austenitic stainless steels and model ferritic Fe-Si-P alloys. The balance between the size and the area density of intergranular particles was found to be one of the most decisive factors influencing sensitivity of the steels to intergranular fracture. The precise dependence of the energy of intergranular fracture on the phosphorus grain boundary concentration was also determined.

Cr-Vacancy Elastic and Chemical Interactions in Irradiated Stainless Steels

1998 ◽  
Vol 540 ◽  
Author(s):  
E. P. Simonen ◽  
S. M. Bruemmer
Keyword(s):  
Grain Boundary ◽  
Point Defects ◽  
Stainless Steels ◽  
Austenitic Stainless Steels ◽  
Solution Annealing ◽  
Chemical Interactions ◽  
Radiation Induced ◽  
Solute Interactions ◽  
Present Evaluation ◽  
Nonequilibrium Segregation

AbstractInteractions between point defects and major solute strongly influence grain boundary concentrations during heat treatment, irradiation and annealing of austenitic stainless steels. Previous approaches to nonequilibrium segregation emphasize only elastic defect-solute interactions. The present evaluation of nonequilibrium concentrations at grain boundaries indicates chemical interactions unique to solution annealing and cooling during thermal nonequilibrium segregation (TNES). Subsequent to TNES, radiation-induced segregation and post-irradiation annealing are modeled and compared with measured changes in grain boundary composition. The latter two mechanisms are controlled by exchanges between vacancies and major solute such as Cr.

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