► Immobilization of Zr-rich radioactive metallic wastes via alloy melting route. ► First detail report on metallurgical characterizations of Fe–Cr–Ni–Zr alloys. ► Identification of suitable base ...alloy composition.
Alloy melting route is currently being considered for radioactive hulls immobilization. Towards this, wide range of alloys, belonging to Zirconium–Iron binary and Zirconium–Stainless steel pseudo-binary systems have been prepared through vacuum arc melting route. Detail microstructural characterization and quantitative phase analyses of these alloys along with interaction study between Zirconium and Stainless steel coupons at elevated temperatures identify Zr(Fe,Cr)
2, Zr(Fe,Cr), Zr
2(Fe,Cr), Zr
3(Fe,Ni), Zr
3(Fe,Cr), Zr
3(Fe,Cr,Ni), β-Zr and α-Zr as the most commonly occurring phases within the system for Zirconium rich bulk compositions. Nano-indentation studies found Zr(Fe,Cr)
2 and Zr(Fe,Cr) as extremely hard, Zr
3(Fe,Ni) as moderately ductile and β-Zr, Zr
2(Fe,Cr) as most ductile ones among the phases present. Steam oxidation studies of the alloys, based on weight gain/loss procedure and microstructural characterization of the mixed oxide layers, suggest that each of the alloys responded to the corrosive environment differently. Fe
2O
3, NiFe
2O
4, NiO, monoclinic ZrO
2 and tetragonal ZrO
2 are found to be most common constituents of the oxide layers developed on the alloys. Integrating the microstructural, mechanical and corrosion properties, ZrFeCrNi3 (Zr: 84.00, Fe: 11.20, Cr: 3.20, Ni: 1.60, in wt.%) is identified as the acceptable base alloy for disposal of radioactive hulls.
The nickel base alloys are susceptible to localized corrosion attack and the major contributing factor in these corrosion mechanisms is the oxide film formed on the alloy. The chromium content in the ...oxide film determines its stability against localized attack that act as precursors for the initiation of stress corrosion cracking (SCC) in the material. The present study aimed at optimizing the hot conditioning parameter by varying the temperature of oxide formation for minimum ion release rate during reactor operation. The surface and in-depth compositional characterization of oxide film formed on Alloy 600 was carried out using micro-laser Raman spectroscopy (MLRS) and glow discharge quadrapole mass spectroscopy (GDQMS) respectively. The relative defect density of oxide films were studied using electrochemical impedance spectroscopy (EIS). The oxide film stability of Alloy 600 in chloride containing environment was correlated to chromium concentration in the film as well as relative defect density.
The Large Hadron Collider (LHC) at CERN will generate two extremely powerful 7 TeV proton beams. Each beam will consist of 2808 bunches with an intensity per bunch of 1.15x10(11) protons so that the ...total number of protons in one beam will be about 3x10(14) and the total energy will be 362 MJ. Each bunch will have a duration of 0.5 ns and two successive bunches will be separated by 25 ns, while the power distribution in the radial direction will be Gaussian with a standard deviation, sigma=0.2 mm. The total duration of the beam will be about 89 mus. Using a 2D hydrodynamic code, we have carried out numerical simulations of the thermodynamic and hydrodynamic response of a solid copper target that is irradiated with one of the LHC beams. These calculations show that only the first few hundred proton bunches will deposit a high specific energy of 400 kJ/g that will induce exotic states of high energy density in matter.
In this article, alumina-aluminide coatings were formed on ferritic-martensitic T91 steel substrate. First, coatings of aluminum were deposited electrochemically on T91 steel in a room temperature ...AlCl3-1-ethyl-3-methyl imidazolium chloride ionic liquid, then the obtained coating was subjected to a two stage heat treatment procedure consisting of prolonged heat treatment of the sample in vacuum at 300 degrees Celsius ,followed by oxidative heat treatment in air at 650 degrees Celsius for 16 hours. X-ray diffraction measurement of the oxidatively heat treated samples indicated formation of Fe-Al and Cr-Al intermetallics and presence of amorphous alumina. Energy dispersive X-ray spectroscopy measurement confirmed 50 wt-% O in the oxidized coating. Microscratch adhesion test conducted on alumina-aluminide coating formed on T91 steel substrate showed no major adhesive detachment up to 20 N loads. However, adhesive failure was observed at a few discrete points on the coating along the scratch track.
This article describes the corrosion behavior of special austenitic alloys for waste management applications. The special stainless steels have controlled levels of alloying and impurity elements and ...inclusion levels. It is shown that "active" inclusions and segregation of chromium along flow lines accelerated IGC of nonsensitized stainless steels. Concentration of Cr^sup +6^ ions in the grooves of dissolved inclusions increased the potential to the transpassive region of the material, leading to accelerated attack. It is shown that a combination of cold working and controlled solution annealing resulted in a microstructure that resisted corrosion even after a sensitization heat treatment. This imparted extra resistance to corrosion by increasing the fraction of "random" grain boundaries above a threshold value. Randomization of grain boundaries made the stainless steels resistant to sensitization, IGC, and intergranular stress corrosion cracking (IGSCC) in even hot chloride environments. The increased corrosion resistance has been attributed to connectivity of random grain boundaries. The reaction mechanism between the molten glass and the material for process pot, alloy 690, during the vitrification process has been shown to result in depletion of chromium from the reacting surfaces. A comparison is drawn between the electrochemical behavior of alloys 33 and 22 in 1 M HC1 at 65 °C. It is shown that a secondary phase formed during welding of alloy 33 impaired corrosion properties in the HC1 environment. PUBLICATION ABSTRACT
Schematic representation of overall experimental and results, indicating attack, after the DL-EPR test, on grain boundaries, twin boundaries and pit-like features within grains at the depth of ...maximum attack. The sensitized specimen also showed severe attack on grain boundaries, however, attack on twin-boundaries and pit-like features were not noticed.
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► Characterization of radiation-induced segregation done by EPR & AFM examination. ► Cr depletion adjacent to carbides due to RIS in irradiated desensitized 304 SS. ► Effectiveness as defect sink: twins
>
pit-like features
>
grain boundary.
Radiation-induced segregation (RIS) in desensitized type 304 stainless steel (SS) was investigated using a combination of electrochemical potentiokinetic reactivation (EPR) test and atomic force microscopy (AFM). Desensitized type 304 SS was irradiated to 0.43
dpa (displacement per atom) using 4.8
MeV protons at 300
°C. The maximum attack in the EPR test for the irradiated desensitized SS was measured at a depth of 70
μm from the surface. Grain boundaries and twin boundaries got attacked and pit-like features within the grains were observed after the EPR test at the depth of 70
μm. The depth of attack, as measured by AFM, was higher at grain boundaries and pit-like features as compared to twin boundaries. It has been shown that the chromium depletion due to RIS takes place at the carbide–matrix as well as at the carbide–carbide interfaces at grain boundaries. The width of attack at grain boundaries after the EPR test of the irradiated desensitized specimen appeared larger due to the dislodgement of carbides at grain boundaries.
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► Characterization of radiation-induced segregation done by EPR and AFM examination. ► Linear features within the matrix noticed after EPR tests on irradiated specimen. ► Formation of ...strain-regions near grain boundaries after irradiation. ► Increased susceptibility to IASCC due to strain-regions near grain boundaries.
The effect of prior cold-work on radiation-induced segregation in proton-irradiated type 304 SS (1.00dpa) was investigated using electrochemical potentiokinetic reactivation (EPR) test followed by atomic force microscopic examination. Attacked linear features were noticed after EPR testing of the irradiated specimen and it was attributed to chromium depletion and/or decoration of strain-regions by point-defects on slip planes. Attack on locations near grain boundaries was also noticed after EPR tests in the irradiated specimen. Electron backscatter diffraction analysis of the irradiated specimen showed increase in Σ1 fraction within the matrix and formation of strain-regions near grain boundaries.
A novel laser surface modification approach to suppress sensitization in AISI 304 (UNS S30400) austenitic stainless steel is described. Surface modification of austenitic stainless steel was carried ...out with a 10-kW carbon dioxide (CO2) laser in both continuous wave and pulse-modulated modes. After laser surface modification, the material was subjected to a sensitization heat treatment at 923 K for 9 h. The degree of sensitization was determined by electrochemical potentiokinetic reactivation test while the susceptibility to intergranular corrosion was determined using the ASTM A262, practice B test. The results of the study demonstrated that the laser-melted surface exhibited significantly higher resistance against sensitization and intergranular corrosion than the base metal. The laser-melted surface, even after being subjected to severe sensitization heat treatment, developed comparable or even a lower degree of sensitization than the base metal in the as-received condition. Enhanced immunity against sensitization of the laser-treated surface is attributed to its duplex microstructure and higher fraction of low-angle grain boundaries. The highlight of the investigation was that a laser surface melting treatment of unstabilized austenitic stainless steel brings about significant reduction in its susceptibility to sensitization during subsequent exposure to a susceptible temperature region and to intergranular corrosion during service.
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