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Fe42Mn28Cr15Co10Si5 is a highly strain-hardenable high-entropy alloy (HEA) that is challenging to machine with traditional metal cutting tools. The electrochemical behavior of this HEA was examined in nitrate- and chloride-based electrolytes to understand the electrochemical machining (ECM) process. Potentiodynamic and potentiostatic tests were conducted on this alloy in 1 M and 2.35 M NaNO3 solutions, with and without additions of 0.01 M nitric acid and 0.01 M citric acid. A 20% NaCl solution was also tested as an electrolyte. Nitrate solutions caused passivation of the HEA, while no passivation was observed in chloride solutions. Surface analysis with X-ray photoelectron spectrometry (XPS) indicated that adding citric acid helped reduce surface passivation. The Faradaic efficiency of ECM increased with higher applied voltage. The chloride solution showed higher Faradaic efficiency than nitrate-based solutions. Specifically, the Faradaic efficiency of 20% NaCl at 10 V is 57.4%, compared to 21.9% for 20% NaNO3 + 0.01 M citric acid at 10 V. Electrochemical parameters, including anodic and cathodic exchange current densities, Tafel slopes, and corrosion current densities, were calculated from the experimental data. The corrosion current densities in the 20% nitrate solutions ranged from 2.35 to 3.2 × 10−5 A/cm2, while the 20% chloride solution had a lower corrosion rate at 1.45 × 10−5 A/cm2. These electrochemical parameters can help predict the dissolution behavior of the HEA in nitrate and chloride solutions and aid in optimizing the ECM process.

Inconel 718 (UNS N07718) is a nickel-base superalloy containing iron that is used at cryogenic temperatures (arctic pipe components) and at high temperatures (gas turbines). This alloy is also used in off-shore oil drilling due to its high overall strength and resistance to corrosion. Inconel 718 components are created by a selective laser melting (SLM) additive manufacturing route and result in isotropic fine-grained microstructures with metastable phases (such as Laves phases) that are not usually present in conventional manufacturing processes. In this work, SLM Inconel 718 alloy specimens were investigated in four different conditions: (1) As-manufactured (AS-AM), (2) Additively manufactured and hot isostatically pressed (AM-HIP), (3) As-manufactured and heat-treated (solution annealing followed by two-step aging), and 4) AM-HIP and heat-treated. Localized corrosion behavior was evaluated at room temperature in a 3.5% NaCl solution at three different pH conditions (pH 1.25, 6.25, and 12.25). Electrochemical tests, including linear polarization, cyclic polarization, potentiostatic conditioning, electrochemical impedance spectroscopy, and Mott–Schottky analyses, were used to compare the corrosion behaviors of the SLM specimens with that of the conventionally wrought IN718 samples. The results showed that the additively manufactured specimens showed better corrosion resistance than the wrought material in the acidic chloride solution, and the AM-HIP specimens exhibited superior corrosion resistance to the as-manufactured ones. Hot isostatic pressing resulted in the visible elimination of the dendritic structure, indicating compositional homogeneity as well as a significant decrease in porosity. In addition, the deleterious secondary phases, such as Laves and δ phases, were not observed in the microstructure of the HIPed samples. The AM-HIP material showed the highest corrosion resistance in all the pH conditions. The two-step aging treatment, in general, resulted in the deterioration of corrosion resistance, which could be attributed to the formation of γ′ and γ″ precipitates that increased the cathodic reaction catalytic activities. In the additively manufactured samples, the presence of the Laves phase was more detrimental to corrosion resistance than any other phases and MC carbide and grain boundary δ phase increased the susceptibility to corrosion in wrought materials.

In this study, cyclic polarization (CP) measurements were conducted on the molybdenum-based titanium–zirconium–molybdenum (TZM) alloy in 3.5% NaCl solutions under varying pH conditions, and the results were compared with those of pure molybdenum. No passivity breakdown was observed during cyclic polarization in acidic and neutral chloride solutions. The surface film formed on the TZM, and pure Mo samples displayed a dual-layered structure, comprising an inner layer of p-type semiconductivity and an outer layer of n-type semiconductivity. The defect density of the n-type layer ranged from 7.5 × 1017 to 7.5 × 1019 cm−3, while the p-type layer had a carrier density ranging from 2 × 1018 to 9 × 1019 cm−3. The pure molybdenum samples demonstrated lower passive current densities, lower charge carrier densities, and higher impedance than the TZM alloy. The lower corrosion resistance of TZM alloy could be attributed to the higher dislocation density, which acted as short-circuit paths for Mo diffusion, and the presence of carbides that exhibited a microgalvanic effect. Overall, this study clarified that the localized corrosion reported in the literature was not due to the breakdown of the passive layer but may be linked to the heterogeneous microstructure.

Nanometric hetero‐interfaces provide a wealth of scientific and engineering opportunities due to their complex and often misunderstood properties that can differ from their respective bulk constituents. In this work, the ability for engineered nanostructures within a bulk U─Mo alloy to arrest simulant fission products is investigated experimentally and computationally. Nanostructured 90 wt% U/ 10 wt% Mo (U‐10Mo) with 7.1 at% Nd is consolidated using spark‐plasma‐ sintering (SPS) techniques and is heat‐treated at 500 °C under vacuum for 24, 100, 500, and 1000 h. Analysis on the sintered and heat‐treated U‐10Mo reveals rapid kinetics in Nd diffusion to nanocluster sites, with evidence of Nd diffusion occurring during sintering and during the following heat‐treatment. The segregation behavior of Nd at two different U─Mo/UN interfaces is computationally verified using density functional theory (DFT) to reinforce experimental data. This work endeavors to engineer uranium mononitride (UN) nanostructures within a metallic nuclear fuel (U─Mo), in order to trap potential fission products (Nd). From consolidation of the nanostructured U─Mo powders all the way to 1000 h at reactor‐like temperatures (500 °C), Nd preferentially migrates to nanostructure boundaries (hetero‐interfaces). This technology can help prevent fuel‐cladding chemical interactions while not reducing fuel smear density within nuclear reactor cores.

Dry storage canisters of used nuclear fuels are fabricated using SUS 304L stainless steel. Chloride-induced stress corrosion cracking (CISCC) is one of the major failure modes of dry storage canisters. The cracked canisters can be repaired by friction stir welding (FSW), a low-heat input ‘solid-phase’ welding process. It is important to evaluate the ClSCC resistance of the friction stir welded material. Stress corrosion cracking (SCC) studies were carried out on mill-annealed base materials and friction stir welded 304L stainless U-bend specimens in 3.5% NaCl + 5 N H2SO4 solution at room temperature and boiling MgCl2 solution at 155 °C. The engineering stress on the outer fiber of the FSW U-bend specimen was ~60% higher than that of the base metal (BM). In spite of the higher stress level of the FSW, both materials (FSW and BM) showed almost similar SCC failure times in the two different test solutions. The SCC occurred in the thermo-mechanically affected zone (TMAZ) of the FSW specimens in the 3.5% NaCl + 5 N H2SO4 solution at room temperature, while the stirred zone (SZ) was relatively crack-free. The failure occurred at the stirred zone when tested in the boiling MgCl2 solution. Hydrogen reduction was the cathodic reaction in the boiling MgCl2 solution, which promoted hydrogen-assisted cracking of the heavily deformed stirred zone. The emergence of the slip step followed by passive film rupture and dissolution of the slip step could be the SCC events in the 3.5% NaCl + 5 N H2SO4 solution at room temperature. However, the slip step height was not sufficient to cause passivity breakdown in the fine-grained SZ. Therefore, the SCC occurred in the partially recrystallized softer TMAZ. Overall, the friction-stirred 304L showed higher tolerance to ClSCC than the 304L base metal.

Laser shock peening of cold rolled Nitinol was carried out at high power density (7 and 9 GW/cm2) and high overlap ratio (90%). Tensile surface residual stresses were generated in the peened material. An enhancement in surface microhardness from 351 for unpeened material to 375 and 394 VHN for the 7 and 9 GW/cm2 samples, respectively, was also observed. However, at a depth of 50 μm, the hardness of the peened material was lower than that of the as-received material. These contrasting observations were attributed to the change in the austenitic phase fraction brought about by laser interactions.

Grade 91 steel (modified 9Cr-1Mo steel) is considered a prospective material for the Next Generation Nuclear Power Plant for application in reactor pressure vessels at temperatures of up to 650 °C. In this study, heat treatment of Grade 91 steel was performed by normalizing and tempering the steel at various temperatures for different periods of time. Optical microscopy, scanning and transmission electron microscopy in conjunction with microhardness profiles and calorimetric plots were used to understand the microstructural evolution including precipitate structures and were correlated with mechanical behavior of the steel. Thermo-Calc™ calculations were used to support the experimental work. Furthermore, carbon isopleth and temperature dependencies of the volume fraction of different precipitates were constructed.

In a loss-of-coolant accident (LOCA) event such as at Fukushima, the core becomes exposed to steam rather than the coolant (water), and the decay heat (from b°, b+, and c decays of short-lived isotopes) being produced in the core continues to heat up the fuel and cladding.1 Above 850°C, the alpha phase (HCP) of zirconium alloys undergoes polymorphic transformation to the beta phase (BCC), which is completed at about 980°C. The oxidation rate of Zr-alloy increases rapidly with increasing temperature at> 800°C to release hydrogen through an extremely exothermic reaction, which leads to the possibility of a hydrogen explosion. According to the U.S. DOE performance metric report, any potential ATF system should be evaluated for all the possible 'performance regimes' such as: fabrication and manufacturability (including licensibility); normal operations and anticipated operational occurrences; postulated accidents (design basis); severe accidents (beyond design basis); and ease of used fuel storage/transport/disposition. Among many other projects, a Georgia Tech-led multi-institutional team under a DOE-funded Integrated Research Program (IRP) developed a conceptual design of an Integral Inherently Safe LWR (I2S-LWR) in which U3Si2 as the ATF fuel and APMT (Fe-22Cr-5Al-3Mo) as the ATF cladding material were considered.5 Although the articles here have been authored by researchers based in the U.S., international research on ATF materials has also been quite active.6 The first article titled, \"Versatile Oxide Films Protect FeCrAl Alloys Under Normal Operation and Accident Conditions in Light Water Power Reactors,\" by Raul Rebak is on the assessment of oxidation resistance of FeCrAl cladding alloy. The following papers are published under the topic \"Accident Tolerant Nuclear Fuels and Cladding Materials\" in the February 2018 issue (vol. 70, no. 2) of JOM and can be accessed via the JOM page at http://link.springer.com/journal/11837/70/2/page/ 1. * \"Versatile Oxide Films Protect FeCrAl Alloys Under Normal Operation and Accident Conditions in Light Water Power Reactors\" by Raul B. Rebak. * \"Oxidation Kinetics of Ferritic Alloys in High- Temperature Steam Environments\" by Stephen S. Parker, Joshua T. White, Peter Hosemann, and Andrew Nelson. * \"Laser and Pressure Resistance Weld of Thin- Wall Cladding for LWR Accident Tolerant Fuels\" by Jian Gan, Nathan Jerred, Emmanuel Perez, and D.C. Haggard. * \"Development of Cold Spray Coatings for Accident Tolerant Fuel Cladding in Light Water Reactors\" by Benjamin Maier, Hwasung Yeom, Greg Johnson, Tyler Dabney, Jorie Walters, Javier Romero, Hemant Shah, Peng Xu, and Kumar Sridharan. * \"Mechanical Properties of Uranium Silicides by Nanoindentation and Finite Elements Modeling\" by Ursula Carvajal-Nunez, Mohamed S. Elbakhshwan, Nathan A. Mara, Joshua T. White, and Andrew T. Nelson. * \"Effect of High Si Content on U3Si2 Fuel Microstructure\" by Jhonathan Rosales, Isabella J. van Rooyen, Subhashish Meher, Rita Hoggan, Clemente Parga, and Jason Harp. * \"Microstructure Evaluation of a U3Si2 Fuel Pin Fabricated via Arc Melt Gravity Drop Casting\" by Rita Hoggan and Jason M. Harp.

Additive Manufacturing (AM) is a transformative manufacturing technology enabling direct fabrication of complex parts layer-by-layer from 3D modeling data. Among AM applications, the fabrication of Functionally Graded Materials (FGMs) has significant importance due to the potential to enhance component performance across several industries. FGMs are manufactured with a gradient composition transition between dissimilar materials, enabling the design of new materials with location-dependent mechanical and physical properties. This study presents a comprehensive review of published literature pertaining to the implementation of Machine Learning (ML) techniques in AM, with an emphasis on ML-based methods for optimizing FGMs fabrication processes. Through an extensive survey of the literature, this review article explores the role of ML in addressing the inherent challenges in FGMs fabrication and encompasses parameter optimization, defect detection, and real-time monitoring. The article also provides a discussion of future research directions and challenges in employing ML-based methods in the AM fabrication of FGMs.