Over the past few years,the Cu element has attracted much attention in duplex stainless steels.It undoubtedly holds advantageous in regulating the two-phase proportion and austenite stability and is also one of the cr...Over the past few years,the Cu element has attracted much attention in duplex stainless steels.It undoubtedly holds advantageous in regulating the two-phase proportion and austenite stability and is also one of the crucial factors affecting the corrosion resistance.However,the systematic research on the impact of Cu addition to lean duplex stainless steels remains insufficient.In this study,a novel Cu-alloyed Mn-N-type 20Cr lean duplex stainless steel was developed and the effect of Cu on the strain hardening capacity and corrosion resistance was analyzed.The results show that the Cu addition increases the volume fraction and stability of the austenite,retards the martensitic transformation,and extends the transformation-induced plasticity effect to a wider strain range.Compared to the Cu-free steel,the plasticity of Cu-containing steel can be increased by~26%.Additionally,the addition of Cu redistributes the Cr and N elements in the ferrite and austenite phases,thereby improving the corrosion resistance of the lean duplex stainless steel.展开更多
Selective laser melting(SLM)is an advanced additive manufacturing technique that enables the fabrication of complex metal components with high density,precision,and design flexibility.A novel Sc-free Al-4.58Mg-1.17Mn-...Selective laser melting(SLM)is an advanced additive manufacturing technique that enables the fabrication of complex metal components with high density,precision,and design flexibility.A novel Sc-free Al-4.58Mg-1.17Mn-1.59Zr-1.45Ti alloy was successfully fabricated via SLM,achieving a relative density of~99.89%.The microstructure of the as-fabricated alloy was characterized by scanning electron microscopy and transmission electron microscopy,which revealed refined equiaxed grains,a high density of low-angle grain boundaries and dislocation structures,as well as Mg segregation along grain boundaries.Additionally,a variety of dispersed precipitates were identified,including Mg-containing oxides,L1_(2)-Al_(3)(Ti_(x),Zr_(1−x)),and Al_(3)Zr particles.Room-temperature tensile tests showed that the alloy exhibits an excellent combination of strength and ductility,with a yield strength of 453.2±12 MPa,an ultimate tensile strength of 515.1±8 MPa,and an elongation of 22.5%±0.3%.The high strength was attributed to the combined effects of grain boundary strengthening,solid solution strengthening,precipitation strengthening,and dislocation strengthening.The developed Sc-free Al-Mg-Mn-Zr-Ti alloy demonstrates significant potential as an economical high-strength lightweight material for SLM-based manufacturing applications.展开更多
Composite nanofiber membranes based on biodegradable poly(lactic acid)(PLA) and cellulose nanofibrils(CNF) were produced via electrospinning. The influence of CNF content on the morphology, thermal properties, and mec...Composite nanofiber membranes based on biodegradable poly(lactic acid)(PLA) and cellulose nanofibrils(CNF) were produced via electrospinning. The influence of CNF content on the morphology, thermal properties, and mechanical properties of PLA/CNF composite nanofiber membranes were characterized by field scanning electron microscopy(FE-SEM), differential scanning calorimetry(DSC), thermogravimetric analysis(TGA), and dynamic mechanical analysis(DMA), respectively. The results show that the PLA/CNF composite nanofibers with smooth, free-bead surface can be successfully fabricated with various CNF contents. The introduction of CNF is an effective approach to improve the crystalline ability, thermal stability and mechanical properties for PLA/CNF composite fibers. The Young's moduli and tensile strength of the PLA/CNF composite nanofiber reach 106.6 MPa and 2.7 MPa when the CNF content is 3%, respectively, which are one times higher and 1.5 times than those of pure PLA nanofiber. Additionally, the water contact angle of PLA/CNF composite nanofiber membranes decreases with the increase of the CNF loading, resulting in the enhancement of their hydrophilicity.展开更多
Due to the extensive application of Al-Si alloys in the automotive and aerospace industries as structural components, an understanding of their microstructural formation, such as dendrite and(Al+Si) eutectic, is of gr...Due to the extensive application of Al-Si alloys in the automotive and aerospace industries as structural components, an understanding of their microstructural formation, such as dendrite and(Al+Si) eutectic, is of great importance to control the desirable microstructure, so as to modify the performance of castings. Since previous major themes of microstructural simulation are dendrite and regular eutectic growth, few efforts have been paid to simulate the irregular eutectic growth. Therefore, a multiphase cellular automaton(CA) model is developed and applied to simulate the time-dependent Al-Si irregular eutectic growth. Prior to model establishment, related experiments were carried out to investigate the influence of cooling rate and Sr modification on the growth of eutectic Si. This CA model incorporates several aspects, including growth algorithms and nucleation criterion, to achieve the competitive and cooperative growth mechanism for nonfaceted-faceted Al-Si irregular eutectic. The growth kinetics considers thermal undercooling, constitutional undercooling, and curvature undercooling, as well as the anisotropic characteristic of eutectic Si growth. The capturing rule takes into account the effects of modification on the silicon growth behaviors.The simulated results indicate that for unmodified alloy, the higher eutectic undercooling results in the higher eutectic growth velocity, and a more refined eutectic microstructure as well as narrower eutectic lamellar spacing. For modified alloy, the eutectic silicon tends to be obvious fibrous morphology and the morphology of eutectic Si is determined by both chemical modifier and cooling rate. The predicted microstructure of Al-7Si alloy under different solidification conditions shows that this proposed model can successfully reproduce both dendrite and eutectic microstructures.展开更多
Bismuth sulfide(Bi_(2)S_(3))has attracted particular interest as a potential anode material for sodium-ion batteries(SIBs).However,the low electrical conductivity and dramatic volumetric change greatly restrict its pr...Bismuth sulfide(Bi_(2)S_(3))has attracted particular interest as a potential anode material for sodium-ion batteries(SIBs).However,the low electrical conductivity and dramatic volumetric change greatly restrict its practical applications.In view of the apparent structural and compositional advantages of metal-organic frameworks(MOFs)derived carbon-based composite,herein,as a proof of concept,Bi_(2)S_(3) spheres coated with the MOF-derived Co_(9)S_(8) and N-doped carbon composite layer(Bi_(2)S_(3)@Co_(9)S_(8)/NC composite spheres)have been rational designed and synthesized.As expected,the core-shell Bi_(2)S_(3)@Co_(9)S_(8)/NC composite spheres exhibit remarkable electrochemical performance in terms of high reversible capacity(597 m Ah g^(-1) after 100 cycles at 0.1 A g^(-1)),good rate capability(341 m Ah g^(-1) at 8 A g^(-1))and long-term cycling stability(458 m Ah g^(-1) after 1000 cycles at 1 A g^(-1))when investigated as anode materials for SIBs.Electrochemical analyses further reveal the favorable reaction kinetics in the Bi_(2)S_(3)@Co_(9)S_(8)/NC composite spheres.In addition,the possible sodium storage mechanism has been studied by ex-situ X-ray diffraction technique.More importantly,a sodium-ion full cell based on Na_(3) V_(2)(PO_(4))_(3)/r GO as cathode and Bi_(2)S_(3)@Co_(9)S_(8)/NC as anode is also fabricated,suggesting their potential for practical applications.It is anticipated that the present work could be extended to construct other advanced electrode materials using MOFs-derived carbon-based composites as surface coating materials for various energy storagerelated applications.展开更多
Due to the layer-by-layer manufacturing characteristics,metallurgical process of selective laser melting(SLM)is inherently dif-ferent in the building direction because of varying conditions,thereby resulting inter-lay...Due to the layer-by-layer manufacturing characteristics,metallurgical process of selective laser melting(SLM)is inherently dif-ferent in the building direction because of varying conditions,thereby resulting inter-layer heterogeneity.To mitigate such anisotropy,it is of great significance to understand the effects of processing parameters on the property evolution and thus metallurgy of fabrication process.This research proposes one-factor-at-a-time experiment to investigate the influences of laser power and scanning speed on the surface qual-ity,microstructures and mechanical properties of selective laser melted Ti-6Al-4V parts.Surface quality is assessed by roughness around the printings while mechanical properties are evaluated through microhardness and tensile strengths.Phases in microstructure are quantified by XRD to correlate with mechanical properties.Fracture morphology is analyzed to understand the effect of defects and microstructure on mechanical performance.The optimized parameter corresponding to best surface quality and mechanical properties has been found respect-ively in laser power of 190 W and scanning speed of 800 mm/s.After optimization,surface roughness has decreased by 44.47%for upper surface.Yielding strength,tensile strength and elongation rate have improved by 13.17%,43.34%and 64.51%,respectively,with similar hardness and Young’s modulus.In addition,heterogeneity of mechanical properties has great improvement by a range of 31.63%-92.68%.展开更多
Ceramic cores are widely used in investment casting,and ideal properties of cores are essential for high-quality castings.Under the circumstances requiring thick cores,solid cores are likely to encounter deformation a...Ceramic cores are widely used in investment casting,and ideal properties of cores are essential for high-quality castings.Under the circumstances requiring thick cores,solid cores are likely to encounter deformation and cracking defects due to the accumulation of shrinkage.Therefore,with the superiority of ceramic stereolithography in producing complex ceramic parts,hollow cores with lattice structures were designed and fabricated.The dimensional accuracy and properties of the green and sintered bodies were evaluated.Results show the dimensional accuracy of sintered cores is controlled within±0.25 mm benefited from the precise green bodies.The mechanical properties are not obviously deteriorated.The bending strength reaches 11.94 MPa at room temperature and 12.87 MPa at 1,500℃ with a creep deformation of 0.345 mm.Furthermore,casting verifications prove that the hollow cores meet the requirements of investment casting.Smooth casting surfaces are obtained,at the same time,the core-removal efficiency is improved by over 3 times.展开更多
Proper matching of cold-rolled deformation and low-temperature short-term aging can simultaneously enhance the strength and ductility of the lean duplex stainless steel. To investigate this, the microstructure evoluti...Proper matching of cold-rolled deformation and low-temperature short-term aging can simultaneously enhance the strength and ductility of the lean duplex stainless steel. To investigate this, the microstructure evolution of cold-rolled and aging steels was observed by using scanning electron microscopy, transmission electron microscopy and electron backscattered diffraction. Additionally, the phase volume fraction was measured using X-ray diffraction. In this study, it was observed that the elongation of 21Cr lean duplex stainless steel significantly increased to 16.7% after undergoing moderate cold deformation (~ 40% reduction) and subsequent aging treatment at 550 ℃ for 30 min. Remarkably, the material still maintained a high yield strength of 1045 MPa. Such an excellent mechanical property was attributed to a unique microstructure combination of fine α'-martensite, twins, coarsened austenite resulting from partial martensite reverse transformation, and two-phase fine layered structure. The result of this study may open up new horizons for the alloy development in order to overcome the low ductility of cold-rolled high-strength lean duplex stainless steel.展开更多
Due to the laminated structure,MAX phases and MAX-phase-like compounds possess outstanding dam-age tolerance capability with good thermal/electrical conductivity and other charming functional prop-erties,showing a bri...Due to the laminated structure,MAX phases and MAX-phase-like compounds possess outstanding dam-age tolerance capability with good thermal/electrical conductivity and other charming functional prop-erties,showing a bright future for structural-functional uses.Here,a new MAX-phase-like ternary car-bide V_(8)P_(6)C with layered characteristics was discovered.Contrary to the alternate stacking of hexagonal-arranged M/A/X atom layers in MAX phases,V_(8)P_(6)C has a layered structure formed by a repeated stacking of the slabs consisting of V_(6)C-octahedrons and VP 6-distorted-octahedrons in three-atomic layers thick.The thermal expansion anisotropy was revealed,with the thermal expansion coefficients(TECs)along a-axis,c-axis,and the average value,equal toα_(a)=8.55(5)μK^(−1),α_(c)=10.23(5)μK^(−1),andα_(L)=9.14(5)μK^(−1),respectively.The dilation along the c-axis was mainly dominated by out-plane V-P bonds be-tween layered slabs.According to the pressure-dependent lattice parameters,the polycrystalline bulk modulus(B_(0)=185(9)GPa)and high compressibility anisotropy factor(B_(a)/B_(c)=1.64)was found.Mean-while,the second-order elastic constants were calculated,and the elastic moduli,E=303 GPa,B=198 GPa,G=122 GPa,andν=0.246,were obtained.And the weak connection between layer slabs by out-plane V1-P bond was revealed by the bond stiffness model,with a bond stiffness close to the M-A bond in MAX phases.Furthermore,good damage tolerance capability was predicted according to Paugh’s ratio(G/B=0.616)and Cauchy pressure(P_(a)=0 GPa,P_(c)=-7.5 GPa),even better than those of typical MAX phases.The discovery of V_(8)P_(6)C provides a new member of MAX-phase-like damage-tolerant ceramic with relatively low density,moderate thermal expansion,and anisotropic compressibility,and the unique lay-ered structure is inspiring for exploring new layered ternary ceramics.展开更多
Magnesium(Mg)alloys are promising materials for cardiovascular stent applications due to their good biocompatibility and biodegradability.However,in vitro and in vivo corrosion tests reveal that Mg alloy stents suffer...Magnesium(Mg)alloys are promising materials for cardiovascular stent applications due to their good biocompatibility and biodegradability.However,in vitro and in vivo corrosion tests reveal that Mg alloy stents suffer from a rapid corrosion rate and severe localized corrosion,which is limiting their widespread application.To solve the problem of uneven degradation of stents,a HTHE(long-time and high-temperature heat treatment,large-reduction-ratio hot extrusion)process is used to manufacture Mg-Zn-Y-Nd alloy microtubes in this study.The heat treatment is to dissolve alloying elements and reduce the size of SPPs,and the hot extrusion is to acquire fine-grained and strongly textured microtubes.The microstructural characterization shows that coarse second phases in as-cast alloy are refined and uniformly distributed in matrix of microtubes.After hot extrusion,microtubes show strong texture with basal plain oriented parallel to the longitudinal section(LS).The corrosion testing indicates that severe localized corrosion occurs on the cross section(CS)while localized corrosion is alleviated on the LS.Based on the different corrosion properties of the LS and CS,HTHEed microtubes are promising for solving the problems of rapid corrosion rate and severe localized corrosion of Mg alloy stents.展开更多
321 phases are an atypical series of MAX phases,in which A=As/P,with superior elastic properties,fea-turing in the MA-triangular-prism bilayers in the crystal structure.Until now,besides Nb 3 As 2 C,the pure phases of...321 phases are an atypical series of MAX phases,in which A=As/P,with superior elastic properties,fea-turing in the MA-triangular-prism bilayers in the crystal structure.Until now,besides Nb 3 As 2 C,the pure phases of the other 321 compounds have not been realized,hampering the study of their intrinsic prop-erties.Here,molten-salt sintering(MSS)and solid-state synthesis(SSS)were applied to synthesize As/P-containing 321 phases and 211 phases.Analyzing the phase composition of the end-product via multiple-phase Rietveld refinement,we found that MSS can effectively improve the purity of P-containing MAX phases,with the phase content up to 99%in Nb_(3)P_(2)C and 75.4(5)%in Nb 2 PC.In contrast,MSS performed poorly on As-containing MAX phases,only 8.9(4)%for Nb 3 As 2 C and 64(2)%for Nb 2 AsC,as opposed to the pure phases obtained by SSS.The experimental analyses combined with first-principles calculations reveal that the dominant formation route of Nb_(3)P_(2)C is through NbP+Nb+C→Nb_(3)P_(2)C.Moreover,we found that the benefits of MSS on P-containing MAX phases are on the facilitation of three consid-ered chemical reaction routes,especially on Nb 2 PC+NbP→Nb_(3)P_(2)C.Furthermore,the intrinsic physical properties and Fermi surface topology of two 321 phases consisting of electron,hole,and open orbits are revealed theoretically and experimentally,in which the electron carriers are dominant in electrical trans-port.The feasible synthesis methods and the formation mechanism are instructive to obtain high-purity As/P-containing MAX phases and explore new MAX phases.Meanwhile,the intrinsic physical properties will give great support for future applications on 321 phases.展开更多
Graded porous scaffold can be applied to study the interactions between cells and scaffold with different pore sizes. Polydimethylsiloxane（PDMS） scaffold with an axial pore size grade was successfully manufactured v...Graded porous scaffold can be applied to study the interactions between cells and scaffold with different pore sizes. Polydimethylsiloxane（PDMS） scaffold with an axial pore size grade was successfully manufactured via vacuum-assisted resin transfer moulding（VARTM） and particle leaching technologies. The properties of graded PDMS scaffolds, including porosity, water absorption, interconnectivity, compression modulus, as well as compression strength were investigated. The results showed that the smaller the size of the NaCl particles is, the higher the porosity and water absorption of graded PDMS scaffolds would be. The graded PDMS scaffold fabricated had a compressive modulus and a compressive strength of 19.69±1.42 kPa and 4.76±0.22 kPa, respectively. Moreover, the graded chitosan（CS）-coated PDMS scaffolds were prepared by using dip-coating technique under low vacuum and their hydrophilicity was examined. It is found that the water contact angle（WCA） will decrease with an increase in the CS solution concentration and the coating time, which indicates that CS-coated PDMS scaffolds exhibit noticeable hydrophilicity compared with graded PDMS scaffold.展开更多
As metallic foams used for energy absorption in the automotive and aerospace industries, recently invented lotus-type porous metals are viewed as potential energy absorbers. Yet, solid conclusion on their eligibility ...As metallic foams used for energy absorption in the automotive and aerospace industries, recently invented lotus-type porous metals are viewed as potential energy absorbers. Yet, solid conclusion on their eligibility as energy absorbers is still in question, particularly when compression is in the direction perpendicular to the axial orientation of cylindrical pores. In this work, the energy absorption of lotus-type porous coppers in the perpendicular direction is investigated at strain rates from 0.001 s^（-1） to^2400 s^（-1）. The energy absorption capacity and the energy absorption efficiency are calculated to be4–16 k J/kg and 0.32–0.7, respectively, slightly inferior to metal foams and the same porous solid compressed in the parallel direction due to the shortened extent of the plateau stress region. The deformation mechanism is examined experimentally in conjunction with finite element modeling. Both suggest that gradual squeeze and collapse of pores are the mechanisms accommodating the energy absorption. The deformation is generally evenly distributed over pore ligaments and independent of strain rate.展开更多
Developing various approaches for preparing high performance materials has long been topics and tasks both for scientists and for engineers.Despite that many methods have been developed for preparing nanomaterials,dev...Developing various approaches for preparing high performance materials has long been topics and tasks both for scientists and for engineers.Despite that many methods have been developed for preparing nanomaterials,developing simple and environment-friendly ways for preparing nanomaterials is very attractive.Here a simple approach of synthesizing Fe3O4 nanoparticles by arc-discharge submerging in water was reported.The results showed that by this method Fe3O4 nanoparticles can be synthesized at large scale.The as-prepared Fe3O4 nanoparticles exhibited uniform spherical shape and their diameters varied with arc-discharging parameters.The experimental results showed that the size of the synthesized Fe3O4 nanoparticles can be controlled through adjusting the processing parameters.Since no vacuum system has been used,the synthesizing process is greatly simplified.In addition,only cheap deionized water and industrial iron bar are used and no pollution or harmful byproducts are found in the synthesis process.It indicated that the present approach is a simple,low-cost and environment-friendly one for preparing nanoparticles.展开更多
In the present work, the effect of Ni doping on the microstructures and properties of Zn-20 Sn high temperature lead-free solder has been investigated. Interestingly,Ni was present as the form of Ni-Zn compounds in th...In the present work, the effect of Ni doping on the microstructures and properties of Zn-20 Sn high temperature lead-free solder has been investigated. Interestingly,Ni was present as the form of Ni-Zn compounds in the microstructure of Zn-20 Sn-xNi alloy.When the Ni-doping amount was 0.2~0.4 wt.%, the presence of δ phase was found, and when the doping amoun was 0.8 wt.%, the presence of γ phase was observed. With the increase of Ni content, the liquidus temperature increased but the solidus temperature did not change obviously. In addition, the microhardness and electrical resistivities of Zn-20 Sn-xNi solder increased gradually. And the spreading area and shear strength increased firstly but decreased afterwards. When the content of Ni was 0.4 wt.%, the spreading area and shear strength of solder reached to be maximum. After the addition of 0.4 wt.% Ni, the microstructure of the interfacial intermetallic compound(IMC) layer of the interface didn't change, but the total thickness of the IMC layer reduced. The δ-phase was embedded in the grain boundary of ε-Cu Zn5, which hindered the diffusion of atoms. The thickness of IMC layer at the interface reduced, which led to the improvement of the shear strength of the interface.展开更多
Hydraulic simulation is one of the critical methods to research the filling mechanism of molten metal in the casting process.However,it only performs on test pieces with relatively simple structures due to the limitat...Hydraulic simulation is one of the critical methods to research the filling mechanism of molten metal in the casting process.However,it only performs on test pieces with relatively simple structures due to the limitation of the preparation method.In this study,the method of photocuring additive manufacturing was used to prepare the complex casting mould from transparent photosensitive resin.The pouring test was carried out under different centrifugal conditions,and the filling process of the gating system,support bars and other positions in the vertical direction was recorded and analyzed.The experimental results show that the internal liquid level and the filling process of the test piece prepared by this method can be observed clearly.The angle between the liquid surface and the horizontal plane in the test piece gradually increases as the centrifugal rotational speed increases,which means the filling process is carried out from outside to inside at high rotational speed.The velocity of the fluid entering the runner increases with the increase of rotational speed,but the filling speeds is less affected by the centrifugal speed at other positions.The liquid flow is continuous and stable during the forward filling process,without splashing or interruption of liquid droplets.展开更多
M_(3)A_(2)X phases,named 321 phases,are an atypical series of MAX phases featuring in the MA-triangular-prism bilayers,with the A=As/P,exhibiting excellent elastic properties.This work systematically studies the therm...M_(3)A_(2)X phases,named 321 phases,are an atypical series of MAX phases featuring in the MA-triangular-prism bilayers,with the A=As/P,exhibiting excellent elastic properties.This work systematically studies the thermal expansion properties of 321 phases.We found their average linear thermal expansion coefficients(TECs),α_(L)=5-6μK^(–1),are the lowest among the reported values of MAX phases.The lowest average TEC was found in Nb_(3)As_(2)C(αa=4.46(4)μK^(–1),αc=5.09(4)μK–1,αL=5.09(4)μK–1).The average TEC and anisotropy factor(αc/αa)of Nb_(3)As_(2)C and Nb_(3)P_(2)C were lower than the ones of the corresponding 211 phases.The best isotropy performance was found in Nb_(3)P_(2)C (αc/αa=1.11).Moreover,our first-principles calculations demonstrate that the weaker chemical bonding between Nb-As/P than Nb-C induces thermal expansion in M_(3)A_(2)X phases.Furthermore,a relatively weaker anharmonic effect in 321 phases than in the 211 phases was revealed by the as-calculated average Grüneisen parameters,which account for the lower TECs in 321 phases.The low TECs and enhanced thermal isotropy make 321 phases outstanding among MAX phases,which could be sound candidates for varying-temperature structural-functional components.展开更多
Specific topographic Ni anchoring on reduced graphene oxide(rGO) composites show an astronomical potential as effective wave absorbers due to the synergistic electromagnetic loss effects.Herein,Ni/rGO composites with ...Specific topographic Ni anchoring on reduced graphene oxide(rGO) composites show an astronomical potential as effective wave absorbers due to the synergistic electromagnetic loss effects.Herein,Ni/rGO composites with different topography were successfully prepared via hydrothermal in-situ reduction method.The structure and morphology characteristics revealed that particle-like,chain-like,coin-like and flower-like Ni were closely anchored onto rGO,respectively.The electromagnetic wave absorption(EMA) performance revealed that chain-like Ni/rGO exhibited the optimal reflection loss of-43.7 dB with a thickness of 1.8 mm as well as the EAB of 6.1 GHz at 2.0 mm among all samples due to the good impedance match and the synergistic dielectric and magnetic losses.Besides,one conclusion can be drawn that excellent magnetic coupling effect and impedance matching were the main reasons for significantly improving the EMA performance.Considering the systematic dependence of morphology on EMA,this work provides a perspective for designing high-performance absorbing materials.展开更多
Similar to other metallic materials,duplex stainless steel dramatically loses its advantage of high ductility as they are strengthened.Here,we produce a gradient nanograined dual-phase structure in the 2101 duplex sta...Similar to other metallic materials,duplex stainless steel dramatically loses its advantage of high ductility as they are strengthened.Here,we produce a gradient nanograined dual-phase structure in the 2101 duplex stainless steel,thus facilitating a superior strength-ductility synergy:a yield strength of 1009.5 MPa being two times higher than that of the as-received sample,a total elongation of 23.4%and a uniform elongation of 5.9%.This novel structure is produced through a processing route of ultrasonic severe surface rolling and annealing,which realizes a superposition of gradient nanostructure and lamellar dual-phase structure with austenite and ferrite.During the tension deformation of gradi-ent nanograined dual-phase structured duplex stainless steel,a significant accumulation of geometrically necessary dislocations occurs.These dislocations are formed to accommodate the deformation incompat-ibility caused by the layer-by-layer difference in strength and hardness of individual phase domains,as well as the inherent difference in properties between the austenite and ferrite domains.This results in a stronger hetero-deformation induced strengthening and hardening significantly contributing to superior mechanical properties.Our study provides a new avenue to develop advanced steels with high strength and ductility.展开更多
The energy absorption characteristics of the lotus-type porous coppers at the strain rate of 10-3 s-1 to N2400 s 1 were systematically investigated. Depending on the relative density and loading rate, the energy absor...The energy absorption characteristics of the lotus-type porous coppers at the strain rate of 10-3 s-1 to N2400 s 1 were systematically investigated. Depending on the relative density and loading rate, the energy absorption capability of the tested samples varied from -20 to -85 MJ m-1, while the energy absorption efficiency fluctuated around N0.6. An energy absorption efficiency curve based approach was proposed for unambiguous identification of the plateau regime, which gave an extension of -0.50 strain range for the presently investigated porous coppers. With detailed observations of cell wall morphologies at various deformation stages, it was suggested that buckling of cell wails was the dominant mechanism mediat- ing the energy absorption in lotus-type porous coppers.展开更多
基金supported by the Jilin Scientific and Technological Development Program(No.YDZJ202201ZYTS669)the National Natural Science Foundation of China(Nos.51974032,52174355,51874043 and 51604034).
文摘Over the past few years,the Cu element has attracted much attention in duplex stainless steels.It undoubtedly holds advantageous in regulating the two-phase proportion and austenite stability and is also one of the crucial factors affecting the corrosion resistance.However,the systematic research on the impact of Cu addition to lean duplex stainless steels remains insufficient.In this study,a novel Cu-alloyed Mn-N-type 20Cr lean duplex stainless steel was developed and the effect of Cu on the strain hardening capacity and corrosion resistance was analyzed.The results show that the Cu addition increases the volume fraction and stability of the austenite,retards the martensitic transformation,and extends the transformation-induced plasticity effect to a wider strain range.Compared to the Cu-free steel,the plasticity of Cu-containing steel can be increased by~26%.Additionally,the addition of Cu redistributes the Cr and N elements in the ferrite and austenite phases,thereby improving the corrosion resistance of the lean duplex stainless steel.
基金supported by the Jilin Scientific and Technological Development Program(No.20240302108GX)the National Natural Science Foundation of China(Nos.51974032,52174355,51874043,and 51604034).
文摘Selective laser melting(SLM)is an advanced additive manufacturing technique that enables the fabrication of complex metal components with high density,precision,and design flexibility.A novel Sc-free Al-4.58Mg-1.17Mn-1.59Zr-1.45Ti alloy was successfully fabricated via SLM,achieving a relative density of~99.89%.The microstructure of the as-fabricated alloy was characterized by scanning electron microscopy and transmission electron microscopy,which revealed refined equiaxed grains,a high density of low-angle grain boundaries and dislocation structures,as well as Mg segregation along grain boundaries.Additionally,a variety of dispersed precipitates were identified,including Mg-containing oxides,L1_(2)-Al_(3)(Ti_(x),Zr_(1−x)),and Al_(3)Zr particles.Room-temperature tensile tests showed that the alloy exhibits an excellent combination of strength and ductility,with a yield strength of 453.2±12 MPa,an ultimate tensile strength of 515.1±8 MPa,and an elongation of 22.5%±0.3%.The high strength was attributed to the combined effects of grain boundary strengthening,solid solution strengthening,precipitation strengthening,and dislocation strengthening.The developed Sc-free Al-Mg-Mn-Zr-Ti alloy demonstrates significant potential as an economical high-strength lightweight material for SLM-based manufacturing applications.
基金Funded by the Outstanding Young Scientific Research Personnel Training Plan in Colleges and Universities of Fujian Province(No.GY-Z160146)the Research Fund of Fujian University of Technology(Nos.GY-Z15091,GY-Z160121)+2 种基金the External Cooperative Projects of Fujian Province(No.2018I0001)the Young Teachers Education Research Project(No.JAT170377)Fujian Province Undergraduate Training Program for Innovation and Entrepreneurship(No.201810388048)
文摘Composite nanofiber membranes based on biodegradable poly(lactic acid)(PLA) and cellulose nanofibrils(CNF) were produced via electrospinning. The influence of CNF content on the morphology, thermal properties, and mechanical properties of PLA/CNF composite nanofiber membranes were characterized by field scanning electron microscopy(FE-SEM), differential scanning calorimetry(DSC), thermogravimetric analysis(TGA), and dynamic mechanical analysis(DMA), respectively. The results show that the PLA/CNF composite nanofibers with smooth, free-bead surface can be successfully fabricated with various CNF contents. The introduction of CNF is an effective approach to improve the crystalline ability, thermal stability and mechanical properties for PLA/CNF composite fibers. The Young's moduli and tensile strength of the PLA/CNF composite nanofiber reach 106.6 MPa and 2.7 MPa when the CNF content is 3%, respectively, which are one times higher and 1.5 times than those of pure PLA nanofiber. Additionally, the water contact angle of PLA/CNF composite nanofiber membranes decreases with the increase of the CNF loading, resulting in the enhancement of their hydrophilicity.
基金financially supported by the National Basic Research Program of China(Grant No.2011CB706801)the National Natural Science Foundation of China(Grant No.51374137,51171089)the National Science and Technology Major Projects(Grant No.2012ZX04012-011,2011ZX04014-052)
文摘Due to the extensive application of Al-Si alloys in the automotive and aerospace industries as structural components, an understanding of their microstructural formation, such as dendrite and(Al+Si) eutectic, is of great importance to control the desirable microstructure, so as to modify the performance of castings. Since previous major themes of microstructural simulation are dendrite and regular eutectic growth, few efforts have been paid to simulate the irregular eutectic growth. Therefore, a multiphase cellular automaton(CA) model is developed and applied to simulate the time-dependent Al-Si irregular eutectic growth. Prior to model establishment, related experiments were carried out to investigate the influence of cooling rate and Sr modification on the growth of eutectic Si. This CA model incorporates several aspects, including growth algorithms and nucleation criterion, to achieve the competitive and cooperative growth mechanism for nonfaceted-faceted Al-Si irregular eutectic. The growth kinetics considers thermal undercooling, constitutional undercooling, and curvature undercooling, as well as the anisotropic characteristic of eutectic Si growth. The capturing rule takes into account the effects of modification on the silicon growth behaviors.The simulated results indicate that for unmodified alloy, the higher eutectic undercooling results in the higher eutectic growth velocity, and a more refined eutectic microstructure as well as narrower eutectic lamellar spacing. For modified alloy, the eutectic silicon tends to be obvious fibrous morphology and the morphology of eutectic Si is determined by both chemical modifier and cooling rate. The predicted microstructure of Al-7Si alloy under different solidification conditions shows that this proposed model can successfully reproduce both dendrite and eutectic microstructures.
基金the financial support from the Central Government Research Programs to Guide the Local Scientific and Technological Development(Grant no.2018L3001)the National Natural Science Foundation of China(Grant nos.51872048 and U1732155)the Natural Science Foundation of Fujian Province,China(Grant no.2018J01677)。
文摘Bismuth sulfide(Bi_(2)S_(3))has attracted particular interest as a potential anode material for sodium-ion batteries(SIBs).However,the low electrical conductivity and dramatic volumetric change greatly restrict its practical applications.In view of the apparent structural and compositional advantages of metal-organic frameworks(MOFs)derived carbon-based composite,herein,as a proof of concept,Bi_(2)S_(3) spheres coated with the MOF-derived Co_(9)S_(8) and N-doped carbon composite layer(Bi_(2)S_(3)@Co_(9)S_(8)/NC composite spheres)have been rational designed and synthesized.As expected,the core-shell Bi_(2)S_(3)@Co_(9)S_(8)/NC composite spheres exhibit remarkable electrochemical performance in terms of high reversible capacity(597 m Ah g^(-1) after 100 cycles at 0.1 A g^(-1)),good rate capability(341 m Ah g^(-1) at 8 A g^(-1))and long-term cycling stability(458 m Ah g^(-1) after 1000 cycles at 1 A g^(-1))when investigated as anode materials for SIBs.Electrochemical analyses further reveal the favorable reaction kinetics in the Bi_(2)S_(3)@Co_(9)S_(8)/NC composite spheres.In addition,the possible sodium storage mechanism has been studied by ex-situ X-ray diffraction technique.More importantly,a sodium-ion full cell based on Na_(3) V_(2)(PO_(4))_(3)/r GO as cathode and Bi_(2)S_(3)@Co_(9)S_(8)/NC as anode is also fabricated,suggesting their potential for practical applications.It is anticipated that the present work could be extended to construct other advanced electrode materials using MOFs-derived carbon-based composites as surface coating materials for various energy storagerelated applications.
基金Project was supported by the Natural Science Foundation of Fujian Province(Grant No.2020J01873)Science and Technology Major Project of Fujian Province(Grant No.2020HZ03018)+1 种基金Fujian Provincial Foreign Cooperation Project of Science and Technology(Grant No.2020I1003)Fujian Provincial Special Project for Marine Economy Development(Grant No.2021-517).
文摘Due to the layer-by-layer manufacturing characteristics,metallurgical process of selective laser melting(SLM)is inherently dif-ferent in the building direction because of varying conditions,thereby resulting inter-layer heterogeneity.To mitigate such anisotropy,it is of great significance to understand the effects of processing parameters on the property evolution and thus metallurgy of fabrication process.This research proposes one-factor-at-a-time experiment to investigate the influences of laser power and scanning speed on the surface qual-ity,microstructures and mechanical properties of selective laser melted Ti-6Al-4V parts.Surface quality is assessed by roughness around the printings while mechanical properties are evaluated through microhardness and tensile strengths.Phases in microstructure are quantified by XRD to correlate with mechanical properties.Fracture morphology is analyzed to understand the effect of defects and microstructure on mechanical performance.The optimized parameter corresponding to best surface quality and mechanical properties has been found respect-ively in laser power of 190 W and scanning speed of 800 mm/s.After optimization,surface roughness has decreased by 44.47%for upper surface.Yielding strength,tensile strength and elongation rate have improved by 13.17%,43.34%and 64.51%,respectively,with similar hardness and Young’s modulus.In addition,heterogeneity of mechanical properties has great improvement by a range of 31.63%-92.68%.
基金supported by the National Natural Science Foundation of China (Grant No. 52175333)Tribology Science Fund of the State Key Laboratory of Tribology,Tsinghua University (Grant No. SKLT2021B05)+1 种基金Foshan Science and Technology Innovation Team Project (Grant No. 2018IT100142)National Science and Technology Major Project of China (Grant No. J2019-VII-0002-0142)
文摘Ceramic cores are widely used in investment casting,and ideal properties of cores are essential for high-quality castings.Under the circumstances requiring thick cores,solid cores are likely to encounter deformation and cracking defects due to the accumulation of shrinkage.Therefore,with the superiority of ceramic stereolithography in producing complex ceramic parts,hollow cores with lattice structures were designed and fabricated.The dimensional accuracy and properties of the green and sintered bodies were evaluated.Results show the dimensional accuracy of sintered cores is controlled within±0.25 mm benefited from the precise green bodies.The mechanical properties are not obviously deteriorated.The bending strength reaches 11.94 MPa at room temperature and 12.87 MPa at 1,500℃ with a creep deformation of 0.345 mm.Furthermore,casting verifications prove that the hollow cores meet the requirements of investment casting.Smooth casting surfaces are obtained,at the same time,the core-removal efficiency is improved by over 3 times.
基金supported by the Jilin Scientific and Technological Development Program(No.YDZJ202201ZYTS669)the National Natural Science Foundation of China(Nos.51974032,52174355,51874043 and 51604034).
文摘Proper matching of cold-rolled deformation and low-temperature short-term aging can simultaneously enhance the strength and ductility of the lean duplex stainless steel. To investigate this, the microstructure evolution of cold-rolled and aging steels was observed by using scanning electron microscopy, transmission electron microscopy and electron backscattered diffraction. Additionally, the phase volume fraction was measured using X-ray diffraction. In this study, it was observed that the elongation of 21Cr lean duplex stainless steel significantly increased to 16.7% after undergoing moderate cold deformation (~ 40% reduction) and subsequent aging treatment at 550 ℃ for 30 min. Remarkably, the material still maintained a high yield strength of 1045 MPa. Such an excellent mechanical property was attributed to a unique microstructure combination of fine α'-martensite, twins, coarsened austenite resulting from partial martensite reverse transformation, and two-phase fine layered structure. The result of this study may open up new horizons for the alloy development in order to overcome the low ductility of cold-rolled high-strength lean duplex stainless steel.
基金supported by the National Science Foundation for Young Scientists of China(No.51902055)the Natural Science Foundation of Fujian Province(No.2021J011077)+1 种基金the Top Young Talents of Eagle Program of Fujian Province(No.KY310255)State Key Laboratory of Structural Chemistry(No.20230020).
文摘Due to the laminated structure,MAX phases and MAX-phase-like compounds possess outstanding dam-age tolerance capability with good thermal/electrical conductivity and other charming functional prop-erties,showing a bright future for structural-functional uses.Here,a new MAX-phase-like ternary car-bide V_(8)P_(6)C with layered characteristics was discovered.Contrary to the alternate stacking of hexagonal-arranged M/A/X atom layers in MAX phases,V_(8)P_(6)C has a layered structure formed by a repeated stacking of the slabs consisting of V_(6)C-octahedrons and VP 6-distorted-octahedrons in three-atomic layers thick.The thermal expansion anisotropy was revealed,with the thermal expansion coefficients(TECs)along a-axis,c-axis,and the average value,equal toα_(a)=8.55(5)μK^(−1),α_(c)=10.23(5)μK^(−1),andα_(L)=9.14(5)μK^(−1),respectively.The dilation along the c-axis was mainly dominated by out-plane V-P bonds be-tween layered slabs.According to the pressure-dependent lattice parameters,the polycrystalline bulk modulus(B_(0)=185(9)GPa)and high compressibility anisotropy factor(B_(a)/B_(c)=1.64)was found.Mean-while,the second-order elastic constants were calculated,and the elastic moduli,E=303 GPa,B=198 GPa,G=122 GPa,andν=0.246,were obtained.And the weak connection between layer slabs by out-plane V1-P bond was revealed by the bond stiffness model,with a bond stiffness close to the M-A bond in MAX phases.Furthermore,good damage tolerance capability was predicted according to Paugh’s ratio(G/B=0.616)and Cauchy pressure(P_(a)=0 GPa,P_(c)=-7.5 GPa),even better than those of typical MAX phases.The discovery of V_(8)P_(6)C provides a new member of MAX-phase-like damage-tolerant ceramic with relatively low density,moderate thermal expansion,and anisotropic compressibility,and the unique lay-ered structure is inspiring for exploring new layered ternary ceramics.
基金financial support of Key Projects of the Joint Fund of the National Natural Science Foundation of China(Grant No:U1804251)the National Key Research and Development Program of China(2016YFC1102403,2018YFC1106703 and 2017YFB0702504)+1 种基金China Scholarship Council for the award of fellowship and funding(No.201707040058)China Scholarship Council for the award of fellowship and funding(No.201607040051)。
文摘Magnesium(Mg)alloys are promising materials for cardiovascular stent applications due to their good biocompatibility and biodegradability.However,in vitro and in vivo corrosion tests reveal that Mg alloy stents suffer from a rapid corrosion rate and severe localized corrosion,which is limiting their widespread application.To solve the problem of uneven degradation of stents,a HTHE(long-time and high-temperature heat treatment,large-reduction-ratio hot extrusion)process is used to manufacture Mg-Zn-Y-Nd alloy microtubes in this study.The heat treatment is to dissolve alloying elements and reduce the size of SPPs,and the hot extrusion is to acquire fine-grained and strongly textured microtubes.The microstructural characterization shows that coarse second phases in as-cast alloy are refined and uniformly distributed in matrix of microtubes.After hot extrusion,microtubes show strong texture with basal plain oriented parallel to the longitudinal section(LS).The corrosion testing indicates that severe localized corrosion occurs on the cross section(CS)while localized corrosion is alleviated on the LS.Based on the different corrosion properties of the LS and CS,HTHEed microtubes are promising for solving the problems of rapid corrosion rate and severe localized corrosion of Mg alloy stents.
基金supported by the National Science Foundation for Young Scientists of China(No.51902055)the Natural Science Foundation of Fujian Province(Nos.2021J011077,2021J05224,and 2020J01898).
文摘321 phases are an atypical series of MAX phases,in which A=As/P,with superior elastic properties,fea-turing in the MA-triangular-prism bilayers in the crystal structure.Until now,besides Nb 3 As 2 C,the pure phases of the other 321 compounds have not been realized,hampering the study of their intrinsic prop-erties.Here,molten-salt sintering(MSS)and solid-state synthesis(SSS)were applied to synthesize As/P-containing 321 phases and 211 phases.Analyzing the phase composition of the end-product via multiple-phase Rietveld refinement,we found that MSS can effectively improve the purity of P-containing MAX phases,with the phase content up to 99%in Nb_(3)P_(2)C and 75.4(5)%in Nb 2 PC.In contrast,MSS performed poorly on As-containing MAX phases,only 8.9(4)%for Nb 3 As 2 C and 64(2)%for Nb 2 AsC,as opposed to the pure phases obtained by SSS.The experimental analyses combined with first-principles calculations reveal that the dominant formation route of Nb_(3)P_(2)C is through NbP+Nb+C→Nb_(3)P_(2)C.Moreover,we found that the benefits of MSS on P-containing MAX phases are on the facilitation of three consid-ered chemical reaction routes,especially on Nb 2 PC+NbP→Nb_(3)P_(2)C.Furthermore,the intrinsic physical properties and Fermi surface topology of two 321 phases consisting of electron,hole,and open orbits are revealed theoretically and experimentally,in which the electron carriers are dominant in electrical trans-port.The feasible synthesis methods and the formation mechanism are instructive to obtain high-purity As/P-containing MAX phases and explore new MAX phases.Meanwhile,the intrinsic physical properties will give great support for future applications on 321 phases.
基金Supported by the Research Fund of Fujian University of Technology(Nos.GY-Z15091,GY-Z160121)the External Cooperative Projects of Fujian Province(No.2018I0001)+2 种基金the Young Teachers Education Research Project(No.JAT170377)the Outstanding Young Scientific Research Personnel Training Plan in Colleges and Universities of Fujian Province(No.GY-Z160146)Fujian Province Undergraduate Training Program for Innovation and Entrepreneurship(No.201710388055)
文摘Graded porous scaffold can be applied to study the interactions between cells and scaffold with different pore sizes. Polydimethylsiloxane（PDMS） scaffold with an axial pore size grade was successfully manufactured via vacuum-assisted resin transfer moulding（VARTM） and particle leaching technologies. The properties of graded PDMS scaffolds, including porosity, water absorption, interconnectivity, compression modulus, as well as compression strength were investigated. The results showed that the smaller the size of the NaCl particles is, the higher the porosity and water absorption of graded PDMS scaffolds would be. The graded PDMS scaffold fabricated had a compressive modulus and a compressive strength of 19.69±1.42 kPa and 4.76±0.22 kPa, respectively. Moreover, the graded chitosan（CS）-coated PDMS scaffolds were prepared by using dip-coating technique under low vacuum and their hydrophilicity was examined. It is found that the water contact angle（WCA） will decrease with an increase in the CS solution concentration and the coating time, which indicates that CS-coated PDMS scaffolds exhibit noticeable hydrophilicity compared with graded PDMS scaffold.
基金financial support from the National Natural Science Foundation of China (Grant No. 50904004)
文摘As metallic foams used for energy absorption in the automotive and aerospace industries, recently invented lotus-type porous metals are viewed as potential energy absorbers. Yet, solid conclusion on their eligibility as energy absorbers is still in question, particularly when compression is in the direction perpendicular to the axial orientation of cylindrical pores. In this work, the energy absorption of lotus-type porous coppers in the perpendicular direction is investigated at strain rates from 0.001 s^（-1） to^2400 s^（-1）. The energy absorption capacity and the energy absorption efficiency are calculated to be4–16 k J/kg and 0.32–0.7, respectively, slightly inferior to metal foams and the same porous solid compressed in the parallel direction due to the shortened extent of the plateau stress region. The deformation mechanism is examined experimentally in conjunction with finite element modeling. Both suggest that gradual squeeze and collapse of pores are the mechanisms accommodating the energy absorption. The deformation is generally evenly distributed over pore ligaments and independent of strain rate.
文摘Developing various approaches for preparing high performance materials has long been topics and tasks both for scientists and for engineers.Despite that many methods have been developed for preparing nanomaterials,developing simple and environment-friendly ways for preparing nanomaterials is very attractive.Here a simple approach of synthesizing Fe3O4 nanoparticles by arc-discharge submerging in water was reported.The results showed that by this method Fe3O4 nanoparticles can be synthesized at large scale.The as-prepared Fe3O4 nanoparticles exhibited uniform spherical shape and their diameters varied with arc-discharging parameters.The experimental results showed that the size of the synthesized Fe3O4 nanoparticles can be controlled through adjusting the processing parameters.Since no vacuum system has been used,the synthesizing process is greatly simplified.In addition,only cheap deionized water and industrial iron bar are used and no pollution or harmful byproducts are found in the synthesis process.It indicated that the present approach is a simple,low-cost and environment-friendly one for preparing nanoparticles.
基金supported by the scientific and technological project in Fujian Province(2015H0008)
文摘In the present work, the effect of Ni doping on the microstructures and properties of Zn-20 Sn high temperature lead-free solder has been investigated. Interestingly,Ni was present as the form of Ni-Zn compounds in the microstructure of Zn-20 Sn-xNi alloy.When the Ni-doping amount was 0.2~0.4 wt.%, the presence of δ phase was found, and when the doping amoun was 0.8 wt.%, the presence of γ phase was observed. With the increase of Ni content, the liquidus temperature increased but the solidus temperature did not change obviously. In addition, the microhardness and electrical resistivities of Zn-20 Sn-xNi solder increased gradually. And the spreading area and shear strength increased firstly but decreased afterwards. When the content of Ni was 0.4 wt.%, the spreading area and shear strength of solder reached to be maximum. After the addition of 0.4 wt.% Ni, the microstructure of the interfacial intermetallic compound(IMC) layer of the interface didn't change, but the total thickness of the IMC layer reduced. The δ-phase was embedded in the grain boundary of ε-Cu Zn5, which hindered the diffusion of atoms. The thickness of IMC layer at the interface reduced, which led to the improvement of the shear strength of the interface.
基金This work was financially supported by the National Science and Technology Major Project of China(Grant No.J2019-Ⅶ-0002-0142)the National Natural Science Foundation of China(Grant No.52175333).
文摘Hydraulic simulation is one of the critical methods to research the filling mechanism of molten metal in the casting process.However,it only performs on test pieces with relatively simple structures due to the limitation of the preparation method.In this study,the method of photocuring additive manufacturing was used to prepare the complex casting mould from transparent photosensitive resin.The pouring test was carried out under different centrifugal conditions,and the filling process of the gating system,support bars and other positions in the vertical direction was recorded and analyzed.The experimental results show that the internal liquid level and the filling process of the test piece prepared by this method can be observed clearly.The angle between the liquid surface and the horizontal plane in the test piece gradually increases as the centrifugal rotational speed increases,which means the filling process is carried out from outside to inside at high rotational speed.The velocity of the fluid entering the runner increases with the increase of rotational speed,but the filling speeds is less affected by the centrifugal speed at other positions.The liquid flow is continuous and stable during the forward filling process,without splashing or interruption of liquid droplets.
基金financially supported by the National Science Foundation for Young Scientists of China(No.51902055)the Natural Science Foundation of Fujian Province(No.2021J011077)the Fuzhou Science and Technology Plan Project(No.2021-P-049).
文摘M_(3)A_(2)X phases,named 321 phases,are an atypical series of MAX phases featuring in the MA-triangular-prism bilayers,with the A=As/P,exhibiting excellent elastic properties.This work systematically studies the thermal expansion properties of 321 phases.We found their average linear thermal expansion coefficients(TECs),α_(L)=5-6μK^(–1),are the lowest among the reported values of MAX phases.The lowest average TEC was found in Nb_(3)As_(2)C(αa=4.46(4)μK^(–1),αc=5.09(4)μK–1,αL=5.09(4)μK–1).The average TEC and anisotropy factor(αc/αa)of Nb_(3)As_(2)C and Nb_(3)P_(2)C were lower than the ones of the corresponding 211 phases.The best isotropy performance was found in Nb_(3)P_(2)C (αc/αa=1.11).Moreover,our first-principles calculations demonstrate that the weaker chemical bonding between Nb-As/P than Nb-C induces thermal expansion in M_(3)A_(2)X phases.Furthermore,a relatively weaker anharmonic effect in 321 phases than in the 211 phases was revealed by the as-calculated average Grüneisen parameters,which account for the lower TECs in 321 phases.The low TECs and enhanced thermal isotropy make 321 phases outstanding among MAX phases,which could be sound candidates for varying-temperature structural-functional components.
基金the financial support for this work by the National Natural Science Foundation of China (Nos.51903223 and U1704162)China Postdoctoral Science Foundation (No.2018M642781)。
文摘Specific topographic Ni anchoring on reduced graphene oxide(rGO) composites show an astronomical potential as effective wave absorbers due to the synergistic electromagnetic loss effects.Herein,Ni/rGO composites with different topography were successfully prepared via hydrothermal in-situ reduction method.The structure and morphology characteristics revealed that particle-like,chain-like,coin-like and flower-like Ni were closely anchored onto rGO,respectively.The electromagnetic wave absorption(EMA) performance revealed that chain-like Ni/rGO exhibited the optimal reflection loss of-43.7 dB with a thickness of 1.8 mm as well as the EAB of 6.1 GHz at 2.0 mm among all samples due to the good impedance match and the synergistic dielectric and magnetic losses.Besides,one conclusion can be drawn that excellent magnetic coupling effect and impedance matching were the main reasons for significantly improving the EMA performance.Considering the systematic dependence of morphology on EMA,this work provides a perspective for designing high-performance absorbing materials.
基金supported by the National Natural Science Foundation of China(Nos.51974032,52174355,51874043,and 51604034)the Jilin Scientific and Technological Develop-ment Program(Nos.20220201106GX and YDZJ202201ZYTS669).
文摘Similar to other metallic materials,duplex stainless steel dramatically loses its advantage of high ductility as they are strengthened.Here,we produce a gradient nanograined dual-phase structure in the 2101 duplex stainless steel,thus facilitating a superior strength-ductility synergy:a yield strength of 1009.5 MPa being two times higher than that of the as-received sample,a total elongation of 23.4%and a uniform elongation of 5.9%.This novel structure is produced through a processing route of ultrasonic severe surface rolling and annealing,which realizes a superposition of gradient nanostructure and lamellar dual-phase structure with austenite and ferrite.During the tension deformation of gradi-ent nanograined dual-phase structured duplex stainless steel,a significant accumulation of geometrically necessary dislocations occurs.These dislocations are formed to accommodate the deformation incompat-ibility caused by the layer-by-layer difference in strength and hardness of individual phase domains,as well as the inherent difference in properties between the austenite and ferrite domains.This results in a stronger hetero-deformation induced strengthening and hardening significantly contributing to superior mechanical properties.Our study provides a new avenue to develop advanced steels with high strength and ductility.
基金financial support from the National Natural Science Foundation of China (Grant No. 50904004)
文摘The energy absorption characteristics of the lotus-type porous coppers at the strain rate of 10-3 s-1 to N2400 s 1 were systematically investigated. Depending on the relative density and loading rate, the energy absorption capability of the tested samples varied from -20 to -85 MJ m-1, while the energy absorption efficiency fluctuated around N0.6. An energy absorption efficiency curve based approach was proposed for unambiguous identification of the plateau regime, which gave an extension of -0.50 strain range for the presently investigated porous coppers. With detailed observations of cell wall morphologies at various deformation stages, it was suggested that buckling of cell wails was the dominant mechanism mediat- ing the energy absorption in lotus-type porous coppers.
