Dispersion-strengthened Steels Research Articles

Practical Design of a Breed-and-Burn Lead-Cooled Fast Reactor with Rotational Fuel Shuffling Strategy

The purpose of this study is to demonstrate a practical core design for a lead-cooled, nitride fueled, rotational fuel shuffling breed-and-burn (RFBB) fast reactor. The core design is based on the Westinghouse Lead Fast Reactor (WH-LFR) and uses natural uranium nitride fuel with a sodium bond encased in oxide dispersion-strengthened steel cladding. Simulations confirmed the potential of the reactor to maintain criticality at the equilibrium state, with a reactivity swing of less than 200 pcm at every cycle interval and an average discharge burnup of 235 MWd/kg heavy metals (HM) for a 1050 effective full-power day refueling interval. Power profiles were maintained stable at the equilibrium state, while the cladding of the discharged fuel incurred over 650 displacements per atom over its entire residency in the core. From a nonproliferation perspective, the plutonium vector for the discharge fuel aligns with reactor-grade fuel standards, with over a 70% concentration of 239Pu and over 22% 240Pu, reducing the risk of weaponization. The adopted control rod system has been shown to offer sufficient negative reactivity of over 19 $ to bring the reactor into a subcritical state. Challenges such as the susceptibility of neutron balance to material thickness and neutron leakage have been addressed, emphasizing the necessity for meticulous design improvements. A steady-state thermohydraulic analysis confirmed the heat removal capacity from the hottest channel, ensuring operational safety. This study confirmed the feasibility of the RFBB strategy for a lead-cooled nitride-fueled fast reactor and sets a precedent for future research in enhancing fuel utilization and safety in nuclear reactors.

New dispersion mechanism for oxide dispersion-strengthened steels by liquid metallurgy

The use of oxide dispersion-strengthened (ODS) alloys in demanding applications can effectively reduce parts’ weights, extend life of use, and enhance overall energy efficiency. But, the current manufacturing of ODS alloys has remained impractical for decades due to poor scalability and extremely high costs. Mass production of ODS steels by liquid metallurgy is therefore crucial to decrease their costs by several orders of magnitude and expand their potential applications. However, oxide nanoparticle (NP) dispersion in molten alloys presents fundamental challenges for liquid metallurgy due to the vastly dissimilar atomic properties between ionocovalent oxides and metals. Here we show, for the first time, that Y2O3 NPs are able to be dispersed in liquid 316L with a 1 % Nb addition. It was discovered that Nb-enriched interfacial layers exist around the Y2O3 NPs in solidified steels after slow cooling. Theoretical analyses reveal that the Nb-enriched interfacial layer induces a higher energy barrier and a significantly lower van der Waals attraction between oxide NPs and liquid Fe for the successful dispersion of oxide NPs in liquid steels. Moreover, Y2O3 and Al2O3 NPs were successfully dispersed in lean steels, such as Fe-Nb and low-C steels. This new dispersion mechanism of oxide NPs opens an exciting pathway for the economical mass manufacturing of various ODS alloys by liquid metallurgy for numerous applications.

The Effects of Irradiation on the Improvement in Oxidation Behavior of MX-ODS Steel in Liquid Pb.

Lead-cooled fast reactors exhibit strong inherent safety performance and good economic features, while material degradation due to corrosion and irradiation is still challenging. Oxide dispersion-strengthened steels are one of the promising candidates for fuel cladding materials. The effects of both irradiation and corrosion on ODS steel need to be further studied. In this work, MX-ODS steel was irradiated by Fe ions at 500 °C up to 46 dpa. Later, the as-received specimen and the irradiated specimen were used to conduct corrosion tests in oxygen-saturated Pb at 550 °C for 1 h. In the as-received specimen, discontinuous oxides penetrated by Pb and Pb in contact with steel matrix were observed, demonstrating unsatisfactory corrosion resistance of the material. However, in the irradiated specimen after corrosion experiment, a protective oxide layer formed and prevented Pb attack. The oxidation behavior differences between the two specimens can be attributed to the defects produced by irradiation and the structural discrepancy in oxides caused by the formation process. A possible mechanism of irradiation on the corrosion is discussed. In the as-received specimen, Fe atoms loss led to voids in the oxides, and lead penetrated the oxides through these voids. In the irradiated specimen, defects left by previous irradiation helped to form a more uniform oxide layer. The adhesive outer magnetite oxide and the Fe ions generated from where grain boundary oxidation developed retarded the presence of voids and made the oxide layer protective.

Microstructure Evolution and Mechanical Properties of a High Cr Oxide Dispersion-Strengthened Steel through STARS Route Followed by Hot Isostatic Pressing

Microstructure Evolution and Mechanical Properties of a High Cr Oxide Dispersion-Strengthened Steel through STARS Route Followed by Hot Isostatic Pressing

Effect of Interface Wettability on Additively Manufactured Metal Matrix Composites: A Case Study of 316L-Y2O3 Oxide Dispersion-Strengthened Steel

Laser powder bed fusion (LPBF) is a fusion-based additive manufacturing process. It has the advantage of allowing the manufacturing of metal matrix composites. This advantage arises from its small melting zone and rapid cooling rate, which minimize the risk of reinforcement segregation. In this work, 0.3 wt% and 1.0 wt% Y2O3 nanoparticles were added to 316L to fabricate oxide dispersion-strengthened (ODS) steels using the LPBF process. Notably, Y2O3 agglomerates were identified in the LPBF-fabricated 316L ODS steels, without inducing grain refinement, while the impact on tensile strength of Y2O3 addition proved negligible. Tensile elongation was decreased due to the poor bonding of the Y2O3 agglomerations to the matrix. The crucial role of the wettability of the reinforcement and the matrix in facilitating grain refinement and strength enhancement is discussed. The poor wettability of the Y2O3 particles and 316L emerged as the primary cause for Y2O3 agglomeration. This finding highlights the importance of addressing wettability issues to optimize the manufacturing process and enhance the overall performance of LPBF-fabricated metal matrix composites.

Study of Precipitates in Oxide Dispersion-Strengthened Steels by SANS, TEM, and APT.

In this work, the nanostructure of oxide dispersion-strengthened steels was studied by small-angle neutron scattering (SANS), transmission electron microscopy (TEM), and atom probe tomography (APT). The steels under study have different alloying systems differing in their contents of Cr, V, Ti, Al, and Zr. The methods of local analysis of TEM and APT revealed a significant number of nanosized oxide particles and clusters. Their sizes, number densities, and compositions were determined. A calculation of hardness from SANS data collected without an external magnetic field, or under a 1.1 T field, showed good agreement with the microhardness of the materials. The importance of taking into account two types of inclusions (oxides and clusters) and both nuclear and magnetic scattering was shown by the analysis of the scattering data.

A Study of the Effect of Magnetic Scattering on the Analysis of the Nanostructure of Oxide Dispersion-Strengthened Steels by Small-Angle Neutron Scattering

A Study of the Effect of Magnetic Scattering on the Analysis of the Nanostructure of Oxide Dispersion-Strengthened Steels by Small-Angle Neutron Scattering

Effects of Cr and Si addition on the high-temperature oxidation resistance in high-Mn alumina-forming oxide dispersion strengthened austenitic steels

Oxide dispersion-strengthened (ODS) steels are promising candidates for constructing nuclear reactors. Considering a high-temperature environment, ODS austenitic steels could provide superior performance compared to the current ODS ferritic steels. To meet the reduced activation requirement, the compositions of ODS austenitic steels have to be carefully adjust. Currently, the authors focus on the ODS austenitic steels with the austenite stabilizer of Mn, and several amounts of Al are added to improve their high-temperature oxidation resistance. This study investigates the third-element effects of Cr and Si on the high-temperature oxidation resistance of high-manganese alumina-forming ODS austenitic steels. Generally, Si-containing steel exhibits superior oxidation resistance owing to the formation of a continuous inner layer of amorphous alumina. In contrast, the Cr-containing steel does not possess a continuous alumina layer, resulting in insufficient oxidation resistance. The reported phenomenon is believed to be a reference for the development of ODS austenitic steels in the future.

Towards enhancing ODS composites in laser powder bed fusion: Investigating the incorporation of laser-generated zirconia nanoparticles in a model iron–chromium alloy

Oxide dispersion-strengthened (ODS) steel is a sought-after composite material known for its high demand in high-temperature and corrosive environments. Achieving the desired ODS steel properties requires specific conditions for the size and nanoparticles (NP) distribution in the printed part. Laser ablation in liquid (LAL) enables precise NP size adjustment. At the same time, the dynamic melt pool solidification in the Laser Powder Bed Fusion (PBF-LB/M) process complements this by creating favorable conditions for successful ODS processing. In this study, ZrO2 NP with a small and narrow particle size distribution (d50 = 3.8 nm; d90 = 10 nm) is produced by LAL. Dielectrophoretic deposition achieves the homogeneous, deformation-free coating of the binary Fe20Cr (wt.-%) matrix powder with NP. PBF-LB/M printed parts out of the oxide-additivated powder exhibit a crack-free structure and a density of up to 98%. Expectedly, the metal matrix grain sizes and room temperature microhardness (~ 220 HV) are not affected by NP addition. NP tracing by 2D simulation indicates a homogeneous NP distribution and less than 10% NP to be agglomerated in the solidified part. Thus, a promising perspective for a complete laser-based process chain for generating and processing ODS alloys is outlined.Graphical abstractTable of Contents

Study of the Nanostructure of Oxide Dispersion-Strengthened Steels with Small-Angle Neutron Scattering

Study of the Nanostructure of Oxide Dispersion-Strengthened Steels with Small-Angle Neutron Scattering

Comprehensive Study of the Impact of Iron-Ion Irradiation at 500°C on the Nanostructure of Oxide Dispersion-Strengthened Steels

Comprehensive Study of the Impact of Iron-Ion Irradiation at 500°C on the Nanostructure of Oxide Dispersion-Strengthened Steels

Study of Nanostructures in High-Chromium Oxide Dispersion-Strengthened Steels

Study of Nanostructures in High-Chromium Oxide Dispersion-Strengthened Steels

Uncertainty and statistics of dislocation-oxide interactions on strength and creep failure of oxide dispersion strengthened steels

Oxide dispersion strengthening (ODS) steels exhibit excellent mechanical and creep properties due to the nanoscale oxide particles as barriers to dislocation motion, for the great application potentials to structural components of advanced nuclear power plants. However, the classical ODS model described by the Orowan mechanism or cutting mechanism only depends upon a single average size, ignoring uncertainty and statistics of dislocation-oxide interactions induced by the spatial and dimensional random distribution of oxide particles. When the oxide particle size is larger than the critical size to determine the interaction mechanism transformation from cutting to looping, the Orowan mechanism and cutting mechanism would exist simultaneously. Here we propose a modified ODS model for strength and creep rate considering the spatial distribution and size distribution of oxide particles, which is more consistent with the experimental result compared to the classical ODS model. In addition, the contribution of oxide particles to the yield strength and creep strength is evaluated quantitatively for various precipitate sizes and volume fractions. It is believed that this model provides an analytical framework to accurately predict the strength and creep rate of ODS steels.

Microstructural Characterization of Novel ZrO2 Dispersion-Strengthened 9Cr Steel by Spark Plasma Sintering

Technologically important Oxide Dispersion-Strengthened steels are synthesized using ZrO2 as a dispersion strengthener instead of conventionally used Y2O3. Powder metallurgical route followed by spark plasma sintering is adopted for synthesizing the material. Detailed microstructural characterization revealed a fine-grained microstructure with finer dispersoids in as-sintered and normalized condition. The stable microstructure is found to be retained even after subjecting the samples at 973 K for as long as 1000 h for long-term thermal aging trials, indicating at a possible superiority of this material over the conventional Oxide Dispersion-Strengthened steels. The yield strength is calculated by making use of microstructural parameters and predictive models, both of which shown a good agreement. Mechanical property analysis through hardness measurements was correlated with microstructural observations and compared with the conventional Oxide Dispersion-Strengthened steels. The collective results indicate ZrO2 as a potential alternate dispersoid for strengthening steel and future scope for vast exploration.

Effect of radio-frequency plasma spheroidization on the microstructure and mechanical properties of 10Cr ferritic oxide dispersion-strengthened steel

Reducing the porosity of irregularly shaped mechanically alloyed oxide dispersion-strengthened (ODS) steel powders is critical for their application at cryogenic temperatures. Although the plasma rotating electrode process has been widely used as a suitable method for producing spherical powders, its high cost and low powder yield impede its application. Thus, we investigated the feasibility of applying plasma spheroidization on ODS steel particles, to reduce their porosity, by investigating the influence of radio-frequency plasma spheroidization on the microstructure and mechanical properties of 10-Cr ODS steel. The ODS steel powder was ball-milled and then spheroidized prior to consolidation. The prepared samples were analyzed using X-ray diffraction, electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM) as well as subjected to tensile and impact tests. The EBSD analysis revealed that the grains in the plasma-spheroidized sample were coarser than those in the non-spheroidized sample, and thus, the room- and cryogenic-temperature Charpy impact strengths of the latter were superior to those of the former sample. TEM analysis showed that the average particle size of plasma-spheroidized ODS steel was slightly higher than that of the non-plasma-spheroidized ODS steel. Furthermore, the room-temperature yield strength of the non-spheroidized ODS was higher than that of the spheroidized ODS because of the finer grains of the former. In the future, plasma spheroidization can be combined with other techniques to obtain completely dense ODS steel with increased upper shelf energies for various advanced and military applications.

Comprehensive Analysis of Nanostructure of Oxide Dispersion-Strengthened Steels by Ultramicroscopy Methods

Comprehensive Analysis of Nanostructure of Oxide Dispersion-Strengthened Steels by Ultramicroscopy Methods

Influence of Fe Ion Irradiation at 500°C on the Nanostructure of Oxide Dispersion-strengthened Steels

Influence of Fe Ion Irradiation at 500°C on the Nanostructure of Oxide Dispersion-strengthened Steels

Study of Nanostructure of Oxide Dispersion-Strengthened Steels by Small-Angle X-Ray Scattering

Study of Nanostructure of Oxide Dispersion-Strengthened Steels by Small-Angle X-Ray Scattering

Features of Synthesis of Y2Ti2O7 Ceramics for the Purpose of Obtaining Dispersion-Strengthened Steels

Features of Synthesis of Y₂Ti₂O₇ Ceramics for the Purpose of Obtaining Dispersion-Strengthened Steels

Synthesis of Nano-Oxide Precipitates by Implantation of Ti, Y and O Ions in Fe-10%Cr: Towards an Understanding of Precipitation in Oxide Dispersion-Strengthened (ODS) Steels.

The properties of oxide dispersion-strengthened steels are highly dependent on the nature and size distribution of their constituting nano-oxide precipitates. A fine control of the processes of synthesis would enable the optimization of pertinent properties for use in various energy systems. This control, however, requires knowledge of the precise mechanisms of nucleation and growth of the nanoprecipitates, which are still a matter of debate. In the present study, nano-oxide precipitates were produced via the implantation of Y, Ti, and O ions in two different sequential orders in an Fe-10%Cr matrix that was subsequently thermally annealed. The results show that the oxides that precipitate are not necessarily favoured thermodynamically, but rather result from complex kinetics aspects related to the interaction between the implanted elements and induced defects. When Y is implanted first, the formation of nanoprecipitates with characteristics similar to those in conventionally produced ODS steels, especially with a core/shell structure, is evidenced. In contrast, when implantation starts with Ti, the precipitation of yttria during subsequent high-temperature annealing is totally suppressed, and corundum Cr2O3 precipitates instead. Moreover, the systematic involvement of {110} matrix planes in orientation relationships with the precipitates, independently of the precipitate nature, suggests matrix restriction effects on the early stages of precipitation.