Small-angle neutron scattering study on the stability of oxide nanoparticles in long-term thermally aged 9Cr-oxide dispersion strengthened steel

A 9 Cr-oxide dispersion strengthened(ODS)steel was thermally aged at 873 K for up to 5000 h.The size distribution and chemical composition of the dispersed oxide nanoparticles were analyzed by small-angle neutron scattering under a magnetic field.Combined with transmission electron microscopy,Vickers micro-hardness tests and electron backscattered diffraction measurements,all the results showed that the thermal treatment had little or no effect on the size distributions and volume fractions of the oxide nanoparticles in the ferromagnetic matrix,which suggested excellent thermal stability of the 9 Cr-ODS steel.

Research progress on preparation technology of oxide dispersion strengthened steel for nuclear energy

Nuclear energy is a low-carbon,safe,efficient,and sustainable clean energy.The new generation of nuclear energy systems operate in harsher environments under higher working temperatures and irradiation doses,while traditional nuclear power materials cannot meet the requirements.The development of high-performance nuclear power materials is a key factor for promoting the development of nuclear energy.Oxide dispersion strengthened(ODS)steel contains a high number density of dispersed nano-oxides and defect sinks and exhibits excellent high temperature creep performance and irradiation swelling resistance.Therefore,ODS steel has been considered as one of the most promising candidate materials for fourth-generation nuclear fission reactor cladding tubes and nuclear fusion reactor blankets.The preparation process significantly influences microstructure of ODS steel.This paper reviews the development and perspective of several preparation processes of ODS steel,including the powder metallurgy process,improved powder metallurgy process,liquid metal forming process,hybrid process,and additive forging.This paper also summarizes and analyzes the relationship between microstructures and the preparation process.After comprehensive consideration,the powder metallurgy process is still the best preparation process for ODS steel.Combining the advantages and disadvantages of the above preparation processes,the trend applied additive forging for extreme manufacturing of large ODS steel components is discussed with the goal of providing a reference for the application and development of ODS steel in nuclear energy.

On the helium bubble swelling in nano-oxide dispersion-strengthened steels

The development of structural materials resistant to harsh radiation environments requires an in-depth understanding of the early stage of the aging processes.In radiation environments with high transmutation helium production rates such as in fusion and spallation applications,even materials with otherwise acceptable radiation stability may suffer from radiation embrittlement related to helium bubble formation.While theoretical modeling of helium-assisted cavity nucleation in pure metals and simple alloys provides some useful guidelines at the atomic scale level,these,however,do not overlap with the size resolution of available experimental techniques.In this study,we employed slow positron beam spectroscopy to characterize the nucleation and growth of nano-scale helium bubbles in martensitic steels strengthened by thermodynamically stable nano-oxide dispersoids.In combination with transmission electron microscopy,we experimentally characterized the evolution of helium bubbles from small clusters of radiation-induced vacancies to large cavities well resolvable by TEM.Superior radiation resistance of oxide-dispersion strengthened steels dominates only in the early stages of bubble evolution,where positron lifetime measurements provide a missing piece of the microstructural puzzle conventionally constructed by TEM.

Development of oxide dispersion strengthened ferritic steels with and without aluminum

Pure Fe, Cr, AI, Ti elemental powders and prealloyed Y203 powder were processed by high energy mechanical milling. The compositions of the mixed powders are designed as Fe-18Cr-0.2Ti-0.35Y2O3 and Fe-18Cr-5Al-0.2Ti-0.35Y2O3 in weight percent. The asmilled powders were consolidated by hot extrusion at 1423 K. The dispersed oxide particles were identified to be titania ＋ yttria for Al-free oxide dispersion strengthened （ODS） steel and alumina ＋ yttria for Al-added ODS steel, respectively. The ultimate tensile strength of Al-free ODS steel was higher than that of Al-added ODS steel over the temperature range of 298-973 K, because of the difference in number density and size of thermally stable oxide particles dispersed in both steel matrices. The strength in the longitudinal direction was lower than that in the transverse direction, probably due to anisotropy of the microstructure with elongated grains in the hot-extrusion direction for the 18%Cr-ODS steels with and without 5% Al.

Current state and prospect on the development of advanced nuclear fuel system materials:A review

The intricate balance between reactor economics and safety necessitates the emergence of new and advanced nuclear systems and,very importantly,advanced materials,which can overcome current shortcomings and bring about more economic nuclear systems with designed-in inherent safety features.These advances will achieve greater safety and better nuclear reactor economics by reaching longer reactor lives with higher levels neutron irradiation,and by providing higher operation temperatures and resistance to more aggressive corrosive environments.This paper provides a review of the current state of research and development on innovative nuclear fuel materials design and development which have the potential of benefiting simultaneously reactor economics and safety.Our discussion focuses on three areas of research:Accident-tolerant Fuels(ATFs),Oxidation Dispersion Strengthened(ODS)steels and High Entropy Alloys(HEAs).The paper also gives a prospective description of future research activities on these materials.

Residual Ferrite Control of 9Cr ODS Steels by Tailoring Reverse Austenite Transformation

By tailoring the reverse austenite transformation behavior of 9 Cr oxide dispersion strengthened(ODS)ferritic/martensitic steels,the residual ferrite in ODS steels can be controlled.The reverse austenite transformation behavior of ODS steels is closely related to the initial microstructure conditions prior to austenite transformation.For the spark plasma sintered steels,both the amount and size of residual ferrite decrease with increasing heating rate.Nevertheless,high heating rate will increase the amount and size of residual ferrite in annealed ODS steels.As an isothermal treatment is performed at temperatures above Ac 1,lower isothermal temperature has a more evident effect on the ferrite distribution in spark plasma sintered steels than that in annealed ones.

A review of friction stir welding of steels： Tool, material flow, microstructure, and properties

Considerable progress has been achieved in friction stir welding （FSW） of steels in every aspect of tool fab- rication, microstructure control and properties evaluation in the past two decades. With the development of reliable welding tools and precise control systems, FSW of steels has reached a new level of technical maturity. High-quality, long welds can be produced in many engineering steels. Compared to traditional fusion welding, FSW exhibits unique advantages producing joints with better properties. As a result of active control of the welding temperature and/or cooling rate, FSW has the capability of fabricating steel joints with excellent toughness and strength. For example, unfavorable phase transformations that usu- ally occur during traditional welding can be avoided and favorable phase fractions in advanced steels can be maintained in the weld zone thus avoiding the typical property degradations associated with fusion welding. If phase transformations do occur during FSW of thick steels, optimization of microstructure and properties can be attained by controlling the heat input and post-weld cooling rate.