The corrosion and corrosion-erosion behaviors of FeNiCrAl high-entropy alloys (HEAs) incorporating Si and Nb/Ti were investigated in lead-bismuth eutectic (LBE). The introduction of alloying elements markedly enhances corrosion resistance, wherein Si may retard oxidation kinetics, and Nb/Ti are potentially associated with the formation of Cr-rich and Al-rich oxides, respectively. Corrosion-erosion testing conducted in dynamic LBE at a relative velocity of 4 m/s reveals a clear order in corrosion-erosion resistance, with the Si-containing HEA exhibiting the highest performance, followed by the Nb/Ti-containing HEA, and the original HEA showing the lowest. The additions of alloying elements reinforce the protective ability of the oxide layer, with Si may playing a particularly critical role in improving oxide layer adhesion to the matrix. Corrosion-erosion morphologies vary considerably across regions of different impact angles, largely governed by the stress distribution induced by the flowing LBE.

Laser based powder bed fusion (LPBF) and powder metallurgy via hot isostatic pressing (PM-HIP) are advanced manufacturing technologies for nuclear components. In the present study, stress corrosion crack (SCC) initiation susceptibility of LPBF 316L stainless steel post-treated by HIP, PM-HIP 316L and also wrought 316L specimens were evaluated in three typical light water reactor environments by U-bend testing and post-exposure characterizations. Results show that LPBF-HIP and PM-HIP 316L have lower SCC susceptibility compared to their wrought counterparts in the selected environments tested. The mechanisms for SCC behavior of samples were discussed.

Deformation processing is essential for Zr alloys as potential structural materials for reprocessing of spent nuclear fuel. Rolled Zr-1.0Ti-0.2Nb alloys with different thickness (20 mm, 10 mm, and 5 mm) were fabricated to reveal effects of deformation degree on corrosion behavior in 12 M HNO3 at 95 degrees C. Generally, increasing deformation degree gradually strengthens corrosion resistance of alloys, attributed to significantly refined grain size. Owing to the reduced concentration of HNO3 in gaseous phase, the corrosion rates are higher than those in liquid phase. The 5 mm alloy with a deformation degree of 90% demonstrates a refined grain size of 11.8 mu m and achieves low corrosion rates of 0.155 & times; 10-3 and 0.176 & times; 10-3 mm/a in liquid and gaseous phases, respectively. Analysis suggests that refined grain promotes the rapid formation of oxides by increasing diffusion channels of oxygen, and especially accelerates the recovery following damage of oxides films during alternating dissolution-passivation processes. Consequently, even in the gaseous phase, a protective oxide film with considerable thickness forms on the 5 mm alloy, effectively mitigating the dissolution and maintaining superior corrosion resistance. The present work offers new insights into optimizing deformation processing for ZrTiNb alloys with potential applications in reprocessing of spent nuclear fuel.

Additively manufactured (AM) stainless steels (SS) are under consideration for molten salt reactors. However, molten salt corrosion of AM SS remains poorly understood. Here we present the mechanisms of corrosion of laser-based powder bed fused (LPBF) 316L SS in FLiNaK + 5 wt. % EuF3 molten salt at 650 °C. Microstructural features of dislocation cells, low-angle grain boundaries, and carbides appear to be the major underlying features influencing corrosion behavior. Corrosion-induced, salt-filled voids follow {100} crystallographic planes rather than AM-induced microstructural features. Dislocation cell structures retain Cr, and yet they appear to slow molten salt corrosion in the long run, with limited grain boundary migration observed. Larger Cr carbides disappear in the salt penetration regions, leaving only Mo carbides. Smaller carbides and remaining high Ni-enrichment layer slow down Cr depletion and molten salt penetration.

Enhancement of fracture mechanics small-scale specimen test techniques is important, especially in the nuclear industry for the safe lifetime extension of power plants. Miniature-sized test specimens enable more efficient use of the reducing amount of reactor pressure vessel surveillance reference materials. This paper studies the limits of specimen miniaturization by means of fracture mechanics testing and determination of reference temperature T0, supported by microstructural characterization, particle analysis, and Finite Element Modelling (FEM). Tests indicate the same reference temperature T0,-102 degrees C, for both the 4 mm and 3 mm thick specimens investigated. Particle distribution analysis showed a statistically sufficient amount of initiating particles in the cross-section of the 3 mm thick specimen. FEM results including comparative analysis of four different specimen thicknesses showed similar stress and strain states in the 3 mm and 4 mm thick specimens. Maximum stress site versus crack initiation location is discussed, as well as the adaptability of ASTM standard E1921 and weakest-link theory regarding the applicability of miniature compact tension specimens with reduced thickness.

Ensuring the safe repurposing of X70 pipelines for hydrogen transport requires understanding how hydrogen interacts with deformation and local stress state. Two specimen geometries-a standard miniature tensile specimen and one with a hole at the gauge centre-are evaluated under in-situ electrochemical hydrogen charging. The effects of current density, pre-strain, and high stress triaxiality (eta approximate to 0.48) are systematically examined. Increasing hydrogen flux reduces ductility sharply, whereas yield strength remains nearly unchanged. Pre-strained specimens exhibit higher embrittlement due to enhanced hydrogen trapping, and stressconcentrated specimens exhibit the most severe loss of plasticity and brittle fracture. Fractographic and crosssectional observations reveal hydrogen-assisted cracks at surface for higher hydrogen fugacity and a transition from ductile to quasi-cleavage fracture. Under similar saturated hydrogen concentration, these results demonstrate that hydrogen fugacity, plastic deformation, and local stress state act synergistically to control embrittlement severity in X70 pipeline steels exposed to hydrogen environment.

Constant-displacement bolt-loaded compact tension specimens of Nickel-based Alloy 52 were exposed to boiling water reactor environment for 12 years, followed by an additional 3 years in post-shutdown cold water conditions in a Swedish nuclear power plant test loop, under a stress intensity factor of 20 MPa root m. After outer surface decontamination and specimen opening, unexpected crack extensions of 3-4.5 mm were observed. The fracture surface and the cross-sectional deformation microstructure were examined by electron microscopies techniques down to the nanoscale. The oxide layer in the region exhibiting unexpected crack growth was notably thin, suggesting that it formed after exposure to elevated operating temperatures. The dominant fracture mode is transgranular, propagating along close-packed {111} planes. The grains contained heterogeneous microstructures with regions enriched in nanometer-sized Ti(N,C) and the zigzag crack paths did not traverse these regions strengthened areas. Extensive shear bands were present near the crack tips, indicating pronounced localized plasticity. Hydrogen reduces stacking fault energy, results in localized plasticity and enhances shear bands formation. Low temperature crack propagation with evident effects of hydrogen was considered as the potential cause of crack propagation in Alloy 52 in the absence of external dynamic loading under post-shutdown cold water chemistry.

This study investigates the influence of microstructures on mechanical behavior and failure mechanisms of laser based powder bed fusion processed nickel-free and 316L stainless steels using small punch testing, nano-indentation, and miniaturized tensile testing. The as-printed 316L with a fully austenitic structure and high-density dislocation cells exhibited a nanohardness of 3.0 GPa, tensile strength of 600 MPa, and elongation close to 60 %, with failure occurring through ductile microvoid coalescence. In contrast, the as-printed nickel-free stainless steel with a fully ferritic matrix and random dislocation networks showed a high nanohardness of 4.94 GPa, but poor ductility of 2 % and transgranular cleavage fracture. Heat treatment at 950 degrees C for 30 min transformed the nickel-free steel into a duplex microstructure (56 % ferrite and 41 % austenite, with a minor 3 % Chi phase), reducing dislocation density and inducing stacking faults. This resulted in moderate improvement in tensile strength as well as ductility and a mixed fracture mode. Post-mortem analysis revealed that Chi phase assisted crack initiation and strain localization was observed near coarse grains. The evolution of low-angle to high-angle grain and twin boundaries promoted plastic deformation. These results highlight the importance of phase engineering and microstructural control in optimizing the ductility and toughness of nickel-free steels.

Austenitic stainless steels used in light water reactor coolant environments can be susceptible to environmentally assisted fatigue due to non-monotonic loading conditions. Effects of a pressurized water reactor (PWR) environment containing hydrogen and cyclic loading parameters on the low cycle fatigue (LCF) behavior of 316L stainless steel were investigated by comprehensive striation spacing evaluation. The exposure to a PWR environment results in a decreased LCF lifetime, an enhanced fatigue crack initiation, and an accelerated fatigue crack growth rate of 316L austenitic stainless steel. The effect of the loading waveform (periodic underload PUL, periodic overload POL, and constant amplitude sawtooth CA) was also evaluated. PUL reduces the low cycle fatigue lifetime, accelerates the fatigue crack growth rate, and advances the cycle where initiation of fatigue crack occurs compared to CA loading.

INCEFA-SCALE is a five-year project supported by the European Commission HORIZON2020 programme. It is the successor to the INCEFA-PLUS programme that ran from 2015 to 2020. INCEFA-SCALE kicked off in September 2020. The objective is to continue work, advancing the ability to predict lifetimes of Nuclear Plant components when subjected to Environmental Assisted Fatigue loading (EAF). It has been generally observed by nuclear plant operators that there appears to be a disconnect between the perceived difficulty of providing an acceptable assessment result with the current EAF methodologies and the good service experience with regard to this specific degradation mechanism. It is internationally recognised that a possible contributor to this discrepancy is the transferability of laboratory-scale tests to real nuclear components. EPRI, in the USA, is leading a series of component-scale environmental fatigue tests that are expected to advance data availability significantly; however, the ability to address transferability of laboratory-scale tests to real component geometries and loadings will still be constrained by limited test data. This is the knowledge gap addressed by INCEFA-SCALE. The project strategy will be (1) the development of comprehensive mechanistic understanding developed through detailed examination of test specimens and MatDB datamining, and (2) testing focussed on particular aspects of component-scale cyclic loading. The project will initially survey and understand the vast amount of test data within JRC’s MatDB database (from the predecessor INCEFA-PLUS project, and from other external sources such as USNRC, EPRI, MHI and the AdFaM project). In parallel, the test programme needs have been agreed, and protocols agreed for managing data, testing, and material examinations consistently. Testing commenced after one year and will run for three years. Finally, the project will deliver guidance on the use of laboratory-scale data for component-scale applications. This paper will report the first year of the project and detail the preparations completed to ensure the project maximises the achievement of its objectives.

This paper provides an overview of the INCEFA-SCALE H2020 project. It is a 5-year project, which began in October 2020, whose main objective is to improve the ability of predicting the lifetime of Nuclear Power Plants components subjected to environmental assisted fatigue. Its strategy is: 1) developing a comprehensive mechanistic understanding through a detailed examination of tested specimens and data mining; and 2) testing focused on particular aspects of component-scale cyclic loading. The project has created tools to survey the fatigue data from different finished projects. The testing programme is now underway and it is focused on studying the effect of variable amplitude loading, environment, surface condition, and geometry on the fatigue life of stainless-steel specimens.

As-received and spent magnesia-chromite refractories from a nickel flash smelting furnace were analyzed and compared to shed light on the interactions between the gas phase and the refractory material, a topic that has not received previous research effort. Based on the results, process-originated gaseous sulfur-containing species, such as SO2 and SO3, played a key role in the refractory reactions. In the absence of a surface deposit, the hot end of the refractory underwent attack by SO2, resulting in sulfation of both the periclase and chromite phases, which has not been reported before. In the presence of a surface deposit, the sulfation of main phases in the near-surface regions did not occur, but sulfur-bearing species diffused deeper into the refractory material, where they reacted with MgO and CaO, forming MgSO4 and CaSO4. In addition to the detected sulfur penetration, impurity elements, e.g., As; K, and Pb, had diffused towards the cold end of the refractory. This suggests these elements could have entered the refractory as gaseous species and then condensed at low enough temperatures.

The observation of a thin oxide film on oxygen free phosphorous doped copper after several days of exposure in supposedly anoxic conditions poses several questions, where the most straight-forward answers regarding sample preparation and handling is oftentimes overlooked. In an effort to minimize the environmental factors contributing to the oxide formation on the copper surface, a flow through cell arrangement was built to investigate the oxide formation at the Cu-Cu2S interface after exposure to anoxic sulfide containing phosphate buffer solution. The post exposure characterization by scanning electron microscopy and focused ion beam revealed no oxide formation on the copper surface in the absence of oxygen, while the exposure of the copper surface during the metallographic sample preparation phase, which employs the use of aerated water, causes the formation of copper oxide. Furthermore, a novel technique for noninvasive, semi-quantitative, and on-line sulfide determination is presented. The anodic current density determined from the linear polarization resistance of copper in sulfide solution was found to linearly increase with sulfide concentration.

Microstructure has a significant effect on material's integrity and in a heterogeneous weld microstructure the discontinuities affect the brittle fracture initiation and propagation and determine the fracture toughness. The knowledge of brittle fracture initiation mechanisms in high-Mn/high-Ni welds is limited. The brittle fracture initiation behaviour of the decommissioned Barseback Unit 2 reactor pressure vessel (RPV) welds of high-Mn/ high-Ni weld metal from three different locations, the RPV head and the beltline regions, were investigated and compared with specimens from the surveillance program with high fluence. Systematic fractography has been performed on impact and fracture toughness specimens and the main features of the brittle fracture initiation in the component weld are presented and discussed. Two main types of initiators are identified as the weakest links to initiate the cleavage fracture and the initiation mechanism is found independent from the operation condition. The high-fluence surveillance specimens have a larger amount of intergranular cracking. The cleavage fracture initiation appears to be independent of the operation conditions but dependent on the welding process and metallurgical features. The findings aid in the development of improved material-property correlations which will result in better computational tools for predicting aging of welds based on microstructure.

This study systematically explores the influence of grain boundary (GB) characteristics on the intergranular stress corrosion cracking (SCC) against high-temperature water. Statistical analyses of GB cracking susceptibility were conducted using stainless steel specimens produced via conventional and additive manufacturing (AM) methods, subjected to various post-treatment conditions, encompassing over 12,000 GBs. Based on the crystallographic statistics, a preliminary investigation was preformed within the latent space to identify the metrics responsible for SCC nucleation. Contrary to conventional perspectives, corrosion-related parameters such as GB plane orientation and GB atomic packing density (GBAPD) are found to be less significant factors. Instead, mechanical parameters, notably GB normal strain/stress and slip discontinuity, emerged as critical factors. Specifically, the Luster-Morris m(y) factor demonstrated strong correlation with GB cracking susceptibility, whereas traditional Schmid factor variations showed minimal association. Lower m(y) values significantly intensified local strain/stress gradients by promoting slip discontinuities, thereby increasing susceptibility to SCC. A machine learning model was developed incorporating key GB parameters, achieving an accuracy of 85 % and demonstrating robust predictive capability across distinct microstructures.

Additive manufacturing (AM) offers multiple economic and ecologic advantages with respect to the conventional manufacturing techniques. Post-processing treatments are typically applied to further improve the AM material’s performance for industrial applications. However, knowledge is still lacking about the hydrogen interaction with these specific post-processed AM microstructures. Therefore, this research focuses on the hydrogen embrittlement of stress relieved (SR) and hot isostatic pressed (HIP) laser powder bed fused (L-PBF) 316L austenitic stainless steel. An in-depth characterization is performed to examine the degradation of L-PBF 316L upon galvanostatic hydrogen charging, using complementary identification techniques. The results show that the microstructure determines the interaction with hydrogen, which regulates the hydrogen uptake capacity. The SR L-PBF 316L has an underlying substructure consisting of dislocation cells, whereas HIP L-PBF 316L largely resembles conventionally processed 316L stainless steel. Furthermore, it is observed that hydrogen charging introduces slip bands and lattice strains in both microstructures. As a result, the L-PBF 316L microstructure can be tuned by a specific post-processing treatment for an optimal resistance against hydrogen assisted degradation.

In this work, nickel-free duplex stainless steel (NiFDSS) and 316L stainless steel were produced by laser powder bed fusion (PBF-LB/M) under optimized parameters, reaching 98.83 % and 99.80 % relative densities, respectively. Microstructural analysis showed transformation from fully ferritic in the as-built condition to duplex after heat treatment (950 degrees C/1 h, followed by water quenching) for NiFDSS. Corrosion resistance was evaluated by potentiodynamic polarization in artificial seawater (0.6 M NaCl with pH 8.2), while tribocorrosion performance was measured in a ball-on-disc setup under the same electrolyte. As-built NiFDSS exhibited a lower corrosion current density (1.30 mu A/cm2) than 316L (1.78 mu A/cm2), and heat treatment further reduced it to 0.65 mu A/cm2, reflecting enhanced corrosion resistance. Under tribocorrosion, NiFDSS and heat-treated NiFDSS maintained lower corrosion rates but incurred higher wear rates than 316L, driven by residual porosity along with cleavage-prone fragmentation in the as-built alloy and sigma-phase-assisted cracking after heat treatment. Overall, PBF-LB/M of NiFDSS provided superior corrosion resistance while exhibiting lower wear performance than 316L. Porosity control through further PBF-LB/M parameters refinement and heat-treatment optimization is required to minimize residual pores and suppress sigma-phase precipitation, thereby improving wear resistance of NiFDSS.

The effects of post heat treatments on the oxidation behavior of laser powder bed fusion (LPBF) printed-316 L stainless steel (SS) in 600 degrees C supercritical CO2 were studied. The oxidation resistance was gradually deteriorated with increasing treatment temperature. That is because: 1, the high dislocation density in LPBF-316 L SS, which promotes the formation of protective oxide film by facilitating the diffusion of active elements, was decreased after heat treatment. 2, the density of twin boundary which is subject to general oxidation was increased, while that of low angle grain boundary which can passivate was decreased remarkably after hot isostatic pressing, thus decreasing the fraction of passivated grain boundaries.

The onset and mechanisms of hydrogen embrittlement are investigated in stress relieved (SR) and hot isostatic pressed (HIP) laser powder bed fused (L-PBF) 316L austenitic stainless steel. An improved resistance of SR L-PBF 316L to hydrogen-assisted degradation is uncovered by complementary modelling and in-depth experimental characterisation, including transmission electron microscopy. Novel insights show that the dislocation cells, characteristic for the SR L-PBF microstructure, form a beneficial hydrogen trap and establish an effective barrier against hydrogen-induced crack propagation and hydrogen embrittlement. Furthermore, the chemical heterogeneity in the dislocation cells contributes to crack arrest. In contrast, the mobile dislocations in HIP L-PBF 316L make this homogeneous microstructure significantly more prone to hydrogen embrittlement due to the promoted hydrogen-induced martensite formation, driving brittle crack propagation. Therefore, a dual HEDE-HELP synergetic mechanism is proposed for the hydrogen-induced embrittlement of SR L-PBF 316L, whereas HIP L-PBF 316L is dominated by the HEDE embrittlement mechanism. These insights highlight the potential of tailored post-processing in L-PBF microstructures, offering promising strategies to reduce hydrogen-assisted degradation in austenitic stainless steels.

The corrosion behavior of laser-based powder bed fused (LPBF) 316 L under various heat-treatment conditions (as-printed, solution annealed and hot isostatic pressed) in lead-bismuth eutectic (LBE) at 550 degrees C is studied. The wrought 316 L and counterpart fabricated by powder metallurgy-hot isostatic pressing (PM-HIP) were investigated as references. LPBF 316 L achieves reduced susceptibility to the LBE environment and acquires a shallower corrosion/dissolution depth in comparison to wrought and PM-HIP 316 L. As-printed and hot isostatic pressed LPBF specimens show restricted discernible phase transformation while the other conditions exhibit significant phase transformation. The enhanced corrosion resistance of LPBF 316 L in LBE is attributed to a dislocation cellular microstructure, a high proportion of low-angle grain boundaries, and elevated chromium and silicon contents. Dislocation cell boundaries and twin boundaries have higher resistance to LBE ingress than the highangle grain boundaries. Compared to the matrix, the preferential corrosion by LBE of LPBF materials at columnar boundaries is related to the carbides and (Si, Mn) enriched oxides formed during LPBF process. LPBF-HIP material exhibits a three-dimensional alternating structure of recrystallized and unrecrystallized areas, effectively impeding LBE ingress and thus can be a promising candidate as the structural material in the LBE system.