Micro-fluidized bed reactor is a new research method for the reduction of iron ore fines. The reactor is op- erated as a differential reactor to ensure a constant gas concentration and temperature within the reactor v...Micro-fluidized bed reactor is a new research method for the reduction of iron ore fines. The reactor is op- erated as a differential reactor to ensure a constant gas concentration and temperature within the reactor volume. In order to understand the dynamic process of the reduction reaction in micro-fluidized bed, a series of kinetic experi- ments were designed. In the micro fluidized bed, the use of shrinking core model describes the dynamic behavior of reduction of iron ore. And the apparent activation energy is calculated in the range of 700--850 ~C while the initial atmosphere is 100% content of CO.展开更多
The inclined micro-fluidized bed(MFB)can enhance heat and mass transfer rates compared to the vertically aligned counterparts,but the increased significance of surface forces and wall effects may cause poor fluidizati...The inclined micro-fluidized bed(MFB)can enhance heat and mass transfer rates compared to the vertically aligned counterparts,but the increased significance of surface forces and wall effects may cause poor fluidization performance.In this paper,the effects of column inclination and different particle-to-bed ratios(d_(P)/d_(B))on the solid hydrodynamics are investigated in an inclined micro-fluidized bed.The results validated the suitability of using the Ergun equation to predict minimum fluidization velocities due to small deviations between 1.01 and 1.81 times the theoretical values,for a particle-to-bed ratio ranging from 0.025 to 0.165 at inclinations between 0°and 10°.Investigation into the effects on bed expansion behavior showed that the bed contracted with an increase in bed inclination.An unexpected observation during the bed expansion was the appearance of a secondary high voidage region and the appearance of strong circulation patterns with an increase in bed inclination.A detailed analysis of this phenomenon suggested the presence of a critical angle at 6°and 10°for the 85μm particles,4×4 mm bed cross-section and 165μm particles,1×1 mm bed cross-section,respectively.However,the liquid-solid back-mixing was observed due to the modified particle trajectories resulted in the disappearance of the high voidage region.This paper gives new insights into the micro-fluidization behavior in inclined beds thus contributing to the development of micro-fluidized beds and their future applications.展开更多
The fiuidization behavior of Geldart A particles in a gas-solid micro-fluidized bed was investigated by Eulerian-Eulerian numerical simulation. The commonly used Gidaspow drag model was tested first. The simulation sh...The fiuidization behavior of Geldart A particles in a gas-solid micro-fluidized bed was investigated by Eulerian-Eulerian numerical simulation. The commonly used Gidaspow drag model was tested first. The simulation showed that the predicted minimum bubbling velocities were significantly lower than the experimental data even when an extremely fine grid size （of approximately one particle diameter） was used. The modified Gibilaro drag model was therefore tested next. The predicted minimum bubbling velocity and bed voidage were in reasonable agreement with the experimental data available in literature. The experimentally observed regime transition phenomena from bubbling to slugging were also reproduced successfully in the simulations. Parametric studies indicated that the solid-wall boundary conditions had a significant impact on the predicted gas and solid flow behavior.展开更多
The bed-expansion characteristics of liquid-solid micro-fluidized beds were experimentally studied. Bed columns with inner diameters of 0.8, 1.45, and 2.3 mm were fabricated based on capillaries. Five parti- cle sizes...The bed-expansion characteristics of liquid-solid micro-fluidized beds were experimentally studied. Bed columns with inner diameters of 0.8, 1.45, and 2.3 mm were fabricated based on capillaries. Five parti- cle sizes in a range of 22-58 t^m were investigated. Bed-expansion curves were plotted using visually recorded bed-expansion heights. The bed expansion and initial fluidization behavior were compared with predictions for conventional-scale beds, Evident differences are reflected in lower expansion ratios and higher minimum fluidization velocities for micro-fluidized beds. These were attributed to the increase in the internal surface area of the particle beds and specific surface area of wall contact. The wall effect for micro-fluidized beds at higher particle/bed diameter ratios caused higher local voidage and an increase in expansion ratio. Correlations for the exponent and proportional coefficient in the Richardson-Zaki equation for micro-fluidized beds were proposed. The minimum fluidization velocities were correlated using a modification of the Ergun equation.展开更多
A novel two-stage reduction process for synthesis of ultrafine nickel powder with a high purity and low density in a fluidized bed reactor has been developed in this work. The raw ultraflne NiO particles are first pre...A novel two-stage reduction process for synthesis of ultrafine nickel powder with a high purity and low density in a fluidized bed reactor has been developed in this work. The raw ultraflne NiO particles are first pre-reduced using hydrogen at lower temperatures （340-400 ℃）, followed by further reduction at higher temperatures （500-600℃）. The self-agglomeration of Ni particles formed during low-temperature reduction decreases the sintering activity of the newly formed ultrafine Ni particles, leading to good fluidization quality, even for the subsequent high-temperature reduction process. The agglomerated Ni particles have a high Ni content （above 99wt%）, a low density （0.78g/cm^3） and a uniform particle size （approximately 100 μm）. A concept design for a novel two-stage fluidized bed reactor process used to produce high-purity Ni powder was also proposed. This approach may be extended to the synthesis of other ultrafine/nanosized metals or metal oxides through a fluidization method.展开更多
A dual-phase synergistic enhancement method was adopted to strengthen the Al-Mn-Mg-Sc-Zr alloy fabricated by laser powder bed fusion(LPBF)by leveraging the unique advantages of Er and TiB_(2).Spherical powders of 0.5w...A dual-phase synergistic enhancement method was adopted to strengthen the Al-Mn-Mg-Sc-Zr alloy fabricated by laser powder bed fusion(LPBF)by leveraging the unique advantages of Er and TiB_(2).Spherical powders of 0.5wt%Er-1wt%TiB_(2)/Al-Mn-Mg-Sc-Zr nanocomposite were prepared using vacuum homogenization technique,and the density of samples prepared through the LPBF process reached 99.8%.The strengthening and toughening mechanisms of Er-TiB_(2)were investigated.The results show that Al_(3)Er diffraction peaks are detected by X-ray diffraction analysis,and texture strength decreases according to electron backscatter diffraction results.The added Er and TiB_(2)nano-reinforcing phases act as heterogeneous nucleation sites during the LPBF forming process,hindering grain growth and effectively refining the grains.After incorporating the Er-TiB_(2)dual-phase nano-reinforcing phases,the tensile strength and elongation at break of the LPBF-deposited samples reach 550 MPa and 18.7%,which are 13.4%and 26.4%higher than those of the matrix material,respectively.展开更多
A debris flow descending through an erodible convex colluvial bed,originating from a landslide dam and its upstream deposits,can entrain massive amounts of sediment,dramatically increasing the debris flow volume.Most ...A debris flow descending through an erodible convex colluvial bed,originating from a landslide dam and its upstream deposits,can entrain massive amounts of sediment,dramatically increasing the debris flow volume.Most existing erosion models assume that bed sediments are fully saturated,although this condition is rarely observed in nature.Therefore,a thorough understanding of debris flow overtopping erosion on a convex unsaturated bed is crucial for quantifying disaster risk.In this study,we experimentally investigated the effects of sediment composition,specifically coarse-grain size distribution and fine particle content,on the pore pressure evolution and entrainment of debris flows overriding a convex unsaturated colluvial bed.The average entrainment rate at convex sites for continuously graded bed sediment was higher than its discontinuous counterpart.The measured pore pressures within the unsaturated bed sediments were primarily generated by the passing debris flows.Furthermore,it was found that these pressures decreased as the fine particle content increased and the coarse-grain size of the erodible substrates decreased.When the coarse-grain size of the debris flow was smaller than that of the bed sediment,only a portion of the eroded material was entrained by the moving debris flow.In contrast,when the coarse-grain size of the debris flow was equal to or greater than that of the bed sediment,nearly all of the eroded material was entrained.The findings of this study could contribute to the assessment of hazard amplification and inform the design of mitigation and prevention strategies.展开更多
Ecological floating bed is an important biological remediation method for water pollution control.During the removal of excess nutrients and pollutants,changes in environmental factors affect the characteristics of mi...Ecological floating bed is an important biological remediation method for water pollution control.During the removal of excess nutrients and pollutants,changes in environmental factors affect the characteristics of microorganisms in aquatic ecosystems.To understand the influences of ecological floating beds on size-fractionated microorganisms,we investigated the community assembly and nitrogen metabolic characteristics of three size-fractionated microorganism groups in the ecological floating bed area,using 18S rDNA,16S rDNA metabarcoding,and metagenomic sequencing techniques.Firstly,we discovered substantial differences between size-fractionated groups in the diversity and compositions of both microeukaryotic and bacterial communities,as well as the influences of floating beds on specific groups.The floating beds appeared to provide more habitats for heterotrophs and symbiotes while potentially inhibiting the growth of certain phytoplankton(cyanobacteria).Secondly,we observed that microeukaryotic and bacterial communities were predominantly influenced by stochastic and deterministic processes,respectively,and they both exhibited distinct patterns across different size-fractionated groups.Notably,microeukaryotic community assembly demonstrated a greater sensitivity to ecological floating beds,as indicated by an increase in dispersal limitation processes.Finally,the nitrogen metabolism functional genes revealed that microbes associated with large-sized particles played a crucial role in dissimilatory nitrate reduction to ammonium(DNRA)and denitrification processes within the floating bed area,thereby facilitating the removal of excess nitrogen nutrients from the water.In contrast,freeliving microorganisms from small-sized groups were linked mainly to the genes involved in nitrogen assimilation and assimilatory nitrate reduction to ammonium(ANRA)processes.These findings help understand the impact of ecological floating beds on the diversity and functional characteristics of microorganism communities in different size-fractionated groups.展开更多
Turbulent flow over gravel beds in open channels is a fundamental yet complex problem in hydraulic engineering,as flow behavior is highly sensitive to channel geometry and bed roughness.In this study,the Volume of Flu...Turbulent flow over gravel beds in open channels is a fundamental yet complex problem in hydraulic engineering,as flow behavior is highly sensitive to channel geometry and bed roughness.In this study,the Volume of Fluid(VOF)method coupled with the standard k-εturbulence model is employed to simulate air-water interactions over gravel beds,with open boundary conditions capturing realistic channel-atmosphere interactions.Numerical simulations are performed to examine how channel design influences the relationship between the friction factor(f)and the Reynolds number(RN).Velocity and VOF contours indicate peak flow near the inlet,with a maximum velocity of 0.64 m/s.The simulations show strong agreement with theoretical predictions,yielding a correlation coefficient of 0.99 for RN,while f and Chezy’s coefficient(C)reach 0.75 and 0.71,respectively.Comparison with experimental measurements shows deviations of approximately 17% for RN,25% for f,and 12% for C.Moreover,further analysis confirms an inverse linear relationship between f and RN,in accordance with classical models such as Bazin’s curves,the Colebrook equation,and Moody’s approximation.Overall,the results demonstrate that the proposed numerical framework reliably captures flow dynamics over gravel beds,offering a robust tool for hydraulic design and performance assessment of open channels.展开更多
In this paper,a novel method for investigating the particle-crushing behavior of breeding particles in a fusion blanket is proposed.The fractal theory and Weibull distribution are combined to establish a theoretical m...In this paper,a novel method for investigating the particle-crushing behavior of breeding particles in a fusion blanket is proposed.The fractal theory and Weibull distribution are combined to establish a theoretical model,and its validity was verified using a simple impact test.A crushable discrete element method(DEM)framework is built based on the previously established theoretical model.The tensile strength,which considers the fractal theory,size effect,and Weibull variation,was assigned to each generated particle.The assigned strength is then used for crush detection by comparing it with its maximum tensile stress.Mass conservation is ensured by inserting a series of sub-particles whose total mass was equal to the quality loss.Based on the crushable DEM framework,a numerical simulation of the crushing behavior of a pebble bed with hollow cylindrical geometry under a uniaxial compression test was performed.The results of this investigation showed that the particle withstands the external load by contact and sliding at the beginning of the compression process,and the results confirmed that crushing can be considered an important method of resisting the increasing external load.A relatively regular particle arrangement aids in resisting the load and reduces the occurrence of particle crushing.However,a limit exists to the promotion of resistance.When the strain increases beyond this limit,the distribution of the crushing position tends to be isotropic over the entire pebble bed.The theoretical model and crushable DEM framework provide a new method for exploring the pebble bed in a fusion reactor,considering particle crushing.展开更多
As the primary functional component of a fusion reactor,the fusion blanket pebble bed,composed of numerous particles,is crucial for tritium breeding,neutron multiplication,and radiation shielding.Particles within trit...As the primary functional component of a fusion reactor,the fusion blanket pebble bed,composed of numerous particles,is crucial for tritium breeding,neutron multiplication,and radiation shielding.Particles within tritium-breeding pebble beds are subjected to prolonged neutron irradiation,high thermal loads,and strong magnetic fields in fusion environments.Such conditions render them susceptible to pulverization and fragmentation.The resulting fragments and powders migrate and are deposited into the gas channel,driven by the purge gas.The reduction in the effective flow area of the gas increases the flow resistance,resulting in tritium retention,degraded heat transfer,and other adverse effects.These conditions impair the thermodynamic properties of the pebble beds and hinder the self-maintenance of tritium.Limited information exists on powder migration and clogging mechanisms in fusion blanket pebble beds,particularly under diverse physical conditions.The aim of this study was to use a computational fluid dynamics model coupled with the discrete element method(CFD-DEM)to numerically explore powder migration and clogging in pebble beds.The model considers factors such as breeder orientation,purge velocity,powder size distribution,and friction coefficient.We propose two migration and clogging mechanisms.One involves powder with a large particle size,and the other does not.The results indicate that the powder migration velocity progresses through three stages:rapid decay,linear decay,and stability.Pebble-bed clogging manifests in two forms:extensive superficial clogging and uniform internal clogging.Two fitted curves were used to depict the migration and clogging tendencies.The powder size distribution significantly influenced the powder migration.The breeder orientation,powder size,and friction coefficient affected the distribution of the clogging powders.However,the impact of the purge velocity on powder migration and clogging in pebble beds was limited,and this effect varied significantly with different particle size ratios.Based on the analysis,a formula is proposed to characterize the behavior of the powder in the pebble beds.The results of this study can aid in analyzing and predicting powder dynamics in pebble beds.展开更多
Zn's natural degradability and biocompatibility make it a promising candidate for implants,however,its mechanical properties remain insufficient for bone applications.In this study,the performance of Zn was enhanc...Zn's natural degradability and biocompatibility make it a promising candidate for implants,however,its mechanical properties remain insufficient for bone applications.In this study,the performance of Zn was enhanced by developing Zn-Cu alloys via laser powder bed fusion(LPBF).Optimal LPBF parameters for forming stable tracks were achieved by adjusting laser power and scanning speed.Under optimized conditions of 100 W and 100 mm/s,high density(99.58%)Zn-Cu alloys with improved hardness(68.2 HV)and yield strength(160 MPa)were achieved.These improvements are attributed to solid solution strengthening,segregation strengthening,and grain refinement.The Zn-Cu alloys also demonstrated favorable degradation behavior,with a rate of 0.16 mm/year.This degradation is primarily driven by micro-galvanic corrosion between the CuZn 5 phase and Zn matrix,along with refined grains and increased grain boundary density.This work demonstrates a viable strategy for fabricating Zn-based implants with enhanced structural integrity and mechanical performance via LPBF.展开更多
Water storage in the Three Gorges Reservoir in China has increased the regional microseismicity.Bedding-rock landslides,one of the most common slope structures in the Three Gorges Reservoir,are highly prone to sliding...Water storage in the Three Gorges Reservoir in China has increased the regional microseismicity.Bedding-rock landslides,one of the most common slope structures in the Three Gorges Reservoir,are highly prone to sliding under seismic loading.Existing research primarily focuses on the stability of bedding rock landslides under strong earthquakes,while studies on the cumulative damage and long-term stability of bedding rock landslides under high-frequency microseismicity remain immature.In this study,we considered bedding rock landslides under high-frequency microseismicity in the Three Gorges Reservoir area as the research subject and equivalent microseismicity as pre-peak cyclic loading.First,we analyzed the shear strength deterioration of rock mass structural planes under pre-peak cyclic loading conditions and found that the deformation and failure of structural planes involve contact and damage effects.The shear strength of the rock mass structural planes under pre-peak cyclic loading conditions is affected by the confining pressure,loading rate,loading amplitude,and number of loading cycles.Among these factors,the shear strength of the structural planes was the most sensitive to the number of loading cycles.As the number of cycles increased,the rock mass structural planes underwent three stages:stress adjustment(increase in shear strength),fatigue damage(gradual decrease in shear strength),and structural failure(rapid decrease in shear strength).The stability of bedding rock landslides under high-frequency microseismicity was analyzed,revealing that the stability of bedding rock landslides under high-frequency microseismicity can be divided into three stages:short-term enhancement,gradual degradation,and rapid deterioration,exhibiting characteristics of gradual and sudden changes.展开更多
Coke oven gas(COG)and natural gas(NG),both high-calorific by-products derived from the steel industry,have gained prominence as alternative fuels in the sintering process,thereby supporting dual objectives of emission...Coke oven gas(COG)and natural gas(NG),both high-calorific by-products derived from the steel industry,have gained prominence as alternative fuels in the sintering process,thereby supporting dual objectives of emission reduction and carbon neutrality.While existing research on hydrogen-rich gas injection has predominantly concentrated on conventional thin-bed sintering,investigations into its application within thick-bed sintering remain comparatively scarce.Thick-bed sintering,recognized for enhancing energy efficiency and increasing sinter output,encounters challenges such as uneven heat distribution and diminished permeability,which can negatively impact process efficiency and product quality.To address these issues,sinter pot experiments were conducted to assess the effects of NG and COG injection on thick-bed sintering performance.Findings reveal that NG injection in thick beds mirrors the behavior observed in conventional thin-bed sintering,effectively optimizing the process and achieving a carbon reduction potential exceeding 10%.In contrast,COG injection in thick-bed conditions demonstrates notable differences,substantially lowering the solid fuel consumption rate but detrimentally affecting sinter strength and overall production.However,by optimizing the timing of COG injection,it is feasible to improve sinter yield while concurrently reducing solid fuel usage.These outcomes provide valuable insights for the advancement of gas injection technologies in thick-bed sintering,thereby contributing to energy conservation and emission mitigation efforts within the sintering industry.展开更多
The densification characterization,phase constitution,precipitation evolution and mechanical performance of Al−Mg−Sc−Zr alloy processed by laser powder bed fusion(LPBF)were systematically investigated.Moreover,the evo...The densification characterization,phase constitution,precipitation evolution and mechanical performance of Al−Mg−Sc−Zr alloy processed by laser powder bed fusion(LPBF)were systematically investigated.Moreover,the evolution of phase constitution and precipitation behavior after heat treatment were characterized by using X-ray diffraction(XRD)and transmission electron microscope(TEM)analysis.The ultimate tensile strength(UTS)of as-built samples ranged from 396.8 to 414.6 MPa as the scanning speed decreased from 1600 to 1000 mm/s.After post heat treatment,the yield strength(YS)increased to(513.1±1.3)MPa,while the UTS increased from(414.6±5.1)to(539.2±1.5)MPa.The significant improvement of mechanical performance was ascribed to the formation of secondary Al3(Sc,Zr)precipitates.展开更多
Laser remelting(LR)was used as an auxiliary post-treatment process for the Ti6Al4V titanium alloys fabricated by laser powder bed fusion(LPBF).Optical microscope(OM),scanning electron microscope(SEM)and electron back ...Laser remelting(LR)was used as an auxiliary post-treatment process for the Ti6Al4V titanium alloys fabricated by laser powder bed fusion(LPBF).Optical microscope(OM),scanning electron microscope(SEM)and electron back scattering diffraction(EBSD)observations showed that the grains in melted zone(MZ)transformed into equiaxial grains with an average size of 1.31μm,and the grains in heat affected zone(HAZ)were refined.Moreover,the texture intensity dropped significantly from 13.86 to 6.35 in MZ and 10.79 in HAZ.The temperature gradient(G)to solidification rate(R)ratio decreased when the laser scanning speed slowed down to a certain extent in the LR process,which effectively improved the highly preferred orientation and filled the hole defects in the surface of LPBF-Ti6Al4V.Furthermore,the hardness,wear resistance and corrosion resistance of the surface of the LPBF samples were improved by LR treatment.展开更多
As the bed depth increases,sintering yield increases,but the productivity decreases.To reveal the reasons for the decrease in productivity and explore targeted solutions,the bed resistance of mixtures,wet zone,and com...As the bed depth increases,sintering yield increases,but the productivity decreases.To reveal the reasons for the decrease in productivity and explore targeted solutions,the bed resistance of mixtures,wet zone,and combustion zone was analyzed in the laboratory.The results showed that the decreased porosity of mixture resulted in the increased bed resistance by 160.56%when the bed depth increased from 600 to 1000 mm.After improving porosity of 1%by adding loosening bars with optimized size and distribution,the bed resistance decreased,and the productivity increased by 5%.The increase in bed depth increased the thickness of the wet zone from 120 to 680 mm and the resistance from 1.56 to 8.83 kPa.By using a three-stage intensive mixer and pre-adding water for granulation,the moisture of mixture was reduced by 0.6%,and the sintering productivity increased by 4%.Besides,the high bed resistance is mainly caused by the increase in the thickness of the combustion zone from 31.9 to 132.7 mm,and the bed resistance increased from 0.70 to 5.62 kPa.The bed resistance of the combustion zone at 900 mm was increased by 90.51%compared to 700 mm.After optimization of the distribution of coke breeze,the thickness of combustion zone at the lower layer decreased from 132.7 to 106.84 mm and permeability improved significantly.展开更多
To enhance the mechanical properties of Mo alloys prepared through laser powder bed fusion(LPBF),a hot isostatic pressing(HIP)treatment was used.Results show that following HIP treatment,the porosity decreases from 0....To enhance the mechanical properties of Mo alloys prepared through laser powder bed fusion(LPBF),a hot isostatic pressing(HIP)treatment was used.Results show that following HIP treatment,the porosity decreases from 0.27%to 0.22%,enabling the elements Mo and Ti to diffuse fully and to distribute more uniformly,and to forming a substantial number of low-angle grain boundaries.The tensile strength soars from 286±32 MPa to 598±22 MPa,while the elongation increases from 0.08%±0.02%to 0.18%±0.02%,without notable alterations in grain morphology during the tensile deformation.HIP treatment eliminates the molten pool boundaries,which are the primary source for premature failure in LPBFed Mo alloys.Consequently,HIP treatment emerges as a novel and effective approach for strengthening the mechanical properties of LPBFed Mo alloys,offering a fresh perspective on producing high-performance Mo-based alloys.展开更多
Laser additively manufactured(LAM)Ni-based superalloys commonly exhibit low strength and high residual stress in the as-built state,requiring post-heat treatment to improve mechanical properties.We propose a modified ...Laser additively manufactured(LAM)Ni-based superalloys commonly exhibit low strength and high residual stress in the as-built state,requiring post-heat treatment to improve mechanical properties.We propose a modified heat treatment(MHT)process that only involves a single-step aging at 650℃ for 4 h to achieve high strength,high ductility,and low residual stress simultaneously in a laser powder bed fusion(LPBF)-processed Inconel 718(IN718)alloy.The MHT treated alloy exhibits comparable tensile strength(1368 MPa)to the conventional solution plus two-step aging(SA)treated alloy(1398 MPa),while the tensile elongation(∼21.7%for MHT treated alloy and 13.4%for SA treated alloy)is 60%higher and the residual stress(∼195 MPa)is 20%lower than the SA treated alloy.The balanced high performance of the MHT IN718 alloy was mainly attributed to the precipitation of abundantγ’’phase with a size of∼5 nm,while the original nano-sized Laves precipitates and dislocation cells were mostly retained.The finer size and higher fraction ofγ”of the MHT sample mainly result from the dislocation structure and compositional variations in the as-built IN718,which promotes precipitation during aging.The retention of Laves phase,and cellular dislocation network in the MHT alloy also contributes to work hardening during tension and suspends the occurrence of necking.This study unveils a unique strengthening and toughening mechanism in the Ni-based superalloy produced by LAM with the presence of abundant Laves precipitates and provides a simple,low energy-consumption and cost-effective heat treatment route for achieving desirable mechanical properties.展开更多
基金Sponsored by National Natural Science Foundation of China (50834007)
文摘Micro-fluidized bed reactor is a new research method for the reduction of iron ore fines. The reactor is op- erated as a differential reactor to ensure a constant gas concentration and temperature within the reactor volume. In order to understand the dynamic process of the reduction reaction in micro-fluidized bed, a series of kinetic experi- ments were designed. In the micro fluidized bed, the use of shrinking core model describes the dynamic behavior of reduction of iron ore. And the apparent activation energy is calculated in the range of 700--850 ~C while the initial atmosphere is 100% content of CO.
基金supported by Newcastle University(Gant No.LOC/150025720/400382711).
文摘The inclined micro-fluidized bed(MFB)can enhance heat and mass transfer rates compared to the vertically aligned counterparts,but the increased significance of surface forces and wall effects may cause poor fluidization performance.In this paper,the effects of column inclination and different particle-to-bed ratios(d_(P)/d_(B))on the solid hydrodynamics are investigated in an inclined micro-fluidized bed.The results validated the suitability of using the Ergun equation to predict minimum fluidization velocities due to small deviations between 1.01 and 1.81 times the theoretical values,for a particle-to-bed ratio ranging from 0.025 to 0.165 at inclinations between 0°and 10°.Investigation into the effects on bed expansion behavior showed that the bed contracted with an increase in bed inclination.An unexpected observation during the bed expansion was the appearance of a secondary high voidage region and the appearance of strong circulation patterns with an increase in bed inclination.A detailed analysis of this phenomenon suggested the presence of a critical angle at 6°and 10°for the 85μm particles,4×4 mm bed cross-section and 165μm particles,1×1 mm bed cross-section,respectively.However,the liquid-solid back-mixing was observed due to the modified particle trajectories resulted in the disappearance of the high voidage region.This paper gives new insights into the micro-fluidization behavior in inclined beds thus contributing to the development of micro-fluidized beds and their future applications.
基金financial support from the Ministry of Science and Technology of China with Grant No.2011YQ12003909the ongoing support through the startup fund awarded to Xiaoxing Liu from the "Hundred Talents Program" of the Institute of Process Engineering,Chinese Academy of Sciences
文摘The fiuidization behavior of Geldart A particles in a gas-solid micro-fluidized bed was investigated by Eulerian-Eulerian numerical simulation. The commonly used Gidaspow drag model was tested first. The simulation showed that the predicted minimum bubbling velocities were significantly lower than the experimental data even when an extremely fine grid size （of approximately one particle diameter） was used. The modified Gibilaro drag model was therefore tested next. The predicted minimum bubbling velocity and bed voidage were in reasonable agreement with the experimental data available in literature. The experimentally observed regime transition phenomena from bubbling to slugging were also reproduced successfully in the simulations. Parametric studies indicated that the solid-wall boundary conditions had a significant impact on the predicted gas and solid flow behavior.
基金The authors are grateful to the National Natural Science Foundation of China （Contract Nos. 21376168 and 91434204） for financial support.
文摘The bed-expansion characteristics of liquid-solid micro-fluidized beds were experimentally studied. Bed columns with inner diameters of 0.8, 1.45, and 2.3 mm were fabricated based on capillaries. Five parti- cle sizes in a range of 22-58 t^m were investigated. Bed-expansion curves were plotted using visually recorded bed-expansion heights. The bed expansion and initial fluidization behavior were compared with predictions for conventional-scale beds, Evident differences are reflected in lower expansion ratios and higher minimum fluidization velocities for micro-fluidized beds. These were attributed to the increase in the internal surface area of the particle beds and specific surface area of wall contact. The wall effect for micro-fluidized beds at higher particle/bed diameter ratios caused higher local voidage and an increase in expansion ratio. Correlations for the exponent and proportional coefficient in the Richardson-Zaki equation for micro-fluidized beds were proposed. The minimum fluidization velocities were correlated using a modification of the Ergun equation.
基金the National Special Project for Development of Major Scientific Equipment(2011YQ12003908)the China National Funds for Distinguished Young Scientists(21325628) for their financial support
文摘A novel two-stage reduction process for synthesis of ultrafine nickel powder with a high purity and low density in a fluidized bed reactor has been developed in this work. The raw ultraflne NiO particles are first pre-reduced using hydrogen at lower temperatures （340-400 ℃）, followed by further reduction at higher temperatures （500-600℃）. The self-agglomeration of Ni particles formed during low-temperature reduction decreases the sintering activity of the newly formed ultrafine Ni particles, leading to good fluidization quality, even for the subsequent high-temperature reduction process. The agglomerated Ni particles have a high Ni content （above 99wt%）, a low density （0.78g/cm^3） and a uniform particle size （approximately 100 μm）. A concept design for a novel two-stage fluidized bed reactor process used to produce high-purity Ni powder was also proposed. This approach may be extended to the synthesis of other ultrafine/nanosized metals or metal oxides through a fluidization method.
基金Shaanxi Province Qin Chuangyuan“Scientist+Engineer”Team Construction Project(2022KXJ-071)2022 Qin Chuangyuan Achievement Transformation Incubation Capacity Improvement Project(2022JH-ZHFHTS-0012)+8 种基金Shaanxi Province Key Research and Development Plan-“Two Chains”Integration Key Project-Qin Chuangyuan General Window Industrial Cluster Project(2023QCY-LL-02)Xixian New Area Science and Technology Plan(2022-YXYJ-003,2022-XXCY-010)2024 Scientific Research Project of Shaanxi National Defense Industry Vocational and Technical College(Gfy24-07)Shaanxi Vocational and Technical Education Association 2024 Vocational Education Teaching Reform Research Topic(2024SZX354)National Natural Science Foundation of China(U24A20115)2024 Shaanxi Provincial Education Department Service Local Special Scientific Research Program Project-Industrialization Cultivation Project(24JC005,24JC063)Shaanxi Province“14th Five-Year Plan”Education Science Plan,2024 Project(SGH24Y3181)National Key Research and Development Program of China(2023YFB4606400)Longmen Laboratory Frontier Exploration Topics Project(LMQYTSKT003)。
文摘A dual-phase synergistic enhancement method was adopted to strengthen the Al-Mn-Mg-Sc-Zr alloy fabricated by laser powder bed fusion(LPBF)by leveraging the unique advantages of Er and TiB_(2).Spherical powders of 0.5wt%Er-1wt%TiB_(2)/Al-Mn-Mg-Sc-Zr nanocomposite were prepared using vacuum homogenization technique,and the density of samples prepared through the LPBF process reached 99.8%.The strengthening and toughening mechanisms of Er-TiB_(2)were investigated.The results show that Al_(3)Er diffraction peaks are detected by X-ray diffraction analysis,and texture strength decreases according to electron backscatter diffraction results.The added Er and TiB_(2)nano-reinforcing phases act as heterogeneous nucleation sites during the LPBF forming process,hindering grain growth and effectively refining the grains.After incorporating the Er-TiB_(2)dual-phase nano-reinforcing phases,the tensile strength and elongation at break of the LPBF-deposited samples reach 550 MPa and 18.7%,which are 13.4%and 26.4%higher than those of the matrix material,respectively.
基金supported by the National Key R&D Program of China(Grant No.2018YFC1505205)the Science and Technology Research Program of the Institute of Mountain Hazards and Environment,Chinese Academy of Sciences(Grant No.IMHE-ZDRW-01)Sichuan Science and Technology Program(Grant No.2024NSFSC0781).
文摘A debris flow descending through an erodible convex colluvial bed,originating from a landslide dam and its upstream deposits,can entrain massive amounts of sediment,dramatically increasing the debris flow volume.Most existing erosion models assume that bed sediments are fully saturated,although this condition is rarely observed in nature.Therefore,a thorough understanding of debris flow overtopping erosion on a convex unsaturated bed is crucial for quantifying disaster risk.In this study,we experimentally investigated the effects of sediment composition,specifically coarse-grain size distribution and fine particle content,on the pore pressure evolution and entrainment of debris flows overriding a convex unsaturated colluvial bed.The average entrainment rate at convex sites for continuously graded bed sediment was higher than its discontinuous counterpart.The measured pore pressures within the unsaturated bed sediments were primarily generated by the passing debris flows.Furthermore,it was found that these pressures decreased as the fine particle content increased and the coarse-grain size of the erodible substrates decreased.When the coarse-grain size of the debris flow was smaller than that of the bed sediment,only a portion of the eroded material was entrained by the moving debris flow.In contrast,when the coarse-grain size of the debris flow was equal to or greater than that of the bed sediment,nearly all of the eroded material was entrained.The findings of this study could contribute to the assessment of hazard amplification and inform the design of mitigation and prevention strategies.
基金Supported by the National Natural Science Foundation of China(Nos.42141003,42176147)the National Key Research and Development Program of China(No.2022YFF0802204)the Xiamen Key Laboratory of Urban Sea Ecological Conservation and Restoration(USER)(Nos.USER2021-1,USER2021-5)。
文摘Ecological floating bed is an important biological remediation method for water pollution control.During the removal of excess nutrients and pollutants,changes in environmental factors affect the characteristics of microorganisms in aquatic ecosystems.To understand the influences of ecological floating beds on size-fractionated microorganisms,we investigated the community assembly and nitrogen metabolic characteristics of three size-fractionated microorganism groups in the ecological floating bed area,using 18S rDNA,16S rDNA metabarcoding,and metagenomic sequencing techniques.Firstly,we discovered substantial differences between size-fractionated groups in the diversity and compositions of both microeukaryotic and bacterial communities,as well as the influences of floating beds on specific groups.The floating beds appeared to provide more habitats for heterotrophs and symbiotes while potentially inhibiting the growth of certain phytoplankton(cyanobacteria).Secondly,we observed that microeukaryotic and bacterial communities were predominantly influenced by stochastic and deterministic processes,respectively,and they both exhibited distinct patterns across different size-fractionated groups.Notably,microeukaryotic community assembly demonstrated a greater sensitivity to ecological floating beds,as indicated by an increase in dispersal limitation processes.Finally,the nitrogen metabolism functional genes revealed that microbes associated with large-sized particles played a crucial role in dissimilatory nitrate reduction to ammonium(DNRA)and denitrification processes within the floating bed area,thereby facilitating the removal of excess nitrogen nutrients from the water.In contrast,freeliving microorganisms from small-sized groups were linked mainly to the genes involved in nitrogen assimilation and assimilatory nitrate reduction to ammonium(ANRA)processes.These findings help understand the impact of ecological floating beds on the diversity and functional characteristics of microorganism communities in different size-fractionated groups.
文摘Turbulent flow over gravel beds in open channels is a fundamental yet complex problem in hydraulic engineering,as flow behavior is highly sensitive to channel geometry and bed roughness.In this study,the Volume of Fluid(VOF)method coupled with the standard k-εturbulence model is employed to simulate air-water interactions over gravel beds,with open boundary conditions capturing realistic channel-atmosphere interactions.Numerical simulations are performed to examine how channel design influences the relationship between the friction factor(f)and the Reynolds number(RN).Velocity and VOF contours indicate peak flow near the inlet,with a maximum velocity of 0.64 m/s.The simulations show strong agreement with theoretical predictions,yielding a correlation coefficient of 0.99 for RN,while f and Chezy’s coefficient(C)reach 0.75 and 0.71,respectively.Comparison with experimental measurements shows deviations of approximately 17% for RN,25% for f,and 12% for C.Moreover,further analysis confirms an inverse linear relationship between f and RN,in accordance with classical models such as Bazin’s curves,the Colebrook equation,and Moody’s approximation.Overall,the results demonstrate that the proposed numerical framework reliably captures flow dynamics over gravel beds,offering a robust tool for hydraulic design and performance assessment of open channels.
基金supported by Anhui Provincial Natural Science Foundation(2408085QA030)Natural Science Research Project of Anhui Educational Committee,China(2022AH050825)+3 种基金Medical Special Cultivation Project of Anhui University of Science and Technology(YZ2023H2C008)the Excellent Research and Innovation Team of Anhui Province,China(2022AH010052)the Scientific Research Foundation for High-level Talents of Anhui University of Science and Technology,China(2021yjrc51)Collaborative Innovation Program of Hefei Science Center,CAS,China(2019HSC-CIP006).
文摘In this paper,a novel method for investigating the particle-crushing behavior of breeding particles in a fusion blanket is proposed.The fractal theory and Weibull distribution are combined to establish a theoretical model,and its validity was verified using a simple impact test.A crushable discrete element method(DEM)framework is built based on the previously established theoretical model.The tensile strength,which considers the fractal theory,size effect,and Weibull variation,was assigned to each generated particle.The assigned strength is then used for crush detection by comparing it with its maximum tensile stress.Mass conservation is ensured by inserting a series of sub-particles whose total mass was equal to the quality loss.Based on the crushable DEM framework,a numerical simulation of the crushing behavior of a pebble bed with hollow cylindrical geometry under a uniaxial compression test was performed.The results of this investigation showed that the particle withstands the external load by contact and sliding at the beginning of the compression process,and the results confirmed that crushing can be considered an important method of resisting the increasing external load.A relatively regular particle arrangement aids in resisting the load and reduces the occurrence of particle crushing.However,a limit exists to the promotion of resistance.When the strain increases beyond this limit,the distribution of the crushing position tends to be isotropic over the entire pebble bed.The theoretical model and crushable DEM framework provide a new method for exploring the pebble bed in a fusion reactor,considering particle crushing.
文摘As the primary functional component of a fusion reactor,the fusion blanket pebble bed,composed of numerous particles,is crucial for tritium breeding,neutron multiplication,and radiation shielding.Particles within tritium-breeding pebble beds are subjected to prolonged neutron irradiation,high thermal loads,and strong magnetic fields in fusion environments.Such conditions render them susceptible to pulverization and fragmentation.The resulting fragments and powders migrate and are deposited into the gas channel,driven by the purge gas.The reduction in the effective flow area of the gas increases the flow resistance,resulting in tritium retention,degraded heat transfer,and other adverse effects.These conditions impair the thermodynamic properties of the pebble beds and hinder the self-maintenance of tritium.Limited information exists on powder migration and clogging mechanisms in fusion blanket pebble beds,particularly under diverse physical conditions.The aim of this study was to use a computational fluid dynamics model coupled with the discrete element method(CFD-DEM)to numerically explore powder migration and clogging in pebble beds.The model considers factors such as breeder orientation,purge velocity,powder size distribution,and friction coefficient.We propose two migration and clogging mechanisms.One involves powder with a large particle size,and the other does not.The results indicate that the powder migration velocity progresses through three stages:rapid decay,linear decay,and stability.Pebble-bed clogging manifests in two forms:extensive superficial clogging and uniform internal clogging.Two fitted curves were used to depict the migration and clogging tendencies.The powder size distribution significantly influenced the powder migration.The breeder orientation,powder size,and friction coefficient affected the distribution of the clogging powders.However,the impact of the purge velocity on powder migration and clogging in pebble beds was limited,and this effect varied significantly with different particle size ratios.Based on the analysis,a formula is proposed to characterize the behavior of the powder in the pebble beds.The results of this study can aid in analyzing and predicting powder dynamics in pebble beds.
基金Projects(52571276,52275395,U24A20120,52475362)supported by the National Natural Science Foundation of ChinaProject(2025JJ30015)supported by the Hunan Provincial Natural Science Foundation,China+3 种基金Project(2023RC3046)supported by the Science and Technology Innovation Program of Hunan Province,ChinaProject(2023YFB4605800)supported by National Key Research and Development Program of ChinaProject(2023CXQD023)supported by the Central South University Innovation-Driven Research Programme,ChinaProject supported by the State Key Laboratory of Precision Manufacturing for Extreme Service Performance,Central South University,China。
文摘Zn's natural degradability and biocompatibility make it a promising candidate for implants,however,its mechanical properties remain insufficient for bone applications.In this study,the performance of Zn was enhanced by developing Zn-Cu alloys via laser powder bed fusion(LPBF).Optimal LPBF parameters for forming stable tracks were achieved by adjusting laser power and scanning speed.Under optimized conditions of 100 W and 100 mm/s,high density(99.58%)Zn-Cu alloys with improved hardness(68.2 HV)and yield strength(160 MPa)were achieved.These improvements are attributed to solid solution strengthening,segregation strengthening,and grain refinement.The Zn-Cu alloys also demonstrated favorable degradation behavior,with a rate of 0.16 mm/year.This degradation is primarily driven by micro-galvanic corrosion between the CuZn 5 phase and Zn matrix,along with refined grains and increased grain boundary density.This work demonstrates a viable strategy for fabricating Zn-based implants with enhanced structural integrity and mechanical performance via LPBF.
基金sponsored by the General Program of the National Natural Science Foundation of China(Grant No.42407221)the Open Fund of State Key Laboratory of Geohazard Prevention and Geoenvironment Protection(Grant No.SKLGP2024K009)the Hubei Provincial Natural Science Foun-dation,China(Grant No.2023AFB567).
文摘Water storage in the Three Gorges Reservoir in China has increased the regional microseismicity.Bedding-rock landslides,one of the most common slope structures in the Three Gorges Reservoir,are highly prone to sliding under seismic loading.Existing research primarily focuses on the stability of bedding rock landslides under strong earthquakes,while studies on the cumulative damage and long-term stability of bedding rock landslides under high-frequency microseismicity remain immature.In this study,we considered bedding rock landslides under high-frequency microseismicity in the Three Gorges Reservoir area as the research subject and equivalent microseismicity as pre-peak cyclic loading.First,we analyzed the shear strength deterioration of rock mass structural planes under pre-peak cyclic loading conditions and found that the deformation and failure of structural planes involve contact and damage effects.The shear strength of the rock mass structural planes under pre-peak cyclic loading conditions is affected by the confining pressure,loading rate,loading amplitude,and number of loading cycles.Among these factors,the shear strength of the structural planes was the most sensitive to the number of loading cycles.As the number of cycles increased,the rock mass structural planes underwent three stages:stress adjustment(increase in shear strength),fatigue damage(gradual decrease in shear strength),and structural failure(rapid decrease in shear strength).The stability of bedding rock landslides under high-frequency microseismicity was analyzed,revealing that the stability of bedding rock landslides under high-frequency microseismicity can be divided into three stages:short-term enhancement,gradual degradation,and rapid deterioration,exhibiting characteristics of gradual and sudden changes.
基金supported by the National Natural Science Foundation of China(Grant No.52474347)Postdoctoral Science Foundation of China(Grant No.2024T171095)the Fundamental Research Funds for the Central Universities(Grant No.2024CDJXY003).
文摘Coke oven gas(COG)and natural gas(NG),both high-calorific by-products derived from the steel industry,have gained prominence as alternative fuels in the sintering process,thereby supporting dual objectives of emission reduction and carbon neutrality.While existing research on hydrogen-rich gas injection has predominantly concentrated on conventional thin-bed sintering,investigations into its application within thick-bed sintering remain comparatively scarce.Thick-bed sintering,recognized for enhancing energy efficiency and increasing sinter output,encounters challenges such as uneven heat distribution and diminished permeability,which can negatively impact process efficiency and product quality.To address these issues,sinter pot experiments were conducted to assess the effects of NG and COG injection on thick-bed sintering performance.Findings reveal that NG injection in thick beds mirrors the behavior observed in conventional thin-bed sintering,effectively optimizing the process and achieving a carbon reduction potential exceeding 10%.In contrast,COG injection in thick-bed conditions demonstrates notable differences,substantially lowering the solid fuel consumption rate but detrimentally affecting sinter strength and overall production.However,by optimizing the timing of COG injection,it is feasible to improve sinter yield while concurrently reducing solid fuel usage.These outcomes provide valuable insights for the advancement of gas injection technologies in thick-bed sintering,thereby contributing to energy conservation and emission mitigation efforts within the sintering industry.
基金support of the Research and Development Program in Key Areas of Guangdong Province,China(No.2019B090907001)the Science and Technology Program of Guangdong Province,China(No.2014B010129002)the National Key R&D Program of China(No.2017YFB0305800)。
文摘The densification characterization,phase constitution,precipitation evolution and mechanical performance of Al−Mg−Sc−Zr alloy processed by laser powder bed fusion(LPBF)were systematically investigated.Moreover,the evolution of phase constitution and precipitation behavior after heat treatment were characterized by using X-ray diffraction(XRD)and transmission electron microscope(TEM)analysis.The ultimate tensile strength(UTS)of as-built samples ranged from 396.8 to 414.6 MPa as the scanning speed decreased from 1600 to 1000 mm/s.After post heat treatment,the yield strength(YS)increased to(513.1±1.3)MPa,while the UTS increased from(414.6±5.1)to(539.2±1.5)MPa.The significant improvement of mechanical performance was ascribed to the formation of secondary Al3(Sc,Zr)precipitates.
基金supported by the National Natural Science Foundation of China(No.51871243)the National Key Laboratory of Strength and Structural Integrity,China(No.ASSIKFJJ202304001)+3 种基金the State Key Laboratory of Precision Blasting and Hubei Key Laboratory of Blasting Engineering,China(No.PBSKL2022C01)the Guangdong-Hong Kong-Macao Joint Laboratory for Neutron Scattering Science and Technology,China(No.HT-CSNS-DG-CD-0092/2021)the Shock and Vibration of Engineering Materials and Structures Key Laboratory of Sichuan Province,China(No.22kfgk06)the Hubei Longzhong Laboratory,China(No.2022KF-08)。
文摘Laser remelting(LR)was used as an auxiliary post-treatment process for the Ti6Al4V titanium alloys fabricated by laser powder bed fusion(LPBF).Optical microscope(OM),scanning electron microscope(SEM)and electron back scattering diffraction(EBSD)observations showed that the grains in melted zone(MZ)transformed into equiaxial grains with an average size of 1.31μm,and the grains in heat affected zone(HAZ)were refined.Moreover,the texture intensity dropped significantly from 13.86 to 6.35 in MZ and 10.79 in HAZ.The temperature gradient(G)to solidification rate(R)ratio decreased when the laser scanning speed slowed down to a certain extent in the LR process,which effectively improved the highly preferred orientation and filled the hole defects in the surface of LPBF-Ti6Al4V.Furthermore,the hardness,wear resistance and corrosion resistance of the surface of the LPBF samples were improved by LR treatment.
基金supported by the Basic Science Center Project for the National Natural Science Foundation of China(No.72088101)the S&T Program of Hebei(No.23564101D).
文摘As the bed depth increases,sintering yield increases,but the productivity decreases.To reveal the reasons for the decrease in productivity and explore targeted solutions,the bed resistance of mixtures,wet zone,and combustion zone was analyzed in the laboratory.The results showed that the decreased porosity of mixture resulted in the increased bed resistance by 160.56%when the bed depth increased from 600 to 1000 mm.After improving porosity of 1%by adding loosening bars with optimized size and distribution,the bed resistance decreased,and the productivity increased by 5%.The increase in bed depth increased the thickness of the wet zone from 120 to 680 mm and the resistance from 1.56 to 8.83 kPa.By using a three-stage intensive mixer and pre-adding water for granulation,the moisture of mixture was reduced by 0.6%,and the sintering productivity increased by 4%.Besides,the high bed resistance is mainly caused by the increase in the thickness of the combustion zone from 31.9 to 132.7 mm,and the bed resistance increased from 0.70 to 5.62 kPa.The bed resistance of the combustion zone at 900 mm was increased by 90.51%compared to 700 mm.After optimization of the distribution of coke breeze,the thickness of combustion zone at the lower layer decreased from 132.7 to 106.84 mm and permeability improved significantly.
基金National Natural Science Foundation of China(52105385)Stable Support Plan Program of Shenzhen Natural Science Fund(20220810132537001)+2 种基金Guangdong Basic and Applied Basic Research Foundation(2022A1515010781)Joint Fund of Henan Province Science and Technology R&D Program(225200810002)Fundamental Research Funds of Henan Academy of Sciences(240621041)。
文摘To enhance the mechanical properties of Mo alloys prepared through laser powder bed fusion(LPBF),a hot isostatic pressing(HIP)treatment was used.Results show that following HIP treatment,the porosity decreases from 0.27%to 0.22%,enabling the elements Mo and Ti to diffuse fully and to distribute more uniformly,and to forming a substantial number of low-angle grain boundaries.The tensile strength soars from 286±32 MPa to 598±22 MPa,while the elongation increases from 0.08%±0.02%to 0.18%±0.02%,without notable alterations in grain morphology during the tensile deformation.HIP treatment eliminates the molten pool boundaries,which are the primary source for premature failure in LPBFed Mo alloys.Consequently,HIP treatment emerges as a novel and effective approach for strengthening the mechanical properties of LPBFed Mo alloys,offering a fresh perspective on producing high-performance Mo-based alloys.
基金financially supported by the Ministry of Science and Technology of China via the National Key Research&Development Plan(Nos.2022YFB3707105 and 2020YFA0405900)Jiangsu Department of Science and Technology via Provincial Key Research&Development(Industrial Foresight and Key Core Technology,No.BE2021037)+1 种基金Department of the National Science Foundation of China(No.52204390)the Natural Science Foundation of Jiangsu Province(No.BK20202010).
文摘Laser additively manufactured(LAM)Ni-based superalloys commonly exhibit low strength and high residual stress in the as-built state,requiring post-heat treatment to improve mechanical properties.We propose a modified heat treatment(MHT)process that only involves a single-step aging at 650℃ for 4 h to achieve high strength,high ductility,and low residual stress simultaneously in a laser powder bed fusion(LPBF)-processed Inconel 718(IN718)alloy.The MHT treated alloy exhibits comparable tensile strength(1368 MPa)to the conventional solution plus two-step aging(SA)treated alloy(1398 MPa),while the tensile elongation(∼21.7%for MHT treated alloy and 13.4%for SA treated alloy)is 60%higher and the residual stress(∼195 MPa)is 20%lower than the SA treated alloy.The balanced high performance of the MHT IN718 alloy was mainly attributed to the precipitation of abundantγ’’phase with a size of∼5 nm,while the original nano-sized Laves precipitates and dislocation cells were mostly retained.The finer size and higher fraction ofγ”of the MHT sample mainly result from the dislocation structure and compositional variations in the as-built IN718,which promotes precipitation during aging.The retention of Laves phase,and cellular dislocation network in the MHT alloy also contributes to work hardening during tension and suspends the occurrence of necking.This study unveils a unique strengthening and toughening mechanism in the Ni-based superalloy produced by LAM with the presence of abundant Laves precipitates and provides a simple,low energy-consumption and cost-effective heat treatment route for achieving desirable mechanical properties.
