Influence of nano-Al_2O_3-reinforced oxide-dispersion-strengthened Cu on the mechanical and tribological properties of Cu-based composites

The mechanical and tribological properties of Cu-based powder metallurgy （P/M） friction composites containing 10wt%-50wt% oxide-dispersion-strengthened （ODS） Cu reinforced with nano-Al2O3 were investigated. Additionally, the friction and wear behaviors as well as the wear mechanism of the Cu-based composites were characterized by scanning electron microscopy （SEM） in conjunction with energy-dispersive X-ray spectroscopy （EDS） elemental mapping. The results indicated that the Cu-based friction composite containing 30wt% ODS Cu exhibited the highest hardness and shear strength. The average and instantaneous friction coefficient curves of this sample, when operated in a high-speed train at a speed of 300 km/h, were similar to those of a commercial disc brake pad produced by Knorr-Bremse AG （Germany）. Additionally, the lowest linear wear loss of the obtained samples was （0.008 ± 0.001） mm per time per face, which is much lower than that of the Knorr-Bremse pad （（0.01 ± 0.001） mm）. The excellent performance of the developed pad is a consequence of the formation of a dense oxide composite layer and its close combination with the pad body.

Influences of oxide content and sintering temperature on microstructures and mechanical properties of intragranular-oxide strengthened iron alloys prepared by spark plasma sintering

How to increase strength without sacrificing ductility has been developed as a key goal in the manufacture of high-performance metals or alloys. Herein, the double-nanophase intragranular yttrium oxide dispersion strengthened iron alloy with high strength and appreciable ductility was fabricated by solution combustion route and subsequent spark plasma sintering, and the influences of yttrium oxide content and sintering temperature on microstructures and mechanical properties were investigated. The results show at the same sintering temperature,with the increase of yttrium oxide content, the relative density of the sintered alloy decreases and the strength increases. For Fe–2wt%Y_(2)O_(3)alloy, as the sintering temperature increases gradually, the compressive strength decreases, while the strain-to-failure increases. The Fe–2wt%Y_(2)O_(3)alloy with 15.5 nm Y_(2)O_(3)particles uniformly distributed into the 147.5 nm iron grain interior sintered at 650℃ presents a high ultimate compressive strength of 1.86 GPa and large strain-to-failure of 29%. The grain boundary strengthening and intragranular second-phase particle dispersion strengthening are the main dominant mechanisms to enhance the mechanical properties of the alloy.

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.

Microstructural Features and Properties of High-hardness and Heat-resistant Dispersion Strengthened Copper by Reaction Milling

The oxide dispersion strengthened copper alloys are attractive due to their excellent combination of thermal and electrical conductivities,high-temperature strength and microstructure stability.To date,the state-of-art to fabrication of them was the internal oxidation （IO） process.In this paper,alumina dispersion strengthened copper （ADSC） powders of nominal composition of Cu-2.5 vol%Al2O3 were produced by reaction milling （RM） process which was an in-situ gas-solid reaction process.The bulk ADSC alloys for electrical and mechanical properties investigation were obtained by sintering and thereafter hot extrusion.After the hot consolidation processes,the fully densified powder compacts can be obtained.The single γ-Al2O3 phase and profile broaden effects are evident in accordance with the results of X-ray diffraction （XRD）;the HRB hardness of the ADSC can be as high as 95;the outcomes should be attributed to the pinning effect of nano γ-Al2O3 on dislocations and grain boundaries in the copper matrix.The electrical conductivity of the ADSC alloy is 55%IACS （International Annealing Copper Standard）.The room temperature hardness of the hot consolidated material was approximately maintained after annealing for 1 h at 900 ℃ in hydrogen atmosphere.In terms of the above merits,the RM process to fabricating ADSC alloys is a promising method to improve heat resistance,hardness,electrical conductivity and wear resistance properties etc.

Effects of dispersoid preforming via multistep sintering of oxide dispersion-strengthened CoCrFeMnNi high-entropy alloy

Dispersoid formation and microstructural evolution in an oxide dispersion-strengthened CoCrFeMnNi high-entropy alloy(HEA)using a newly designed multistep sintering process are investigated.The proposed multistep sintering consists of a dispersoid preforming heat treatment of as-milled 0.1 wt%Y_(2)O_(3)-CoCrFeMnNi high-entropy alloy powders at 800℃,followed by sintering at 800–1000℃ under uniaxial pressure.In the conventional single-step sintered bulk,the coarsened BCC Y_(2)O_(3)dispersoids mainly form with an incoherent interface with the HEA matrix.In contrast,finer FCC Y_(2)O_(3)dispersoids,an atypical form of Y_(2)O_(3),are formed in the matrix region after multistep sintering.Nucleation of FCC Y_(2)O_(3)disper-soids is initiated on the favorable facet,the{111}plane of the austenitic matrix,with the formation of a semi-coherent interface with the matrix during the dispersoid preforming heat treatment and it maintains its refined size even after sintering.It is found that dispersoid preforming prior to sintering appears promising to control the finer dispersoid formation and refined grain structure.

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.

Relationship of the Yttrium Compounds with the Alloying Method in ODS Ferritic Stainless Steel

The relationship of the yttrium compounds with its alloying method has been studied, the alloying methods studied including MA and CA (Mechanical Alloying and Chemical Alloying). The results show that the compound in CA steel is Y2Ti2O7 but that in MA steel is Y2O3. The statistical analysis confirms that the titanium contents in the two compounds are different apparently. However, the yttrium content maintains constant.

NICKEL-BASE ALLOY SHEET ALLOYS USED IN AEROSPACE APPLICATIONS

Many gas turbine components are made from nickel alloy sheet. Most are used for directing or containing gases at high temperatures and pressures where metal temperatures can be as high as 1090℃ (2000°F). These applications included combustor systems, casings and liners, transition and exhaust ducting, afterburners, and thrust reversere. Light weight components and sub-assemblies call for alloy sheet with high levels of stength and oxidation resistance. Complex component design calls for excellent ductility and ease of fabrication.The wide range of nickel alloy sheet alloys presently used in aircraft and land-based gas turbines is briefly described and typical properties presented. New sheet alloy developments, involving INCONEL￣* alloys 625LCF, 718SPF and MA754, are presented including the process routes involved and material properties.

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.

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.

Effect of Silicon and Aluminum Addition on Corrosion Behavior of ODS Iron-Based Alloys in Liquid Lead–Bismuth Eutectic

The long-term corrosion behaviors of four variants of oxide dispersion strengthened(ODS)iron-based alloys in the stagnant oxygen-saturated lead–bismuth eutectic(LBE)at 550℃ were studied herein.The effects of silicon and aluminum content on the thickness,morphology and composition of the oxide scale were explored with the aid of X-ray diffraction(XRD),scanning electron microscopy(SEM),electron probe micro-analyzer(EPMA)and X-ray photoelectron spectroscopy(XPS).The addition of 1.5 wt%silicon is not able to contribute to forming a protective external silicon oxide film on the surface of aluminum-free ODS iron-based alloy,while the addition of aluminum promotes the formation of a thin and continuous alumina oxide scale.In the meantime,an appropriate amount of silicon becomes the heterogeneous nucleation site for alumina during the initial stage of oxidation,giving rise to the rapid formation of a protective alumina scale.However,excessive silicon has a negative impact on the formation of continuous alumina scale,because it may compete with aluminum to absorb more oxygen.The result of oxidation kinetics in ODS iron-based alloy shows that the parabolic rate constant of the alumina oxide scale is 3–4 orders of magnitude lower than that of the scale mainly composed of iron and chromium oxide.

Hot deformation behavior and microstructure features of FeCrAl-ODS alloy

The hot deformation behavior of FeCrAl-ODS alloys at temperatures of 1050-1200℃ and strain rates of 0.001-1 s^(-1),investigated.The peak stress of FeCrAl-ODS alloy during hot deformation decreased with increasing temperature and decreasing strain rate.In addition,the stress-strain curves show a dynamic softening phenomenon according to the shape of the flow curves.Based on the Arrhenius-type model,a constitutive equation and processing map of FeCrAl-ODS alloy were established.Thereafter,we proposed optimum processing parameters of 1200℃ and 0.001 s^(-1)based on the processing map.Compared with FeCrAl alloys,there was no significant phenomenon of grain coarsening during hot deformation in FeCrAl-ODS alloy.In the electron backscattered diffraction images,both recrystallized and recovered grains were observed in the matrix under dfferent deformation conditions.The fraction of dynamically recrystallized grains in the matrix under the deformation of 1100 C/0.001 s^(-1)(42.5%)was significantly higher than that at 1200℃/0.001 s^(-1)(10.6%),which was consistent with the stress-strain curves.

Microstructure and mechanical property of NbTaTiV refractory high-entropy alloy with different Y_(2)O_(3) contents

In this study,NbTaTiV refractory high-entropy alloys(RHEAs) reinforced with dispersed oxides were successfully designed and fabricated by mechanical alloying and subsequent spark plasma sintering(SPS).The effects of Y_(2)O_(3) content on the microstructure and mechanical properties have been systematically studied.The results show that the oxide dispersion strengthening(ODS) RHEAs are mainly composed of body centered cubic(BCC) matrix and multiscale oxides,including submicron Ti-(N,O) particles,nano-sized Y-Ti-O particles and nano-sized Y_(2)O_(3) particles.The ODS-RHEAs have excellent mechanical properties due to the multisc ale oxides.With the content of Y_(2)O_(3) increasing from 1 wt% to 3 wt% Y_(2)O_(3),the compressive yield strength of the ODSRHEAs significantly increases from 1528 to 1866 MPa,while the fracture strain slightly reduces from 22% to 16%.The enhancement of the mechanical property is mainly attributed to the increased amount of multisc ale oxide particles and the refined grain structure.

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.

The effects of Y pre-alloying on the in-situ dispersoids of ODS Co Cr Fe Mn Ni high-entropy alloy

Oxide dispersion strengthened CoCrFeMnNi high-entropy alloys(ODS-HEAs)were prepared using two different powder preparation methods classified by yttrium addition strategy to investigate the effects of in-situ and ex-situ oxide dispersoid formation on the microstructure and mechanical properties.Systematic micro structural analysis was carried out by X-ray diffraction(XRD),electron backscattered diffraction(EBSD),high-resolution transmission electron microscopy(HRTEM),atom probe tomography(APT),and small-angle neutron scattering(SANS).Cryo-milled powder analysis,grain structure evolution after spark plasma sintering,dispersoid characteristics,and matrix/dispersoid interface structure analysis of the insitu and ex-situ dispersoids within the high-entropy alloy(HEA)matrix were performed.The in-situ dispersoid formation was dominantly observed in the Y-alloyed ODS-HEA through the construction of a coherent interface relationship with complex chemical composition,leading to an increase in the Zener pinning forces on the grain boundary movement.ODS-HEA with in-situ oxide dispersoids enhanced the formation of ultrafine-grained structures with an average diameter of 330 nm at a sintering temperature of 1173 K.This study shows that the Y pre-alloying method is efficient in achieving fine coherent dispersoids with an ultra fine-grained structure,resulting in an enhancement of the tensile strength of the CoCrFeMnNi HEA.

Thermal stability of additively manufactured austenitic 304L ODS alloy

Thermal stability and high-temperature mechanical properties of a 304 L austenitic oxide dispersion strengthened(ODS)alloy manufactured via laser powder bed fusion(LPBF)are examined in this work.Additively manufactured 304 L ODS alloy samples were aged at temperatures of 1000,1100,and 1200℃for 100 h in an argon atmosphere.Microstructure characterization of LPBF 304 L ODS alloy before and after the thermal stability experiments revealed that despite the annihilation of dislocations,induced cellular substructure by the LPBF process was partially retained in the ODS alloy even after aging at1200℃.The size of Y-Si-O nanoparticles after aging at 1200℃increased from 25 to 50 nm.EBSD analysis revealed that nanoparticles retained the microstructure of LPBF 304 L ODS and hindered recrystallization and further grain growth.At 600℃and 800℃,the yield stress of the 290 and 145 MPa were measured,respectively,which are substantially higher than 113 MPa,and 68 MPa for 304 L at the same temperatures.Furthermore,the creep properties of LPBF 304 L ODS alloy were evaluated at a temperature of 700℃under three applied stresses of 70,85,and 100 MPa yielding a stress exponent(n)of 7.7;the minimum creep rate at 100 MPa was found to be about two orders of magnitude lower than found in the literature for wrought 304 L stainless steel.

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.