Effects of various rare earth oxides on morphology and size of oxide dispersion strengthening(ODS)-W and ODS-Mo alloy powders

Ultrafine oxide dispersion strengthening(ODS)-Mo and ODS-W alloy powders containing different types of oxide nanoparticles were successfully synthesized by spraying method(solid−liquid mixing method)combined with the reductions with carbon black and hydrogen in sequence.It is concluded that the solution concentration and type of rare earth oxide have no effect on the grain size of ODS-Mo alloy powder,but have obvious effect on that of ODS-W alloy powder.The higher the concentration of rare earth solution is,the smaller the average grain size of ODS-W alloy powder is.Furthermore,compared with doping with CeO_(2),the grain sizes of reduction products of La_(2)O_(3) and Y_(2)O_(3) doped WO_(3) are relatively larger.Compared with the undoped case,there is almost no change for grain size of ODS-Mo alloy powder,while the grain size of ODS-W alloy powder becomes much larger.This is probably due to the appearance of the composite oxide(such as La_(2)WO_(6))formed by the reaction between tungsten oxide and rare earth oxides,which promotes the heterogeneous nucleation and growth of tungsten grains during the reduction process of ODS-W,while there is no complex oxide composed of molybdenum and rare earth oxides in the reduction process of ODS-Mo.

Discrete dislocation plasticity analysis of dispersion strengthening in oxide dispersion strengthened(ODS) steels

A discrete dislocation plasticity analysis of dispersion strengthening in oxide dispersion strengthened(ODS) steels was described. Parametric dislocation dynamics(PDD) simulation of the interaction between an edge dislocation and randomly distributed spherical dispersoids(Y2O3) in bcc iron was performed for measuring the influence of the dispersoid distribution on the critical resolved shear stress(CRSS). The dispersoid distribution was made using a method mimicking the Ostwald growth mechanism. Then, an edge dislocation was introduced, and was moved under a constant shear stress condition. The CRSS was extracted from the result of dislocation velocity under constant shear stress using the mobility(linear) relationship between the shear stress and the dislocation velocity. The results suggest that the dispersoid distribution gives a significant influence to the CRSS, and the influence of dislocation dipole, which forms just before finishing up the Orowan looping mechanism, is substantial in determining the CRSS, especially for the interaction with small dispersoids. Therefore, the well-known Orowan equation for determining the CRSS cannot give an accurate estimation, because the influence of the dislocation dipole in the process of the Orowan looping mechanism is not accounted for in the equation.

Study on two-phase cloud dispersion from liquefied CO_(2) release

The knowledge of two-phase cloud dispersion mechanism from HLG(hazardous liquefied gas) release is the prerequisite for accurate assessment and precise rescue of such accidents. In this paper, an experiment of two-phase cloud dispersion from liquefied CO_(2) hole release is performed. The source terms, such as vapour mass fraction, release velocity and mean droplet diameter, are calculated based on thermodynamic theory. Taking phase transition of CO_(2) droplets to gas into account, CFD(computational fluid dynamics) model for two-phase cloud dispersion is established. The predicted cloud temperatures at the downstream agree well with the experimental data, with the maximum relative error of 5.8% and average relative error of 2.3%. The consequence distances in the downstream direction and in the crosswise direction calculated through two-phase model are larger than those through single-phase model,with the relative differences of 57.8% and 53.6% respectively. CO_(2) concentration calculated by twophase model is smaller in the vicinity of release hole, and larger beyond 0.135 m downstream. A smaller leakage rate results in a lower CO_(2) concentration and a higher cloud temperature.

A New Dispersion-strengthening Phase in an Aged RST Al-8Fe-2Mo-2Zr-2Nd-0.7Ti-1.6Si Alloy

An effective dispersion-strengthening phase in Al-8Fe-2Mo-2Zr-2Nd-0.7Ti-1.6Si alloy was identified to be an aged precipitate phase with possible chemical stoichiometry of Al_(20)(Ti,Mo)_2 Nd and fcc crystal structure with a_o=1.455 nm.The structure was determined to be Fm3m space group.

Microstructure evolution of alumina dispersion strengthened copper alloy deformed under different conditions

Microstructure and texture evolution of Cu-0.23%Al2O3 dispersion strengthened copper alloy, deformed at room temperature or cryogenic temperature, were investigated. The main textures in hot-extruded specimen were Brass {011} 〈211〉 and Cube {100} 〈100〉. Textures of Brass {011} 〈211〉 and Goss {011} 〈100〉 were observed in specimen after deformation at room temperature; while textures of Brass {011} 〈211〉, Goss {011} 〈100〉 and S {123} 〈634〉 were detected after deformation at cryogenic temperature. It is believed that the additional Al2O3 nanoparticles can result in dislocation pinning effect, which can further lead to the suppression of dislocations cross-slip. While in the specimen deformed at cryogenic temperature, both pinning effect and cryogenic temperature are responsible for the formation of Brass, Goss and S textures.

High temperature mechanical behavior of alumina dispersion strengthened copper alloy with high content of alumina

The microstructure and its effects on the high temperature mechanical behavior of Cu-2.7%Al_2O_3 （volume fraction） dispersion strengthened copper （ADSC） alloy were investigated. The results indicate that fine alumina particles are uniformly distributed in the copper matrix, while a few coarse ones are distributed on the grain boundaries. Tensile tests results show that Hall-Petch mechanism is the main contribution to the yield strength of ADSC alloy at room temperature. Its high temperature strength is attributed to the strong pinning effects of alumina particles on the grain and sub-grain boundaries with dislocations. The ultimate tensile strength can reach 237 MPa and the corresponding yield strength reaches 226 MPa at 700℃. Tensile fracture morphology indicates that the ADSC alloy shows brittleness at elevated temperatures. Creep tests results demonstrate that the steady state creep rates at 400 ℃ are lower than those at 700 ℃. The stress exponents at 400 ℃ and 700℃ are 7 and 5, respectively, and the creep strain rates of the ADSC alloy are controlled by dislocation core diffusion and lattice diffusion.

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.

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.

Microstructure and compression properties of fine Al2O3 particles dispersion strengthened molybdenum alloy

The Mo alloys reinforced by Al2O3 particles were fabricated by hydrothermal synthesis and powder metallurgy. The microstructures of Mo-Al2O3 alloys were studied by using XRD, SEM and TEM. The results show that Al2O3 particles, existing as a stable hexagonal phase(α-Al2O3), are uniformly dispersed in Mo matrix. The ultrafine α-Al2O3 particles remarkably refine grain size and increase dislocation density of Mo alloys. Moreover, a good interfacial bonding zone between α-Al2O3 and Mo grain is obtained. The crystallographic orientations of the interface of the Al2O3 particles and Mo matrix are [111]a-Al2O3//[111]Mo and(112)a-Al2O3//(0 11)Mo. Due to the effect of secondary phase and dislocation strengthening, the yield strength of Mo-2.0 vol.%Al2O3 alloy annealed at 1200 ℃ is approximately 56.0% higher than that of pure Mo. The results confirm that the addition of Al2O3 particles is a promising method to improve the mechanical properties of Mo alloys.

Fabrication,microstructures and mechanical properties of ZrO_2 dispersion-strengthened Q345 steel

ZrO2 dispersion-strengthened Q345 steel with different ZrO2 contents（0%, 0.5% and 1.2%, mass fraction） was fabricated through combining middle frequency induction furnace melting and cored-wire injection technologies. The microstructure and fracture surface morphology of ZrO2 dispersion-strengthened Q345 steel in casting, normalizing and quenching states were observed using optical microscopy, scanning electron microscopy and transmission electron microscopy. Also, strengthening and fracture mechanisms of the alloys were analyzed. Results showed that the dispersed ZrO2 particles added into Q345 matrix significantly enhanced its strength, and the main strengthening mechanism was the formation of dislocation cells and pinning effect caused by the addition of ZrO2 particles. Apart from that, the hard martensite phase, grain refinement and high ZrO2 particles content also played important roles in strengthening effect. Furthermore, the nanoindentation was also performed to further reveal the strengthening effect and mechanism of dispersed ZrO2 particles in Q345 steel. Results showed that the hardness of ZrO2 dispersion-strengthened Q345 steel increased with the increase of ZrO2 content.

Comparison study on the annealing behaviors of dispersion strengthened copper alloys with different nanoparticles

The hardness measurement,optical microscopy （OM）,and transmission electron microscopy （TEM） microstructure observation on the annealing behaviors of Cu-Al2O3 （2.25 vol.% and 0.54 vol.% Al2O3） and Cu-0.52vol.%Nb alloys were carried out. The results show that with the increase of annealing temperature,the hardness of Cu-Al2O3 alloys decreases slowly. No change of the fiber structure formed by cold rolling in the Cu-2.25vol.%Al2O3 alloy is observed even after annealing at 900℃and the higher dislocation density can still be observed by TEM. Less combination of fiber formed by cold rolling and subgrains are observed in the Cu-0.54vol.%Al2O3 alloy annealed at 900℃. With the increase of annealing temperature,the hardness of the Cu-0.52vol.%Nb alloy exhibits a general decreasing trend,and its falling rate is higher than that of the Cu-Al2O3 alloys,indicating that its ability of resistance to softening at elevated temperature is weaker than that of the Cu-Al2O3 alloys. However,when annealed at a temperature of 300-400℃,probably owing to the precipitation strengthening of niobium,the hardness of the Cu-0.52vol.%Nb alloy arises slightly. The fibers formed by cold rolling be-come un-clear and un-straight and have less combination,and considerably more subgrains are observed by TEM.

Influence of nano-scaled dispersed second phase on substructure of deformed dispersion strengthened copper alloy

The deformation behavior of dispersion strengthened copper alloy Cu-Al2O3 was studied by TEM. The results show that nano-scaled dispersed second phase not only increases dislocation density in matrix, but also has an important influence on the dislocation substructure. The presence of fine dispersed Al2 O3 particles results in a uniform and random dislocation distribution in matrix copper and causes the difficulty in formation of dislocation cell structure and the decrease in the amount of cell structure during deformation. Deformation gives rise to much more dislocations and dislocation cells form more difficultly and the decrease in the cell size with the increase of dispersion degree.

Microstructures and properties of Al_2O_3 dispersion-strengthened copper alloys prepared through different methods

Al2O3 dispersion copper alloy powder was prepared by intemal oxidation, and three consolidation methods--high-velocity compaction （HVC）, hot pressing （HP）, and hot extrusion （HE）--were used to prepare Al2O3 dispersion-strengthened copper （Cu-Al2O3） alloys. The microstructures and properties of these alloys were investigated and compared. The results show that the alloys prepared by the HP and HE methods exhibited the coarsest and finest grain sizes, respectively. The alloy prepared by the HVC method exhibited the lowest relative density （98.3% vs. 99.5% for HP and 100% for HE）, which resulted in the lowest electrical conductivity （81% IACS vs. 86% IACS for HP and 87% IACS for HE）. However, this alloy also exhibited the highest hardness （77 HRB vs. 69 HRB for HP and 70 HRB for HE）, the highest compressive strength （443 MPa vs. 386 MPa for I/P and 378 MPa for HE）, and the best hardness retention among the investigated alloys. The results illustrate that the alloy prepared by the HVC method exhibits high softening temperature and good mechanical properties at high temperatures, which imply long service life when used as spot-welding electrodes.

Study on WC dispersion-strengthened copper

Dispersion-strengthened copper (DSC) with WC as dispersoid was prepared bymeans of mechanical alloying (MA) following the traditional powder metallurgy (P/M) route. Influenceof WC content on the properties of material was discussed in detail, and result shows that when thevolume fraction of WC is 1.6%, the material achieves the best overall property, and a little moreparticle addition led to a less superior property owing to occurrence of particle agglomeration. Theas-sintered composite was designed to undergo a deformation of 75%. It is proved that appropriatedeformation is helpful to attain a higher density and consequently better properties. Deformedmaterial was then exposed to elevated temperature to test its effect on material. Annealing for 1 hat 1173K caused material to recover quite completely, but no obvious recrystallization was observed.It's supposed the particles handicaps motion of dislocations and material demonstrates goodretention of strength with substantial improvement in elongation.

Influence of annealing treatment on properties and microstructures of alumina dispersion strengthened copper alloy

Alumina dispersion strengthened copper（ADSC） alloy was produced by internal oxidation. The hardness, ultimate tensile strength and electrical conductivity measurements and microstructure observation on the produced 0.12%ADSC （0.24% Al2O3, mass fraction） and 0.25%ADSC （0.50% Al2O3） subjected to different annealing treatments were conducted. The results show that the microstructure of the produced ADSC is characterized by an uniform distribution of nano-Al2O3 particles in Cu-matrix; the particles range in size from 20 to 50 nm with an interparticle spacing of 30100 nm. The produced 0.12%ADSC can maintain more than 87% hardness retention after 900 ℃, 1 h annealing treatment; the recrystallization can be largely retarded and is not fully completed even after annealing at 1 000 ℃ for 1 h, followed by cold deformation of 84%; local grain growth can be observed after 1 050 ℃, 1 h annealing treatment. The results also show that increasing either the alumina content or cold deformation degree increases the hardness of the produced ADSC.

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.

Fabrication and properties of low oxygen grade Al_2O_3 dispersion strengthened copper alloy

The low oxygen grade Al 2O 3 dispersion strengthened copper alloy without hydrogen fired expansion was fabricated by the technique of vacuum hot press and hot extrusion. The mechanical and electrical properties measurements and microstructures observation on as hot extruded, as cold drawn and as annealed Cu Al 2O 3 alloy were conducted. The results show that the addition of a suitable amount of boron in the alloy can lower the residual free oxygen content and then inhibit the hydrogen fired expansion. The density, σ b, σ 0.2 , hardness, δ and electrical conductivity of the alloy reach 8.86 g/cm 3(relative density of 99.6%), 340 MPa, 250 MPa, HB95, 24% and 93%(IACS) respectively after hot extruded with the extrusion ratio of 30∶1. Its properties have no change after annealed at 900 ℃ for 1 h. Its strength increases after cold drawing, while its ductility and electrical conductivity drop gradually. Various properties of the cold drawn alloy can recover to those of as extruded after annealed at 900 ℃ for 1 h without the occurrence of recrystallization.

Effect of cold rolling on properties and microstructures of dispersion strengthened copper alloys

Mechanical properties and microstructures of unidirectionally and tandem rolled alumina dispersion strengthened copper(ADSC)alloys under different conditions were investigated by tensile test,optical microscopy(OM),transmission electron microscopy(TEM)and scanning electron microscopy(SEM).For unidirectionally rolled ADSC alloys,their strengths and elongations in the longitudinal direction are higher than those in the transverse direction under both cold rolling and annealing conditions.Once fracture appears in their longitudinal stress—strain curves,sudden reduction of overall stress level before complete fracture can be observed in the transverse tensile curves.The anisotropy of mechanical properties for the ADSC alloy can be greatly improved by tandem cold rolling.And no sudden reduction of overall stress level appears in the stress—strain curves for tandem rolled ADSC alloys.The differences of their microstructures and tensile fractures were analyzed.In order to compare the differences of tensile fracture mechanism in different directions,longitudinal and transverse fracture models for unidirectionally rolled ADSC alloys were also introduced.

Deformation behavior of dispersion-strengthened copper at high temperature

The deformation behavior of dispersion-strengthened copper with different compositions was investigated by hot compression simulation tests on a Gleeble-1500 thermal-mechanical simulator. The microstructure during deformation at high temperature was also studied. The result shows that at the beginning of hot compression simulation, the flowing stress of the dispersion-strengthened copper quickly attains a peak value and the stress shows a greater decrease when the temperature is higher and the strain rate is lower. The dispersion particles lead to an obvious increase in the recrystallization temperature. Under experimental conditions, dynamic recovery is the main softening method. The constitutive equation at high temperature of 1.2%Al2O3-0.4%WC/Cu is obtained.