Ceramic cores with complex structures and optimized properties are critical for hollow turbine blades applied in aeroengines.Compared to traditional methods,additive manufacturing(AM)presents great advantages in formi...Ceramic cores with complex structures and optimized properties are critical for hollow turbine blades applied in aeroengines.Compared to traditional methods,additive manufacturing(AM)presents great advantages in forming complex ceramic cores,but how to balance the porosity and strength is an enormous challenge.In this work,alumina ceramic cores with high porosity,moderate strength,and low high-temperature deflection were prepared using stereolithography(SLA)3D printing by a novel powder gradation design strategy.The contradiction between porosity and flexural strength is well adjusted when the mass ratio of the coarse,medium,and fine particles is 2:1:1 and the sintering temperature is 1600℃.The fracture mode of coarse particles in sintered SLA 3D printing ceramic transforms from intergranular fracture to transgranular fracture with the increase of sintering temperature and the proportion of fine powders in powder system.The sintered porosity has a greater influence on the high-temperature deflection of SLA 3D printed ceramic cores than grain size.On this basis,a"non-skeleton"microstructure model of SLA 3D printed alumina ceramic cores is created to explain the relationship between the sintering process and properties.As a result,high porosity(36.4%),appropriate strength(50.1 MPa),and low high-temperature deflection(2.27 mm)were achieved by optimizing particle size gradation and sintering process,which provides an insight into the important enhancement of the comprehensive properties of SLA 3D printed ceramic cores.展开更多
A new kind of corrosion resistant steelfor cargo oiltanks（COT）was developed.The influences of finalrolling temperature,cooling rate,and finalcooling temperature on microstructure were investigated.The proper rolling...A new kind of corrosion resistant steelfor cargo oiltanks（COT）was developed.The influences of finalrolling temperature,cooling rate,and finalcooling temperature on microstructure were investigated.The proper rolling process parameters were obtained through multi-pass thermalsimulation test.The finalrolling temperature is about 820 ℃,the finalcooling temperature is about 600 ℃,and the cooling rate should be controlled between 10 ℃/s and 20 ℃/s.Based on the above analysis of the results,three groups of rolling samples by thermo mechanicalcontrolprocess are prepared.The tensile strength,yield strength,and toughness of the corrosion resistant steelare measured,which meet the requirements of DH36 steel,it can instruct the actualrolling production.The corrosion behaviour is also researched by weight loss and electrochemicalimpedance spectroscopic method,and it is found that the steelhas good corrosion resistance performance,the best one is No.3 steel,the corrosion rate of which is about 1/4 of the accepted criterion.展开更多
The corrosion resistance of the developed 400 MPa grade rebar was evaluated by a series of experiments, including cycles of corrosion-accelerating tests in the simulated concrete pore solution and reinforced concrete ...The corrosion resistance of the developed 400 MPa grade rebar was evaluated by a series of experiments, including cycles of corrosion-accelerating tests in the simulated concrete pore solution and reinforced concrete cube corrosion-accelerating tests and in situ exposure experiments in chloride ions condition. In addition, the tensile and bending properties and the connection adaptability of the developed rebar were investigated. The results verify that the comprehensive properties of the corrosion-resistant rebar are excellent. The tensile and bending properties of the rebar are up to the standard of GB1499-2007. The common welding method and the mechanical connection technology of knob-cut roiled parallel thread splicing are suitable for the rebar.展开更多
When a redundant robot performs a fault-tolerant operation for locked joint failures, its fault tolerant properties should include dexterity and sudden change of joint velocity at the moment of locking failed joints a...When a redundant robot performs a fault-tolerant operation for locked joint failures, its fault tolerant properties should include dexterity and sudden change of joint velocity at the moment of locking failed joints and the dexterity during the post-failure. Firstly three fault-tolerant indexes, reduced condition number, sudden change of relative joint velocity and centrality are proposed, which can comprehensively evaluate the kinematical performance of a redundant robot during its entire fault-tolerant operations. Then, the influence of the initial postures of robot＇s end-effector on these fault-tolerant indexes is analyzed with a planar robot and a spatial robot. Simulation results show that for a given task the joint trajectory with the best comprehensive effect of fault tolerance can be determined by optimizing the initial posture of a robot.展开更多
High entropy alloy(HEA)has attracted great interests as one of the promising multifunctional materials in marine applications.However,Cu as an effective biocide tends to form segregation in HEA,which could deteriorate...High entropy alloy(HEA)has attracted great interests as one of the promising multifunctional materials in marine applications.However,Cu as an effective biocide tends to form segregation in HEA,which could deteriorate corrosion and induce brittle fracture.Herein,we report a strategy to tailor the existing form of Cu in HEA from undesired large-scale segregation to uniform distribution with dispersed nanoscale precipitation,while retaining the unique structure characteristics of HEA.Eliminating Cu segregation improves toughness and avoids serious corrosion in the grain boundary.Uniform distribution with dispersed nanoscale precipitation of Cu further enhances the antifouling and lubricating abilities of Cu-doped HEA.Tailored AlCoCrFeNiCu_(0.5)HEA in this work has excellent comprehensive properties combining good mechanical properties,outstanding antifouling abilities,superior resistance to corrosion and wear.Furthermore,the corresponded mechanisms are discussed in terms of Cu-segregation-eliminated,nanoscale-Cu-precipitate-forming and comprehensive properties.展开更多
Alloys with composition of Mg_(96-x)Gd_3Zn_1Li_x(at.%)(x=0, 2, 4, and 6) were prepared by conventional casting. The microstructures of these alloys under as-cast and solid-solution conditions have been observed, and t...Alloys with composition of Mg_(96-x)Gd_3Zn_1Li_x(at.%)(x=0, 2, 4, and 6) were prepared by conventional casting. The microstructures of these alloys under as-cast and solid-solution conditions have been observed, and the mechanical properties were investigated. The results showed that Li is an effective element to refine the grains and break the eutectic networks in as-cast MgGd_3Zn_1 alloy. During solid solution treatment, these broken eutectic networks are spheroidized and highly dispersed. In addition, plentiful lamellar long period stacking ordered(LPSO) phases are precipitated in an α-Mg matrix when the Li addition is not more than 4%. Solid-solution treated Mg_(92)Gd_3Zn_1Li_4 alloy exhibits an optimal ultimate tensile strength(UTS) of 226 MPa and elongation of 5.8%. The strength of MgGd_3Zn_1 alloy is improved significantly, meanwhile, the toughness is apparently increased.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
1.Introduction The strength of metallic materials can be ameliorated by introducing boundaries,precipitates,or defects as obstacles to dislocation movement[1].However,high strength is generally obtained at the sacrifi...1.Introduction The strength of metallic materials can be ameliorated by introducing boundaries,precipitates,or defects as obstacles to dislocation movement[1].However,high strength is generally obtained at the sacrifice of plastic deformation capability[2].Lately,many strategies have been proposed to improve the comprehensive properties of materials,among which manipulating stacking fault energy(SFE)is effective[3–5].展开更多
Compared to traditional superhard materials with high electron density and short,strong covalent bonds,alloy materials mainly composed of metallic bonding structures typically have great toughness and lower hardness.B...Compared to traditional superhard materials with high electron density and short,strong covalent bonds,alloy materials mainly composed of metallic bonding structures typically have great toughness and lower hardness.Breaking through the limits of alloy materials is a preface and long-term topic,which is of great significance and value for improving the comprehensive mechanical properties of alloy materials.Here,we report on the discovery of a cubic alloy semiconducting material Ti_(2)Co with a large Vickers of hardness K_(v)^(exp)∼6.7GPa and low fracture toughness of K_(IC)^(exp)∼1.51MPa·m^(1/2).Unexpectedly,the K_(v)^(exp)∼6.7GPa is nearly triple of the K_(v)^(cal)∼2.66GPa predicted by density functional theory(DFT)calculations and theK_(IC)^(exp)∼1.51MPa·m^(1/2)is about one or two orders of magnitude smaller than that of ordinary titanium alloy materials(K_(IC)^(exp)∼30-120MPa·m^(1/2)).These specifications place Ti_(2)Co far from the phase space of the known alloy materials.Upon incorporation of oxygen into structural void positions,both values were simultaneously improved for Ti_(4)Co_(2)O to∼9.7GPa and∼2.19MPa·m^(1/2),respectively.Further DFT calculations on the electron localization function of Ti_(4)Co_(2)X(X=B,C,N,O)vs.the interstitial elements indicate that these simultaneous improvements originate from the coexistence of Ti-Co metallic bonds,the emergence of newly oriented Ti-X covalent bonds,and the increase of electron concentration.Moreover,the large difference between K_(v)^(exp)and K_(v)^(cal)of Ti_(2)Co suggests underlying mechanism concerning the absence of the O(16d)or Ti_(2)-O bonds in the O-(Ti_(2))_(6) octahedron.This discovery proposes a new pathway to simultaneously improve the comprehensive mechanical performances and illuminates the path of exploring superconducting materials with excellent mechanical performances.展开更多
Alloying with transition metal elements akin to Sm(CoFeCuZr)z can effectively enhance the magnetic properties of SmCo-based permanent magnets.However,the effects of transition metals doping on its magnetic properties,...Alloying with transition metal elements akin to Sm(CoFeCuZr)z can effectively enhance the magnetic properties of SmCo-based permanent magnets.However,the effects of transition metals doping on its magnetic properties,detailed atomic occupancy and the mechanism for structural stability remain unclear.Specifically,for SmCo3 magnets,there is minimal theoretical study available.Herein,based on first-principles calculations,we systematically investigated the influence of 3d transition metals(TMs)doping on the structural stability,magnetic properties and electronic characteristics of SmCo3 magnets.Our results show that Sc,Ti,V,Fe,Ni,Cu and Zn preferentially occupy the 18h lattice site,while Cr and Mn occupy the 3b and 6c lattice sites,respectively.Doping with Ti,Cr,Mn,Fe,Ni,Cu and Zn contributes to enhancing the stability of SmCo3,whereas the doping of Sc and V adversely affects structural stability.The magnetic calculations reveal that Cr,Mn and Fe doping significantly enhances the total magnetic moment.It is also found that lower concentrations of Cr doping can significantly enhance the magnetocrystalline anisotropy energy(MAE).More intriguingly,when the doping concentrations of Sc,Ni and Cu reach 14.81 at%,22.22 at%and 22.22 at%,respectively,the magnetic easy axis of the system shifts from out-of-plane to in-plane.The optimal doping concentration of Fe in the SmCo_(3) system is determined to be 37.04 at%.The Curie temperature of pure SmCo_(3) is 483.9 K.Our theoretical study offers valuable theoretical guidance for experimental exploration toward SmCo-based permanent magnets with higher performance.展开更多
1.Introduction The strength-ductility trade-offdilemma has long been a per-sistent challenge in Al matrix composites(AMCs)[1,2].This is-sue primarily arises from the agglomeration of reinforcements at the grain bounda...1.Introduction The strength-ductility trade-offdilemma has long been a per-sistent challenge in Al matrix composites(AMCs)[1,2].This is-sue primarily arises from the agglomeration of reinforcements at the grain boundaries(GBs),which restricts local plastic flow dur-ing the plastic deformation and leads to stress concentration[3,4].Recently,the development of concepts aimed at achieving hetero-geneous grain has emerged as a promising approach for enhanc-ing comprehensive mechanical properties[5,6].展开更多
Novel Al-Sn-Bi anodes with and without lanthanum （La） were prepared.To evaluate the corrosion properties of the anodes,constant current and dynamic loop tests were carried out to determine its efficiency and corrosi...Novel Al-Sn-Bi anodes with and without lanthanum （La） were prepared.To evaluate the corrosion properties of the anodes,constant current and dynamic loop tests were carried out to determine its efficiency and corrosion rate.Optical microscopy （OM）,transmission electron microscopy （TEM） and energy spectrum analysis techniques were used to examine and analyze microstructure and corrosion behavior of the specimens.The result showed that the Al-Sn-Bi anodes with La additions revealed higher current efficiency and anticorrosion in artificial environment.Segregation phase of anodes with La additions got more homogenous than that without La additions.Its grains were fined and the amount of segregation Fe-phase was reduced.展开更多
In the rapidly evolving aerospace sector,the quest for sophisticated thermal barrier coating(TBC)materials has intensified.These materials are primarily sought for their superior comprehensive thermal characteristics,...In the rapidly evolving aerospace sector,the quest for sophisticated thermal barrier coating(TBC)materials has intensified.These materials are primarily sought for their superior comprehensive thermal characteristics,which include a low thermal conductivity coupled with a high coefficient of thermal expansion(CTE)that synergizes with the substrate.In our study,we adopt a solid-state method to synthesize a series of high-entropy rare-earth cerates:La_(2)Ce_(2)O_(7)(1RC),(La_(1/2)Nd_(1/2))2Ce_(2)O_(7)(2RC),(La_(1/3)Nd_(1/3)Sm_(1/3))_(2)Ce_(2)O_(7)(3RC),(La_(1/4)Nd_(1/4)Sm_(1/4)Eu_(1/4))_(2)Ce_(2)O_(7)(4RC),and(La_(1/5)Nd_(1/5)Sm_(1/5)Eu_(1/5)Gd_(1/5))_(2)Ce_(2)O_(7)(5RC),all sintered at 1,600℃ for 10 h.We thoroughly examine their phase structure,morphology,elemental distribution,and thermal properties.Our in-depth analysis of the phonon scattering mechanisms reveals that 4RC and 5RC exhibit exceptional thermal properties:high CTEs of 13.00×10^(−6) K^(−1) and 12.77×10^(−6) K^(−1) at 1,400℃,and low thermal conductivities of 1.55 W/(m·K)and 1.68 W/(m·K)at 1,000℃,respectively.Compared to other TBC systems,4RC and 5RC stand out for their excellent thermal characteristics.This study significantly contributes to the development of high-entropy oxides for TBC applications.展开更多
Bistatic forward-looking synthetic aperture radar（SAR） has many advantages and applications owing to its twodimensional imaging capability.There could be various imaging configurations because of the geometric flexi...Bistatic forward-looking synthetic aperture radar（SAR） has many advantages and applications owing to its twodimensional imaging capability.There could be various imaging configurations because of the geometric flexibility of bistatic platforms,resulting in kinds of models built independently among which there could be some similar even the same motion features.Comprehensive research on such systems in a more comprehensive and general point of view is required to address their difference and consistency.Property analysis of bistatic forwardlooking SAR with arbitrary geometry is achieved including stripmap and spotlight modes on airborne platform,missile-borne platform,and hybrid platform of both.Emphasis is placed on azimuth space variance of some key parameters significantly affecting the subsequent imaging processing,based on which the frequency spectra are further described and compared considering respective features of different platforms for frequency imaging algorithm developing.Simulation results confirm the effectiveness and correctness of our analysis.展开更多
Alloying combined with plastic deformation processing is widely used to improve mechanical properties of pure Zn.As-cast Zn and its alloys are brittle.Beside plastic deformation processing,no effective method has yet ...Alloying combined with plastic deformation processing is widely used to improve mechanical properties of pure Zn.As-cast Zn and its alloys are brittle.Beside plastic deformation processing,no effective method has yet been found to eliminate the brittleness and even endow room temperature super-ductility.Second phase,induced by alloying,not only largely determines the ability of plastic deformation,but also influences strength,corrosion rate and cytotoxicity.Controlling second phase is important for designing biodegradable Zn alloys.In this review,knowledge related to second phases in biodegradable Zn alloys has been analyzed and summarized,including characteristics of binary phase diagrams,volume fraction of second phase in function of atomic percentage of an alloying element,and so on.Controversies about second phases in Zn-Li,Zn-Cu and Zn-Fe systems have been settled down,which benefits future studies.The effects of alloying elements and second phases on microstructure,strength,ductility,corrosion rate and cytotoxicity have been neatly summarized.Mg,Mn,Li,Cu and Ag are recommended as the major alloying elements,owing to their prominent beneficial effects on at least one of the above properties.In future,synergistic effects of these elements should be more thoroughly investigated.For other nutritional elements,such as Fe and Ca,refining second phase is a matter of vital concern.展开更多
基金financially supported by the National Natural Science Foundation of China(Nos.52130204,52174376,51822405)Guangdong Basic and Applied Basic Research Foundation(No.21201910250000848)+5 种基金Science and Technology Innovation Team Plan of Shaan Xi Province(No.2021TD-17)The Youth Innovation Team of Shaanxi UniversitiesJoint Research Funds of the Department of Science&Technology of Shaanxi Province and NPU(2020GXLH-Z-024)Key R&D Program of Shaan Xi Province(No.2019ZDLGY 04-04)Fundamental Research Funds for the Central Universities(No.D5000210902)Innovation Foundation for Doctor Dissertation of Northwestern Polytechnical University(Nos.CX2021056 and CX2021066),China。
文摘Ceramic cores with complex structures and optimized properties are critical for hollow turbine blades applied in aeroengines.Compared to traditional methods,additive manufacturing(AM)presents great advantages in forming complex ceramic cores,but how to balance the porosity and strength is an enormous challenge.In this work,alumina ceramic cores with high porosity,moderate strength,and low high-temperature deflection were prepared using stereolithography(SLA)3D printing by a novel powder gradation design strategy.The contradiction between porosity and flexural strength is well adjusted when the mass ratio of the coarse,medium,and fine particles is 2:1:1 and the sintering temperature is 1600℃.The fracture mode of coarse particles in sintered SLA 3D printing ceramic transforms from intergranular fracture to transgranular fracture with the increase of sintering temperature and the proportion of fine powders in powder system.The sintered porosity has a greater influence on the high-temperature deflection of SLA 3D printed ceramic cores than grain size.On this basis,a"non-skeleton"microstructure model of SLA 3D printed alumina ceramic cores is created to explain the relationship between the sintering process and properties.As a result,high porosity(36.4%),appropriate strength(50.1 MPa),and low high-temperature deflection(2.27 mm)were achieved by optimizing particle size gradation and sintering process,which provides an insight into the important enhancement of the comprehensive properties of SLA 3D printed ceramic cores.
基金Funded by the National Key Technology Research and Development Program of the Ministry of Science and Technology of China during the“12th Five-Year Plan”(No.2011BAE25B03)
文摘A new kind of corrosion resistant steelfor cargo oiltanks（COT）was developed.The influences of finalrolling temperature,cooling rate,and finalcooling temperature on microstructure were investigated.The proper rolling process parameters were obtained through multi-pass thermalsimulation test.The finalrolling temperature is about 820 ℃,the finalcooling temperature is about 600 ℃,and the cooling rate should be controlled between 10 ℃/s and 20 ℃/s.Based on the above analysis of the results,three groups of rolling samples by thermo mechanicalcontrolprocess are prepared.The tensile strength,yield strength,and toughness of the corrosion resistant steelare measured,which meet the requirements of DH36 steel,it can instruct the actualrolling production.The corrosion behaviour is also researched by weight loss and electrochemicalimpedance spectroscopic method,and it is found that the steelhas good corrosion resistance performance,the best one is No.3 steel,the corrosion rate of which is about 1/4 of the accepted criterion.
基金Sponsored by National High-Tech Research and Development Program of China(2006AA03Z518)National KeyTechnology Research and Development Program in 11th Five-Year Plan of China(2007BAE30B05)
文摘The corrosion resistance of the developed 400 MPa grade rebar was evaluated by a series of experiments, including cycles of corrosion-accelerating tests in the simulated concrete pore solution and reinforced concrete cube corrosion-accelerating tests and in situ exposure experiments in chloride ions condition. In addition, the tensile and bending properties and the connection adaptability of the developed rebar were investigated. The results verify that the comprehensive properties of the corrosion-resistant rebar are excellent. The tensile and bending properties of the rebar are up to the standard of GB1499-2007. The common welding method and the mechanical connection technology of knob-cut roiled parallel thread splicing are suitable for the rebar.
基金National Natural Science Foundation of China (No.50775002)Academic Human Resources Devel-opment in Institution of Higher Learning Under the Jurisdiction of Beijing Municipality, China.
文摘When a redundant robot performs a fault-tolerant operation for locked joint failures, its fault tolerant properties should include dexterity and sudden change of joint velocity at the moment of locking failed joints and the dexterity during the post-failure. Firstly three fault-tolerant indexes, reduced condition number, sudden change of relative joint velocity and centrality are proposed, which can comprehensively evaluate the kinematical performance of a redundant robot during its entire fault-tolerant operations. Then, the influence of the initial postures of robot＇s end-effector on these fault-tolerant indexes is analyzed with a planar robot and a spatial robot. Simulation results show that for a given task the joint trajectory with the best comprehensive effect of fault tolerance can be determined by optimizing the initial posture of a robot.
基金the National Key R&D Program of China(No.2018YFB2000100)the National Natural Science Foundation of China(Nos.51701227 and 51775532)the support of the Taishan Scholars Program of Shandong Province and the Outstanding Talents of Qingdao Innovations。
文摘High entropy alloy(HEA)has attracted great interests as one of the promising multifunctional materials in marine applications.However,Cu as an effective biocide tends to form segregation in HEA,which could deteriorate corrosion and induce brittle fracture.Herein,we report a strategy to tailor the existing form of Cu in HEA from undesired large-scale segregation to uniform distribution with dispersed nanoscale precipitation,while retaining the unique structure characteristics of HEA.Eliminating Cu segregation improves toughness and avoids serious corrosion in the grain boundary.Uniform distribution with dispersed nanoscale precipitation of Cu further enhances the antifouling and lubricating abilities of Cu-doped HEA.Tailored AlCoCrFeNiCu_(0.5)HEA in this work has excellent comprehensive properties combining good mechanical properties,outstanding antifouling abilities,superior resistance to corrosion and wear.Furthermore,the corresponded mechanisms are discussed in terms of Cu-segregation-eliminated,nanoscale-Cu-precipitate-forming and comprehensive properties.
基金supported by the National Natural Science Foundation of China(Nos.50571073,51574175 and 51474153)the Ph. D. Programs Foundation of Ministry of Education of China(20111402110004)the Natural Science Foundation of Shanxi Province(Nos.2009011028-3 and 2012011022-1)
文摘Alloys with composition of Mg_(96-x)Gd_3Zn_1Li_x(at.%)(x=0, 2, 4, and 6) were prepared by conventional casting. The microstructures of these alloys under as-cast and solid-solution conditions have been observed, and the mechanical properties were investigated. The results showed that Li is an effective element to refine the grains and break the eutectic networks in as-cast MgGd_3Zn_1 alloy. During solid solution treatment, these broken eutectic networks are spheroidized and highly dispersed. In addition, plentiful lamellar long period stacking ordered(LPSO) phases are precipitated in an α-Mg matrix when the Li addition is not more than 4%. Solid-solution treated Mg_(92)Gd_3Zn_1Li_4 alloy exhibits an optimal ultimate tensile strength(UTS) of 226 MPa and elongation of 5.8%. The strength of MgGd_3Zn_1 alloy is improved significantly, meanwhile, the toughness is apparently increased.
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financially supported by the National Natural Science Foundation of China(NSFC)under grant No.52371100.
文摘1.Introduction The strength of metallic materials can be ameliorated by introducing boundaries,precipitates,or defects as obstacles to dislocation movement[1].However,high strength is generally obtained at the sacrifice of plastic deformation capability[2].Lately,many strategies have been proposed to improve the comprehensive properties of materials,among which manipulating stacking fault energy(SFE)is effective[3–5].
基金supported by the National Key Research and Development Program of China(Grant Nos.2024YFA1408400,2023YFA1406100,2023YFA1607400,2022YFA1403800,and 2022YFA1403203)the National Natural Science Foundation of China(Grant Nos.12474055,12404067,12025408,52025026,and U23A6003)+3 种基金the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB33000000)the Chinese Academy of Sciences President’s International Fellowship Initiative(Grant No.2024PG0003)the Outstanding Member of Youth Promotion Association of Chinese Academy of Sciences(Grant No.Y2022004)supported by the CAC station of Synergetic Extreme Condition User Facility(SECUF,https://cstr.cn/31123.02.SECUF)。
文摘Compared to traditional superhard materials with high electron density and short,strong covalent bonds,alloy materials mainly composed of metallic bonding structures typically have great toughness and lower hardness.Breaking through the limits of alloy materials is a preface and long-term topic,which is of great significance and value for improving the comprehensive mechanical properties of alloy materials.Here,we report on the discovery of a cubic alloy semiconducting material Ti_(2)Co with a large Vickers of hardness K_(v)^(exp)∼6.7GPa and low fracture toughness of K_(IC)^(exp)∼1.51MPa·m^(1/2).Unexpectedly,the K_(v)^(exp)∼6.7GPa is nearly triple of the K_(v)^(cal)∼2.66GPa predicted by density functional theory(DFT)calculations and theK_(IC)^(exp)∼1.51MPa·m^(1/2)is about one or two orders of magnitude smaller than that of ordinary titanium alloy materials(K_(IC)^(exp)∼30-120MPa·m^(1/2)).These specifications place Ti_(2)Co far from the phase space of the known alloy materials.Upon incorporation of oxygen into structural void positions,both values were simultaneously improved for Ti_(4)Co_(2)O to∼9.7GPa and∼2.19MPa·m^(1/2),respectively.Further DFT calculations on the electron localization function of Ti_(4)Co_(2)X(X=B,C,N,O)vs.the interstitial elements indicate that these simultaneous improvements originate from the coexistence of Ti-Co metallic bonds,the emergence of newly oriented Ti-X covalent bonds,and the increase of electron concentration.Moreover,the large difference between K_(v)^(exp)and K_(v)^(cal)of Ti_(2)Co suggests underlying mechanism concerning the absence of the O(16d)or Ti_(2)-O bonds in the O-(Ti_(2))_(6) octahedron.This discovery proposes a new pathway to simultaneously improve the comprehensive mechanical performances and illuminates the path of exploring superconducting materials with excellent mechanical performances.
基金supported by the National Key Research and Development Program of China(No.2022YFB3505301)the National Key Research and Development Program of Shanxi Province(No.202302050201014)+2 种基金the National Natural Science Foundation of China(No.12304148)the Natural Science Basic Research Program of Shanxi Province(No.202203021222219)the China Postdoctoral Science Foundation(No.2023M731452).
文摘Alloying with transition metal elements akin to Sm(CoFeCuZr)z can effectively enhance the magnetic properties of SmCo-based permanent magnets.However,the effects of transition metals doping on its magnetic properties,detailed atomic occupancy and the mechanism for structural stability remain unclear.Specifically,for SmCo3 magnets,there is minimal theoretical study available.Herein,based on first-principles calculations,we systematically investigated the influence of 3d transition metals(TMs)doping on the structural stability,magnetic properties and electronic characteristics of SmCo3 magnets.Our results show that Sc,Ti,V,Fe,Ni,Cu and Zn preferentially occupy the 18h lattice site,while Cr and Mn occupy the 3b and 6c lattice sites,respectively.Doping with Ti,Cr,Mn,Fe,Ni,Cu and Zn contributes to enhancing the stability of SmCo3,whereas the doping of Sc and V adversely affects structural stability.The magnetic calculations reveal that Cr,Mn and Fe doping significantly enhances the total magnetic moment.It is also found that lower concentrations of Cr doping can significantly enhance the magnetocrystalline anisotropy energy(MAE).More intriguingly,when the doping concentrations of Sc,Ni and Cu reach 14.81 at%,22.22 at%and 22.22 at%,respectively,the magnetic easy axis of the system shifts from out-of-plane to in-plane.The optimal doping concentration of Fe in the SmCo_(3) system is determined to be 37.04 at%.The Curie temperature of pure SmCo_(3) is 483.9 K.Our theoretical study offers valuable theoretical guidance for experimental exploration toward SmCo-based permanent magnets with higher performance.
基金support by the National Natural Science Foundation of China(Grant Nos.U23A20546 and 52271010)the Chinese National Natural Science Fund for Distinguished Young Scholars(Grant No.52025015)the Natural Science Foundation of Tianjin City(No.21JCZDJC00510).
文摘1.Introduction The strength-ductility trade-offdilemma has long been a per-sistent challenge in Al matrix composites(AMCs)[1,2].This is-sue primarily arises from the agglomeration of reinforcements at the grain boundaries(GBs),which restricts local plastic flow dur-ing the plastic deformation and leads to stress concentration[3,4].Recently,the development of concepts aimed at achieving hetero-geneous grain has emerged as a promising approach for enhanc-ing comprehensive mechanical properties[5,6].
基金the Industrial Investment Fund of General Research Institute for Non-ferrous Metals for financial support
文摘Novel Al-Sn-Bi anodes with and without lanthanum （La） were prepared.To evaluate the corrosion properties of the anodes,constant current and dynamic loop tests were carried out to determine its efficiency and corrosion rate.Optical microscopy （OM）,transmission electron microscopy （TEM） and energy spectrum analysis techniques were used to examine and analyze microstructure and corrosion behavior of the specimens.The result showed that the Al-Sn-Bi anodes with La additions revealed higher current efficiency and anticorrosion in artificial environment.Segregation phase of anodes with La additions got more homogenous than that without La additions.Its grains were fined and the amount of segregation Fe-phase was reduced.
基金This work was supported by the Instrument and equipment development,Chinese Academy of Sciences[YJKYYQ20210030]Shanghai Science and Technology Innovation Action Plan[21142201100].
文摘In the rapidly evolving aerospace sector,the quest for sophisticated thermal barrier coating(TBC)materials has intensified.These materials are primarily sought for their superior comprehensive thermal characteristics,which include a low thermal conductivity coupled with a high coefficient of thermal expansion(CTE)that synergizes with the substrate.In our study,we adopt a solid-state method to synthesize a series of high-entropy rare-earth cerates:La_(2)Ce_(2)O_(7)(1RC),(La_(1/2)Nd_(1/2))2Ce_(2)O_(7)(2RC),(La_(1/3)Nd_(1/3)Sm_(1/3))_(2)Ce_(2)O_(7)(3RC),(La_(1/4)Nd_(1/4)Sm_(1/4)Eu_(1/4))_(2)Ce_(2)O_(7)(4RC),and(La_(1/5)Nd_(1/5)Sm_(1/5)Eu_(1/5)Gd_(1/5))_(2)Ce_(2)O_(7)(5RC),all sintered at 1,600℃ for 10 h.We thoroughly examine their phase structure,morphology,elemental distribution,and thermal properties.Our in-depth analysis of the phonon scattering mechanisms reveals that 4RC and 5RC exhibit exceptional thermal properties:high CTEs of 13.00×10^(−6) K^(−1) and 12.77×10^(−6) K^(−1) at 1,400℃,and low thermal conductivities of 1.55 W/(m·K)and 1.68 W/(m·K)at 1,000℃,respectively.Compared to other TBC systems,4RC and 5RC stand out for their excellent thermal characteristics.This study significantly contributes to the development of high-entropy oxides for TBC applications.
基金supported by the National Natural Science Foundation of China(6100121161303035+1 种基金61471283)the Fundamental Research Funds for the Central Universities(K5051202016)
文摘Bistatic forward-looking synthetic aperture radar（SAR） has many advantages and applications owing to its twodimensional imaging capability.There could be various imaging configurations because of the geometric flexibility of bistatic platforms,resulting in kinds of models built independently among which there could be some similar even the same motion features.Comprehensive research on such systems in a more comprehensive and general point of view is required to address their difference and consistency.Property analysis of bistatic forwardlooking SAR with arbitrary geometry is achieved including stripmap and spotlight modes on airborne platform,missile-borne platform,and hybrid platform of both.Emphasis is placed on azimuth space variance of some key parameters significantly affecting the subsequent imaging processing,based on which the frequency spectra are further described and compared considering respective features of different platforms for frequency imaging algorithm developing.Simulation results confirm the effectiveness and correctness of our analysis.
基金financially supported by National Key R&D Program of China(2016YFC1102500).
文摘Alloying combined with plastic deformation processing is widely used to improve mechanical properties of pure Zn.As-cast Zn and its alloys are brittle.Beside plastic deformation processing,no effective method has yet been found to eliminate the brittleness and even endow room temperature super-ductility.Second phase,induced by alloying,not only largely determines the ability of plastic deformation,but also influences strength,corrosion rate and cytotoxicity.Controlling second phase is important for designing biodegradable Zn alloys.In this review,knowledge related to second phases in biodegradable Zn alloys has been analyzed and summarized,including characteristics of binary phase diagrams,volume fraction of second phase in function of atomic percentage of an alloying element,and so on.Controversies about second phases in Zn-Li,Zn-Cu and Zn-Fe systems have been settled down,which benefits future studies.The effects of alloying elements and second phases on microstructure,strength,ductility,corrosion rate and cytotoxicity have been neatly summarized.Mg,Mn,Li,Cu and Ag are recommended as the major alloying elements,owing to their prominent beneficial effects on at least one of the above properties.In future,synergistic effects of these elements should be more thoroughly investigated.For other nutritional elements,such as Fe and Ca,refining second phase is a matter of vital concern.
