The mechanism of radiation-induced segregation in Fe–Cr alloys was modeled using the inverse Kirkendall mechanism and compared to experimental measurements over a range of temperatures, bulk Cr ...compositions, and irradiation dose. The model showed that over a large temperature range chromium was enriched at sinks by interstitial migration, and at very high temperatures it was depleted by diffusing opposite to the vacancy flux. Experimental results and model predictions were in good qualitative and quantitative agreement with regard to the temperature dependence of segregation and the crossover from Cr enrichment to Cr depletion. The inverse Kirkendall mechanism was also in agreement with experimental findings that observed a decreasing amount of Cr enrichment with increasing bulk Cr composition. The effects of solute drag were modeled within the inverse Kirkendall framework, but were unable to account for either the crossover from Cr enrichment to Cr depletion or the magnitudes of segregation measured in experiments.
Thus far, a number of studies have investigated the irradiation evolution of oxide nanoparticles in b.c.c. Fe-Cr based oxide dispersion strengthened (ODS) alloys. But given the inconsistent ...experimental conditions, results have been widely variable and inconclusive. Crystal structure and chemistry changes differ from experiment to experiment, and the total nanoparticle volume fraction has been observed to both increase and decrease. Furthermore, there has not yet been a comprehensive review of the archival literature. In this paper, we summarize the existing studies on nanoparticle irradiation evolution. We note significant observations with respect to oxide nanoparticle crystallinity, composition, size, and number density. We discuss four possible contributing mechanisms for nanoparticle evolution: ballistic dissolution, Ostwald ripening, irradiation-enhanced diffusion, and homogeneous nucleation. Finally, we propose future directions to achieve a more comprehensive understanding of irradiation effects on oxide nanoparticles in ODS alloys.
A systematic approach to measuring radiation-induced segregation (RIS) was used on four ferritic–martensitic (F–M) alloys: T91, HCM12A, HT9, and a Fe–9Cr model alloy, irradiated with 2.0MeV protons ...over a range of doses (1–10dpa) and temperatures (300–700°C). The experimental conditions are established so as to isolate the dependence of RIS on the experimental parameters: temperature, dose and bulk composition. RIS is measured at prior austenite grain boundaries (PAGBs) using the STEM/EDX technique. Chromium is found to enrich at PAGBs in all conditions with the exception being T91 irradiated to 3dpa at 700°C. The magnitude of enrichment is small (<2at%). Minor elements Si, Ni, and Cu also enrich consistently. A bell-shaped temperature dependence of RIS is observed in all elements. The amount of Cr enrichment decreases as a function of increasing bulk Cr concentration. Lastly, it is found that the 9Cr model alloy reaches a steady-state Cr RIS behavior at approximately 7dpa, while the T91 reaches what may be a steady state near 3dpa, then the amount of enrichment decreases at 10dpa.
This paper provides an overview of advanced scanning transmission electron microscopy (STEM) techniques used for characterization of irradiated BCC Fe-based alloys. Advanced STEM methods provide the ...high-resolution imaging and chemical analysis necessary to understand the irradiation response of BCC Fe-based alloys. The use of STEM with energy dispersive x-ray spectroscopy (EDX) for measurement of radiation-induced segregation (RIS) is described, with an illustrated example of RIS in proton- and self-ion irradiated T91. Aberration-corrected STEM-EDX for nanocluster/nanoparticle imaging and chemical analysis is also discussed, and examples are provided from ion-irradiated oxide dispersion strengthened (ODS) alloys. Finally, STEM techniques for void, cavity, and dislocation loop imaging are described, with examples from various BCC Fe-based alloys.
Laser welding is attractive for numerous applications requiring materials joining, due to its low energy input. However, it is unknown how the laser welding process influences the ...microstructure-property relationship across the weldment. The objective of this study is to determine the strengthening mechanisms in the weld metal, base metal, and heat affected zone (HAZ) of an AISI 304/308L stainless steel (SS) laser weldment. Scanning electron microscopy (SEM) with electron backscattered diffraction (EBSD) scanning and transmission electron microscopy (TEM) was used to evaluate the microstructure, and static nanoindentation was used to evaluate strength across the weldment. Although the HAZ has a finer dendritic grain structure, its higher hardness compared to the base and weld metal cannot be explained by the Hall-Petch relationship. Therefore, a new strengthening model for weldments that considers the evolution in grain boundary size and orientation angle, as well as dislocation density, precipitation, and solid solution is proposed. Notably, core-shell Ti-C-N precipitation, which provides Orowan dislocation bypass strengthening, is found to be a major contributor to strengthening in the HAZ. The proposed model predictions fall within 10% of experimentally measured properties for all three regions of the analyzed weldment.
FeCrAl alloys are being investigated as candidate materials for light water reactor fuel claddings. The chemical composition of FeCrAl determines its resistance to corrosion under normal operating ...conditions. The purpose of this paper is to investigate the effect of 0, 1, 3 wt% Ni addition on the passivation characteristics of Fe17Cr5.5Al in oxygenated and hydrogenated simulated reactor waters for 3-month immersion. Current results show that Ni addition improves the passivation of FeCrAl under oxygenated condition and decreases the mass loss under hydrogenated conditions.
•Ni addition effect on FeCrAl oxidation behavior was studied for the first time.•Ni addition promotes passivation of FeCrAl under oxygenated BWR-NWC condition.•Cr and Al oxide form on Ni-containing FeCrAl under BWR-NWC in only three months.•Ni addition decreases the mass loss of FeCrAl under hydrogenated PWR and BWR-HWC.
Amorphous ceramics are a unique class of materials with unusual properties and functionalities. While these materials are known to crystallize when subjected to thermal annealing, they have sometimes ...been observed to crystallize athermally when exposed to extreme irradiation environments. Because irradiation is almost universally understood to introduce disorder into materials, these observations of irradiation-induced ordering or crystallization are unusual and may partially explain the limited research into this phenomenon. However, the archival literature presents a growing body of evidence of these irradiation-induced amorphous-to-crystalline (a-to-c) phase transformations in ceramics. In this perspective, the summary and review of examples from the literature of irradiation-induced a-to-c transformations for various classifications of ceramics are provided. This work will highlight irradiation conditions and material parameters that appear most influential for activating a-to-c transformations, identify trends, examine possible mechanisms, and discuss the impact of a-to-c transformations on material properties. Finally, future research directions that will enable researchers to harness a-to-c transformations to tailor materials behaviors will be provided.
Batteries and electrochemical capacitors (ECs) are of critical importance for applications such as electric vehicles, electric grids, and mobile devices. However, the performance of existing battery ...and EC technologies falls short of meeting the requirements of high energy/high power and long durability for increasing markets such as the automotive industry, aerospace, and grid-storage utilizing renewable energies. Therefore, improving energy storage materials performance metrics is imperative. In the past two decades, radiation has emerged as a new means to modify functionalities in energy storage materials. There exists a common misconception that radiation with energetic ions and electrons will always cause radiation damage to target materials, which might potentially prevent its applications in electrochemical energy storage systems. But in this review, we summarize recent progress in radiation effects on materials for electrochemical energy storage systems to show that radiation can have both beneficial and detrimental effects on various types of energy materials. Prior work suggests that fundamental understanding toward the energy loss mechanisms that govern the resulting microstructure, defect generation, interfacial properties, mechanical properties, and eventual electrochemical properties is critical. We discuss radiation effects in the following categories: (1) defect engineering, (2) interface engineering, (3) radiation-induced degradation, and (4) radiation-assisted synthesis. We analyze the significant trends and provide our perspectives and outlook on current research and future directions in research seeking to harness radiation as a method for enhancing the synthesis and performance of battery materials.
Batteries and electrochemical capacitors (ECs) are of critical importance for applications such as electric vehicles, electric grids, and mobile devices.
Localized deformation, including that by the deformation-induced shearing martensitic phase transformation, is responsible for hardening and embrittlement in irradiated face-centered cubic alloys. ...These localized deformation processes can have profound consequences on the mechanical integrity of common structural metals used in extreme radiation environments such as nuclear reactors. This article aims to review and understand exactly how irradiation affects the martensitic phase transformation in face-centered cubic alloys, with an emphasis on austenitic stainless steel, given its ubiquity in the archival literature. The influence of irradiation on stacking fault energy and subsequent implications on the phase transformation are discussed. Mechanisms by which irradiation-induced microstructures enhance the phase transformation are also described, including the surface energy contribution of irradiation-induced cavities (i.e., voids and bubbles) toward the critical martensite nucleation energy, and partial dislocation–cavity interactions. A deformation mechanism map illustrates how irradiation-induced cavities can modulate the martensitic transformation pathway.
Austenitic stainless steel D9 is a candidate for Generation IV nuclear reactor structural materials due to its enhanced irradiation tolerance and high-temperature creep strength compared to ...conventional 300-series stainless steels. But, like other austenitic steels, D9 is susceptible to irradiation-induced clustering of Ni and Si, the mechanism for which is not well understood. This study utilizes atom probe tomography (APT) to characterize the chemistry and morphology of Ni-Si nanoclusters in D9 following neutron or proton irradiation to doses ranging from 5-9 displacements per atom (dpa) and temperatures ranging from 430-683 °C. Nanoclusters form only after neutron irradiation and exhibit classical coarsening with increasing dose and temperature. The nanoclusters have Ni
Si stoichiometry in a Ni core-Si shell structure. This core-shell structure provides insight into a potentially unique nucleation and growth mechanism-nanocluster cores may nucleate through local, spinodal-like compositional fluctuations in Ni, with subsequent growth driven by rapid Si diffusion. This study underscores how APT can shed light on an unusual irradiation-induced nanocluster nucleation mechanism active in the ubiquitous class of austenitic stainless steels.
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