There is a pressing need for high-performance,high-strength low-alloy structural(HSLA)steels in various engineering fields,such as hydraulic components,engineering machinery,bridges,ships,and pressure vessels.In this ...There is a pressing need for high-performance,high-strength low-alloy structural(HSLA)steels in various engineering fields,such as hydraulic components,engineering machinery,bridges,ships,and pressure vessels.In this study,a gradient dislocation-cell structure is introduced into an HSLA steel through ultrasonic severe surface rolling.The cell size is approximately 614 nm at the topmost surface layer,and increases with increasing the depth.Most of the cell walls have a misorientation ranging from 2°to 15°,indicating they belong to low angle grain boundaries(LAGBs),while some cell walls have a misorientation of less than 2°,corresponding to dense dislocation walls(DDWs).This unique gradient structure offers an exceptional combination of strength and ductility,with a high yield strength of 522.3±1.4 MPa and an accepted elongation of 25.5±1.7%.The morphology and size of the dislocation cells remain remarkably stable after uniaxial tension,demonstrating their efficacy as effective barriers hindering dislocation movement and thus enhancing strength and hardness.This gradient dislocation-cell structure facilitates inhomogeneous plastic deformation during uniaxial tensile loading,resulting in a pronounced accumulation of geometrically necessary dislocations(GNDs).These GNDs play a significant role in conferring favorable mechanical properties by inducing hetero-deformation-induced(HDI)strengthening effects and forest hardening effects.This study presents a promising avenue for achieving the desired mechanical properties in HSLA steel.展开更多
Phase change heat transfer devices like heat pipes are widely utilized in temperature control and heat transfer.However,the traditional single uniform wick makes it hard to meet the requirements of capillary pressure ...Phase change heat transfer devices like heat pipes are widely utilized in temperature control and heat transfer.However,the traditional single uniform wick makes it hard to meet the requirements of capillary pressure and permeability for high-performance heat pipes,thus limiting the improvement of heat transfer performance.In this paper,a gradient structure wick sintered by 316 L stainless steel powder is designed.The capillary performance is tested and characterized through permeability test experiments and capillary rise infrared test experiments.Moreover,the influence of different particle sizes of sintered powder on the capillary performance of the wick structure is studied.The experimental results indicate that the capillary pressure and permeability of the gradient structure wick are significantly improved compared with the traditional single structure wick.Its capillary performance parameter S(K·Pcap)is enhanced by more than 30%,providing an effective alternative for the wick of two-phase heat exchange devices.展开更多
Bifunctional materials possessing both high electrical conductivity and thermal conductivity hold promise for integrating electromagnetic wave(EMW)absorption with thermal management capabilities,thereby addressing sig...Bifunctional materials possessing both high electrical conductivity and thermal conductivity hold promise for integrating electromagnetic wave(EMW)absorption with thermal management capabilities,thereby addressing signal crosstalk and heat accumulation issues in integrated electronic devices.However,the opposing effects of percolation phenomena on thermal conduction and microwave absorption hinder the integration of these properties.Herein,diospyros cauliflora-shaped CF@PDA@Fe_(3)O_(4)(MCF)was synthesized via a solvothermal method.The introduced heterogeneous interfaces enhance EMW absorption while impeding charge transport between adjacent carbon fibers(CFs),thereby suppressing percolation effects.Subsequently,magnetic-field-induced alignment of MCFs constructs thermally conductive pathways along the temperature gradient direction.By streamlining heat transfer routes and reducing filler-matrix interfaces,thermal conductivity is significantly enhanced.When the mass fraction of MCF is 20 wt.%,the composite achieves an effective absorption bandwidth of 4.2 GHz and a minimal reflection loss of 49.77 dB,while its thermal conductivity increases by 400%compared to pure polydimethylsiloxane(PDMS).This study proposes a synergistic strategy to concurrently enhance thermal conductivity and EMW absorption in composites,offering a new pathway for developing electronic packaging materials with efficient heat dissipation and broadband EMW absorption.展开更多
Star-shaped lattice structures with a negative Poisson’s ratio(NPR)effect exhibit excellent energy absorption capacity,making them highly promising for applications in aerospace,vehicles,and civil protection.While pr...Star-shaped lattice structures with a negative Poisson’s ratio(NPR)effect exhibit excellent energy absorption capacity,making them highly promising for applications in aerospace,vehicles,and civil protection.While previous research has primarily focused on single-walled cells,there is limited investigation into negative Poisson’s ratio structures with nested multi-walled cells.This study designed three star-shaped cell structures and three lattice configurations,analyzing the Poisson’s ratio,stress–strain relationship,and energy absorption capacity through tensile experiments and finite element simulations.Among the single structures,the star-shaped configuration r3 demonstrated the best elastic modulus,NPR effect,and energy absorption effect.In contrast,the uniform lattice structure R3 exhibited the highest tensile strength and energy absorption capacity.Additionally,the stress intensity and energy absorption of gradient structures increased with the number of layers.This study aims to provide a theoretical reference for the application of NPR materials in safety protection across civil and vehicle engineering,as well as other fields.展开更多
The effects of gradient structure on the microstructure and properties of coated cemented carbides were researched with optical microscopy （OM）, scanning electron microscopy （SEM）, strength measurements, and cutti...The effects of gradient structure on the microstructure and properties of coated cemented carbides were researched with optical microscopy （OM）, scanning electron microscopy （SEM）, strength measurements, and cutting tests. It shows that vacuum sintering of WC-Ti（C, N）-TaC-Co cemented carbides results in the formation of a surface ductile zone. The ductile zone prevents crack propagation and leads to the increase of transverse rupture strength of the substrate. The impact resistance of coated gradient inserts was obviously improved on the basis of maintaining resistance to abrasion and the forming mechanism of the gradient structure was also analyzed.展开更多
In the present paper,a microwave absorber with nanoscale gradient structure was proposed for enhancing the electromagnetic absorption performance.The inorganic-organic competitive coating strategy was employed,which c...In the present paper,a microwave absorber with nanoscale gradient structure was proposed for enhancing the electromagnetic absorption performance.The inorganic-organic competitive coating strategy was employed,which can effectively adjust the thermodynamic and kinetic reactions of iron ions during the solvothermal process.As a result,Fe nanoparticles can be gradually decreased from the inner side to the surface across the hollow carbon shell.The results reveal that it offers an outstanding reflection loss value in combination with broadband wave absorption and flexible adjustment ability,which is superior to other relative graded distribution structures and satisfied with the requirements of lightweight equipment.In addition,this work elucidates the intrinsic microwave regulation mechanism of the multiscale hybrid electromagnetic wave absorber.The excellent impedance matching and moderate dielectric parameters are exhibited to be the dominative factors for the promotion of microwave absorption performance of the optimized materials.This strategy to prepare gradient-distributed microwave absorbing materials initiates a new way for designing and fabricating wave absorber with excellent impedance matching property in practical applications.展开更多
In this study,CoCrFeMnNi high-entropy alloys(HEAs)with a surface gradient nanostructure were produced using industrial shot blasting,which improved their mechanical properties compared to the untreated alloy.The sever...In this study,CoCrFeMnNi high-entropy alloys(HEAs)with a surface gradient nanostructure were produced using industrial shot blasting,which improved their mechanical properties compared to the untreated alloy.The severely plastically deformed(SPD)surface layer had a multi-scale hierarchical structure with a high density of stacking faults,deformation nanotwins,and amorphous domains.The depth of the SPD layer steadily increased as the shot-blasting time increased.The differences in the microhardness and tensile strength before and after shotblasting demonstrated the significant effect of the SPD layer on the mechanical performance.The microhardness of the homogenized HEA was~5 GPa.In comparison,the maximum microhardness of the specimens after 20 min of shot blasting was~8.0 GPa at the surface.The yield strength also improved by 178%,and a large ductility of~36%was retained.Additional nanograin boundary,stacking fault,and twin strengthening within the gradientnanostructured surface layer caused the strength to increase.During tensile deformation,strain concentration began at the surface of the specimen and gradually spread to the interior.Thus,the gradient-nanostructured surface layer with improved strain hardening can prevent early necking and ensure steady plastic deformation so that high toughness is achieved.展开更多
Gradient nanostructure was introduced to enhance the strength and ductility via deformation incompatibility accommodated by geometrical necessary dislocations for most metallic materials recently.However,few intensive...Gradient nanostructure was introduced to enhance the strength and ductility via deformation incompatibility accommodated by geometrical necessary dislocations for most metallic materials recently.However,few intensive researches were carried out to investigate the effect of gradient structure on the deformation twin evolution and resulting performance improvements.In the present paper,we produced gradient-structured AZ31 Mg alloy with fine-grain layers,parallel twin laminates and a coarse-grain core from two upmost surfaces to the center of plate.Surprisingly,this architected Mg alloy exhibited simultaneous enhancement of strength and ductility.Subsequent microstructural observations demonstrated that abundant twin-twin interactions resulting from higher strength and multi-axial stress state could make great contributions to the increase of work-hardening capability.This was further proved by the measurement of full-field strain evolution during the plastic deformation.Such a design strategy may provide a new path for producing advanced structure materials in which the deformation twinning works as one of the dominant plasticity mechanisms.展开更多
This study explored a multi-mechanism approach to improving the mechanical properties of a Co CrFe Mn Ni high-entropy alloy through non-equiatomic alloy design and processing.The alloy design ensures a single-phase fa...This study explored a multi-mechanism approach to improving the mechanical properties of a Co CrFe Mn Ni high-entropy alloy through non-equiatomic alloy design and processing.The alloy design ensures a single-phase face-centered cubic structure while lowering the stacking fault energy to encourage the formation of deformation twins and stacking faults by altering the equiatomic composition of the alloy.The processing strategy applied helped create a hierarchical grain size gradient microstructure with a high nanotwins population.This was achieved by means of rotationally accelerated shot peening(RASP).The non-equiatomic Co Cr Fe Mn Ni high-entropy alloy achieved a yield strength of 750 MPa,a tensile strength of 1050 MPa,and tensile uniform elongation of 27.5%.The toughness of the alloy was 2.53×10^(10)k J/m^(3),which is about 2 times that of the same alloy without the RASP treatment.The strength increase is attributed to the effects of grain boundary strengthening,dislocation strengthening,twin strengthening,and hetero-deformation strengthening associated with the heterogeneous microstructure of the alloy.The concurrent occurrence of the multiple deformation mechanisms,i.e.,dislocation deformation,twining deformation and microband deformation,contributes to achieving a suitable strain hardening of the alloy that helps to prevent early necking and to assure steady plastic deformation for high toughness.展开更多
Laser additive manufacturing (AM) of lattice structures with light weight, excellent impact resistance, and energy absorption performance is receiving considerable attention in aerospace, transportation, and mechanica...Laser additive manufacturing (AM) of lattice structures with light weight, excellent impact resistance, and energy absorption performance is receiving considerable attention in aerospace, transportation, and mechanical equipment application fields. In this study, we designed four gradient lattice structures (GLSs) using the topology optimization method, including the unidirectional GLS, the bi-directional increasing GLS, the bi-directional decreasing GLS and the none-GLS. All GLSs were manufactureed by laser powder bed fusion (LPBF). The uniaxial compression tests and finite element analysis were conducted to investigate the influence of gradient distribution features on deformation modes and energy absorption performance of GLSs. The results showed that, compared with the 45° shear fracture characteristic of the none-GLS, the unidirectional GLS, the bi-directional increasing GLS and the bi-directional decreasing GLS had the characteristics of the layer-by-layer fracture, showing considerably improved energy absorption capacity. The bi-directional increasing GLS showed a unique combination of shear fracture and layer-by-layer fracture, having the optimal energy absorption performance with energy absorption and specific energy absorption of 235.6 J and 9.5 J g-1 at 0.5 strain, respectively. Combined with the shape memory effect of NiTi alloy, multiple compression-heat recovery experiments were carried out to verify the shape memory function of LPBF-processed NiTi GLSs. These findings have potential value for the future design of GLSs and the realization of shape memory function of NiTi components through laser AM.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
Multi-principal-element alloys(MPEAs)are attracting increasing attentions because of their high strength and ductility,high fracture toughness,excellent corrosion resistance,outstanding thermal-softening resistance an...Multi-principal-element alloys(MPEAs)are attracting increasing attentions because of their high strength and ductility,high fracture toughness,excellent corrosion resistance,outstanding thermal-softening resistance and high oxidation resistance.Moreover,gradient structures(GSs)have been shown to be effective in alleviating the strength-ductility trade-off although strength and ductility are mutually exclusive properties for metals,which provides an opportunity for developing highperformance MPEAs.Here,we summarized four processing methods for creating GSs in MPEAs,including rotationally accelerated shot peening(RASP),ultra-precision machining technology(UPMT),cyclic dynamic torsion(CDT),and ultrasonic surface rolling processing(USRP).Principles,advantages,disadvantages,and typical applications of these methods are discussed in this work.展开更多
As a typical energetic composite,polytetrafluoroethylene(PTFE)/aluminum(Al)has been widely applied in explosives,pyrotechnics,and propellants due to its ultra-high energy density and intense exothermic reaction.In thi...As a typical energetic composite,polytetrafluoroethylene(PTFE)/aluminum(Al)has been widely applied in explosives,pyrotechnics,and propellants due to its ultra-high energy density and intense exothermic reaction.In this work,the radial gradient(RG)structure of PTFE/Al cylinders with three different PTFE morphologies(200 nm and 5μm particles and 5μm fiber)and content changes are prepared by 3D printing technology.The effect of radial gradient structure on the pressure output of PTFE/Al has been studied.Compared with the morphology change of PTFE,the change of component content in the gradient structure has an obvious effect on the pressure output of the PTFE/Al cylinder.Furthermore,the relationships of the morphology,content of PTFE and the combustion reaction of the PTFE/Al cylinder reveal that the cylinder shows a more complex flame propagation process than others.These results could provide a strategy to improve the combustion and pressure output of PTFE/Al.展开更多
Bone-mimicking gradient porous NiTi shape memory alloys(SMAs)are promising for orthopedic im-plants due to their distinctive superelastic functional properties.However,premature plastic deformation in weak areas such ...Bone-mimicking gradient porous NiTi shape memory alloys(SMAs)are promising for orthopedic im-plants due to their distinctive superelastic functional properties.However,premature plastic deformation in weak areas such as thinner struts,nodes,and sharp corners severely deteriorates the superelasticity of gradient porous NiTi SMAs.In this work,we prepared gradient porous NiTi SMAs with a porosity of 50%by additive manufacturing(AM)and achieved a remarkable improvement of superelasticity by a simple solution treatment regime.After solution treatment,phase transformation temperatures dropped signif-icantly,the dislocation density decreased,and partial intergranular Ti-rich precipitates were transferred into the grain.Compared to as-built samples,the strain recovery rate of solution-treated samples was nearly doubled at a pre-strain of 6%(up to 90%),and all obtained a stable recoverable strain of more than 4%.The remarkable superelasticity improvement was attributed to lower phase transformation tem-peratures,fewer dislocations,and the synergistic strengthening effect of intragranular multi-scale Ti-Ni precipitates.Notably,the gradient porous structure played a non-negligible role in both superelasticity deterioration and improvement.The microstructure evolution of the solution-treated central strut after constant 10 cycles and the origin of the stable superelastic response of gradient porous NiTi SMAs were revealed.This work provides an accessible strategy for improving the superelastic performance of gra-dient porous NiTi SMAs and proposes a key strategy for achieving such high-performance architectured materials.展开更多
A new technology-rotationally accelerated shot peening（RASP）, was developed to prepare gradient structured materials. By using centrifugal acceleration principle and large steel balls, the RASP technology can produc...A new technology-rotationally accelerated shot peening（RASP）, was developed to prepare gradient structured materials. By using centrifugal acceleration principle and large steel balls, the RASP technology can produce much higher impact energy compared to conventional shot peening. As a proof-of-concept demonstration, the RASP was utilized to refine the surface layer in pure copper（Cu） with an average grain size of 85 nm. The grain size increases largely from surface downwards the bulk, forming an800 ？m thick gradient-structured surface layer and consequently a micro-hardness gradient. The difference between the RASP technology and other established techniques in preparing gradient structured materials is discussed. The RASP technology exhibits a promoting future for large-scale manufacturing of gradient materials.展开更多
Inspired by the gradient structure of the nature,two gradient lattice structures,i.e.,unidirectional gradient lattice(UGL)and bidirectional gradient lattice(BGL),are proposed based on the body-centered cubic(BCC)latti...Inspired by the gradient structure of the nature,two gradient lattice structures,i.e.,unidirectional gradient lattice(UGL)and bidirectional gradient lattice(BGL),are proposed based on the body-centered cubic(BCC)lattice to obtain specially designed mechanical behaviors,such as load-bearing and energy absorption capacities.First,a theoretical model is proposed to predict the initial stiffness of the gradient lattice structure under compressive loading,and validated against quasi-static compression tests and finite element models(FEMs).The deformation and failure mechanisms of the two structures are further studied based on experiments and simulations.The UGL structure exhibits a layer-by-layer failure mode,which avoids structure-wise shear failure in uniform structures.The BGL structure presents a symmetry deformation pattern,and the failure initiates at the weakest part.Finally,the energy absorption behaviors are also discussed.This study demonstrates the potential application of gradient lattice structures in load-transfer-path modification and energy absorption by topology design.展开更多
Nanocrystalline metals with high Gibbs free energy have a strong tendency towards thermally driven grain growth,thus understanding the critical size or temperature of grain growth is vital for their applications.The i...Nanocrystalline metals with high Gibbs free energy have a strong tendency towards thermally driven grain growth,thus understanding the critical size or temperature of grain growth is vital for their applications.The investigations of thermal stability were usually conducted on the materials with a homogeneous structure;however,these methods are time-consuming and expensive.In the present work,we reveal a high-throughput experimental strategy to characterize the size-dependent thermal stability via annealing the gradient structured Ni.Employing this method,the critical size of grain growth(d_(c))at a given annealing temperature was rapidly determined.The critical size of grain growth was~95 nm when annealed at 503 K for 3 h,which is consistent with the value reported in the homogeneous structured Ni.Furthermore,this critical size was found to be identical in three types of gradient structured Ni,i.e.,independent on the gradient structure.Our present work demonstrates a high-throughput strategy for exploring the critical size of grain growth and size-dependent thermal stability of metals.展开更多
Copper foils with gradient structure in thickness direction and different roughnesses on two surfaces were fabricated by double rolling. The two surface morphologies of double-rolled copper foils are quite different, ...Copper foils with gradient structure in thickness direction and different roughnesses on two surfaces were fabricated by double rolling. The two surface morphologies of double-rolled copper foils are quite different, and the surface roughness values are 61 and 1095 nm, respectively. The roughness value of matt surface can meet the requirement for bonding the resin matrix with copper foils used for flexible printed circuit boards, thus may omit traditional roughening treatment; the microstructure of double-rolled copper foils demonstrates an obviously asymmetric gradient feature. From bright surface to matt surface in thickness direction, the average grain size first increases from 2.3 to 7.4 μm and then decreases to 3.6 μm; compared with conventional rolled copper foils, the double-rolled copper foils exhibit a remarkably increased bending fatigue life, and the increased range is about 16.2%.展开更多
Structures with single gradient and dual gradients have been designed and fabricated in an Al_(0.5)Cr_(0.9)FeNi_(2.5)V_(0.2) medium entropy alloy.Structures with dual gradients(with increasing grain size and a decreas...Structures with single gradient and dual gradients have been designed and fabricated in an Al_(0.5)Cr_(0.9)FeNi_(2.5)V_(0.2) medium entropy alloy.Structures with dual gradients(with increasing grain size and a decreasing volume fraction of nanoprecipitates from the surface to the center)were observed to show much better dynamic shear properties compared to both structures with single grainsize gradient and coarse-grained structures with homogeneously distributed nanoprecipitates.Thus,the dual gradients have a synergetic strengthening/toughening effect as compared to the sole effect of a single gradient and the sole precipitation effect.Initiation of the adiabatic shear band(ASB)is delayed and propagation of ASB is slowed down in structures with dual gradients compared to structures with single gradients,resulting in better dynamic shear properties.A higher magnitude of strain gradient and higher density of geometrically necessary dislocations are induced in the structures with dual gradients,resulting in extra strain hardening.Higher density dislocations,stacking faults,and Lomer-Cottrell locks can be accumulated by the interactions between these defects and B2/L1_(2) precipitates,due to the higher volume fraction of nanoprecipitates in the surface layer of the structures with dual gradients,which could retard the early strain localization in the surface layer for better dynamic shear properties.展开更多
X-ray diffraction (XRD) analysis on different polished surfaces normal to the hot pressing direction reveals that the phase compositions of the polished surfaces from the outside to the inside are pure TiC, Ti_3AlC_2+...X-ray diffraction (XRD) analysis on different polished surfaces normal to the hot pressing direction reveals that the phase compositions of the polished surfaces from the outside to the inside are pure TiC, Ti_3AlC_2+TiC, pure Ti_3AlC_2 and Ti_2AlC+Ti_3AlC_2, no matter elemental powder or TiC is used as raw materials. It is found that ternary-layered carbide Ti_2AlC samples synthesized at 1500 ℃ by hot-pressing sintering are inhomogeneous and have a gradient structure.Electron probe X-ray micro-analysis (EPMA) indicates that the Al content along the hot pressing axis is parabolic, it is the highest in the center and the lowest at the both ends, while the Ti content is constant along the axis. The experimental result reveals that the evaporation of Al in samples in an open system during hot pressing sintering results in a gradient structure.展开更多
基金Supported by National Natural Science Foundation of China(Grant No.U1910212)the Priority Academic Program Development of Jiangsu Higher Education Institutions。
文摘There is a pressing need for high-performance,high-strength low-alloy structural(HSLA)steels in various engineering fields,such as hydraulic components,engineering machinery,bridges,ships,and pressure vessels.In this study,a gradient dislocation-cell structure is introduced into an HSLA steel through ultrasonic severe surface rolling.The cell size is approximately 614 nm at the topmost surface layer,and increases with increasing the depth.Most of the cell walls have a misorientation ranging from 2°to 15°,indicating they belong to low angle grain boundaries(LAGBs),while some cell walls have a misorientation of less than 2°,corresponding to dense dislocation walls(DDWs).This unique gradient structure offers an exceptional combination of strength and ductility,with a high yield strength of 522.3±1.4 MPa and an accepted elongation of 25.5±1.7%.The morphology and size of the dislocation cells remain remarkably stable after uniaxial tension,demonstrating their efficacy as effective barriers hindering dislocation movement and thus enhancing strength and hardness.This gradient dislocation-cell structure facilitates inhomogeneous plastic deformation during uniaxial tensile loading,resulting in a pronounced accumulation of geometrically necessary dislocations(GNDs).These GNDs play a significant role in conferring favorable mechanical properties by inducing hetero-deformation-induced(HDI)strengthening effects and forest hardening effects.This study presents a promising avenue for achieving the desired mechanical properties in HSLA steel.
文摘Phase change heat transfer devices like heat pipes are widely utilized in temperature control and heat transfer.However,the traditional single uniform wick makes it hard to meet the requirements of capillary pressure and permeability for high-performance heat pipes,thus limiting the improvement of heat transfer performance.In this paper,a gradient structure wick sintered by 316 L stainless steel powder is designed.The capillary performance is tested and characterized through permeability test experiments and capillary rise infrared test experiments.Moreover,the influence of different particle sizes of sintered powder on the capillary performance of the wick structure is studied.The experimental results indicate that the capillary pressure and permeability of the gradient structure wick are significantly improved compared with the traditional single structure wick.Its capillary performance parameter S(K·Pcap)is enhanced by more than 30%,providing an effective alternative for the wick of two-phase heat exchange devices.
基金supported by Sichuan Natural Science Foundation Project(No.2024NSFSC0146)the open research fund of School of Chemistry and Chemical Engineering,Henan Normal University(No.2021YB03).
文摘Bifunctional materials possessing both high electrical conductivity and thermal conductivity hold promise for integrating electromagnetic wave(EMW)absorption with thermal management capabilities,thereby addressing signal crosstalk and heat accumulation issues in integrated electronic devices.However,the opposing effects of percolation phenomena on thermal conduction and microwave absorption hinder the integration of these properties.Herein,diospyros cauliflora-shaped CF@PDA@Fe_(3)O_(4)(MCF)was synthesized via a solvothermal method.The introduced heterogeneous interfaces enhance EMW absorption while impeding charge transport between adjacent carbon fibers(CFs),thereby suppressing percolation effects.Subsequently,magnetic-field-induced alignment of MCFs constructs thermally conductive pathways along the temperature gradient direction.By streamlining heat transfer routes and reducing filler-matrix interfaces,thermal conductivity is significantly enhanced.When the mass fraction of MCF is 20 wt.%,the composite achieves an effective absorption bandwidth of 4.2 GHz and a minimal reflection loss of 49.77 dB,while its thermal conductivity increases by 400%compared to pure polydimethylsiloxane(PDMS).This study proposes a synergistic strategy to concurrently enhance thermal conductivity and EMW absorption in composites,offering a new pathway for developing electronic packaging materials with efficient heat dissipation and broadband EMW absorption.
基金support of the National Natural Science Foundation of China(12202038)the Fundamental Research Funds for the Central Universities(FRF-TP-22-028A1).
文摘Star-shaped lattice structures with a negative Poisson’s ratio(NPR)effect exhibit excellent energy absorption capacity,making them highly promising for applications in aerospace,vehicles,and civil protection.While previous research has primarily focused on single-walled cells,there is limited investigation into negative Poisson’s ratio structures with nested multi-walled cells.This study designed three star-shaped cell structures and three lattice configurations,analyzing the Poisson’s ratio,stress–strain relationship,and energy absorption capacity through tensile experiments and finite element simulations.Among the single structures,the star-shaped configuration r3 demonstrated the best elastic modulus,NPR effect,and energy absorption effect.In contrast,the uniform lattice structure R3 exhibited the highest tensile strength and energy absorption capacity.Additionally,the stress intensity and energy absorption of gradient structures increased with the number of layers.This study aims to provide a theoretical reference for the application of NPR materials in safety protection across civil and vehicle engineering,as well as other fields.
文摘The effects of gradient structure on the microstructure and properties of coated cemented carbides were researched with optical microscopy （OM）, scanning electron microscopy （SEM）, strength measurements, and cutting tests. It shows that vacuum sintering of WC-Ti（C, N）-TaC-Co cemented carbides results in the formation of a surface ductile zone. The ductile zone prevents crack propagation and leads to the increase of transverse rupture strength of the substrate. The impact resistance of coated gradient inserts was obviously improved on the basis of maintaining resistance to abrasion and the forming mechanism of the gradient structure was also analyzed.
基金the National Natural Science Foundation of China(52102372,52162007,52163032)China Postdoctoral Science Foundation(2022M712321)the Jiangsu Province Postdoctoral Research Funding Program(2021K473C).
文摘In the present paper,a microwave absorber with nanoscale gradient structure was proposed for enhancing the electromagnetic absorption performance.The inorganic-organic competitive coating strategy was employed,which can effectively adjust the thermodynamic and kinetic reactions of iron ions during the solvothermal process.As a result,Fe nanoparticles can be gradually decreased from the inner side to the surface across the hollow carbon shell.The results reveal that it offers an outstanding reflection loss value in combination with broadband wave absorption and flexible adjustment ability,which is superior to other relative graded distribution structures and satisfied with the requirements of lightweight equipment.In addition,this work elucidates the intrinsic microwave regulation mechanism of the multiscale hybrid electromagnetic wave absorber.The excellent impedance matching and moderate dielectric parameters are exhibited to be the dominative factors for the promotion of microwave absorption performance of the optimized materials.This strategy to prepare gradient-distributed microwave absorbing materials initiates a new way for designing and fabricating wave absorber with excellent impedance matching property in practical applications.
基金financially supported by Shenzhen Science and Technology Program(No.JCYJ20210324121011031)the National Natural Science Foundation of China(Nos.51871132 and 51971120)+2 种基金the Free Exploring Basic Research Project of Shenzhen Virtual University Park(No.2021Szvup069)the Opening Project of the State Key Laboratory of Explosion Science and Technology(Beijing Institutes of Technology)(No.KFJJ21-08M)the Natural Science Foundation of Shandong Province(No.ZR2020ME002)。
文摘In this study,CoCrFeMnNi high-entropy alloys(HEAs)with a surface gradient nanostructure were produced using industrial shot blasting,which improved their mechanical properties compared to the untreated alloy.The severely plastically deformed(SPD)surface layer had a multi-scale hierarchical structure with a high density of stacking faults,deformation nanotwins,and amorphous domains.The depth of the SPD layer steadily increased as the shot-blasting time increased.The differences in the microhardness and tensile strength before and after shotblasting demonstrated the significant effect of the SPD layer on the mechanical performance.The microhardness of the homogenized HEA was~5 GPa.In comparison,the maximum microhardness of the specimens after 20 min of shot blasting was~8.0 GPa at the surface.The yield strength also improved by 178%,and a large ductility of~36%was retained.Additional nanograin boundary,stacking fault,and twin strengthening within the gradientnanostructured surface layer caused the strength to increase.During tensile deformation,strain concentration began at the surface of the specimen and gradually spread to the interior.Thus,the gradient-nanostructured surface layer with improved strain hardening can prevent early necking and ensure steady plastic deformation so that high toughness is achieved.
基金This work was financially supported by National Natural Science Foundation of China(Grant Nos.11772268 and 12025205).The authors would like to appreciate the researchers in Nanjing university of science and technology for their support in preparation of gradient structured materials.
文摘Gradient nanostructure was introduced to enhance the strength and ductility via deformation incompatibility accommodated by geometrical necessary dislocations for most metallic materials recently.However,few intensive researches were carried out to investigate the effect of gradient structure on the deformation twin evolution and resulting performance improvements.In the present paper,we produced gradient-structured AZ31 Mg alloy with fine-grain layers,parallel twin laminates and a coarse-grain core from two upmost surfaces to the center of plate.Surprisingly,this architected Mg alloy exhibited simultaneous enhancement of strength and ductility.Subsequent microstructural observations demonstrated that abundant twin-twin interactions resulting from higher strength and multi-axial stress state could make great contributions to the increase of work-hardening capability.This was further proved by the measurement of full-field strain evolution during the plastic deformation.Such a design strategy may provide a new path for producing advanced structure materials in which the deformation twinning works as one of the dominant plasticity mechanisms.
基金the support of Basic Science Center Program for Multiphase Evolution in Hyper-gravity of the National Natural Science Foundation of China(51988101)NSFC programs(52071003,91860202,11604006)+4 种基金Beijing Municipal Education Commission Project(PXM2020014204000021 and PXM2019014204500032)Beijing Outstanding Young Scientists Projects(BJJWZYJH01201910005018)Beijing Natural Science Foundation(Z180014)“111”project(DB18015)the support by the Australian Research Council(DP190102990)to his work in this study。
文摘This study explored a multi-mechanism approach to improving the mechanical properties of a Co CrFe Mn Ni high-entropy alloy through non-equiatomic alloy design and processing.The alloy design ensures a single-phase face-centered cubic structure while lowering the stacking fault energy to encourage the formation of deformation twins and stacking faults by altering the equiatomic composition of the alloy.The processing strategy applied helped create a hierarchical grain size gradient microstructure with a high nanotwins population.This was achieved by means of rotationally accelerated shot peening(RASP).The non-equiatomic Co Cr Fe Mn Ni high-entropy alloy achieved a yield strength of 750 MPa,a tensile strength of 1050 MPa,and tensile uniform elongation of 27.5%.The toughness of the alloy was 2.53×10^(10)k J/m^(3),which is about 2 times that of the same alloy without the RASP treatment.The strength increase is attributed to the effects of grain boundary strengthening,dislocation strengthening,twin strengthening,and hetero-deformation strengthening associated with the heterogeneous microstructure of the alloy.The concurrent occurrence of the multiple deformation mechanisms,i.e.,dislocation deformation,twining deformation and microband deformation,contributes to achieving a suitable strain hardening of the alloy that helps to prevent early necking and to assure steady plastic deformation for high toughness.
基金supported by the financial support from the National Natural Science Foundation of China(Nos.51735005 and U1930207)the Basic Strengthening Program(No.2019-JCJQ-JJ-331)+1 种基金National Natural Science Founda-tion of China for Creative Research Groups(No.51921003)the 15th Batch of‘Six Talents Peaks’Innovative Talents Team Program(No.TD-GDZB-001).
文摘Laser additive manufacturing (AM) of lattice structures with light weight, excellent impact resistance, and energy absorption performance is receiving considerable attention in aerospace, transportation, and mechanical equipment application fields. In this study, we designed four gradient lattice structures (GLSs) using the topology optimization method, including the unidirectional GLS, the bi-directional increasing GLS, the bi-directional decreasing GLS and the none-GLS. All GLSs were manufactureed by laser powder bed fusion (LPBF). The uniaxial compression tests and finite element analysis were conducted to investigate the influence of gradient distribution features on deformation modes and energy absorption performance of GLSs. The results showed that, compared with the 45° shear fracture characteristic of the none-GLS, the unidirectional GLS, the bi-directional increasing GLS and the bi-directional decreasing GLS had the characteristics of the layer-by-layer fracture, showing considerably improved energy absorption capacity. The bi-directional increasing GLS showed a unique combination of shear fracture and layer-by-layer fracture, having the optimal energy absorption performance with energy absorption and specific energy absorption of 235.6 J and 9.5 J g-1 at 0.5 strain, respectively. Combined with the shape memory effect of NiTi alloy, multiple compression-heat recovery experiments were carried out to verify the shape memory function of LPBF-processed NiTi GLSs. These findings have potential value for the future design of GLSs and the realization of shape memory function of NiTi components through laser AM.
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the support of Qilu Young Talent Program from Shandong University and the State Key Lab of Advanced Metals and Materials (No.2021-Z10)the financial support from the Scientific Research Program Funded by Shaanxi Provincial Education Department (No.19JK0039)
文摘Multi-principal-element alloys(MPEAs)are attracting increasing attentions because of their high strength and ductility,high fracture toughness,excellent corrosion resistance,outstanding thermal-softening resistance and high oxidation resistance.Moreover,gradient structures(GSs)have been shown to be effective in alleviating the strength-ductility trade-off although strength and ductility are mutually exclusive properties for metals,which provides an opportunity for developing highperformance MPEAs.Here,we summarized four processing methods for creating GSs in MPEAs,including rotationally accelerated shot peening(RASP),ultra-precision machining technology(UPMT),cyclic dynamic torsion(CDT),and ultrasonic surface rolling processing(USRP).Principles,advantages,disadvantages,and typical applications of these methods are discussed in this work.
基金supported by the National Natural Science Foundation of China(Grant Nos.11872341 and 22075261)。
文摘As a typical energetic composite,polytetrafluoroethylene(PTFE)/aluminum(Al)has been widely applied in explosives,pyrotechnics,and propellants due to its ultra-high energy density and intense exothermic reaction.In this work,the radial gradient(RG)structure of PTFE/Al cylinders with three different PTFE morphologies(200 nm and 5μm particles and 5μm fiber)and content changes are prepared by 3D printing technology.The effect of radial gradient structure on the pressure output of PTFE/Al has been studied.Compared with the morphology change of PTFE,the change of component content in the gradient structure has an obvious effect on the pressure output of the PTFE/Al cylinder.Furthermore,the relationships of the morphology,content of PTFE and the combustion reaction of the PTFE/Al cylinder reveal that the cylinder shows a more complex flame propagation process than others.These results could provide a strategy to improve the combustion and pressure output of PTFE/Al.
基金the financial support of the National Natural Science Foundation under Grant No.52274387project support by the Shanghai Science and Technology Com-mission(Grant No.20S31900100).
文摘Bone-mimicking gradient porous NiTi shape memory alloys(SMAs)are promising for orthopedic im-plants due to their distinctive superelastic functional properties.However,premature plastic deformation in weak areas such as thinner struts,nodes,and sharp corners severely deteriorates the superelasticity of gradient porous NiTi SMAs.In this work,we prepared gradient porous NiTi SMAs with a porosity of 50%by additive manufacturing(AM)and achieved a remarkable improvement of superelasticity by a simple solution treatment regime.After solution treatment,phase transformation temperatures dropped signif-icantly,the dislocation density decreased,and partial intergranular Ti-rich precipitates were transferred into the grain.Compared to as-built samples,the strain recovery rate of solution-treated samples was nearly doubled at a pre-strain of 6%(up to 90%),and all obtained a stable recoverable strain of more than 4%.The remarkable superelasticity improvement was attributed to lower phase transformation tem-peratures,fewer dislocations,and the synergistic strengthening effect of intragranular multi-scale Ti-Ni precipitates.Notably,the gradient porous structure played a non-negligible role in both superelasticity deterioration and improvement.The microstructure evolution of the solution-treated central strut after constant 10 cycles and the origin of the stable superelastic response of gradient porous NiTi SMAs were revealed.This work provides an accessible strategy for improving the superelastic performance of gra-dient porous NiTi SMAs and proposes a key strategy for achieving such high-performance architectured materials.
基金supports from the National Natural Science Foundation of China (Grant No. 51301092)Pangu Foundation are acknowledged
文摘A new technology-rotationally accelerated shot peening（RASP）, was developed to prepare gradient structured materials. By using centrifugal acceleration principle and large steel balls, the RASP technology can produce much higher impact energy compared to conventional shot peening. As a proof-of-concept demonstration, the RASP was utilized to refine the surface layer in pure copper（Cu） with an average grain size of 85 nm. The grain size increases largely from surface downwards the bulk, forming an800 ？m thick gradient-structured surface layer and consequently a micro-hardness gradient. The difference between the RASP technology and other established techniques in preparing gradient structured materials is discussed. The RASP technology exhibits a promoting future for large-scale manufacturing of gradient materials.
基金the National Natural Science Foundation of China(Grant Nos.11972049 and 12002050)National Key Laboratory Foundation of Science and Technology on Materials under Shock and Im-pact(Grant No.6142902200401)Opening Fund of State Key Laboratory of Nonlinear Mechanics.
文摘Inspired by the gradient structure of the nature,two gradient lattice structures,i.e.,unidirectional gradient lattice(UGL)and bidirectional gradient lattice(BGL),are proposed based on the body-centered cubic(BCC)lattice to obtain specially designed mechanical behaviors,such as load-bearing and energy absorption capacities.First,a theoretical model is proposed to predict the initial stiffness of the gradient lattice structure under compressive loading,and validated against quasi-static compression tests and finite element models(FEMs).The deformation and failure mechanisms of the two structures are further studied based on experiments and simulations.The UGL structure exhibits a layer-by-layer failure mode,which avoids structure-wise shear failure in uniform structures.The BGL structure presents a symmetry deformation pattern,and the failure initiates at the weakest part.Finally,the energy absorption behaviors are also discussed.This study demonstrates the potential application of gradient lattice structures in load-transfer-path modification and energy absorption by topology design.
基金financially supported by the National Key Research and Development Program of China(No.2017YFB0702003)the National Natural Science Foundation of China(No.51871217)support from the Youth Innovation Promotion Association,Chinese Academy of Sciences(No.2020194)。
文摘Nanocrystalline metals with high Gibbs free energy have a strong tendency towards thermally driven grain growth,thus understanding the critical size or temperature of grain growth is vital for their applications.The investigations of thermal stability were usually conducted on the materials with a homogeneous structure;however,these methods are time-consuming and expensive.In the present work,we reveal a high-throughput experimental strategy to characterize the size-dependent thermal stability via annealing the gradient structured Ni.Employing this method,the critical size of grain growth(d_(c))at a given annealing temperature was rapidly determined.The critical size of grain growth was~95 nm when annealed at 503 K for 3 h,which is consistent with the value reported in the homogeneous structured Ni.Furthermore,this critical size was found to be identical in three types of gradient structured Ni,i.e.,independent on the gradient structure.Our present work demonstrates a high-throughput strategy for exploring the critical size of grain growth and size-dependent thermal stability of metals.
基金financially support by the National Key Technology Research and Development Program of the Ministry of Science and Technology of China (No.2011BAE23B02)the Fundamental Research Funds for the Central Universities of China (No.FRF-TP-10-002B)
文摘Copper foils with gradient structure in thickness direction and different roughnesses on two surfaces were fabricated by double rolling. The two surface morphologies of double-rolled copper foils are quite different, and the surface roughness values are 61 and 1095 nm, respectively. The roughness value of matt surface can meet the requirement for bonding the resin matrix with copper foils used for flexible printed circuit boards, thus may omit traditional roughening treatment; the microstructure of double-rolled copper foils demonstrates an obviously asymmetric gradient feature. From bright surface to matt surface in thickness direction, the average grain size first increases from 2.3 to 7.4 μm and then decreases to 3.6 μm; compared with conventional rolled copper foils, the double-rolled copper foils exhibit a remarkably increased bending fatigue life, and the increased range is about 16.2%.
基金supported by the National Natural Science Foundation of China (Nos.52192591,12202459,and 11790293)the NSFC Basic Science Center Program for“Multiscale Problems in Nonlinear Mechanics” (No.11988102)the fellowship of China Postdoctoral Science Foundation (No.2021M703292).
文摘Structures with single gradient and dual gradients have been designed and fabricated in an Al_(0.5)Cr_(0.9)FeNi_(2.5)V_(0.2) medium entropy alloy.Structures with dual gradients(with increasing grain size and a decreasing volume fraction of nanoprecipitates from the surface to the center)were observed to show much better dynamic shear properties compared to both structures with single grainsize gradient and coarse-grained structures with homogeneously distributed nanoprecipitates.Thus,the dual gradients have a synergetic strengthening/toughening effect as compared to the sole effect of a single gradient and the sole precipitation effect.Initiation of the adiabatic shear band(ASB)is delayed and propagation of ASB is slowed down in structures with dual gradients compared to structures with single gradients,resulting in better dynamic shear properties.A higher magnitude of strain gradient and higher density of geometrically necessary dislocations are induced in the structures with dual gradients,resulting in extra strain hardening.Higher density dislocations,stacking faults,and Lomer-Cottrell locks can be accumulated by the interactions between these defects and B2/L1_(2) precipitates,due to the higher volume fraction of nanoprecipitates in the surface layer of the structures with dual gradients,which could retard the early strain localization in the surface layer for better dynamic shear properties.
文摘X-ray diffraction (XRD) analysis on different polished surfaces normal to the hot pressing direction reveals that the phase compositions of the polished surfaces from the outside to the inside are pure TiC, Ti_3AlC_2+TiC, pure Ti_3AlC_2 and Ti_2AlC+Ti_3AlC_2, no matter elemental powder or TiC is used as raw materials. It is found that ternary-layered carbide Ti_2AlC samples synthesized at 1500 ℃ by hot-pressing sintering are inhomogeneous and have a gradient structure.Electron probe X-ray micro-analysis (EPMA) indicates that the Al content along the hot pressing axis is parabolic, it is the highest in the center and the lowest at the both ends, while the Ti content is constant along the axis. The experimental result reveals that the evaporation of Al in samples in an open system during hot pressing sintering results in a gradient structure.
