► Effect of strain RIS in proton-irradiated SS 304 studied using EPR followed by AFM. ► Residual strain within grains reduced Cr depletion at grain boundaries due to RIS. ► Attack during EPR of ...irradiated SS 304 observed on linear features within grains. ► Strain-regions within grains decorated by point defects & appeared as linear features.
The effect of residual strain on radiation-induced segregation in proton-irradiated type 304 stainless steel was investigated using electrochemical potentiokinetic reactivation (EPR) test followed by atomic force microscopic examination. The specimens were irradiated to 0.43 and 0.86
dpa. Microstructural observation after EPR of irradiated specimens showed negligible attack on grain boundaries. Attacked linear features were noticed after EPR testing of irradiated specimens while such features were not observed for un-irradiated as-received or irradiated solution-annealed specimen. The presence of linear features after EPR testing of irradiated specimens was attributed to decoration of strain-regions within the matrix by point-defects generated due to irradiation.
• High fraction of twin boundaries obtained using thermo-mechanical processing. • Electrochemical evaluation of radiation-induced segregation. • Effect of high fraction of twins on radiation-induced ...segregation. • Twin boundaries act as sinks, reduced point defect adsorption at grain boundaries.
The effect of high fraction of twin boundaries on radiation-induced segregation (RIS) in type 304 stainless steel (SS) was investigated using 4.8MeV proton beam at 300°C. Type 304 SS samples were irradiated to 0.86 and 1.00 displacement per atom (dpa) and characterization of RIS was done using Electrochemical Potentiokinetic Reactivation (EPR) tests at different depth from the surface. Localized attack on different microstructural features, grain and twin boundaries and in-grain pit-like features, was further evaluated by atomic force microscopy. The results clearly indicated that attack was mostly confined to twin boundaries, implying that the twin boundaries acted as a preferred defect sink.
With the progress made in 2015, the beams produced by the CERN Proton Synchrotron using multiturn extraction (MTE) have been delivered to the Super Proton Synchrotron (SPS) for the fixed-target ...physics run. Operation successfully started in the second half of September 2015 and continued until the end of the proton physics program by mid November. In this paper the overall performance and beam quality is discussed in detail considering the complete chain of accelerators, from the PS-Booster to the SPS. Moreover, a thorough comparison of the global performance of the MTE scheme against the previously used technique, the so-called continuous transfer (CT), is also carried out.
Stainless steels usually contain some amounts of sulfide type of inclusions which are known to affect their corrosion behavior in mild aqueous chloride solutions. The life of the stainless steel ...components is severely affected as the manganese sulfide inclusions dissolve and the reaction products at the site of inclusions lead to pitting corrosion. The pits so formed as well as manganese sulfide inclusions, being local heterogeneities were studied by a microprobing technique called scanning electrochemical microscopy. In order to demonstrate how this local probing technique can be optimally used to investigate the corrosion behavior of inclusion containing austenitic stainless steels, different experimental parameters were varied one by one. The effect of different factors such as substrate potential, rate of scanning and concentration of chloride was studied in detail. The study shows that a scan rate of 0.32μm/s (3.2μm step distance for 10s hold time) for 50μm by 50μm scans and a scan rate of 0.1μm/s (1μm step distance for 10s hold time) for 20μm by 20μm scans produced optimum results throughout the study.
► MnS inclusions were studied by scanning electrochemical microscopy (SECM). ► We studied inclusions in austenitic stainless steels by varying different factors. ► Scan rate of 0.1μm/s is ideal for 20×20μm scans. ► Scan rate of 0.32μm/s is ideal for 50×50μm scans. ► Lower potentials and mild environments lead to lower initiation and growth of pitting.
► Rolled non-sensitised material simulating constrained weldment used for testing. ► Nitrogen (N) in SS 304L adversely affects the IGSCC crack growth rate (CGR). ► Three fold increase in CGR occurred ...due to increase in N from 0.08 to 0.16
wt.%. ► Increase in CGR attributed to higher yield strength and dynamic strain aging. ► Clear intergranular fracture observed in these experiments.
Effect of nitrogen level in strain hardened stainless steel (SS) on crack growth rate (CGR) in simulated boiling water reactor conditions has been the focus of this study. Type 304 LN stainless steel has been used in a warm rolled condition containing two different levels of nitrogen. Clear intergranular (IG) fracture was observed in both the stainless steels. The CGR increased 3 times in the stainless steel with higher level of nitrogen at all levels of dissolved oxygen and this was related to the increase in yield strength due to rolling and dynamic strain aging (DSA).
The paper describes an experimental study aimed at suppressing stress corrosion cracking susceptibility of machined 304L stainless steel specimens through laser shock peening. The study also ...evaluates a new approach of oblique laser shock peening to suppress stress corrosion cracking susceptibility of internal surface of type 304L stainless steel tube. The results of the study, performed with an indigenously developed 2.5 J/7 ns Nd:YAG laser, demonstrated that laser shock peening effectively suppresses chloride stress corrosion cracking susceptibility of machined surface of type 304L stainless steel. In the investigated range of incident laser power density (3.2-6.4 GW/cm
2
), machined specimens peened with power density of 4.5 and 6.4 GW/cm
2
displayed lower stress corrosion cracking susceptibility considerably than those treated with 3.2 and 3.6 GW/cm
2
in boiling magnesium chloride test. Oblique laser shock peening, performed on machined internal surface of a type 304L stainless steel tube (OD = 111 mm; ID = 101 mm), was successful in introducing residual compressive surface stresses which brought about significant suppression of its stress corrosion cracking susceptibility. The technique of oblique laser shock peening, in spite of its inherent limitations on the length of peened region being limited by tube internal diameter and the need for access from both the sides, presents a simplified approach for peening internal surface of small tubular components.
In this study, UO2 coating was deposited by direct current (DC) electrolysis from an aqueous electrolyte containing UO2(NO3)2 as source of uranium. Deposition parameters such as electrolyte pH, ...temperature and current density were optimized in order to obtain a smooth adherent UO2 coating on metallic substrates. The effect of pH, temperature and current density on the deposition rate and on faradic current efficiency (CE) was studied in detail. The study revealed that the control over pH of the electrolyte was more important in comparison to temperature and current density to obtain a smooth deposition of UO2 from this uranyl nitrate-oxalate complex electrolyte. Grazing incidence X-ray diffraction (GI-XRD) of the as-deposited coating with a broad peak confirmed amorphous to ultra-nanocrystalline deposition. Upon vacuum annealing at higher temperature, the as-deposited coating transformed into nanocrystalline fcc UO2 with the appearance of sharper (111), (220), (220), (222) XRD reflections. The average grain size obtained was 13.2 nm for the sample annealed at 700 degree C. In the presence of air, the fcc UO2 coating was transformed largely into the hcp U3O8 phase with a small percentage of hcp UO3 at temperatures higher than 400 degree C. The surface morphology of the as-deposited coating showed a granular morphology with the appearance of few cracks. Upon annealing at 700 degree C, the film showed a network of cracks throughout the surface with numerous pores inside the UO2 matrix. Composition analysis by EDS of the film confirmed the presence of uranium and oxygen. Cross-sectional FESEM analysis of the focused ion beam (FIB) cut samples confirmed deposition of a 6 mu m thick UO2 coating. Upon annealing at 700 degree C, it converted into a highly porous UO2 coating with improved adhesion with the substrate.
The structural materials of reprocessing and waste management plants are made from AISI Type 304L (UNS S30403) grade austenitic stainless steels and are prone to localized corrosion attack like ...intergranular corrosion (IGC). It is very important to detect and characterize this attack non-destructively. An ultrasonic-based, non-destructive evaluation technique has been developed to detect and estimate the depth of IGC attack in Type 304 (UNS S30400) stainless steel grade plate. Samples with varying degrees of IGC attack were generated in laboratory and used for this study. Ultrasonic measurement involved determination of sound velocity in longitudinal mode, longitudinal to shear velocity ratio, sound attenuation measurement, and spectral analysis. The elastic modulus measurement using a nano-hardness tester was carried out to formulate the basis of change in sound velocity in the IGC-attacked samples as compared to the virgin sample. This paper gives the details on the sample preparation method used for generation of IGC attack in Type 304 stainless steel plate and reports the results of ultrasonic measurement on the characterization of IGC attack. The results are compared with maximum depth of IGC attack estimated by microscopic examination.
3.5–4.75 mg cm
−2
thick UO
2
coatings were electrodeposited using alkaline uranyl nitrate-ammonium oxalate bath on alloy 600 onto which nickel and copper interlayers were previously electrochemically ...formed. Micro laser Raman spectroscopy of annealed coating confirmed the formation of UO
2
by showing a peak at 447 cm
−1
. Scanning electron microscopy showed uniform morphology with an average grain size of 1 µm. Glow discharge optical emission spectroscopy revealed no significant diffusion of nickel and copper into UO
2
due to annealing. Rutherford backscattering spectroscopy showed increased thickness of annealed coating. Scratch adhesion test indicated improved cohesive and adhesive strength of coating after annealing.
Understanding the effect of nitrogen content on the crack growth rate (CGR) due to intergranular stress corrosion cracking (IGSCC) in high temperature (288
°C) pure water, in non-sensitised and ...strain-hardened stainless steel (SS) type 304 LN was the focus of this study. Non-sensitised SS containing two different levels of nitrogen (0.08 and 0.16
wt.%) in the solution annealed condition was strain-hardened by cross-rolling at 200
°C (warm rolling). It has earlier been reported that SS with a higher nitrogen level in the warm rolled condition has a higher CGR in high temperature pure water. Tensile testing was carried out using both the SS in the warm rolled as well as in the solution annealed condition at 288
°C. Samples were prepared for transmission electron microscopy (TEM) from the warm rolled SS and from the tensile tested (at 288
°C) specimens. TEM studies indicated that twinning and shear band formation were the major modes of deformation due to rolling at 200
°C and these feature were observed to terminate at grain boundaries, leading to regions of higher strain and stresses at grain boundaries. Higher nitrogen SS has higher grain boundary strain and stresses making the grain boundary regions more susceptible to IGSCC, resulting in higher CGR values. At 288
°C dislocation entanglement and cross-slip were the predominant modes of deformation.
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