The utilization of iron coke provides a green pathway for low-carbon ironmaking.To uncover the influence mechanism of iron ore on the behavior and kinetics of iron coke gasification,the effect of iron ore on the micro...The utilization of iron coke provides a green pathway for low-carbon ironmaking.To uncover the influence mechanism of iron ore on the behavior and kinetics of iron coke gasification,the effect of iron ore on the microstructure of iron coke was investigated.Furthermore,a comparative study of the gasification reactions between iron coke and coke was conducted through non-isothermal thermogravimetric method.The findings indicate that compared to coke,iron coke exhibits an augmentation in micropores and specific surface area,and the micropores further extend and interconnect.This provides more adsorption sites for CO_(2) molecules during the gasification process,resulting in a reduction in the initial gasification temperature of iron coke.Accelerating the heating rate in non-isothermal gasification can enhance the reactivity of iron coke.The metallic iron reduced from iron ore is embedded in the carbon matrix,reducing the orderliness of the carbon structure,which is primarily responsible for the heightened reactivity of the carbon atoms.The kinetic study indicates that the random pore model can effectively represent the gasification process of iron coke due to its rich pore structure.Moreover,as the proportion of iron ore increases,the activation energy for the carbon gasification gradually decreases,from 246.2 kJ/mol for coke to 192.5 kJ/mol for iron coke 15wt%.展开更多
Brazing filler metals are widely applied,which serve as an industrial adhesive in the joining of dissimilar structures.With the continuous emergence of new structures and materials,the demand for novel brazing filler ...Brazing filler metals are widely applied,which serve as an industrial adhesive in the joining of dissimilar structures.With the continuous emergence of new structures and materials,the demand for novel brazing filler metals is ever-increasing.It is of great significance to investigate the optimized composition design methods and to establish systematic design guidelines for brazing filler metals.This study elucidated the fundamental rules for the composition design of brazing filler metals from a three-dimensional perspective encompassing the basic properties of applied brazing filler metals,formability and processability,and overall cost.The basic properties of brazing filler metals refer to their mechanical properties,physicochemical properties,electromagnetic properties,corrosion resistance,and the wettability and fluidity during brazing.The formability and processability of brazing filler metals include the processes of smelting and casting,extrusion,rolling,drawing and ring-making,as well as the processes of granulation,powder production,and the molding of amorphous and microcrystalline structures.The cost of brazing filler metals corresponds to the sum of materials value and manufacturing cost.Improving the comprehensive properties of brazing filler metals requires a comprehensive and systematic consideration of design indicators.Highlighting the unique characteristics of brazing filler metals should focus on relevant technical indicators.Binary or ternary eutectic structures can effectively enhance the flow spreading ability of brazing filler metals,and solid solution structures contribute to the formability.By employing the proposed design guidelines,typical Ag based,Cu based,Zn based brazing filler metals,and Sn based solders were designed and successfully applied in major scientific and engineering projects.展开更多
The study of the oxygen evolution reaction(OER)mechanism is vital for advancing our understanding of this pivotal energy conversion process.This review synthesizes recent advancements in OER mechanism,emphasizing the ...The study of the oxygen evolution reaction(OER)mechanism is vital for advancing our understanding of this pivotal energy conversion process.This review synthesizes recent advancements in OER mechanism,emphasizing the intricate relationship between catalytic mechanisms and catalyst design.This review discusses the connotation and cutting-edge progress of traditional mechanisms such as adsorbate evolution mechanism(AEM)and lattice oxygen mechanism(LOM)as well as emerging pathways including oxide path mechanism(OPM),oxo-oxo coupling mechanism(OCM),and intramolecular oxygen coupling mechanism(IMOC)etc.Innovative research progress on the coexistence and transformation of multiple mechanisms is highlighted,and the intrinsic factors that influence these dynamic processes are summarized.Advanced characterization techniques and theoretical modeling are underscored as indispensable tools for revealing these complex interactions.This review provides guiding principles for mechanism-based catalyst design.Finally,in view of the multidimensional challenges currently faced by OER mechanisms,prospects for future research are given to bridge the gap between mechanism innovation and experimental verification and application.This comprehensive review provides valuable perspectives for advancing clean energy technologies and achieving sustainable development.展开更多
The excavation of deep tunnels crossing faults is highly prone to triggering rockburst disasters,which has become a significant engineering issue.In this study,taking the fault-slip rockbursts from a deep tunnel in so...The excavation of deep tunnels crossing faults is highly prone to triggering rockburst disasters,which has become a significant engineering issue.In this study,taking the fault-slip rockbursts from a deep tunnel in southwestern China as the engineering prototype,large-scale three-dimensional(3D)physical model tests were conducted on a 3D-printed complex geological model containing two faults.Based on the selfdeveloped 3D loading system and excavation device,the macroscopic failure of fault-slip rockbursts was simulated indoors.The stress,strain,and fracturing characteristics of the surrounding rock near the two faults were systematically evaluated during excavation and multistage loading.The test results effectively revealed the evolution and triggering mechanism of fault-slip rockbursts.After the excavation of a highstress tunnel,stress readjustment occurred.Owing to the presence of these two faults,stress continued to accumulate in the rock mass between them,leading to the accumulation of fractures.When the shear stress on a fault surface exceeded its shear strength,sudden fault slip and dislocation occurred,thus triggering rockbursts.Rockbursts occurred twice in the vault between the two faults,showing obvious intermittent characteristics.The rockburst pit was controlled by two faults.When the faults remained stable,tensile failure predominated in the surrounding rock.However,when the fault slip was triggered,shear failure in the surrounding rock increased.These findings provide valuable insights for enhancing the comprehension of fault-slip rockbursts.展开更多
Accurate assessment of coal brittleness is crucial in the design of coal seam drilling and underground coal mining operations.This study proposes a method for evaluating the brittleness of gas-bearing coal based on a ...Accurate assessment of coal brittleness is crucial in the design of coal seam drilling and underground coal mining operations.This study proposes a method for evaluating the brittleness of gas-bearing coal based on a statistical damage constitutive model and energy evolution mechanisms.Initially,integrating the principle of effective stress and the Hoek-Brown criterion,a statistical damage constitutive model for gas-bearing coal is established and validated through triaxial compression tests under different gas pressures to verify its accuracy and applicability.Subsequently,employing energy evolution mechanism,two energy characteristic parameters(elastic energy proportion and dissipated energy proportion)are analyzed.Based on the damage stress thresholds,the damage evolution characteristics of gas bearing coal were explored.Finally,by integrating energy characteristic parameters with damage parameters,a novel brittleness index is proposed.The results demonstrate that the theoretical curves derived from the statistical damage constitutive model closely align with the test curves,accurately reflecting the stress−strain characteristics of gas-bearing coal and revealing the stress drop and softening characteristics of coal in the post-peak stage.The shape parameter and scale parameter represent the brittleness and macroscopic strength of the coal,respectively.As gas pressure increases from 1 to 5 MPa,the shape parameter and the scale parameter decrease by 22.18%and 60.45%,respectively,indicating a reduction in both brittleness and strength of the coal.Parameters such as maximum damage rate and peak elastic energy storage limit positively correlate with coal brittleness.The brittleness index effectively captures the brittleness characteristics and reveals a decrease in brittleness and an increase in sensitivity to plastic deformation under higher gas pressure conditions.展开更多
Activating both metal and lattice oxygen sites for efficient oxygen evolution reactions(OER)is a critical challenge.This study pioneers a novel approach,employing cobalt-nickel glycerate solid spheres(CoNi-G SSs)as se...Activating both metal and lattice oxygen sites for efficient oxygen evolution reactions(OER)is a critical challenge.This study pioneers a novel approach,employing cobalt-nickel glycerate solid spheres(CoNi-G SSs)as self-sacrificial templates to synthesize yolk-shell structured CoNi-G SSs@ZIF-67 nanospheres.The derived NiCo2S4@CoS2/MoS2 double-shelled hollow nanospheres integrate the adsorbate evolution mechanism(AEM)and lattice oxygen mechanism(LOM),enabling synergistic dual catalytic pathways.Nickel modulation facilitates active species reconstruction in NiCo_(2)S_(4),enhancing lattice oxygen activity and optimizing the LOM pathway.Characterization results indicate that anode activation triggered the redox processes of metal and lattice oxygen sites,involving the formation and re-filling of oxygen vacancies.Additionally,the CoS_(2)/MoS_(2) heterostructure enhances the AEM pathway,as supported by density functional theory calculations,which demonstrate optimized adsorption of intermediates for both hydrogen evolution reaction and OER.The assembled anion exchange membrane water splitting device can deliver a catalytic current of 500 mA cm^(-2) at 1.74 V under commercial catalytic operating conditions(1 mol L^(-1) KOH)for 150 h,with negligible degradation.This work provides important insights into the understanding of OER mechanisms and the design of high-performance water-splitting electrocatalysts,while also opening new avenues for developing multifunctional materials with multi-shell structures.展开更多
The microstructure evolution and deformation mechanism of a DZ125 superalloy during high-temperature creep were studied by means of microstructure observation and creep-property tests.The results show that at the init...The microstructure evolution and deformation mechanism of a DZ125 superalloy during high-temperature creep were studied by means of microstructure observation and creep-property tests.The results show that at the initial stage of high-temperature creep,two sets of dislocations with different Burgers vectors move and meet inγmatrix channels,and react to form a quadrilateral dislocation network.Andγ′phases with raft-like microstructure are generated after the formation of dislocation networks.As creep progresses,the quadrilateral dislocation network is gradually transformed into hexagonal and quadrilateral dislocation networks.During steady stage of creep,the superalloy undergoes deformation with the mechanism that a great number of dislocations slip and climb in the matrix across the raft-likeγ′phases.At the later stage of creep,the raft-likeγ′phases are sheared by dislocations at the breakage of dislocation networks,and then alternate slip occurs,which distorts and breaks the raft-likeγ′/γphases,resulting in the accumulation of micropores at the raft-likeγ′/γinterfaces and the formation of microcracks.As creep continues,the microcracks continue to expand until creep fracture occurs,which is the damage and fracture mechanism of the alloy at the later stage of creep at high temperature.展开更多
The microstructure evolution and strengthening mechanism of WE54 alloy with different hard-plate rolling(HPR)processes were systematically investigated.The results suggest that the mechanical properties of the as-roll...The microstructure evolution and strengthening mechanism of WE54 alloy with different hard-plate rolling(HPR)processes were systematically investigated.The results suggest that the mechanical properties of the as-rolled alloys are significantly enhanced compared to those of the as-cast alloy.When subjected to three rolling passes at 450℃ and 490℃,grain refinement occurs due to dynamic recrystallization.A mixed-grain structure is formed after a single pass rolling with a substantial reduction(65%)at 490℃.The dynamic recrystallization(DRX)mechanism of the alloy during the HPR includes continuous dynamic recrystallization(CDRX),discontinuous dynamic recrystallization(DDRX),and twin-induced recrystallization(TDRX).The WE54 alloy exhibits the highest strength after three passes of HPR at 450℃,with tensile strength and yield strength of 374 and 323 MPa,respectively.The significant improvement in the mechanical properties of the alloy is primarily attributed to fine-grain strengthening,solid solution strengthening,and dislocation strengthening.展开更多
Clarifying the mechanisms that control the evolution of territorial space patterns is essential for regulating and optimizing the geographical structure and processes related to sustainable development.Using the Guang...Clarifying the mechanisms that control the evolution of territorial space patterns is essential for regulating and optimizing the geographical structure and processes related to sustainable development.Using the Guangdong and Guangxi sections of the Pearl River Basin as examples,the transfer-matrix method and standard deviation ellipse model were applied to characterize the evolution of territorial space patterns from 1990 to 2020.A trend surface analysis and the Theil index were used to analyze regional differences in the evolution process,and geodetectors were used to identify the underlying mechanisms of the changes.There were three key results.(1)In these critical areas of the Pearl River Basin,agricultural and ecological spaces have rapidly declined due to urban expansion,with transfers between these spaces dominating the evolution of territorial space patterns.Spatial pattern changes in the Guangdong section were more intense than in the Guangxi section.(2)Regional differences in urban space have decreased,whereas differences in agricultural and ecological spaces have intensified.Driven by socio-economic growth,the cross-regional transfers of territorial space have created a“high in the east,while low in the west”inter-regional difference,and a“high in the south,while low in the north”intra-regional difference shaped by natural conditions.The regional differences in space patterns were greater in Guangdong than in Guangxi.(3)The evolution of watershed territorial space patterns resulted from scale changes,locational shifts,structural reorganizations,and directional changes driven by multiple factors.Natural environment,social life,economic development,and policy factors played foundational,leading,key driving,and guiding roles,respectively.Additionally,the regional differences in the evolution of watershed territorial space patterns originated from the differential transmission of the influence of various factors affecting spatial evolution.Enhancing urban space efficiency,restructuring agricultural space,and optimizing ecological space are key strategies for building a complementary and synergistic territorial space pattern in the basin.展开更多
Globalization has resulted in a notable rise in the flow of high-skilled talent from emerging countries to developed nations. Current research on transnational talent flow mainly focuses on the destination countries, ...Globalization has resulted in a notable rise in the flow of high-skilled talent from emerging countries to developed nations. Current research on transnational talent flow mainly focuses on the destination countries, with less attention given to the perspective of the sending countries, particularly lacking a dynamic discussion on its impact on technological evolution in the origin countries. Based on the OECD REGPAT database, this paper aims to explore how talent groups migrating to developed countries facilitate the return of knowledge and technology to emerging countries and achieve breakthroughs in their technological evolution paths, while further discussing the potential mechanisms involved. The findings of this paper are as follows:(1) The technological development of emerging countries is a path-dependent process, where countries often branch into new technologies related to their preexisting knowledge base. Consequently, knowledge feedback from high-skilled talents increases the likelihood of sending countries developing unrelated technologies.(2) The mobility of talents across borders fosters more international collaborations and citations for patents that are unrelated to the local knowledge base, thus enriching the technological paths of sending countries.(3) The mobility of high-skilled talents primarily affects complex technologies, which have significant economic effects that encourage imitation by other countries.However, the effect on novel technologies is less significant due to their strong geographical stickiness. In general, this paper addresses the gaps in existing research on talent outflow and the technological evolution of origin countries, providing empirical evidence for the positive role of transnational talent mobility in the technological catch-up of emerging nations.Besides, it offers recommendations for talent export, import, and innovation policy formulation in these countries.展开更多
The hot deformation behavior of GH3230 superalloy under selected deformation conditions ranging from 950 to 1150℃with strain rates ranging from 0.01 to 10 s^(–1)was studied through isothermal hot compression experim...The hot deformation behavior of GH3230 superalloy under selected deformation conditions ranging from 950 to 1150℃with strain rates ranging from 0.01 to 10 s^(–1)was studied through isothermal hot compression experiments.Based on the obtained flow stresses,a strain-compensated Arrhenius-type model was developed for the description of hot deformation behavior,and the consistency of the predicted flow stresses with the experimental values confirms the accuracy of the developed model.Furthermore,the processing maps were constructed and classified into the instability domain,low-dissipation stability domain and high-dissipation stability domain in accordance with the dynamic material model and the instability criterion.Microstructure observations indicated that the instability domain exhibits the adiabatic shear bands formation,and the low-power dissipation domain exhibits partial dynamic recrystallization(DRX),with the temperature increase/strain rate decrease being favorable for the DRX.The high-dissipation stability domain was occupied by uniformly fine equiaxed grains,and was identified as the optimal processing window,which corresponds to the deformation conditions at 1070–1150℃ with strain rates ranging from 0.01 to 0.15 s^(–1).Moreover,various DRX mechanisms are observed to occur during the hot deformation,which include the discontinuous dynamic recrystallization,characterized by nucleation at bulged boundaries,the continuous dynamic recrystallization with subgrain progressive rotation and the particle stimulated nucleation mechanism with stimulated nucleation of carbide particles.展开更多
Understanding the mechanical behavior and failure characteristics of anisotropic sedimentary rocks under true-triaxial in-situ stress conditions is critical in understanding and mitigating damaging formation slippage ...Understanding the mechanical behavior and failure characteristics of anisotropic sedimentary rocks under true-triaxial in-situ stress conditions is critical in understanding and mitigating damaging formation slippage in subsurface reservoirs and containment structures.In particular,threshold conditions where structure dominates over intact failure remain undefined.By conducting systematic true-triaxial compression tests,we followed the evolution of deformation and failure in sedimentary rocks across a documented spectrum of lithological and structural characteristics in order to quantify and then classify this cross-impact.The failure features were characterized using acoustic emission(AE)monitoring,optical imaging,X-ray CT scans,and thin-section analysis.We characterized structural and deformational anisotropies in order to define the risk of structurally controlled slip failure.We identified three deformational and failure modes dominated by(Ⅰ)purely stress-controlled failure,(Ⅱ)mixed stress--structure-controlled failure,and(Ⅲ)purely structurally controlled failure.As structural overprinting increased,failure mechanisms were found to shift progressively from Type Ⅰ to Ⅲ,thereby progressively capturing inherent rock anisotropy and complex fabric as well as ductile failure.This transition was characterized in terms of two parameters that alternately characterize structural(α)and deformational anisotropies(β)of rocks with these related to key visual,mechanical,and acoustic(AE)indicators.The greater the α(α>2),the higher the β(β>0),the more likely the transition from brittle failure to structurally controlled ductile shear reactivation along the bedding.展开更多
Nearly undamaged joints of electron beam welded(EBW)dual-phase Mg-8Li-3Al-2Zn-0.5Y alloy were achieved with joint coefficients exceeding 95%.All specimens were fractured at the base metal(BM),implying a significant de...Nearly undamaged joints of electron beam welded(EBW)dual-phase Mg-8Li-3Al-2Zn-0.5Y alloy were achieved with joint coefficients exceeding 95%.All specimens were fractured at the base metal(BM),implying a significant departure from conventional fracture modes of welded joints.The fusion zone(FZ)consists of ultrafine acicular α-Mg and equiaxed β-Li,with grain sizes reduced by approximately 90% and 80%,respectively,compared to the base metal.This results in a significant increase in microhardness of about 40%.A unique multiphase mixture was observed in the heat-affected zone(HAZ),which mainly consists of lamellar eutectoid structures,fine precipitates zone,and numerous fine Mg_(3)(Al,Zn)particles.This mixture was transformed from typical Li(Al,Zn)(a common softening phase)undergoing atomic diffusion and solid-state phase transformation during welding.It introduces a synergistic strengthening effect,making the heat-affected zone no longer the weakest part of the joint.This study provides valuable insights into the electron beam welding technology for Mg-Li alloys and offers theoretical support for manufacturing high-quality joints.展开更多
In this study,the hot deformation behavior and microstructural evolution of the GH 4706 alloy under various thermal processing parameters(TPPs)were investigated through hot deformation experiments and electron backsca...In this study,the hot deformation behavior and microstructural evolution of the GH 4706 alloy under various thermal processing parameters(TPPs)were investigated through hot deformation experiments and electron backscatter diffraction(EBSD)microstructural characterization.The findings suggest that increasing hot compression temperature(T)and reducing strain rate(ε)enhance the degree of dynamic recrystallization(DRX),significantly reducing flow stress and weakening texture intensity.Increasing strain(ε)promotes DRX,with the overall texture strength initially increasing before decreasing.During hot compression at 1000−1100℃,discontinuous dynamic recrystallization(DDRX),continuous dynamic recrystallization(CDRX),and twin-induced dynamic recrystallization(TDRX)jointly influence texture development.Among these,DDRX plays a dominant role,with numerous DDRX grains exhibiting dispersed orientations,significantly contributing to texture weakening.The CDRX mechanism induces a limited number of randomly oriented grains within the deformed grains,and its contribution to texture weakening is enhanced with increasingεand decreasing T.The TDRX mechanism generates DRX grains withinΣ3 twin boundaries deviating from their theoretical orientation,and these grains inherit the twin orientation,exerting a limited effect on texture weakening.These findings provide a theoretical foundation for a deeper understanding of DRX behavior and texture evolution in the GH 4706 during hot working.展开更多
Against the background of“carbon peak and carbon neutrality,”it is of great practical significance to develop non-blast furnace ironmaking technology for the sustainable development of steel industry.Carbon-bearing ...Against the background of“carbon peak and carbon neutrality,”it is of great practical significance to develop non-blast furnace ironmaking technology for the sustainable development of steel industry.Carbon-bearing iron ore pellet is an innovative burden of direct reduction ironmaking due to its excellent self-reducing property,and the thermal strength of pellet is a crucial metallurgical property that affects its wide application.The carbon-bearing iron ore pellet without binders(CIPWB)was prepared using iron concentrate and anthracite,and the effects of reducing agent addition amount,size of pellet,reduction temperature and time on the thermal compressive strength of CIPWB during the reduction process were studied.Simultaneously,the mechanism of the thermal strength evolution of CIPWB was revealed.The results showed that during the low-temperature reduction process(300-500℃),the thermal compressive strength of CIPWB linearly increases with increasing the size of pellet,while it gradually decreases with increasing the anthracite ratio.When the CIPWB with 8%anthracite is reduced at 300℃for 60 min,the thermal strength of pellet is enhanced from 13.24 to 31.88 N as the size of pellet increases from 8.04 to 12.78 mm.Meanwhile,as the temperature is 500℃,with increasing the anthracite ratio from 2%to 8%,the thermal compressive strength of pellet under reduction for 60 min remarkably decreases from 41.47 to 8.94 N.Furthermore,in the high-temperature reduction process(600-1150℃),the thermal compressive strength of CIPWB firstly increases and then reduces with increasing the temperature,while it as well as the temperature corresponding to the maximum strength decreases with increasing the anthracite ratio.With adding 18%anthracite,the thermal compressive strength of pellet reaches the maximum value at 800℃,namely 35.00 N,and obtains the minimum value at 1050℃,namely 8.60 N.The thermal compressive strength of CIPWB significantly depends on the temperature,reducing agent dosage,and pellet size.展开更多
Understanding the storage mechanisms in CO_(2)flooding is crucial,as many carbon capture,utilization,and storage(CCUS)projects are related to enhanced oil recovery(EOR).CO_(2)storage in reservoirs across large timesca...Understanding the storage mechanisms in CO_(2)flooding is crucial,as many carbon capture,utilization,and storage(CCUS)projects are related to enhanced oil recovery(EOR).CO_(2)storage in reservoirs across large timescales undergoes the two storage stages of oil displacement and well shut-in,which cover mul-tiple replacement processes of injection-production synchronization,injection only with no production,and injection-production stoppage.Because the controlling mechanism of CO_(2)storage in different stages is unknown,the evolution of CO_(2)storage mechanisms over large timescales is not understood.A math-ematical model for the evaluation of CO_(2)storage,including stratigraphic,residual,solubility,and mineral trapping in low-permeability tight sandstone reservoirs,was established using experimental and theoret-ical analyses.Based on a detailed geological model of the Huaziping Oilfield,calibrated with reservoir permeability and fracture characteristic parameters obtained from well test results,a dynamic simulation of CO_(2)storage for the entire reservoir life cycle under two scenarios of continuous injection and water-gas alternation were considered.The results show that CO_(2)storage exhibits the significant stage charac-teristics of complete storage,dynamic storage,and stable storage.The CO_(2)storage capacity and storage rate under the continuous gas injection scenario(scenario 1)were 6.34×10^(4)t and 61%,while those under the water-gas alternation scenario(scenario 2)were 4.62×10^(4)t and 46%.The proportions of stor-age capacity under scenarios 1 and 2 for structural or stratigraphic,residual,solubility,and mineral trap-ping were 33.36%,33.96%,32.43%,and 0.25%;and 15.09%,38.65%,45.77%,and 0.49%,respectively.The evolution of the CO_(2)storage mechanism showed an overall trend:stratigraphic and residual trapping first increased and then decreased,whereas solubility trapping gradually decreased,and mineral trapping continuously increased.Based on these results,an evolution diagram of the CO_(2)storage mechanism of low-permeability tight sandstone reservoirs across large timescales was established.展开更多
High-performance 24CrNiMo steel was fabricated using Laser Powder Bed Fusion (LPBF). Subsequent quenching treatment was applied and the influence of quenching temperatures on micro-structure evolution and properties w...High-performance 24CrNiMo steel was fabricated using Laser Powder Bed Fusion (LPBF). Subsequent quenching treatment was applied and the influence of quenching temperatures on micro-structure evolution and properties was systematically characterised and analysed. The micro-structure of the as-built steel consisted of two parts. The first part comprised martensite with twins combined with ω-Fe nano-particles, and the second part consisted of lower bainite in the molten pool, as well as upper bainite, granular bainite and tempered martensite in the heat-affected zone. With the quenching temperatures varying from 800℃ to 950℃, the micro-structure gradually transformed from acicular ferrite + martensite to tempered martensite +θ-Fe3C carbides, and the grain size exhibited noticeable growth. Moreover, quenching treatments could eliminate the anisotropy and inhomogeneity of the micro-structure. The rod-shaped nanosized η-Fe2C and θ-Fe3C precipitates were clearly observed, which were converted from ω-Fe and distributed at multiple angles in the lath. The size and number of nano-precipitates, triggered by the high self-tempering degree of martensite, gradually increased. The relationships among grain size, the twins, dislocation density and nano-precipitation and the dramatically improved performance of quenched samples were analysed using strengthening mechanisms. After quenching at 850℃, the as-built 24CrNiMo steel attained ultra-high mechanical properties including hardness, Ultimate Tensile Strength (UTS), Elongation (El) and impact energy with values of 480.9 HV_(1), 1611.4 MPa, 9.8% and 42.8 J, respectively. Meanwhile, both the wear and thermal fatigue resistance increased by approximately 40%. This study demonstrated that LPBF-fabricated 24CrNiMo steel, with matching good performances, can be achieved using a subsequent one-step quenching process.展开更多
The effects of accumulative hot rolling followed by solution treatment on the microstructural evolution and fracture behavior of 30CrMo/316L multilayered composites have been investigated.A scanning electron microscop...The effects of accumulative hot rolling followed by solution treatment on the microstructural evolution and fracture behavior of 30CrMo/316L multilayered composites have been investigated.A scanning electron microscope equipped with an electron backscatter diffraction probe,a laser confocal microscope,an electron probe microanalysis,and a universal testing machine were employed to characterize the microstructures and mechanical properties.The results indicate that solution treatment transformed the microstructure of the 30CrMo layer from ferrite to martensite,while the 316L layer remained austenitic but transitioned from the rolled to the recrystallized state.Additionally,solution treatment significantly enhanced the mechanical properties of the composite,leading to an increase in yield strength and ultimate tensile strength to 744 and 1106 MPa,respectively—258 and 276 MPa higher than those of the hot-rolled plate.The enhancement in strength is primarily attributed to the formation of high-strength martensite in the 30CrMo layer.During deformation,the composite interface effectively impeded crack propagation and induced step-like deflection.However,the formation of cross-layer grains facilitated crack nucleation at grain boundaries,leading to rapid crack propagation and instantaneous fracture.Therefore,preventing the formation of cross-layer grains during the heat treatment process is crucial,as their presence weakens the interfacial strengthening effect of the composite plate.This study provides valuable insights for the design and development of multi-layered steels.展开更多
To address the issue of extreme thermal-induced arching in CRTS II slab tracks due to joint damage,an optimized joint repair model was proposed.First,the formula for calculating the safe temperature rise of the track ...To address the issue of extreme thermal-induced arching in CRTS II slab tracks due to joint damage,an optimized joint repair model was proposed.First,the formula for calculating the safe temperature rise of the track was derived based on the principle of stationary potential energy.Considering interlayer evolution and structural crack propagation,an optimized joint repair model for the track was established and validated.Subsequently,the impact of joint repair on track damage and arch stability under extreme temperatures was studied,and a comprehensive evaluation of the feasibility of joint repair and the evolution of damage after repair was conducted.The results show that after the joint repair,the temperature rise of the initial damage of the track structure can be increased by 11℃.Under the most unfavorable heating load with a superimposed temperature gradient,the maximum stiffness degradation index SDEG in the track structure is reduced by about 81.16%following joint repair.The joint repair process could effectively reduce the deformation of the slab arching under high temperatures,resulting in a reduction of 93.96%in upward arching deformation.After repair,with the damage to interfacing shear strength,the track arch increases by 2.616 mm.展开更多
The differences between shouldered and shoulderless tools in the micro-friction stir welding of 0.8 mm thin plates were evaluated.Employing a suite of advanced characterization methods,including white light interferom...The differences between shouldered and shoulderless tools in the micro-friction stir welding of 0.8 mm thin plates were evaluated.Employing a suite of advanced characterization methods,including white light interferometry,electron backscatter diffraction(EBSD),and scanning electron microscopy,the formation of weld surface,joint microstructure distribution,and fracture characteristics were studied.The enhancement mechanism of mechanical properties was explained through the Hall-Petch relationship and Taylor's hardening law.Results indicate that the main reason for the increased yield strength observed in shoulderless tool joints is the combined mechanism of dislocation strengthening and fine-grain strengthening.Specifically,the utilization of shouldered tools results in a smooth weld surface,with an average grain size of 11.24μm and a high-angle grain boundary content of 16.80%in the nugget zone.The primary texture components are the{011}<100>Goss and{112}<111>copper textures,yielding a maximum texture strength of 3.70.Simultaneously,the fracture dimples exhibit a reduction in size and an increase in depth.Whereas the welds produced with shoulderless tools display slight burrs on the surface.The experimental results demonstrate that the average grain size in the nugget zone of these joints is significantly reduced to 0.59μm,while the high-angle grain boundary content reaches 34.34%.This process is accompanied by the formation of{111}<110>Shear textures and{001}<110>rotated cubic textures as the main components,resulting in a significant increase in maximum texture strength to 6.65.展开更多
基金financially supported by the National Science Foundation of China(Nos.51974212 and 52274316)the China Baowu Low Carbon Metallurgy Innovation Foundation(No.BWLCF202116)+1 种基金the Science and Technology Major Project of Wuhan(No.2023020302020572)the Foundation of Key Laboratory for Ferrous Metallurgy and Resources Utilization of Ministry of Education(No.FMRUlab23-04)。
文摘The utilization of iron coke provides a green pathway for low-carbon ironmaking.To uncover the influence mechanism of iron ore on the behavior and kinetics of iron coke gasification,the effect of iron ore on the microstructure of iron coke was investigated.Furthermore,a comparative study of the gasification reactions between iron coke and coke was conducted through non-isothermal thermogravimetric method.The findings indicate that compared to coke,iron coke exhibits an augmentation in micropores and specific surface area,and the micropores further extend and interconnect.This provides more adsorption sites for CO_(2) molecules during the gasification process,resulting in a reduction in the initial gasification temperature of iron coke.Accelerating the heating rate in non-isothermal gasification can enhance the reactivity of iron coke.The metallic iron reduced from iron ore is embedded in the carbon matrix,reducing the orderliness of the carbon structure,which is primarily responsible for the heightened reactivity of the carbon atoms.The kinetic study indicates that the random pore model can effectively represent the gasification process of iron coke due to its rich pore structure.Moreover,as the proportion of iron ore increases,the activation energy for the carbon gasification gradually decreases,from 246.2 kJ/mol for coke to 192.5 kJ/mol for iron coke 15wt%.
基金National Natural Science Foundation of China(U22A20191)。
文摘Brazing filler metals are widely applied,which serve as an industrial adhesive in the joining of dissimilar structures.With the continuous emergence of new structures and materials,the demand for novel brazing filler metals is ever-increasing.It is of great significance to investigate the optimized composition design methods and to establish systematic design guidelines for brazing filler metals.This study elucidated the fundamental rules for the composition design of brazing filler metals from a three-dimensional perspective encompassing the basic properties of applied brazing filler metals,formability and processability,and overall cost.The basic properties of brazing filler metals refer to their mechanical properties,physicochemical properties,electromagnetic properties,corrosion resistance,and the wettability and fluidity during brazing.The formability and processability of brazing filler metals include the processes of smelting and casting,extrusion,rolling,drawing and ring-making,as well as the processes of granulation,powder production,and the molding of amorphous and microcrystalline structures.The cost of brazing filler metals corresponds to the sum of materials value and manufacturing cost.Improving the comprehensive properties of brazing filler metals requires a comprehensive and systematic consideration of design indicators.Highlighting the unique characteristics of brazing filler metals should focus on relevant technical indicators.Binary or ternary eutectic structures can effectively enhance the flow spreading ability of brazing filler metals,and solid solution structures contribute to the formability.By employing the proposed design guidelines,typical Ag based,Cu based,Zn based brazing filler metals,and Sn based solders were designed and successfully applied in major scientific and engineering projects.
文摘The study of the oxygen evolution reaction(OER)mechanism is vital for advancing our understanding of this pivotal energy conversion process.This review synthesizes recent advancements in OER mechanism,emphasizing the intricate relationship between catalytic mechanisms and catalyst design.This review discusses the connotation and cutting-edge progress of traditional mechanisms such as adsorbate evolution mechanism(AEM)and lattice oxygen mechanism(LOM)as well as emerging pathways including oxide path mechanism(OPM),oxo-oxo coupling mechanism(OCM),and intramolecular oxygen coupling mechanism(IMOC)etc.Innovative research progress on the coexistence and transformation of multiple mechanisms is highlighted,and the intrinsic factors that influence these dynamic processes are summarized.Advanced characterization techniques and theoretical modeling are underscored as indispensable tools for revealing these complex interactions.This review provides guiding principles for mechanism-based catalyst design.Finally,in view of the multidimensional challenges currently faced by OER mechanisms,prospects for future research are given to bridge the gap between mechanism innovation and experimental verification and application.This comprehensive review provides valuable perspectives for advancing clean energy technologies and achieving sustainable development.
基金funding support from the National Natural Science Foundation of China(Grant Nos.42177136 and 52309126).
文摘The excavation of deep tunnels crossing faults is highly prone to triggering rockburst disasters,which has become a significant engineering issue.In this study,taking the fault-slip rockbursts from a deep tunnel in southwestern China as the engineering prototype,large-scale three-dimensional(3D)physical model tests were conducted on a 3D-printed complex geological model containing two faults.Based on the selfdeveloped 3D loading system and excavation device,the macroscopic failure of fault-slip rockbursts was simulated indoors.The stress,strain,and fracturing characteristics of the surrounding rock near the two faults were systematically evaluated during excavation and multistage loading.The test results effectively revealed the evolution and triggering mechanism of fault-slip rockbursts.After the excavation of a highstress tunnel,stress readjustment occurred.Owing to the presence of these two faults,stress continued to accumulate in the rock mass between them,leading to the accumulation of fractures.When the shear stress on a fault surface exceeded its shear strength,sudden fault slip and dislocation occurred,thus triggering rockbursts.Rockbursts occurred twice in the vault between the two faults,showing obvious intermittent characteristics.The rockburst pit was controlled by two faults.When the faults remained stable,tensile failure predominated in the surrounding rock.However,when the fault slip was triggered,shear failure in the surrounding rock increased.These findings provide valuable insights for enhancing the comprehension of fault-slip rockbursts.
基金Project(52274096)supported by the National Natural Science Foundation of ChinaProject(WS2023A03)supported by the State Key Laboratory Cultivation Base for Gas Geology and Gas Control,China。
文摘Accurate assessment of coal brittleness is crucial in the design of coal seam drilling and underground coal mining operations.This study proposes a method for evaluating the brittleness of gas-bearing coal based on a statistical damage constitutive model and energy evolution mechanisms.Initially,integrating the principle of effective stress and the Hoek-Brown criterion,a statistical damage constitutive model for gas-bearing coal is established and validated through triaxial compression tests under different gas pressures to verify its accuracy and applicability.Subsequently,employing energy evolution mechanism,two energy characteristic parameters(elastic energy proportion and dissipated energy proportion)are analyzed.Based on the damage stress thresholds,the damage evolution characteristics of gas bearing coal were explored.Finally,by integrating energy characteristic parameters with damage parameters,a novel brittleness index is proposed.The results demonstrate that the theoretical curves derived from the statistical damage constitutive model closely align with the test curves,accurately reflecting the stress−strain characteristics of gas-bearing coal and revealing the stress drop and softening characteristics of coal in the post-peak stage.The shape parameter and scale parameter represent the brittleness and macroscopic strength of the coal,respectively.As gas pressure increases from 1 to 5 MPa,the shape parameter and the scale parameter decrease by 22.18%and 60.45%,respectively,indicating a reduction in both brittleness and strength of the coal.Parameters such as maximum damage rate and peak elastic energy storage limit positively correlate with coal brittleness.The brittleness index effectively captures the brittleness characteristics and reveals a decrease in brittleness and an increase in sensitivity to plastic deformation under higher gas pressure conditions.
文摘Activating both metal and lattice oxygen sites for efficient oxygen evolution reactions(OER)is a critical challenge.This study pioneers a novel approach,employing cobalt-nickel glycerate solid spheres(CoNi-G SSs)as self-sacrificial templates to synthesize yolk-shell structured CoNi-G SSs@ZIF-67 nanospheres.The derived NiCo2S4@CoS2/MoS2 double-shelled hollow nanospheres integrate the adsorbate evolution mechanism(AEM)and lattice oxygen mechanism(LOM),enabling synergistic dual catalytic pathways.Nickel modulation facilitates active species reconstruction in NiCo_(2)S_(4),enhancing lattice oxygen activity and optimizing the LOM pathway.Characterization results indicate that anode activation triggered the redox processes of metal and lattice oxygen sites,involving the formation and re-filling of oxygen vacancies.Additionally,the CoS_(2)/MoS_(2) heterostructure enhances the AEM pathway,as supported by density functional theory calculations,which demonstrate optimized adsorption of intermediates for both hydrogen evolution reaction and OER.The assembled anion exchange membrane water splitting device can deliver a catalytic current of 500 mA cm^(-2) at 1.74 V under commercial catalytic operating conditions(1 mol L^(-1) KOH)for 150 h,with negligible degradation.This work provides important insights into the understanding of OER mechanisms and the design of high-performance water-splitting electrocatalysts,while also opening new avenues for developing multifunctional materials with multi-shell structures.
基金Guizhou Province Science and Technology Plan Project(QKHJC-ZK[2024]yiban604)Guizhou Province Science and Technology Plan Project(CXTD[2021]008)+4 种基金Bijie City Science and Technology Project(BKLH[2023]9)Technology Project of Bijie City(BKLH[2023]36)Natural Science Research Project of Guizhou Higher Education Institutions of China(QJJ[2023]047)Science and Technology Project of Guizhou Department of Transportation(2022-121-011)Sanmenxia City Science and Technology Bureau Science and Technology Research Project(2022002005)。
文摘The microstructure evolution and deformation mechanism of a DZ125 superalloy during high-temperature creep were studied by means of microstructure observation and creep-property tests.The results show that at the initial stage of high-temperature creep,two sets of dislocations with different Burgers vectors move and meet inγmatrix channels,and react to form a quadrilateral dislocation network.Andγ′phases with raft-like microstructure are generated after the formation of dislocation networks.As creep progresses,the quadrilateral dislocation network is gradually transformed into hexagonal and quadrilateral dislocation networks.During steady stage of creep,the superalloy undergoes deformation with the mechanism that a great number of dislocations slip and climb in the matrix across the raft-likeγ′phases.At the later stage of creep,the raft-likeγ′phases are sheared by dislocations at the breakage of dislocation networks,and then alternate slip occurs,which distorts and breaks the raft-likeγ′/γphases,resulting in the accumulation of micropores at the raft-likeγ′/γinterfaces and the formation of microcracks.As creep continues,the microcracks continue to expand until creep fracture occurs,which is the damage and fracture mechanism of the alloy at the later stage of creep at high temperature.
基金financially supported by the Natural Science Basic Research Program of Shaanxi Province,China(No.2023-JC-QN-0581)Advanced Power Specialty,China(No.YK22C-9)。
文摘The microstructure evolution and strengthening mechanism of WE54 alloy with different hard-plate rolling(HPR)processes were systematically investigated.The results suggest that the mechanical properties of the as-rolled alloys are significantly enhanced compared to those of the as-cast alloy.When subjected to three rolling passes at 450℃ and 490℃,grain refinement occurs due to dynamic recrystallization.A mixed-grain structure is formed after a single pass rolling with a substantial reduction(65%)at 490℃.The dynamic recrystallization(DRX)mechanism of the alloy during the HPR includes continuous dynamic recrystallization(CDRX),discontinuous dynamic recrystallization(DDRX),and twin-induced recrystallization(TDRX).The WE54 alloy exhibits the highest strength after three passes of HPR at 450℃,with tensile strength and yield strength of 374 and 323 MPa,respectively.The significant improvement in the mechanical properties of the alloy is primarily attributed to fine-grain strengthening,solid solution strengthening,and dislocation strengthening.
基金National Social Science Foundation Program,No.22VRC163National Natural Science Foundation of China,No.42061043+1 种基金Postgraduate Research&Practice Innovation Program of Jiangsu Province,No.KYCX24_1008Innovation Project of Guangxi Graduate Education,No.YCSW2024473。
文摘Clarifying the mechanisms that control the evolution of territorial space patterns is essential for regulating and optimizing the geographical structure and processes related to sustainable development.Using the Guangdong and Guangxi sections of the Pearl River Basin as examples,the transfer-matrix method and standard deviation ellipse model were applied to characterize the evolution of territorial space patterns from 1990 to 2020.A trend surface analysis and the Theil index were used to analyze regional differences in the evolution process,and geodetectors were used to identify the underlying mechanisms of the changes.There were three key results.(1)In these critical areas of the Pearl River Basin,agricultural and ecological spaces have rapidly declined due to urban expansion,with transfers between these spaces dominating the evolution of territorial space patterns.Spatial pattern changes in the Guangdong section were more intense than in the Guangxi section.(2)Regional differences in urban space have decreased,whereas differences in agricultural and ecological spaces have intensified.Driven by socio-economic growth,the cross-regional transfers of territorial space have created a“high in the east,while low in the west”inter-regional difference,and a“high in the south,while low in the north”intra-regional difference shaped by natural conditions.The regional differences in space patterns were greater in Guangdong than in Guangxi.(3)The evolution of watershed territorial space patterns resulted from scale changes,locational shifts,structural reorganizations,and directional changes driven by multiple factors.Natural environment,social life,economic development,and policy factors played foundational,leading,key driving,and guiding roles,respectively.Additionally,the regional differences in the evolution of watershed territorial space patterns originated from the differential transmission of the influence of various factors affecting spatial evolution.Enhancing urban space efficiency,restructuring agricultural space,and optimizing ecological space are key strategies for building a complementary and synergistic territorial space pattern in the basin.
基金National Natural Science Foundation of China,No.42122006, No.41971154, No.42271201Key Project of National Natural Science Foundation of China,No.41731278。
文摘Globalization has resulted in a notable rise in the flow of high-skilled talent from emerging countries to developed nations. Current research on transnational talent flow mainly focuses on the destination countries, with less attention given to the perspective of the sending countries, particularly lacking a dynamic discussion on its impact on technological evolution in the origin countries. Based on the OECD REGPAT database, this paper aims to explore how talent groups migrating to developed countries facilitate the return of knowledge and technology to emerging countries and achieve breakthroughs in their technological evolution paths, while further discussing the potential mechanisms involved. The findings of this paper are as follows:(1) The technological development of emerging countries is a path-dependent process, where countries often branch into new technologies related to their preexisting knowledge base. Consequently, knowledge feedback from high-skilled talents increases the likelihood of sending countries developing unrelated technologies.(2) The mobility of talents across borders fosters more international collaborations and citations for patents that are unrelated to the local knowledge base, thus enriching the technological paths of sending countries.(3) The mobility of high-skilled talents primarily affects complex technologies, which have significant economic effects that encourage imitation by other countries.However, the effect on novel technologies is less significant due to their strong geographical stickiness. In general, this paper addresses the gaps in existing research on talent outflow and the technological evolution of origin countries, providing empirical evidence for the positive role of transnational talent mobility in the technological catch-up of emerging nations.Besides, it offers recommendations for talent export, import, and innovation policy formulation in these countries.
基金the National Key Research and Development Program of China(No.2016YFB0700505)the National Natural Science Foundation of China(No.51571020).
文摘The hot deformation behavior of GH3230 superalloy under selected deformation conditions ranging from 950 to 1150℃with strain rates ranging from 0.01 to 10 s^(–1)was studied through isothermal hot compression experiments.Based on the obtained flow stresses,a strain-compensated Arrhenius-type model was developed for the description of hot deformation behavior,and the consistency of the predicted flow stresses with the experimental values confirms the accuracy of the developed model.Furthermore,the processing maps were constructed and classified into the instability domain,low-dissipation stability domain and high-dissipation stability domain in accordance with the dynamic material model and the instability criterion.Microstructure observations indicated that the instability domain exhibits the adiabatic shear bands formation,and the low-power dissipation domain exhibits partial dynamic recrystallization(DRX),with the temperature increase/strain rate decrease being favorable for the DRX.The high-dissipation stability domain was occupied by uniformly fine equiaxed grains,and was identified as the optimal processing window,which corresponds to the deformation conditions at 1070–1150℃ with strain rates ranging from 0.01 to 0.15 s^(–1).Moreover,various DRX mechanisms are observed to occur during the hot deformation,which include the discontinuous dynamic recrystallization,characterized by nucleation at bulged boundaries,the continuous dynamic recrystallization with subgrain progressive rotation and the particle stimulated nucleation mechanism with stimulated nucleation of carbide particles.
基金funded by the joint fund of the National Key Research and Development Program of China(No.2021YF C2902101)National Natural Science Foundation of China(Grant No.52374084)+2 种基金Open Foundation of National Energy Shale Gas R&D(Experiment)Center(2022-KFKT-12)the 111 Project(B17009)support from the G.Albert Shoemaker endowment。
文摘Understanding the mechanical behavior and failure characteristics of anisotropic sedimentary rocks under true-triaxial in-situ stress conditions is critical in understanding and mitigating damaging formation slippage in subsurface reservoirs and containment structures.In particular,threshold conditions where structure dominates over intact failure remain undefined.By conducting systematic true-triaxial compression tests,we followed the evolution of deformation and failure in sedimentary rocks across a documented spectrum of lithological and structural characteristics in order to quantify and then classify this cross-impact.The failure features were characterized using acoustic emission(AE)monitoring,optical imaging,X-ray CT scans,and thin-section analysis.We characterized structural and deformational anisotropies in order to define the risk of structurally controlled slip failure.We identified three deformational and failure modes dominated by(Ⅰ)purely stress-controlled failure,(Ⅱ)mixed stress--structure-controlled failure,and(Ⅲ)purely structurally controlled failure.As structural overprinting increased,failure mechanisms were found to shift progressively from Type Ⅰ to Ⅲ,thereby progressively capturing inherent rock anisotropy and complex fabric as well as ductile failure.This transition was characterized in terms of two parameters that alternately characterize structural(α)and deformational anisotropies(β)of rocks with these related to key visual,mechanical,and acoustic(AE)indicators.The greater the α(α>2),the higher the β(β>0),the more likely the transition from brittle failure to structurally controlled ductile shear reactivation along the bedding.
基金financially supported by the National Defense Basic Research Program(No.JCKY2023204A005)Project of High Modulus Magnesium Alloy Forgings(JXXT-2023-014hbza)+1 种基金Research Program of Joint Research Center of Advanced Spaceflight Technologies(No.USCAST2023-3)Major Scientific and Technological Innovation Project of Luoyang(No.2201029A).
文摘Nearly undamaged joints of electron beam welded(EBW)dual-phase Mg-8Li-3Al-2Zn-0.5Y alloy were achieved with joint coefficients exceeding 95%.All specimens were fractured at the base metal(BM),implying a significant departure from conventional fracture modes of welded joints.The fusion zone(FZ)consists of ultrafine acicular α-Mg and equiaxed β-Li,with grain sizes reduced by approximately 90% and 80%,respectively,compared to the base metal.This results in a significant increase in microhardness of about 40%.A unique multiphase mixture was observed in the heat-affected zone(HAZ),which mainly consists of lamellar eutectoid structures,fine precipitates zone,and numerous fine Mg_(3)(Al,Zn)particles.This mixture was transformed from typical Li(Al,Zn)(a common softening phase)undergoing atomic diffusion and solid-state phase transformation during welding.It introduces a synergistic strengthening effect,making the heat-affected zone no longer the weakest part of the joint.This study provides valuable insights into the electron beam welding technology for Mg-Li alloys and offers theoretical support for manufacturing high-quality joints.
基金Project(2022YFB3705103)supported by the National Key R&D Program,China。
文摘In this study,the hot deformation behavior and microstructural evolution of the GH 4706 alloy under various thermal processing parameters(TPPs)were investigated through hot deformation experiments and electron backscatter diffraction(EBSD)microstructural characterization.The findings suggest that increasing hot compression temperature(T)and reducing strain rate(ε)enhance the degree of dynamic recrystallization(DRX),significantly reducing flow stress and weakening texture intensity.Increasing strain(ε)promotes DRX,with the overall texture strength initially increasing before decreasing.During hot compression at 1000−1100℃,discontinuous dynamic recrystallization(DDRX),continuous dynamic recrystallization(CDRX),and twin-induced dynamic recrystallization(TDRX)jointly influence texture development.Among these,DDRX plays a dominant role,with numerous DDRX grains exhibiting dispersed orientations,significantly contributing to texture weakening.The CDRX mechanism induces a limited number of randomly oriented grains within the deformed grains,and its contribution to texture weakening is enhanced with increasingεand decreasing T.The TDRX mechanism generates DRX grains withinΣ3 twin boundaries deviating from their theoretical orientation,and these grains inherit the twin orientation,exerting a limited effect on texture weakening.These findings provide a theoretical foundation for a deeper understanding of DRX behavior and texture evolution in the GH 4706 during hot working.
基金support of the National Natural Science Foundation of China(52074080,52004001,and 51574002).
文摘Against the background of“carbon peak and carbon neutrality,”it is of great practical significance to develop non-blast furnace ironmaking technology for the sustainable development of steel industry.Carbon-bearing iron ore pellet is an innovative burden of direct reduction ironmaking due to its excellent self-reducing property,and the thermal strength of pellet is a crucial metallurgical property that affects its wide application.The carbon-bearing iron ore pellet without binders(CIPWB)was prepared using iron concentrate and anthracite,and the effects of reducing agent addition amount,size of pellet,reduction temperature and time on the thermal compressive strength of CIPWB during the reduction process were studied.Simultaneously,the mechanism of the thermal strength evolution of CIPWB was revealed.The results showed that during the low-temperature reduction process(300-500℃),the thermal compressive strength of CIPWB linearly increases with increasing the size of pellet,while it gradually decreases with increasing the anthracite ratio.When the CIPWB with 8%anthracite is reduced at 300℃for 60 min,the thermal strength of pellet is enhanced from 13.24 to 31.88 N as the size of pellet increases from 8.04 to 12.78 mm.Meanwhile,as the temperature is 500℃,with increasing the anthracite ratio from 2%to 8%,the thermal compressive strength of pellet under reduction for 60 min remarkably decreases from 41.47 to 8.94 N.Furthermore,in the high-temperature reduction process(600-1150℃),the thermal compressive strength of CIPWB firstly increases and then reduces with increasing the temperature,while it as well as the temperature corresponding to the maximum strength decreases with increasing the anthracite ratio.With adding 18%anthracite,the thermal compressive strength of pellet reaches the maximum value at 800℃,namely 35.00 N,and obtains the minimum value at 1050℃,namely 8.60 N.The thermal compressive strength of CIPWB significantly depends on the temperature,reducing agent dosage,and pellet size.
基金supported by the National Key Research and Development Program of China(2022YFE0206700).
文摘Understanding the storage mechanisms in CO_(2)flooding is crucial,as many carbon capture,utilization,and storage(CCUS)projects are related to enhanced oil recovery(EOR).CO_(2)storage in reservoirs across large timescales undergoes the two storage stages of oil displacement and well shut-in,which cover mul-tiple replacement processes of injection-production synchronization,injection only with no production,and injection-production stoppage.Because the controlling mechanism of CO_(2)storage in different stages is unknown,the evolution of CO_(2)storage mechanisms over large timescales is not understood.A math-ematical model for the evaluation of CO_(2)storage,including stratigraphic,residual,solubility,and mineral trapping in low-permeability tight sandstone reservoirs,was established using experimental and theoret-ical analyses.Based on a detailed geological model of the Huaziping Oilfield,calibrated with reservoir permeability and fracture characteristic parameters obtained from well test results,a dynamic simulation of CO_(2)storage for the entire reservoir life cycle under two scenarios of continuous injection and water-gas alternation were considered.The results show that CO_(2)storage exhibits the significant stage charac-teristics of complete storage,dynamic storage,and stable storage.The CO_(2)storage capacity and storage rate under the continuous gas injection scenario(scenario 1)were 6.34×10^(4)t and 61%,while those under the water-gas alternation scenario(scenario 2)were 4.62×10^(4)t and 46%.The proportions of stor-age capacity under scenarios 1 and 2 for structural or stratigraphic,residual,solubility,and mineral trap-ping were 33.36%,33.96%,32.43%,and 0.25%;and 15.09%,38.65%,45.77%,and 0.49%,respectively.The evolution of the CO_(2)storage mechanism showed an overall trend:stratigraphic and residual trapping first increased and then decreased,whereas solubility trapping gradually decreased,and mineral trapping continuously increased.Based on these results,an evolution diagram of the CO_(2)storage mechanism of low-permeability tight sandstone reservoirs across large timescales was established.
基金co-supported by the National Key Research and Development Program of China (No. 2022YFB4600500)the National Natural Science Foundation of China (No. 52235006)
文摘High-performance 24CrNiMo steel was fabricated using Laser Powder Bed Fusion (LPBF). Subsequent quenching treatment was applied and the influence of quenching temperatures on micro-structure evolution and properties was systematically characterised and analysed. The micro-structure of the as-built steel consisted of two parts. The first part comprised martensite with twins combined with ω-Fe nano-particles, and the second part consisted of lower bainite in the molten pool, as well as upper bainite, granular bainite and tempered martensite in the heat-affected zone. With the quenching temperatures varying from 800℃ to 950℃, the micro-structure gradually transformed from acicular ferrite + martensite to tempered martensite +θ-Fe3C carbides, and the grain size exhibited noticeable growth. Moreover, quenching treatments could eliminate the anisotropy and inhomogeneity of the micro-structure. The rod-shaped nanosized η-Fe2C and θ-Fe3C precipitates were clearly observed, which were converted from ω-Fe and distributed at multiple angles in the lath. The size and number of nano-precipitates, triggered by the high self-tempering degree of martensite, gradually increased. The relationships among grain size, the twins, dislocation density and nano-precipitation and the dramatically improved performance of quenched samples were analysed using strengthening mechanisms. After quenching at 850℃, the as-built 24CrNiMo steel attained ultra-high mechanical properties including hardness, Ultimate Tensile Strength (UTS), Elongation (El) and impact energy with values of 480.9 HV_(1), 1611.4 MPa, 9.8% and 42.8 J, respectively. Meanwhile, both the wear and thermal fatigue resistance increased by approximately 40%. This study demonstrated that LPBF-fabricated 24CrNiMo steel, with matching good performances, can be achieved using a subsequent one-step quenching process.
基金supported by the National Key Research and Development Program of China(No.2018YFA0707304).
文摘The effects of accumulative hot rolling followed by solution treatment on the microstructural evolution and fracture behavior of 30CrMo/316L multilayered composites have been investigated.A scanning electron microscope equipped with an electron backscatter diffraction probe,a laser confocal microscope,an electron probe microanalysis,and a universal testing machine were employed to characterize the microstructures and mechanical properties.The results indicate that solution treatment transformed the microstructure of the 30CrMo layer from ferrite to martensite,while the 316L layer remained austenitic but transitioned from the rolled to the recrystallized state.Additionally,solution treatment significantly enhanced the mechanical properties of the composite,leading to an increase in yield strength and ultimate tensile strength to 744 and 1106 MPa,respectively—258 and 276 MPa higher than those of the hot-rolled plate.The enhancement in strength is primarily attributed to the formation of high-strength martensite in the 30CrMo layer.During deformation,the composite interface effectively impeded crack propagation and induced step-like deflection.However,the formation of cross-layer grains facilitated crack nucleation at grain boundaries,leading to rapid crack propagation and instantaneous fracture.Therefore,preventing the formation of cross-layer grains during the heat treatment process is crucial,as their presence weakens the interfacial strengthening effect of the composite plate.This study provides valuable insights for the design and development of multi-layered steels.
基金Project(K2022G038)supported by the Science Technology Research and Development Program of China State Railway Group Co.,LtdProject(52178405)supported by the National Natural Science Foundation of China。
文摘To address the issue of extreme thermal-induced arching in CRTS II slab tracks due to joint damage,an optimized joint repair model was proposed.First,the formula for calculating the safe temperature rise of the track was derived based on the principle of stationary potential energy.Considering interlayer evolution and structural crack propagation,an optimized joint repair model for the track was established and validated.Subsequently,the impact of joint repair on track damage and arch stability under extreme temperatures was studied,and a comprehensive evaluation of the feasibility of joint repair and the evolution of damage after repair was conducted.The results show that after the joint repair,the temperature rise of the initial damage of the track structure can be increased by 11℃.Under the most unfavorable heating load with a superimposed temperature gradient,the maximum stiffness degradation index SDEG in the track structure is reduced by about 81.16%following joint repair.The joint repair process could effectively reduce the deformation of the slab arching under high temperatures,resulting in a reduction of 93.96%in upward arching deformation.After repair,with the damage to interfacing shear strength,the track arch increases by 2.616 mm.
基金National Nature Science Foundation of China(52261013)。
文摘The differences between shouldered and shoulderless tools in the micro-friction stir welding of 0.8 mm thin plates were evaluated.Employing a suite of advanced characterization methods,including white light interferometry,electron backscatter diffraction(EBSD),and scanning electron microscopy,the formation of weld surface,joint microstructure distribution,and fracture characteristics were studied.The enhancement mechanism of mechanical properties was explained through the Hall-Petch relationship and Taylor's hardening law.Results indicate that the main reason for the increased yield strength observed in shoulderless tool joints is the combined mechanism of dislocation strengthening and fine-grain strengthening.Specifically,the utilization of shouldered tools results in a smooth weld surface,with an average grain size of 11.24μm and a high-angle grain boundary content of 16.80%in the nugget zone.The primary texture components are the{011}<100>Goss and{112}<111>copper textures,yielding a maximum texture strength of 3.70.Simultaneously,the fracture dimples exhibit a reduction in size and an increase in depth.Whereas the welds produced with shoulderless tools display slight burrs on the surface.The experimental results demonstrate that the average grain size in the nugget zone of these joints is significantly reduced to 0.59μm,while the high-angle grain boundary content reaches 34.34%.This process is accompanied by the formation of{111}<110>Shear textures and{001}<110>rotated cubic textures as the main components,resulting in a significant increase in maximum texture strength to 6.65.
