Bubbles are prevalent defects on the oxidized surfaces of ultra-high temperature carbides,compromis-ing structural stability and oxidation resistance.Despite their significance,the formation mechanisms and microstruct...Bubbles are prevalent defects on the oxidized surfaces of ultra-high temperature carbides,compromis-ing structural stability and oxidation resistance.Despite their significance,the formation mechanisms and microstructural evolution of bubbles during ultra-high temperature oxidation remain inadequately understood.To address this gap,the bubble behaviors of multicomponent carbides,including(Hf,Ti)C,(Hf,Zr,Ti)C,(Hf,Zr,Ti,Ta)C,and(Hf,Zr,Ti,Nb)C,were investigated under oxidation conditions at 2500℃.The roles of various elements were elucidated through first-principles calculations.Results show that the for-mation of a dense composite oxide layer is essential for bubble generation,with the release of gaseous products serving as the primary driving force.The microstructure of the bubbles is influenced by the ma-trix composition.The addition of Ti,Ta,and Nb significantly lowers the surface energy of the shell oxides,providing preferential nucleation sites for bubbles.The progressive oxidation of Ti leads to the formation of a“TiO_(2)-TiO-HfO_(2)”multilayerstructureat thebubbletop,which evolvesintoadendriticstructurewith prolonged oxidation.Ta and Nb further modulate the size and number of bubbles by altering the compo-sition and surface energy of the shell oxides.展开更多
This study investigates the bond performance at the interfacial region shared by Ultra-High Performance Concrete(UHPC)and steel tubes through push-out tests.This study examines how changes in steel fiber volumetric ra...This study investigates the bond performance at the interfacial region shared by Ultra-High Performance Concrete(UHPC)and steel tubes through push-out tests.This study examines how changes in steel fiber volumetric ratio and thickness of steel tube influence the bond strength characteristics.The results show that as the enhancement of the steel tube wall thickness,the ultimate bond strength at the interface improves significantly,whereas the initial bond strength exhibits only slight variations.The influence of steel fiber volumetric ratio presents a nonlinear trend,with initial bond strength decreasing at low fiber content and increasing significantly as fiber content rises.Additionally,finite element(FE)simulations were applied to replicate the experimental conditions,and the outcomes showed strong correlation with the experimental data,confirming the exactitude of the FE model in predicting the bond behavior at the UHPC-Steel interface.These findings provide valuable insights for optimizing the design of UHPC-Filled steel tubes in high-performance structure.展开更多
In order to enable efficient and cost-effective rehabilitation of surface-worn hydraulic supports,the synthesis and characterization of a novel Ti(N,B)/AISI431 composite coating formed on the surface of 27MnSi steel a...In order to enable efficient and cost-effective rehabilitation of surface-worn hydraulic supports,the synthesis and characterization of a novel Ti(N,B)/AISI431 composite coating formed on the surface of 27MnSi steel are explored via an exothermic in-situ reaction using the ultra-high speed laser cladding(EHLA in German)technique in combination with direct reaction synthesis(DRS).The aim is to mitigate the high residual stress and interfacial stress gradient in the remanufactured AISI431 coating on 27SiMn steel substrate and enhance surface wear resistance.The microstructure,phase composition and interface characteristics are carefully investigated.Much improved wear performance of the composite coating is revealed,mainly attributed to the in-situ formed Ti(N,B)precipitates,refined microstructure,broadened interface zone and reduced residual stress,benefited from the exothermic in-situ Ti(N,B)-reaction.The potential of combining ultra-high speed laser cladding with DRS is demonstrated to create coatings with tailored properties,providing valuable insights for developing advanced wear-resistant materials for industrial applications using EHLA.展开更多
Poly(vinylidene fluoride)(PVDF)foam has received widespread attention due to its high strength,and excellent combination of flame-retardancy,antibacterial performance,and chemical stability.However,the foaming ability...Poly(vinylidene fluoride)(PVDF)foam has received widespread attention due to its high strength,and excellent combination of flame-retardancy,antibacterial performance,and chemical stability.However,the foaming ability of conventional PvDF is severely limited by its rapid crystallization kinetics and poor melt strength.Although ultra-high molecular weight PVDF(H-PVDF)theoretically offers prolonged melt elasticity favorable for foaming,the extremely high melt viscosity poses substantial processing challenges,and its foaming behavior has remained largely unexplored.To address these issues,this study proposes a novel fabrication strategy combining solvent casting with microcellular foaming to prepare H-PVDF foams.Dynamic mechanical analysis and differential scanning calorimetry reveal that extensive chain entanglements in H-PVDF impose constraints on crystallization and significantly enhance melt strength.By tuning the processing parameters,the distinctive foaming be-havior of H-PVDF under various conditions is systematically elucidated.Remarkably,a record-high expansion ratio of 55.6-fold is achieved,ac-companied by a highly uniform and fine cellular structure.The resulting H-PVDF foams exhibit a low thermal conductivity of 31.8 mW·m^(-1).K^(-1),while retaining excellent compressive strength,flame-retardancy,and hydrophobicity.These outstanding properties highlight the great potential of H-PVDF foams as the thermal insulation materials for applications in aerospace,energy infrastructure,and other extreme environments.展开更多
Ultra-high strength steel(UHSS)fabricated via laser additive manufacturing(LAM)holds significant promise for applications in defense,aerospace,and other high-performance sectors.However,its response to high-impact loa...Ultra-high strength steel(UHSS)fabricated via laser additive manufacturing(LAM)holds significant promise for applications in defense,aerospace,and other high-performance sectors.However,its response to high-impact loading remains insufficiently understood,particularly regarding the influence of energy density on its dynamic mechanical behavior.In this study,scanning electron micro-scopy,electron backscatter diffraction,and image recognition techniques were employed to investigate the microstructural variations of LAM-fabricated UHSS under different energy density conditions.The dynamic mechanical behavior of the material was characterized using a Split Hopkinson Pressure Bar system in combination with high-speed digital image correlation.The study reveals the spatiotemporal evolution of surface strain and crack formation,as well as the underlying dynamic fracture mechanisms.A clear correlation was established between the microstructures formed under varying energy densities and the resulting dynamic mechanical strength of the material.Results demonstrate that optimal material density is achieved at energy densities of 292 and 333 J/mm^(3).In contrast,energy densities exceeding 333 J/mm^(3) induce keyhole defects,compromising structural integrity.Dynamic performance is strongly dependent on material density,with peak impact resistance observed at 292 J/mm^(3)-where strength is 8.4%to 17.6%higher than that at 500 J/mm^(3).At strain rates≥2000 s^(-1),the material reaches its strength limit at approximately 110μs,with the initial crack appearing within 12μs,followed by rapid failure.Conversely,at strain rates≤1500 s^(-1),only microcracks and adiabatic shear bands are detected.A transition in fracture surface morphology from ductile to brittle is observed with increasing strain rate.These findings offer critical insights into optimizing the dynamic mechanical properties of LAM-fabricated UHSS and provide a valuable foundation for its deployment in high-impact environments.展开更多
It is well known that transition metal sulfides(TMS)(i.e.,NiS_(2))undergo electrochemical reconstructions to generate highly active Ni_(3)S_(2) during the process of hydrogen evolution reaction(HER)under overpotential...It is well known that transition metal sulfides(TMS)(i.e.,NiS_(2))undergo electrochemical reconstructions to generate highly active Ni_(3)S_(2) during the process of hydrogen evolution reaction(HER)under overpotentials of<500 mV.However,at higher overpotentials,Ni_(3)S_(2) can theoretically be further restructured into Ni and thus form Ni/Ni_(3)S_(2) heterogeneous interface structures,which may provide opportunities to further enhance HER activity of NiS_(2).Here,we selected NiS_(2) as a model electrocatalyst and investigated the influence of the reconstruction results induced from regular to ultrahigh overpotentials on its electrocatalytic hydrogen precipitation performance.The experimental results showed that the most significant enhancement of hydrogen precipitation performance was obtained for the NiS_(2)@CC-900(900 means 900 mV overpotential)sample after the ultra-high overpotential induced reconstruction.Compared with the initial overpotential of 161 mV(10 mA cm^(-2)),the overpotential of the reconstructed sample reduced by 67 mV(42%).The characterization results showed that an ultra-high overpotential of 900 mV induced deep reconstruction of NiS_(2),formed highly reactive Ni/Ni_(3)S_(2) heterogeneous interfaces,which is more conducive to improved HER performance and match well with theoretical calculations results.We demonstrated ultrahigh overpotential was an effective strategy to induce NiS_(2) deeply reconstruction and significantly improve its HER performance,and this strategy was also applicable to CoS_(2) and FeS_(2).This study provides an extremely simple and universal pathway for the reasonable construction of efficient electrocatalysts by induced TMS deeply reconstruction.展开更多
The effects of prior austenite and primary carbides on the mechanical properties of a novel 2.5 GPa grade steel were investigated by treating at various solid-solution temperatures.The ultimate tensile strength and Ch...The effects of prior austenite and primary carbides on the mechanical properties of a novel 2.5 GPa grade steel were investigated by treating at various solid-solution temperatures.The ultimate tensile strength and Charpy U-notch impact energy initially increased and subsequently decreased as the solid-solution temperature rose,while the yield strength consistently decreased.The size of prior austenite grain and martensite block always increased with rising the solid-solution temperature,and austenite grain growth activation energy is 274,969 J/mol.The growth of prior austenite was restricted by primary carbides M6C and MC.The dissolution of the primary carbides not only enhanced solid-solution strengthening and secondary hardening effects but also increased the volume fraction of retained austenite.The increase in the ultimate tensile strength and Charpy U-notch impact energy was primarily attributed to the dissolution of the primary carbides M6C and MC,while the decrease was due to the increase in the size of prior austenite grain and martensite block.Exceptional combination of strength,ductility and toughness with ultimate tensile strength of 2511 MPa,yield strength of 1920 MPa,elongation of 9.5%,reduction of area of 41%and Charpy U-notch impact energy of 19.5 J was obtained when experimental steel was solid-solution treated at 1020℃.展开更多
Ultra-high dose rate flash radiotherapy(FLASH-RT)has attracted wide attention in the field of radiotherapy in recent years.For FLASH-RT,radiation is delivered at a very high dose rate[usually thousands of times compar...Ultra-high dose rate flash radiotherapy(FLASH-RT)has attracted wide attention in the field of radiotherapy in recent years.For FLASH-RT,radiation is delivered at a very high dose rate[usually thousands of times compared with conventional radiotherapy(CONV-RT)]in an extremely short time.This novel irradiation technique shows a protective effect on normal tissues,also known as the flash effect.At the same time,FLASH-RT is comparable to CONV-RT in terms of tumorkilling efficacy.As basic research dedicates to uncover the mechanisms by which FLASH-RT reduces radiation-induced normal tissue damage,clinical trials of FLASH-RT have been gradually conducted worldwide.This article systematically reviews the evidence of the feasibility and safety of FLASH-RT in clinical practice and offers insights into the future translation of this technology in clinic.展开更多
Integrating thick/thin film sensors into component systems has emerged as a prevalent approach for monitoring in extreme environments.However,traditional vapor deposition methods face obstacles,including complex fabri...Integrating thick/thin film sensors into component systems has emerged as a prevalent approach for monitoring in extreme environments.However,traditional vapor deposition methods face obstacles,including complex fabrication processes and the degradation of sensitive materials at extremely high temperatures.This work delineates the development of a polysilazane composite dual-layer thick-film Negative Temperature Coefficient(NTC)thermistor characterized by its suitability for extreme temperatures and robust bond strength achieved through an advanced near-net-shape printing methodology.High-temperature resistant La(Ca)CrO_(3)/polysilazane films were printed as the sensitive layer,while a dense layer formed by Cr_(2)O_(3)/polysilazane was used as the protective layer.The bilayer structure resulted in a 2.5-fold increase in adhesion strength compared to the single-layer La(Ca)CrO_(3)/polysilazane films.Experimental results indicate that the dual-layer thick-film NTC thermistor can be operated long-term at 1300℃ with a resistance drift rate of 0.9%/h and survive short-term exposure to temperatures up to 1550℃.As a proof of concept,this work applied 3D printing technology to fabricate a polysilazane composite dual-layer thick-film NTC thermistor on the surface of turbine blades and demonstrated its functionality under flame impingement at nearly 1300℃.Such flexible 3D printing techniques pave the way for a new paradigm in manufacturing sensors capable of withstanding ultra-high temperatures.展开更多
Background:Polygonum multiflorum-induced liver injury(PM-DILI)has significantly hindered its clinical application and development.Methods:This study investigates the variation in content and toxicity of dian-thrones,t...Background:Polygonum multiflorum-induced liver injury(PM-DILI)has significantly hindered its clinical application and development.Methods:This study investigates the variation in content and toxicity of dian-thrones,the toxic components of P.multiflorum,during different processing cycles.We employed the ultra-high-performance liquid chromatography triple quadrupole mass spectrometry method to quantify six dianthrones in raw P.multiflorum and formulations processed with a method called nine cycles of steaming and sunning.Additionally,toxicity assessments were conducted using human normal liver cell line L02 and zebrafish embryos.Results:Results indicate a gradual reduction in dianthrones content with increasing processing cycles.Processed formulations exhibited significantly reduced cytotoxic-ity in L02 cells and hepatotoxicity in zebrafish embryos.Conclusions:Our findings elucidate the relationship between processing cycles and P.multiflorum toxicity,providing theoretical support for its safe use.展开更多
To meet the increasing demand for continuously enhancing engineering performance and energy efficiency in a variety of aerospace and energy applications,structural materials with high strength at ultra-high temperatur...To meet the increasing demand for continuously enhancing engineering performance and energy efficiency in a variety of aerospace and energy applications,structural materials with high strength at ultra-high temperatures are urgently required.In the past decade,refractory multi-principal element alloys(RMPEAs),particularly those containing elements with high melting temperatures(T_(m))such as W and Ta(hereafter denoted as WTa-RMPEAs),have garnered extensive interest due to their exceptional strengths and thermally stability at high temperatures.Characterized by high T_(m),sluggish diffusion,and severe lattice distortion,WTa-RMPEAs exhibit chemical composition fluctuations at different scales,leading to unique mechanical properties and deformation behavior.In this paper,an initial summary is provided of the mechanical properties of typical WTa-RMPEAs at room and high temperatures and the differences in deformation behavior and underlying mechanisms between RMPEAs and conventional alloys are discussed.Additionally,strengthening and toughening strategies and the suggested deformation mechanisms were reviewed.Finally,the challenges in revealing the actual deformation mechanism of WTa-RMPEAs were described,and a brief perspective on the future research of the mechanical behavior of WTa-RMPEAs was proposed.展开更多
Carbon fiber reinforced ultra-high temperature ceramic （UHTC） composites, consisting of carbon fibers embedded in a UHTC-matrix or a C-SiC-UHTC-matrix, are deemed as the most viable class of materials that can overc...Carbon fiber reinforced ultra-high temperature ceramic （UHTC） composites, consisting of carbon fibers embedded in a UHTC-matrix or a C-SiC-UHTC-matrix, are deemed as the most viable class of materials that can overcome the poor fracture toughness and thermal shock resistance of monolithic UHTC ma- terials, and also improve the oxidation resistance and ablation resistance of C/C and C/SiC composites at ultra-high temperatures. In this review, we summarize the different processing routes of the compos- ites based on the UHTC introducing methods, including chemical vapor infiltration/deposition （CVI/D）, precursor infiltration and pyrolysis （PIP）, reactive melt infiltration （RMI）, slurry infiltration （SI）. in-sito reaction, hot pressing （HP）, etc; and the advantages and drawbacks of each method are briefly dis- cussed. The carbon fiber reinforced UHTC composites can be highly tailorable materials in terms of fiber. interface, and matrix. From the perspective of service environmental applications for engine propul- sions anti hypersonic vehicles, the material designs （mainly focusing on the composition, quantity, structure of matrix, as well as the architecture of carbon fibers, UHTCs and pores）, their relevant processing routes and properties （emphasizing on the mechanical and ablation properties） are discussed in this paper. In addition, we propose a material architecture to realize the multi-function through changing the distri- bution of carbon fibers, UHTCs and pores, which will be an important issue for future development of carbon fiber reinforced UHTC composites.展开更多
The influence of rust layers on the corrosion behavior of ultra-high strength steel 300M subjected to a simulated coastal atmosphere was investigated by corrosion weight loss, surface analysis techniques, and electroc...The influence of rust layers on the corrosion behavior of ultra-high strength steel 300M subjected to a simulated coastal atmosphere was investigated by corrosion weight loss, surface analysis techniques, and electrochemical methods. The results exhibit the presence of a large proportion of γ-FeOOH and α-FeOOH and a small amount of Fe3O4 in the outer rust layer. During the wet-dry cyclic process, the bonding performance and the density of outer rust layer deteriorate with the thickness of outer rust. The inner rust layer plays a main role on protectiveness, which can be attributed to the formation of an ultra-dense and adherent rust film with major constituent of α-FeOOH and α-Fe2O3 on the steel.展开更多
The directionally solidified samples of an ultra-high temperature Nb-Si-Ti-Hf-Cr-Al alloy have been prepared with the use of an electron beam floating zone melting (EBFZM) furnace, and their microstructural characteri...The directionally solidified samples of an ultra-high temperature Nb-Si-Ti-Hf-Cr-Al alloy have been prepared with the use of an electron beam floating zone melting (EBFZM) furnace, and their microstructural characteristics have been analyzed. All the primary dendrites of Nb solid solution (Nbss), eutectic colonies of Nba, plus (Nb, Ti)3 Si/(Nb, Ti)5 Si3 and chains of (Nb, Ti)3 Si/(Nb, Ti)5 Si3 plates align along the growth direction of the samples. With increasing of the withdrawing rate, the microstructure is refined, and the amounts of Nbss+ (Nb, Ti)3 Si/(Nb, Ti)5 Si3 eutectic colonies and (Nb, Ti)3 Si/(Nb, Ti)5 Si3 plates increase. There appear nodes in the (Nb, Ti)3 Si/(Nb, Ti)5 Si3 plates.展开更多
The hierarchical martensitic features in ultra-high strength stainless steel(UHSSS),including the prior austenite grains,martensite packets,blocks and laths with the descending size,were refined to various extents by ...The hierarchical martensitic features in ultra-high strength stainless steel(UHSSS),including the prior austenite grains,martensite packets,blocks and laths with the descending size,were refined to various extents by employing different thermomechanical processes and then carefully characterized.Their relation to yield strength and impact toughness was analyzed.We conclude that the refinement of martensitic structures could lead to the significant increase of yield strength,which follows the Hall-Petch relation with the effect grain size defined by high angle boundaries(HABs).Impact toughness of UHSSS depends on the frequency and capability for retained austenite(RA)grains at both HABs and martensite lath boundaries to trap the propagating cracks via strain-induced transformation,in which the film-like RA grains at lath boundaries appear to make the greater contribution.展开更多
The effects of Nb on the thermal stability and impact toughness of ultra-high intrinsic coercivity of Nd-Fe-B magnets were investigated.The results showed that the addition of Nb could improve the thermal stability,an...The effects of Nb on the thermal stability and impact toughness of ultra-high intrinsic coercivity of Nd-Fe-B magnets were investigated.The results showed that the addition of Nb could improve the thermal stability,and obviously increased the impact toughness of sintered Nd-Fe-B magnets.The optimum thermal stability of sintered Nd-Fe-B magnets was obtained when the content of Nb was 1.0 at.%.The maximum impact toughness of sintered Nd-Fe-B magnets was obtained when the content of Nb was 1.5 at.%,but the magnetic properties of sintered Nd-Fe-B magnets drastically deteriorated when the content of Nb increased from 1.0 at.% to 1.5 at.%.The microstructure showed that overfull Nb addition made many ultra-fine grains get together,which led to the density of sintered Nd-Fe-B magnets decline and drastically deteriorated the magnetic properties of sintered Nd-Fe-B magnets.展开更多
An 1100 MPa grade ultra-high strength steel with different martensite fine structures, characterized by prior austenite grain size, martensite packet size, block width and lath width, was studied by various heat treat...An 1100 MPa grade ultra-high strength steel with different martensite fine structures, characterized by prior austenite grain size, martensite packet size, block width and lath width, was studied by various heat treatment processes. The result shows that with decreasing prior austenite grain size, both the packet size and block width decrease, while the lath width has virtually no change. Accordingly, both strength and toughness increase, while total elongation decreases. The yield strength has a Hall Petch type relationship with the prior austenite grain size, packet size and block width, and the block width may be regarded as a key factor influencing strength. On the other hand, the ductile to brittle transition temperature （DBTT） is found to be more related lo the packet size, which may be considered as a dominant factor influencing toughness.展开更多
Starting with the Ertan arch dam （240 m high, 3300 MW） in 2000, China successfully built a total of seven ultra-high arch dams over 200 m tall by the end of 2014. Among these, the ]inping 1 （305 m）, Xiaowan （294...Starting with the Ertan arch dam （240 m high, 3300 MW） in 2000, China successfully built a total of seven ultra-high arch dams over 200 m tall by the end of 2014. Among these, the ]inping 1 （305 m）, Xiaowan （294.5m）, and Xiluodu （285.5 m） arch dams have reached the 300 m height level （i.e., near or over 300 m）, making them the tallest arch dams in the world. The design and construction of these 300 m ultra-high arch dams posed significant challenges, due to high water pressures, high seismic de- sign criteria, and complex geological conditions. The engineering team successfully tackled these chal- lenges and made critical breakthroughs, especially in the area of safety control. In this paper, the author summarizes various key technological aspects involved in the design and construction of 300 m ultra- high arch dams, including the strength and stability of foundation rock, excavation of the dam base and surface treatment, dam shape optimization, safety design guidelines, seismic analysis and design, treatment of a complex foundation, concrete temperature control, and crack prevention. The experience gained from these projects should be valuable for future practitioners.展开更多
Ultra-high strain rate impact tests were conducted by Split-Hopkinson pressure bar to investigate the microstructure evolution and impact deformation mechanism of a solution treated casting AM80 Mg alloy at 25, 150 an...Ultra-high strain rate impact tests were conducted by Split-Hopkinson pressure bar to investigate the microstructure evolution and impact deformation mechanism of a solution treated casting AM80 Mg alloy at 25, 150 and 250 ℃ with a strain rate of 5000 s^(-1). The microcrack and dynamic recrystallization(DRX) preferentially nucleate at grain boundary(GB) and twin boundary(TB), especially at the intersections between GBs and TBs, and then propagate along twin direction. In contrast, the adiabatic shear bands preferentially occur at high-density twined regions. At 25 ℃, the dominated deformation mechanisms are basal slip and twinning. As deformation temperature increases to 150and 250℃, the deformation gradually shifts to be dominated by a coordinated mechanism among non-basal slip, twinning and DRX. The flow stress behavior and deformation mechanism indicate that the degree of decrease in flow stress with temperature is associated with the change of deformation mode.展开更多
A new spheroidizing process of ultra-high carbon steel （UHCS） containing C 1.55%, Cr 1.45%, and Al 1.5% in mass percent has been proposed. The effect of processing parameters on the microstructure was analyzed. The ...A new spheroidizing process of ultra-high carbon steel （UHCS） containing C 1.55%, Cr 1.45%, and Al 1.5% in mass percent has been proposed. The effect of processing parameters on the microstructure was analyzed. The UHCS produced by this new process has a microstructure with recrystallized ferrite matrix and fine and uniform carbide particles. After this spheroidizing, the UHCS exhibits good mechanical properties at ambient temperature, for example σb= 1 100 MPa, σs =915 MPa, δ=8% and high ratio of σs/σb.展开更多
基金financially supported by National Natural Science Foundation of China(No.52072410).
文摘Bubbles are prevalent defects on the oxidized surfaces of ultra-high temperature carbides,compromis-ing structural stability and oxidation resistance.Despite their significance,the formation mechanisms and microstructural evolution of bubbles during ultra-high temperature oxidation remain inadequately understood.To address this gap,the bubble behaviors of multicomponent carbides,including(Hf,Ti)C,(Hf,Zr,Ti)C,(Hf,Zr,Ti,Ta)C,and(Hf,Zr,Ti,Nb)C,were investigated under oxidation conditions at 2500℃.The roles of various elements were elucidated through first-principles calculations.Results show that the for-mation of a dense composite oxide layer is essential for bubble generation,with the release of gaseous products serving as the primary driving force.The microstructure of the bubbles is influenced by the ma-trix composition.The addition of Ti,Ta,and Nb significantly lowers the surface energy of the shell oxides,providing preferential nucleation sites for bubbles.The progressive oxidation of Ti leads to the formation of a“TiO_(2)-TiO-HfO_(2)”multilayerstructureat thebubbletop,which evolvesintoadendriticstructurewith prolonged oxidation.Ta and Nb further modulate the size and number of bubbles by altering the compo-sition and surface energy of the shell oxides.
基金supported by grants from the Natural Science Foundation of Fujian Province(2021J011062)Minjiang Scholars Funding(GY-633Z21067).
文摘This study investigates the bond performance at the interfacial region shared by Ultra-High Performance Concrete(UHPC)and steel tubes through push-out tests.This study examines how changes in steel fiber volumetric ratio and thickness of steel tube influence the bond strength characteristics.The results show that as the enhancement of the steel tube wall thickness,the ultimate bond strength at the interface improves significantly,whereas the initial bond strength exhibits only slight variations.The influence of steel fiber volumetric ratio presents a nonlinear trend,with initial bond strength decreasing at low fiber content and increasing significantly as fiber content rises.Additionally,finite element(FE)simulations were applied to replicate the experimental conditions,and the outcomes showed strong correlation with the experimental data,confirming the exactitude of the FE model in predicting the bond behavior at the UHPC-Steel interface.These findings provide valuable insights for optimizing the design of UHPC-Filled steel tubes in high-performance structure.
基金financially supported by the National Key Research and Development Program of China(No.2023YFB4606200)Technical Development Foundation of China Academy of Machinery Science and Technology Group(No.812201Q9)+2 种基金Fundamental Research Funds of National Institute of Metrology of China(No.AKYRC2401)Beijing Natural Science Foundation(No.2222093)the National Key Research and Development Program of China(No.2021YFB3702003)。
文摘In order to enable efficient and cost-effective rehabilitation of surface-worn hydraulic supports,the synthesis and characterization of a novel Ti(N,B)/AISI431 composite coating formed on the surface of 27MnSi steel are explored via an exothermic in-situ reaction using the ultra-high speed laser cladding(EHLA in German)technique in combination with direct reaction synthesis(DRS).The aim is to mitigate the high residual stress and interfacial stress gradient in the remanufactured AISI431 coating on 27SiMn steel substrate and enhance surface wear resistance.The microstructure,phase composition and interface characteristics are carefully investigated.Much improved wear performance of the composite coating is revealed,mainly attributed to the in-situ formed Ti(N,B)precipitates,refined microstructure,broadened interface zone and reduced residual stress,benefited from the exothermic in-situ Ti(N,B)-reaction.The potential of combining ultra-high speed laser cladding with DRS is demonstrated to create coatings with tailored properties,providing valuable insights for developing advanced wear-resistant materials for industrial applications using EHLA.
基金supported by the National Natural Science Foundation of China(No.52175341)Shandong Provincial Natural Science Foundation(No.ZR2022JQ24)+2 种基金Funding Project of Jinan City's New Twenty Items for Colleges and Universities(No.202333038)Excellent Young Team Project of Central Universities(No.2023QNTD002)Qingdao Key Technology Research and Industrialization Demonstration Project(No.24-1-2-qljh-10-gx).
文摘Poly(vinylidene fluoride)(PVDF)foam has received widespread attention due to its high strength,and excellent combination of flame-retardancy,antibacterial performance,and chemical stability.However,the foaming ability of conventional PvDF is severely limited by its rapid crystallization kinetics and poor melt strength.Although ultra-high molecular weight PVDF(H-PVDF)theoretically offers prolonged melt elasticity favorable for foaming,the extremely high melt viscosity poses substantial processing challenges,and its foaming behavior has remained largely unexplored.To address these issues,this study proposes a novel fabrication strategy combining solvent casting with microcellular foaming to prepare H-PVDF foams.Dynamic mechanical analysis and differential scanning calorimetry reveal that extensive chain entanglements in H-PVDF impose constraints on crystallization and significantly enhance melt strength.By tuning the processing parameters,the distinctive foaming be-havior of H-PVDF under various conditions is systematically elucidated.Remarkably,a record-high expansion ratio of 55.6-fold is achieved,ac-companied by a highly uniform and fine cellular structure.The resulting H-PVDF foams exhibit a low thermal conductivity of 31.8 mW·m^(-1).K^(-1),while retaining excellent compressive strength,flame-retardancy,and hydrophobicity.These outstanding properties highlight the great potential of H-PVDF foams as the thermal insulation materials for applications in aerospace,energy infrastructure,and other extreme environments.
基金supported by the Science and Technology Project of Fire Rescue Bureau of Ministry of Emergency Management,China(No.2022XFZD05)the S&T Program of Hebei,China(No.22375419D).
文摘Ultra-high strength steel(UHSS)fabricated via laser additive manufacturing(LAM)holds significant promise for applications in defense,aerospace,and other high-performance sectors.However,its response to high-impact loading remains insufficiently understood,particularly regarding the influence of energy density on its dynamic mechanical behavior.In this study,scanning electron micro-scopy,electron backscatter diffraction,and image recognition techniques were employed to investigate the microstructural variations of LAM-fabricated UHSS under different energy density conditions.The dynamic mechanical behavior of the material was characterized using a Split Hopkinson Pressure Bar system in combination with high-speed digital image correlation.The study reveals the spatiotemporal evolution of surface strain and crack formation,as well as the underlying dynamic fracture mechanisms.A clear correlation was established between the microstructures formed under varying energy densities and the resulting dynamic mechanical strength of the material.Results demonstrate that optimal material density is achieved at energy densities of 292 and 333 J/mm^(3).In contrast,energy densities exceeding 333 J/mm^(3) induce keyhole defects,compromising structural integrity.Dynamic performance is strongly dependent on material density,with peak impact resistance observed at 292 J/mm^(3)-where strength is 8.4%to 17.6%higher than that at 500 J/mm^(3).At strain rates≥2000 s^(-1),the material reaches its strength limit at approximately 110μs,with the initial crack appearing within 12μs,followed by rapid failure.Conversely,at strain rates≤1500 s^(-1),only microcracks and adiabatic shear bands are detected.A transition in fracture surface morphology from ductile to brittle is observed with increasing strain rate.These findings offer critical insights into optimizing the dynamic mechanical properties of LAM-fabricated UHSS and provide a valuable foundation for its deployment in high-impact environments.
文摘It is well known that transition metal sulfides(TMS)(i.e.,NiS_(2))undergo electrochemical reconstructions to generate highly active Ni_(3)S_(2) during the process of hydrogen evolution reaction(HER)under overpotentials of<500 mV.However,at higher overpotentials,Ni_(3)S_(2) can theoretically be further restructured into Ni and thus form Ni/Ni_(3)S_(2) heterogeneous interface structures,which may provide opportunities to further enhance HER activity of NiS_(2).Here,we selected NiS_(2) as a model electrocatalyst and investigated the influence of the reconstruction results induced from regular to ultrahigh overpotentials on its electrocatalytic hydrogen precipitation performance.The experimental results showed that the most significant enhancement of hydrogen precipitation performance was obtained for the NiS_(2)@CC-900(900 means 900 mV overpotential)sample after the ultra-high overpotential induced reconstruction.Compared with the initial overpotential of 161 mV(10 mA cm^(-2)),the overpotential of the reconstructed sample reduced by 67 mV(42%).The characterization results showed that an ultra-high overpotential of 900 mV induced deep reconstruction of NiS_(2),formed highly reactive Ni/Ni_(3)S_(2) heterogeneous interfaces,which is more conducive to improved HER performance and match well with theoretical calculations results.We demonstrated ultrahigh overpotential was an effective strategy to induce NiS_(2) deeply reconstruction and significantly improve its HER performance,and this strategy was also applicable to CoS_(2) and FeS_(2).This study provides an extremely simple and universal pathway for the reasonable construction of efficient electrocatalysts by induced TMS deeply reconstruction.
基金supported financially by National Key Research and Development Program of China(No.2022YFB3705200)Heilongjiang Province's Key Technology Project:‘Leading the Charge with Open Competition’(No.2023ZXJ04A02)Youth Program of CISRI Funding under Grant(No.S-23T60190B).
文摘The effects of prior austenite and primary carbides on the mechanical properties of a novel 2.5 GPa grade steel were investigated by treating at various solid-solution temperatures.The ultimate tensile strength and Charpy U-notch impact energy initially increased and subsequently decreased as the solid-solution temperature rose,while the yield strength consistently decreased.The size of prior austenite grain and martensite block always increased with rising the solid-solution temperature,and austenite grain growth activation energy is 274,969 J/mol.The growth of prior austenite was restricted by primary carbides M6C and MC.The dissolution of the primary carbides not only enhanced solid-solution strengthening and secondary hardening effects but also increased the volume fraction of retained austenite.The increase in the ultimate tensile strength and Charpy U-notch impact energy was primarily attributed to the dissolution of the primary carbides M6C and MC,while the decrease was due to the increase in the size of prior austenite grain and martensite block.Exceptional combination of strength,ductility and toughness with ultimate tensile strength of 2511 MPa,yield strength of 1920 MPa,elongation of 9.5%,reduction of area of 41%and Charpy U-notch impact energy of 19.5 J was obtained when experimental steel was solid-solution treated at 1020℃.
文摘Ultra-high dose rate flash radiotherapy(FLASH-RT)has attracted wide attention in the field of radiotherapy in recent years.For FLASH-RT,radiation is delivered at a very high dose rate[usually thousands of times compared with conventional radiotherapy(CONV-RT)]in an extremely short time.This novel irradiation technique shows a protective effect on normal tissues,also known as the flash effect.At the same time,FLASH-RT is comparable to CONV-RT in terms of tumorkilling efficacy.As basic research dedicates to uncover the mechanisms by which FLASH-RT reduces radiation-induced normal tissue damage,clinical trials of FLASH-RT have been gradually conducted worldwide.This article systematically reviews the evidence of the feasibility and safety of FLASH-RT in clinical practice and offers insights into the future translation of this technology in clinic.
基金supported by the National Key R&D Program of China(No.2022YFB3203900).
文摘Integrating thick/thin film sensors into component systems has emerged as a prevalent approach for monitoring in extreme environments.However,traditional vapor deposition methods face obstacles,including complex fabrication processes and the degradation of sensitive materials at extremely high temperatures.This work delineates the development of a polysilazane composite dual-layer thick-film Negative Temperature Coefficient(NTC)thermistor characterized by its suitability for extreme temperatures and robust bond strength achieved through an advanced near-net-shape printing methodology.High-temperature resistant La(Ca)CrO_(3)/polysilazane films were printed as the sensitive layer,while a dense layer formed by Cr_(2)O_(3)/polysilazane was used as the protective layer.The bilayer structure resulted in a 2.5-fold increase in adhesion strength compared to the single-layer La(Ca)CrO_(3)/polysilazane films.Experimental results indicate that the dual-layer thick-film NTC thermistor can be operated long-term at 1300℃ with a resistance drift rate of 0.9%/h and survive short-term exposure to temperatures up to 1550℃.As a proof of concept,this work applied 3D printing technology to fabricate a polysilazane composite dual-layer thick-film NTC thermistor on the surface of turbine blades and demonstrated its functionality under flame impingement at nearly 1300℃.Such flexible 3D printing techniques pave the way for a new paradigm in manufacturing sensors capable of withstanding ultra-high temperatures.
基金National Natural Science Foundation of China,Grant/Award Number:81973476Chinese Society of Toxicology,Grant/Award Number:CST2021CT101。
文摘Background:Polygonum multiflorum-induced liver injury(PM-DILI)has significantly hindered its clinical application and development.Methods:This study investigates the variation in content and toxicity of dian-thrones,the toxic components of P.multiflorum,during different processing cycles.We employed the ultra-high-performance liquid chromatography triple quadrupole mass spectrometry method to quantify six dianthrones in raw P.multiflorum and formulations processed with a method called nine cycles of steaming and sunning.Additionally,toxicity assessments were conducted using human normal liver cell line L02 and zebrafish embryos.Results:Results indicate a gradual reduction in dianthrones content with increasing processing cycles.Processed formulations exhibited significantly reduced cytotoxic-ity in L02 cells and hepatotoxicity in zebrafish embryos.Conclusions:Our findings elucidate the relationship between processing cycles and P.multiflorum toxicity,providing theoretical support for its safe use.
基金supported by the National Natural Science Foundation of China(Nos.52201171,52225103,12335017)the Fundamental Research Funds for the Central Universities,China(No.FRF-IDRY-23-001)+1 种基金the Funds for Creative Research Groups of China(No.51921001)China United Gas Turbin Technology Co.,Ltd.under the project of J721.
文摘To meet the increasing demand for continuously enhancing engineering performance and energy efficiency in a variety of aerospace and energy applications,structural materials with high strength at ultra-high temperatures are urgently required.In the past decade,refractory multi-principal element alloys(RMPEAs),particularly those containing elements with high melting temperatures(T_(m))such as W and Ta(hereafter denoted as WTa-RMPEAs),have garnered extensive interest due to their exceptional strengths and thermally stability at high temperatures.Characterized by high T_(m),sluggish diffusion,and severe lattice distortion,WTa-RMPEAs exhibit chemical composition fluctuations at different scales,leading to unique mechanical properties and deformation behavior.In this paper,an initial summary is provided of the mechanical properties of typical WTa-RMPEAs at room and high temperatures and the differences in deformation behavior and underlying mechanisms between RMPEAs and conventional alloys are discussed.Additionally,strengthening and toughening strategies and the suggested deformation mechanisms were reviewed.Finally,the challenges in revealing the actual deformation mechanism of WTa-RMPEAs were described,and a brief perspective on the future research of the mechanical behavior of WTa-RMPEAs was proposed.
基金supported by the Major Program of Aerospace Advanced Manufacturing Technology Research Foundation NSFC and CASC, China (Grant No. U1537204)the Research Fund of Youth Innovation Promotion Association CAS, China (Grant No. 2014171)
文摘Carbon fiber reinforced ultra-high temperature ceramic （UHTC） composites, consisting of carbon fibers embedded in a UHTC-matrix or a C-SiC-UHTC-matrix, are deemed as the most viable class of materials that can overcome the poor fracture toughness and thermal shock resistance of monolithic UHTC ma- terials, and also improve the oxidation resistance and ablation resistance of C/C and C/SiC composites at ultra-high temperatures. In this review, we summarize the different processing routes of the compos- ites based on the UHTC introducing methods, including chemical vapor infiltration/deposition （CVI/D）, precursor infiltration and pyrolysis （PIP）, reactive melt infiltration （RMI）, slurry infiltration （SI）. in-sito reaction, hot pressing （HP）, etc; and the advantages and drawbacks of each method are briefly dis- cussed. The carbon fiber reinforced UHTC composites can be highly tailorable materials in terms of fiber. interface, and matrix. From the perspective of service environmental applications for engine propul- sions anti hypersonic vehicles, the material designs （mainly focusing on the composition, quantity, structure of matrix, as well as the architecture of carbon fibers, UHTCs and pores）, their relevant processing routes and properties （emphasizing on the mechanical and ablation properties） are discussed in this paper. In addition, we propose a material architecture to realize the multi-function through changing the distri- bution of carbon fibers, UHTCs and pores, which will be an important issue for future development of carbon fiber reinforced UHTC composites.
基金financially supported by the National Natural Science Foundation of China (No. 51171011)
文摘The influence of rust layers on the corrosion behavior of ultra-high strength steel 300M subjected to a simulated coastal atmosphere was investigated by corrosion weight loss, surface analysis techniques, and electrochemical methods. The results exhibit the presence of a large proportion of γ-FeOOH and α-FeOOH and a small amount of Fe3O4 in the outer rust layer. During the wet-dry cyclic process, the bonding performance and the density of outer rust layer deteriorate with the thickness of outer rust. The inner rust layer plays a main role on protectiveness, which can be attributed to the formation of an ultra-dense and adherent rust film with major constituent of α-FeOOH and α-Fe2O3 on the steel.
基金supported by the National Natural Science Foundation of China(No.50271056)National High Technical Research and Development Programme of China(No.2003AA305810)the Special Research Fund for Doctoral Disciplines in Colleges and Universities of M.0.E,China(No.20020699025).
文摘The directionally solidified samples of an ultra-high temperature Nb-Si-Ti-Hf-Cr-Al alloy have been prepared with the use of an electron beam floating zone melting (EBFZM) furnace, and their microstructural characteristics have been analyzed. All the primary dendrites of Nb solid solution (Nbss), eutectic colonies of Nba, plus (Nb, Ti)3 Si/(Nb, Ti)5 Si3 and chains of (Nb, Ti)3 Si/(Nb, Ti)5 Si3 plates align along the growth direction of the samples. With increasing of the withdrawing rate, the microstructure is refined, and the amounts of Nbss+ (Nb, Ti)3 Si/(Nb, Ti)5 Si3 eutectic colonies and (Nb, Ti)3 Si/(Nb, Ti)5 Si3 plates increase. There appear nodes in the (Nb, Ti)3 Si/(Nb, Ti)5 Si3 plates.
基金the support from the National Key Research and Development Program of China(2016YFB0300202 and 2016YFB0300102)the Fundamental Research Funds for the Central Universities(No.FRF-TP-18-002C2)。
文摘The hierarchical martensitic features in ultra-high strength stainless steel(UHSSS),including the prior austenite grains,martensite packets,blocks and laths with the descending size,were refined to various extents by employing different thermomechanical processes and then carefully characterized.Their relation to yield strength and impact toughness was analyzed.We conclude that the refinement of martensitic structures could lead to the significant increase of yield strength,which follows the Hall-Petch relation with the effect grain size defined by high angle boundaries(HABs).Impact toughness of UHSSS depends on the frequency and capability for retained austenite(RA)grains at both HABs and martensite lath boundaries to trap the propagating cracks via strain-induced transformation,in which the film-like RA grains at lath boundaries appear to make the greater contribution.
基金supported by the National High Technology Research and Development Program of China(2007AA03Z438)the National Natural Science Foundations of China(50871032)
文摘The effects of Nb on the thermal stability and impact toughness of ultra-high intrinsic coercivity of Nd-Fe-B magnets were investigated.The results showed that the addition of Nb could improve the thermal stability,and obviously increased the impact toughness of sintered Nd-Fe-B magnets.The optimum thermal stability of sintered Nd-Fe-B magnets was obtained when the content of Nb was 1.0 at.%.The maximum impact toughness of sintered Nd-Fe-B magnets was obtained when the content of Nb was 1.5 at.%,but the magnetic properties of sintered Nd-Fe-B magnets drastically deteriorated when the content of Nb increased from 1.0 at.% to 1.5 at.%.The microstructure showed that overfull Nb addition made many ultra-fine grains get together,which led to the density of sintered Nd-Fe-B magnets decline and drastically deteriorated the magnetic properties of sintered Nd-Fe-B magnets.
文摘An 1100 MPa grade ultra-high strength steel with different martensite fine structures, characterized by prior austenite grain size, martensite packet size, block width and lath width, was studied by various heat treatment processes. The result shows that with decreasing prior austenite grain size, both the packet size and block width decrease, while the lath width has virtually no change. Accordingly, both strength and toughness increase, while total elongation decreases. The yield strength has a Hall Petch type relationship with the prior austenite grain size, packet size and block width, and the block width may be regarded as a key factor influencing strength. On the other hand, the ductile to brittle transition temperature （DBTT） is found to be more related lo the packet size, which may be considered as a dominant factor influencing toughness.
文摘Starting with the Ertan arch dam （240 m high, 3300 MW） in 2000, China successfully built a total of seven ultra-high arch dams over 200 m tall by the end of 2014. Among these, the ]inping 1 （305 m）, Xiaowan （294.5m）, and Xiluodu （285.5 m） arch dams have reached the 300 m height level （i.e., near or over 300 m）, making them the tallest arch dams in the world. The design and construction of these 300 m ultra-high arch dams posed significant challenges, due to high water pressures, high seismic de- sign criteria, and complex geological conditions. The engineering team successfully tackled these chal- lenges and made critical breakthroughs, especially in the area of safety control. In this paper, the author summarizes various key technological aspects involved in the design and construction of 300 m ultra- high arch dams, including the strength and stability of foundation rock, excavation of the dam base and surface treatment, dam shape optimization, safety design guidelines, seismic analysis and design, treatment of a complex foundation, concrete temperature control, and crack prevention. The experience gained from these projects should be valuable for future practitioners.
基金supported by the National Natural Science Foundation of China (Nos. 51975201 and 52071139)the Natural Science Foundation of Hunan Province (No.2019JJ50586)。
文摘Ultra-high strain rate impact tests were conducted by Split-Hopkinson pressure bar to investigate the microstructure evolution and impact deformation mechanism of a solution treated casting AM80 Mg alloy at 25, 150 and 250 ℃ with a strain rate of 5000 s^(-1). The microcrack and dynamic recrystallization(DRX) preferentially nucleate at grain boundary(GB) and twin boundary(TB), especially at the intersections between GBs and TBs, and then propagate along twin direction. In contrast, the adiabatic shear bands preferentially occur at high-density twined regions. At 25 ℃, the dominated deformation mechanisms are basal slip and twinning. As deformation temperature increases to 150and 250℃, the deformation gradually shifts to be dominated by a coordinated mechanism among non-basal slip, twinning and DRX. The flow stress behavior and deformation mechanism indicate that the degree of decrease in flow stress with temperature is associated with the change of deformation mode.
基金Item Sponsored by Provincial Natural Science Foundation of Hebei Province of China (500023)
文摘A new spheroidizing process of ultra-high carbon steel （UHCS） containing C 1.55%, Cr 1.45%, and Al 1.5% in mass percent has been proposed. The effect of processing parameters on the microstructure was analyzed. The UHCS produced by this new process has a microstructure with recrystallized ferrite matrix and fine and uniform carbide particles. After this spheroidizing, the UHCS exhibits good mechanical properties at ambient temperature, for example σb= 1 100 MPa, σs =915 MPa, δ=8% and high ratio of σs/σb.
