Compared with the conventional Charpy impact test method,the oscillographic impact test can help in the behavioral analysis of materials during the fracture process.In this study,the trade-off relationship between the...Compared with the conventional Charpy impact test method,the oscillographic impact test can help in the behavioral analysis of materials during the fracture process.In this study,the trade-off relationship between the strength and toughness of a DZ2 axle steel at various tempering temperatures and the cause of the improvement in impact toughness was evaluated.The tempering process dramatically influenced carbide precipitation behavior,which resulted in different aspect ratios of carbides.Impact toughness improved along with the rise in tempering temperature mainly due to the increase in energy required in impact crack propagation.The characteristics of the impact crack propagation process were studied through a comprehensive analysis of stress distribution,oscilloscopic impact statistics,fracture morphology,and carbide morphology.The poor impact toughness of low-tempering-temperature specimens was attributed to the increased number of stress concentration points caused by carbide morphology in the small plastic zone during the propagation process,which resulted in a mixed distribution of brittle and ductile fractures on the fracture surface.展开更多
Natural fish scales demonstrate outstanding mechanical efficiency owing to their elaborate architectures and thereby may serve as ideal prototypes for the architectural design of man-made materials.Here bioinspired ma...Natural fish scales demonstrate outstanding mechanical efficiency owing to their elaborate architectures and thereby may serve as ideal prototypes for the architectural design of man-made materials.Here bioinspired magnesium composites with fish-scale-like orthogonal plywood and double-Bouligand architectures were developed by pressureless infiltration of a magnesium melt into the woven contextures of continuous titanium fibers.The composites exhibit enhanced strength and work-hardening ability compared to those estimated from a simple mixture of their constituents at ambient to elevated temperatures.In particular,the double-Bouligand architecture can effectively deflect cracking paths,alleviate strain localization,and adaptively reorient titanium fibers within the magnesium matrix during the deformation of the composite,representing a successful implementation of the property-optimizing mechanisms in fish scales.The strength of the composites,specifically the effect of their bioinspired architectures,was interpreted based on the adaptation of classical laminate theory.This study may offer a feasible approach for developing new bioinspired metal-matrix composites with improved performance and provide theoretical guidance for their architectural designs.展开更多
Nanostructured materials are being actively developed,while it remains an open question how to rapidly scale them up to bulk engineering materials for broad industrial applications.This study propose an industrial app...Nanostructured materials are being actively developed,while it remains an open question how to rapidly scale them up to bulk engineering materials for broad industrial applications.This study propose an industrial approach to rapidly fabricate high-strength large-size nanostructured metal matrix composites and attempts to investigate and optimize the deposition process and strengthening mechanism.Here,advanced nanocrystalline aluminum matrix composites(nanoAMCs)were assembled for the first time by a novel nano-additive manufacturing method that was guided by numerical simulations(i.e.the in-flight particle model and the porefree deposition model).The present nanoAMC with a mean grain size<50 nm in matrix exhibited hardness eight times higher than the bulk aluminum and shows the highest hardness among all Al–Al2O3 composites reported to date in the literature,which are the outcome of controlling multiscale strengthening mechanisms from tailoring solution atoms,dislocations,grain boundaries,precipitates,and externally introduced reinforcing particles.The present high-throughput strategy and method can be extended to design and architect advanced coatings or bulk materials in a highly efficient(synthesizing a nanostructured bulk with dimensions of 50×20×4 mm^(3) in 9 min)and highly flexible(regulating the gradient microstructures in bulk)way,which is conducive to industrial production and application.展开更多
The deformation, damage, fracture, plasticity and melting phenomenon induced by shear fracture were investigated and summarized for Zr-, Cu-, Ti- and Mg-based bulk metallic glasses (BMGs) and their composites. The s...The deformation, damage, fracture, plasticity and melting phenomenon induced by shear fracture were investigated and summarized for Zr-, Cu-, Ti- and Mg-based bulk metallic glasses (BMGs) and their composites. The shear fracture angles of these BMG materials often display obvious differences under compression and tension, and follow either the Mohr-Coulomb criterion or the unified tensile fracture criterion. The compressive plasticity of the composites is always higher than the tensile plasticity, leading to a significant inconsistency. The enhanced plasticity of BMG composites containing ductile dendrites compared to monolithic glasses strongly depends on the details of the microstructure of the composites. A deformation and damage mechanism of pseudo-plasticity, related to local cracking, is proposed to explain the inconsistency of plastic deformation under tension and compression. Besides, significant melting on the shear fracture surfaces was observed. It is suggested that melting is a common phenomenon in these materials with high strength and high elastic energy, as it is typical for BMGs and their composites failing under shear fracture. The melting mechanism can be explained by a combined effect of a significant temperature rise in the shear bands and the instantaneous release of the large amount of elastic energy stored in the material.展开更多
As the main source of the vacuum arc plasma,cathode spots(CSs)play an important role on the behaviors of the vacuum arc.Their characteristics are affected by many factors,especially by the magnetic field.In this paper...As the main source of the vacuum arc plasma,cathode spots(CSs)play an important role on the behaviors of the vacuum arc.Their characteristics are affected by many factors,especially by the magnetic field.In this paper,the characteristics of the plasma jet from a single CS in vacuum arc under external axial magnetic field(AMF)are studied.A multi-species magneto-hydro-dynamic(MHD)model is established to describe the vacuum arc.The anode temperature is calculated by the anode activity model based on the energy flux obtained from the MHD model.The simulation results indicate that the external AMF has a significant effect on the characteristic of the plasma jet.When the external AMF is high enough,a bright spot appears on the anode surface.This is because with a higher AMF,the contraction of the diffused arc becomes more obvious,leading to a higher energy flux to the anode and thus a higher anode temperature.Then more secondary plasma can be generated near the anode,and the brightness of the‘anode spot’increases.During this process,the arc appearance gradually changes from a cone to a dumbbell shape.In this condition,the arc is in the diffuse mode.The appearance of the plasma jet calculated in the model is consistent with the experimental results.展开更多
Electrical contact materials are generally Ag-or Cu-based composites and play a critical role in ensuring the reliability and efficiency of electrical equipments and electronic instruments.The MAX(M is an early transi...Electrical contact materials are generally Ag-or Cu-based composites and play a critical role in ensuring the reliability and efficiency of electrical equipments and electronic instruments.The MAX(M is an early transition metal,A is an element from III or IV main groups,and X is carbon or/and nitrogen)phase ceramics display a unique combination of properties and may serve as an ideal reinforcement phase for electrical contact materials.The biological materials evolved in nature generally exhibit three-dimensional(3D)interpenetrating-phase architectures,which may offer useful inspiration for the architectural design of electrical contact materials.Here,a series of bi-continuous Ag-Ti_(3)SiC_(2) MAX phase composites with high ceramic contents exceeding 50 vol.%and having micron-and ultrafine-scaled 3D interpenetrating-phase architectures,wherein both constituents were continuous and mutually interspersed,were exploited by pressureless infiltration of Ag melt into partially sintered Ti_(3)SiC_(2) scaffolds.The mechanical and electrical properties as well as the friction and wear performance of the composites were investigated and revealed to be closely dependent on the ceramic contents and characteristic structural dimensions.The composites exhibited a good combination of properties with high hardness over 2.3 GPa,high flexural strength exceeding 530 MPa,decent fracture toughness over 10 MPa·m^(1/2),and good wear resistance with low wear rate at an order of 10^(-5)mm^(3)/(N·m),which were much superior compared to the counterparts made by powder metallurgy methods.In particular,the hardness,electrical conductivity,strength,and fracture toughness of the composites demonstrated a simultaneous improvement as the structure was refined from micron-to ultrafine-scales at equivalent ceramic contents.The good combination of properties along with the facile processing route makes the Ag-Ti_(3)SiC_(2)3D interpenetrating-phase composites appealing for electrical contact applications.展开更多
Fatigue properties of high-strength steels become more and more sensitive to inclusions with enhancing the ultimate tensile strength (UTS) because the inclusions often cause a relatively low fatigue strength and a lar...Fatigue properties of high-strength steels become more and more sensitive to inclusions with enhancing the ultimate tensile strength (UTS) because the inclusions often cause a relatively low fatigue strength and a large scatter of fatigue lives. In this work, four S–N curves and more than 200 fatigue fracture morphologies were comprehensively investigated with a special focus on the size and type of inclusions at the fatigue cracking origin in GCr15 steel with a wide strength range by different heat treatments after high-cycle fatigue (HCF). It is found that the percentage of fatigue failure induced by the inclusion including Al2 O3 and TiN gradually increases with increasing the UTS, while the percentage of failure at sample surfaces decreases conversely and the fatigue strength first increases and then decreases. Besides, it is interestingly noted that the inclusion sizes at the cracking origin for TiN are smaller than that for Al2 O3 because the stress concentration factor for TiN is larger than that for Al2 O3 based on the finite element simulation. For the first time, a new fatigue cracking criterion including the isometric inclusion size line in the strength-toughness coordinate system with specific physical meaning was established to reveal the relationship among the UTS, fracture toughness, and the critical inclusion size considering different types of inclusions based on the fracture mechanics. And the critical inclusion size of Al2 O3 is about 1.33 times of TiN. The fatigue cracking criterion could be used to judge whether fatigue fracture occurred at inclusions or not and provides a theoretical basis for controlling the scale of different inclusion types for high-strength steels. Our work may offer a new perspective on the critical inclusion size in terms of the inclusion types, which is of scientific interest and has great merit to industrial metallurgical control for anti-fatigue design.展开更多
Mg(and Mg alloys)and Ti(and Ti alloys)are two important classes of metallic implant materials which are respectively completely degradable and non-degradable after implantation.Making composites composed of them offer...Mg(and Mg alloys)and Ti(and Ti alloys)are two important classes of metallic implant materials which are respectively completely degradable and non-degradable after implantation.Making composites composed of them offers the promise for combining their property advantages for bone repair.Here,we present a Mg-Ti composite fabricated by pressureless infiltration of pure Mg melt into 3D printed Ti scaffold,and demonstrate a potential of the composite for use as new partially degradable and bioactive implant materials.The composite has such architecture that the Mg and Ti phases are topologically bicontinuous and mutually interspersed in 3D space,and exhibits several advantages over its constituents,such as higher strengths than as-cast pure Mg and Ti scaffold along with lower Young’s modulus than dense Ti.Additionally,the degradation of Mg phase may induce the formation and ingrowth of new bone tissues into the Ti scaffold to form mechanical interlocking between them;in this process,the Ti scaffold provides constant support and Young’s modulus adaptively decreases toward that of bone.Despite the accelerated corrosion than pure Mg,the composite remains non-cytotoxic and does not cause obvious adverse reactions after implantation as revealed by in vitro and in vivo experiments.This study may offer a new possibility for combining mechanical durability and bioactivity in implant materials,and allow for customized and targeted design of the implant.展开更多
“Brittle”metallic glass(MG)usually fractures catastrophically in a shattering mode under macroscopic compression,because cleavage cracking of splitting that originates from extrinsic flaws dominates the failure of s...“Brittle”metallic glass(MG)usually fractures catastrophically in a shattering mode under macroscopic compression,because cleavage cracking of splitting that originates from extrinsic flaws dominates the failure of such alloys,which brings challenges for studying yield strength.Here we show that the plastic yielding behavior in a brittle Fe-based MG can be successfully activated by decreasing the sample size to micrometer scale to avoid the possible large tensile stress concentrators.The yield strength was found to be at least 33%higher than the fracture strength measured with bulk samples for the present brittle MG.The results further demonstrate that the critical stresses for shear band initiation and propagation are size-independent,while the required stress for cleavage cracking increases with decreasing sample size.The competition of thermodynamic driving forces between the two processes of shear banding and cleavage cracking hence leads to the size-induced brittle-to ductile-transition.These findings clarify the physical nature of the strength of“brittle”MG,implying the great opportunity for using high-strength brittle MGs in devices with small dimensions.展开更多
Conventional fatigue tests on complex components are difficult to sample,time-consuming and expensive.To avoid such problems,several popular machine learning(ML)algorithms were used and compared to predict fatigue lif...Conventional fatigue tests on complex components are difficult to sample,time-consuming and expensive.To avoid such problems,several popular machine learning(ML)algorithms were used and compared to predict fatigue life of gray cast iron(GCI)with the complex microstructures.The feature analysis shows that the fatigue life of GCI is mainly influenced by the external environment such as the stress amplitude,and the internal microstructure parameters such as the percentage of graphite,graphite length,stress concentration factor at the graphite tip,matrix microhardness and Brinell hardness.For simplicity,collected datasets with some of the above features were used to train ML models including back-propagation neural network(BPNN),random forest(RF)and eXtreme gradient boosting(XGBoost).The comparison results suggest that the three models could predict the fatigue lives of GCI,while the implemented RF algorithm is the best performing model.Moreover,the S–N curves fitted by the Basquin relation in the predicted data have a mean relative error of 15%compared to the measured data.The results have demonstrated the advantages of ML,which provides a generic way to predict the fatigue life of GCI for reducing time and cost.展开更多
The structures of tungsten and tungsten carbide scaffolds play a key role in determining the properties of their infiltrated composites for multifunctional applications.However,it is challenging to construct and contr...The structures of tungsten and tungsten carbide scaffolds play a key role in determining the properties of their infiltrated composites for multifunctional applications.However,it is challenging to construct and control the architectures by means of self-assembly in W/WC systems because of their large densities.Here we present the development of unidirectionally porous architectures,with high porosities exceeding 65 vol.%,for W and WC scaffolds which in many respects reproduce the design motif of natural wood using a direct ice-templating technique.This was achieved by adjusting the viscosities of suspensions to retard sedimentation during freezing.The processing,structural characteristics and mechanical properties of the resulting scaffolds were investigated with the correlations between them explored.Quantitative relationships were established to describe their strengths based on the mechanics of cellular solids by taking into account both inter-and intra-lamellar pores.The fracture mechanisms were also identified,especially in light of the porosity.This study extends the effectiveness of the ice-templating technique for systems with large densities or particle sizes.It further provides preforms for developing new natureinspired multifunctional materials,as represented by W/WC-Cu composites.展开更多
High-entropy alloys(HEAs)are composed of multiple principal elements and exhibit not only remarkable mechanical properties,but also promising potentials for developing numerous new compositions.To fully realize such p...High-entropy alloys(HEAs)are composed of multiple principal elements and exhibit not only remarkable mechanical properties,but also promising potentials for developing numerous new compositions.To fully realize such potentials,highthroughput preparation and characterization technologies are especially useful;thereby,the fast evaluations of mechanical properties will be urgently required.Revealing the relation between strength and hardness is of significance for quickly predicting the strength of materials through simple hardness testing.However,up to now the strength-hardness relation for HEAs is still a puzzle.In this work,the relations between tensile or compressive strength and Vickers hardness of various HEAs with hundreds of compositions at room temperature are investigated,and finally,the solution for estimating the strengths of HEAs from their hardness values is achieved.Data for hundreds of different HEAs were extracted from studies reported in the period from 2010 to 2020.The results suggested that the well-known three-time relation(i.e.,hardness equals to three times the magnitude of strength)works for nearly all HEAs,except for a few brittle HEAs which show quite high hardness but low strength due to early fracture.However,for HEAs with different phase structures,different strengths should be applied in using the 3-time relation,i.e.,yield strength for low ductility body-centered cubic(BCC)HEAs and ultimate strength for highly plastic and work-hardenable face-centered cubic(FCC)HEAs.As for dual-phase or multi-phase HEAs,similar 3-time relations can be also found.The present approach sheds light on the mechanisms of hardness and also provides useful guidelines for quick estimation of strength from hardness for various HEAs.展开更多
Notch is a very important geometry with widespread applications in engineering structural components. Finding a universal equation to predict the effect of notch on strength of materials is of much significance for st...Notch is a very important geometry with widespread applications in engineering structural components. Finding a universal equation to predict the effect of notch on strength of materials is of much significance for structural design and materials selection. In the present work, we tried to find this universal equation from experimental results of metallic glasses (MGs) and other materials as well as theoretical derivations based on a universal fracture criterion (Qu and Zhang, Sci. Rep. 3 (2013) 1117). Experimental results showed that the notch effect of the studied MG was affected by the notch geometry characterized by the stress concentration factor Kt. As Kt becomes smaller, the notch strength ratio (NSR, which is the ratio of nominal ultimate tensile strength (UTS) of the notched sample to UTS of the unnotched sample) increases. By comparing MGs with other materials like brittle ceramics and ductile for ductile metals but smaller for brittle effect on strength of materials: NSR = equation was found to be consistent with crystalline metals, we find that when Kt is same, the NSR is larger ceramics. Theoretically, we derived a universal equation for notch M/Kt, where M is a constant related to materials. This universal the experimental results.展开更多
The microscopic Bouligand-type architectures of fish scales demonstrate a notable efficiency in enhancing the damage tolerance of materials;nevertheless,it is challenging to reproduce in metals.Here bioinspired tungst...The microscopic Bouligand-type architectures of fish scales demonstrate a notable efficiency in enhancing the damage tolerance of materials;nevertheless,it is challenging to reproduce in metals.Here bioinspired tungsten-copper composites with different Bouligand-type architectures mimicking fish scales were fabricated by infiltrating a copper melt into woven contextures of tungsten fibers.These composites exhibit a synergetic enhancement in both strength and ductility at room temperature along with an improved resistance to high-temperature oxidization.The strengths were interpreted by adapting the classical laminate theory to incorporate the characteristics of Bouligand-type architectures.In particular,under load the tungsten fibers can reorient adaptively within the copper matrix by their straightening,stretching,interfacial sliding with the matrix,and the cooperative kinking deformation of fiber grids,representing a successful implementation of the optimizing mechanisms of the Bouligand-type architectures to enhance strength and toughness.This study may serve to promote the development of new high-performance tungsten-copper composites for applications,e.g.,as electrical contacts or heat sinks,and offer a viable approach for constructing bioinspired architectures in metallic materials.展开更多
The microstructures and stress-controlled fatigue behavior of austenitic stainless steel(AISI 316 L stainless steel)fabricated via laser-powder bed fusion(L-PBF)technique were investigated.For L-PBF process,zigzag las...The microstructures and stress-controlled fatigue behavior of austenitic stainless steel(AISI 316 L stainless steel)fabricated via laser-powder bed fusion(L-PBF)technique were investigated.For L-PBF process,zigzag laser scanning strategy(scan rotation between successive layer was 0°,ZZ sample)and crosshatching layer scanning strategy(scan rotation between successive layer was 67°,CH sample)were employed.By inducing different thermal history,it is found that the scan strategies of laser beam have a significant impact on grain size and morphology.Fatigue cracks generally initiated from persistent slip bands(PSBs)or grain boundaries(GBs).It is observed that PSBs could transfer the melt pool boundaries(MPBs)continuously.The MPBs have better strain compatibility compared with grain boundaries(GBs),thus MPBs would not be the initiation site of fatigue cracks.A higher fatigue limit strength could be achieved by employing a crosshatching scanning strategy.For the CH sample,fatigue cracks also initiated from GBs and PSBs.However,fatigue crack initiated from process-induced defects were observed in ZZ sample in high-cycle regions.Solidification microstructures and defects characteristics are important factors affecting the fatigue performance of L-PBF 316 L stainless.Process-induced defects originated from fluid instability can be effectively reduced by adjusting the laser scan strategy.展开更多
The microstructure and fatigue and tensile properties of 316 L stainless steel fabricated via laser powder bed fusion(L-PBF)were investigated.Two 316 L stainless steel specimens with different loading directions which...The microstructure and fatigue and tensile properties of 316 L stainless steel fabricated via laser powder bed fusion(L-PBF)were investigated.Two 316 L stainless steel specimens with different loading directions which are either perpendicular to or parallel to building direction were prepared by L-PBF process.The results of X-ray diffraction tomography showed that there was no significant difference in morphology and size/distribution of the defects in the HB and VB samples.Since long axis of columnar grains is generally parallel to the build direction,the fatigue crack encounters more grain boundaries in VB samples under cyclic loading,which led to enhanced fatigue resistance of VB samples compared with HB sample.In contrast to HB sample,the VB sample has a higher fatigue strength due to a higher resistance to localized plastic deformation under cyclic loading.The differences in fatigue properties of L-PBF 316 L SS with different build directions were predominantly controlled by solidification microstructures.展开更多
Twin boundaries(TBs) are key factors influencing the mechanical properties of crystalline materials. We have investigated the intrinsic fatigue cracking mechanisms of TBs during the past decade. The effects of TB or...Twin boundaries(TBs) are key factors influencing the mechanical properties of crystalline materials. We have investigated the intrinsic fatigue cracking mechanisms of TBs during the past decade. The effects of TB orientations on the fatigue cracking mechanisms were revealed via cyclic deformation of a series of grown Cu bicrystals with a sole TB. Furthermore, the combined effects of crystallographic orientation and stacking fault energy(SFE) on the fatigue cracking mechanisms were clarified through cyclic deformation of polycrystalline Cu and Cu alloys. Both developments were reviewed in this report which will provide implications to optimize the interfacial design for the improvement of fatigue performance of metallic materials.展开更多
Friction and wear performance is critical for dental materials which are inevitably subject to reciprocating friction against opposing teeth in applications.Here in-vitro friction and wear behavior of bioinspired cera...Friction and wear performance is critical for dental materials which are inevitably subject to reciprocating friction against opposing teeth in applications.Here in-vitro friction and wear behavior of bioinspired ceramic-polymer composites,which possess nacre-like lamellar and brick-and-mortar architectures and resemble human teeth in their stiffness and hardness,against human tooth enamel were quantitatively investigated to imitate actual service conditions in line with standardized testing configuration.The composites were revealed to exhibit different wear mechanisms and lead to differing extents of wear to the opposing tooth enamel depending on their specific architectural types and orientations.In particular,the brick-and-mortar architecture displayed much less wear than the lamellar one,without obviously roughening the contact surfaces with enamel owing to its high ceramic content,and as such did not accelerate the wear of enamel as compared to smooth ceramics.Such characteristics,combined with its unique stiffness and hardness matching those of human enamel as well as the good fracture toughness and machinability,endow the composite with a promising potential for dental applications.This work may provide an experimental basis to this end and may also give insights towards designing new bioinspired wear-resistant materials for reducing friction and wear.展开更多
The replacement of synthetic foam materials using natural biological ones is of great significance for saving energy/resources and reducing environmental pollutions.Here we characterized the microstructure and mechani...The replacement of synthetic foam materials using natural biological ones is of great significance for saving energy/resources and reducing environmental pollutions.Here we characterized the microstructure and mechanical properties of natural cornstalk pith,which has a large annual output yet lacks an effective exploitation,and evaluated its feasibility for applications as a substitute for synthetic foam materials.The cornstalk pith was revealed to be a cellular material composed of closed cells elongated along the growth direction of com plant and reinforced by well-aligned vascular bundles penetrating the foam matrix.The compressive behavior is featured by a stable stress plateau which is favorable for energy absorption with its mechanical properties largely dependent on the hydration state and loading configuration.In particular,the initial dimension and mechanical properties of cornstalk pith can be effectively recovered after deformation simply by hydration treatment owing to swelling effect caused by the turgor pressure from osmosis.The cornstalk pith demonstrates an outstanding combination of low density and high energy absorption efficiency among various foam materials,specifically with its plateau stress and energy absorption comparable or even superior to those of some typical synthetic foam materials.These along with the huge resources and good biodegradability make it a promising natural energy absorbing cellular material for replacing synthetic counterparts.展开更多
基金the National Natural Science Foundation of China(Nos.52001310 and 52130002)the National Science and Technology Major Project(No.J2019-VI-0019-0134)+1 种基金KC Wong Education Foundation(No.GJTD-2020-09)Institute of Metal Res earch Innovation Fund(No.2023-ZD01)。
文摘Compared with the conventional Charpy impact test method,the oscillographic impact test can help in the behavioral analysis of materials during the fracture process.In this study,the trade-off relationship between the strength and toughness of a DZ2 axle steel at various tempering temperatures and the cause of the improvement in impact toughness was evaluated.The tempering process dramatically influenced carbide precipitation behavior,which resulted in different aspect ratios of carbides.Impact toughness improved along with the rise in tempering temperature mainly due to the increase in energy required in impact crack propagation.The characteristics of the impact crack propagation process were studied through a comprehensive analysis of stress distribution,oscilloscopic impact statistics,fracture morphology,and carbide morphology.The poor impact toughness of low-tempering-temperature specimens was attributed to the increased number of stress concentration points caused by carbide morphology in the small plastic zone during the propagation process,which resulted in a mixed distribution of brittle and ductile fractures on the fracture surface.
基金the financial support by the National Key R&D Program of China under grant number 2020YFA0710404the National Natural Science Foundation of China under grant number 51871216+6 种基金the KC Wong Education Foundation(GJTD-2020-09)the Liao Ning Revitalization Talents Programthe State Key Laboratory for Modification of Chemical Fibers and Polymer Materials at Donghua Universitythe Opening Project of Jiangsu Province Key Laboratory of High-End Structural Materials under grant number hsm1801the Opening Project of National Key Laboratory of Shock Wave and Detonation Physics under grant number 6142A03203002the Youth Innovation Promotion Association CASsupported by the Multi-University Research Initiative under grant number AFOSR-FA9550-151-0009 from the Air Force Office of Scientific Research
文摘Natural fish scales demonstrate outstanding mechanical efficiency owing to their elaborate architectures and thereby may serve as ideal prototypes for the architectural design of man-made materials.Here bioinspired magnesium composites with fish-scale-like orthogonal plywood and double-Bouligand architectures were developed by pressureless infiltration of a magnesium melt into the woven contextures of continuous titanium fibers.The composites exhibit enhanced strength and work-hardening ability compared to those estimated from a simple mixture of their constituents at ambient to elevated temperatures.In particular,the double-Bouligand architecture can effectively deflect cracking paths,alleviate strain localization,and adaptively reorient titanium fibers within the magnesium matrix during the deformation of the composite,representing a successful implementation of the property-optimizing mechanisms in fish scales.The strength of the composites,specifically the effect of their bioinspired architectures,was interpreted based on the adaptation of classical laminate theory.This study may offer a feasible approach for developing new bioinspired metal-matrix composites with improved performance and provide theoretical guidance for their architectural designs.
基金received from Inno Tech Alberta (Dr Gary Fisher)the Major Innovation Fund (MIF) Program+5 种基金Imperial Oilthe Province of Alberta-Ministry of Jobs,Economy and Innovationthe Natural Science and Engineering Research Council of Canadafinancial support from Youth Talent Promotion Project of China Association for Science and Technology(Grant No. YESS20200120)the Youth Innovation Promotion Association CAS (Grant Nos. 2022189)Distinguished Scholar Project of Institute of Metal Research CAS (Grant No.2019000179)
文摘Nanostructured materials are being actively developed,while it remains an open question how to rapidly scale them up to bulk engineering materials for broad industrial applications.This study propose an industrial approach to rapidly fabricate high-strength large-size nanostructured metal matrix composites and attempts to investigate and optimize the deposition process and strengthening mechanism.Here,advanced nanocrystalline aluminum matrix composites(nanoAMCs)were assembled for the first time by a novel nano-additive manufacturing method that was guided by numerical simulations(i.e.the in-flight particle model and the porefree deposition model).The present nanoAMC with a mean grain size<50 nm in matrix exhibited hardness eight times higher than the bulk aluminum and shows the highest hardness among all Al–Al2O3 composites reported to date in the literature,which are the outcome of controlling multiscale strengthening mechanisms from tailoring solution atoms,dislocations,grain boundaries,precipitates,and externally introduced reinforcing particles.The present high-throughput strategy and method can be extended to design and architect advanced coatings or bulk materials in a highly efficient(synthesizing a nanostructured bulk with dimensions of 50×20×4 mm^(3) in 9 min)and highly flexible(regulating the gradient microstructures in bulk)way,which is conducive to industrial production and application.
基金financially supported by the National Natural Science Foundation of China(NSFC)under Gtrant No.50401019the“Hun-dred of Talent Project"by Chinese Academy of Sciences+1 种基金National Outstanding Young Scientist Foundation for Z.F.Zhang under Grant No.50625103the financial support of the Alexander-von-Humboldt(AvH)Foundation.
文摘The deformation, damage, fracture, plasticity and melting phenomenon induced by shear fracture were investigated and summarized for Zr-, Cu-, Ti- and Mg-based bulk metallic glasses (BMGs) and their composites. The shear fracture angles of these BMG materials often display obvious differences under compression and tension, and follow either the Mohr-Coulomb criterion or the unified tensile fracture criterion. The compressive plasticity of the composites is always higher than the tensile plasticity, leading to a significant inconsistency. The enhanced plasticity of BMG composites containing ductile dendrites compared to monolithic glasses strongly depends on the details of the microstructure of the composites. A deformation and damage mechanism of pseudo-plasticity, related to local cracking, is proposed to explain the inconsistency of plastic deformation under tension and compression. Besides, significant melting on the shear fracture surfaces was observed. It is suggested that melting is a common phenomenon in these materials with high strength and high elastic energy, as it is typical for BMGs and their composites failing under shear fracture. The melting mechanism can be explained by a combined effect of a significant temperature rise in the shear bands and the instantaneous release of the large amount of elastic energy stored in the material.
基金supported by National Natural Science Foundation of China(Nos.U1866202 and 51877164)State Key Laboratory of Electrical Insulation and Power Equipment Fund(No.EIPE19128)。
文摘As the main source of the vacuum arc plasma,cathode spots(CSs)play an important role on the behaviors of the vacuum arc.Their characteristics are affected by many factors,especially by the magnetic field.In this paper,the characteristics of the plasma jet from a single CS in vacuum arc under external axial magnetic field(AMF)are studied.A multi-species magneto-hydro-dynamic(MHD)model is established to describe the vacuum arc.The anode temperature is calculated by the anode activity model based on the energy flux obtained from the MHD model.The simulation results indicate that the external AMF has a significant effect on the characteristic of the plasma jet.When the external AMF is high enough,a bright spot appears on the anode surface.This is because with a higher AMF,the contraction of the diffused arc becomes more obvious,leading to a higher energy flux to the anode and thus a higher anode temperature.Then more secondary plasma can be generated near the anode,and the brightness of the‘anode spot’increases.During this process,the arc appearance gradually changes from a cone to a dumbbell shape.In this condition,the arc is in the diffuse mode.The appearance of the plasma jet calculated in the model is consistent with the experimental results.
基金supports from the National Key R&D Program of China(No.2020YFA0710404)the National Natural Science Foundation of China(No.52173269),the KC Wong Education Foundation(No.GJTD-2020-09)the Liaoning Revitalization Talents Program,and the Youth Innovation Promotion Association CAS(No.2019191).
文摘Electrical contact materials are generally Ag-or Cu-based composites and play a critical role in ensuring the reliability and efficiency of electrical equipments and electronic instruments.The MAX(M is an early transition metal,A is an element from III or IV main groups,and X is carbon or/and nitrogen)phase ceramics display a unique combination of properties and may serve as an ideal reinforcement phase for electrical contact materials.The biological materials evolved in nature generally exhibit three-dimensional(3D)interpenetrating-phase architectures,which may offer useful inspiration for the architectural design of electrical contact materials.Here,a series of bi-continuous Ag-Ti_(3)SiC_(2) MAX phase composites with high ceramic contents exceeding 50 vol.%and having micron-and ultrafine-scaled 3D interpenetrating-phase architectures,wherein both constituents were continuous and mutually interspersed,were exploited by pressureless infiltration of Ag melt into partially sintered Ti_(3)SiC_(2) scaffolds.The mechanical and electrical properties as well as the friction and wear performance of the composites were investigated and revealed to be closely dependent on the ceramic contents and characteristic structural dimensions.The composites exhibited a good combination of properties with high hardness over 2.3 GPa,high flexural strength exceeding 530 MPa,decent fracture toughness over 10 MPa·m^(1/2),and good wear resistance with low wear rate at an order of 10^(-5)mm^(3)/(N·m),which were much superior compared to the counterparts made by powder metallurgy methods.In particular,the hardness,electrical conductivity,strength,and fracture toughness of the composites demonstrated a simultaneous improvement as the structure was refined from micron-to ultrafine-scales at equivalent ceramic contents.The good combination of properties along with the facile processing route makes the Ag-Ti_(3)SiC_(2)3D interpenetrating-phase composites appealing for electrical contact applications.
基金financially sup-ported by the National Natural Science Foundation of China(NSFC)(Grant Nos.52001310,52130002,and 51771208)the Strategic Pri-ority Research Program of the Chinese Academy of Sciences(Grant No.XDC04040502)+3 种基金the National Science and Technology Major Project(No.J2019-VI-0019-0134)Outstanding Postgraduate Inno-vative Research Project of Institute of Metal Research,CAS(No.1193002090)KC Wong Education Foundation(No.GJTD-2020-09)Institute of Metal Research Innovation Fund(No.2023-ZD01).
文摘Fatigue properties of high-strength steels become more and more sensitive to inclusions with enhancing the ultimate tensile strength (UTS) because the inclusions often cause a relatively low fatigue strength and a large scatter of fatigue lives. In this work, four S–N curves and more than 200 fatigue fracture morphologies were comprehensively investigated with a special focus on the size and type of inclusions at the fatigue cracking origin in GCr15 steel with a wide strength range by different heat treatments after high-cycle fatigue (HCF). It is found that the percentage of fatigue failure induced by the inclusion including Al2 O3 and TiN gradually increases with increasing the UTS, while the percentage of failure at sample surfaces decreases conversely and the fatigue strength first increases and then decreases. Besides, it is interestingly noted that the inclusion sizes at the cracking origin for TiN are smaller than that for Al2 O3 because the stress concentration factor for TiN is larger than that for Al2 O3 based on the finite element simulation. For the first time, a new fatigue cracking criterion including the isometric inclusion size line in the strength-toughness coordinate system with specific physical meaning was established to reveal the relationship among the UTS, fracture toughness, and the critical inclusion size considering different types of inclusions based on the fracture mechanics. And the critical inclusion size of Al2 O3 is about 1.33 times of TiN. The fatigue cracking criterion could be used to judge whether fatigue fracture occurred at inclusions or not and provides a theoretical basis for controlling the scale of different inclusion types for high-strength steels. Our work may offer a new perspective on the critical inclusion size in terms of the inclusion types, which is of scientific interest and has great merit to industrial metallurgical control for anti-fatigue design.
基金supported by the National Key R&D Program of China(No.2020YFA0710404)the National Natural Science Foundation of China(Nos.51871216 and 52173269)the Youth Innovation Promotion Association CAS.
文摘Mg(and Mg alloys)and Ti(and Ti alloys)are two important classes of metallic implant materials which are respectively completely degradable and non-degradable after implantation.Making composites composed of them offers the promise for combining their property advantages for bone repair.Here,we present a Mg-Ti composite fabricated by pressureless infiltration of pure Mg melt into 3D printed Ti scaffold,and demonstrate a potential of the composite for use as new partially degradable and bioactive implant materials.The composite has such architecture that the Mg and Ti phases are topologically bicontinuous and mutually interspersed in 3D space,and exhibits several advantages over its constituents,such as higher strengths than as-cast pure Mg and Ti scaffold along with lower Young’s modulus than dense Ti.Additionally,the degradation of Mg phase may induce the formation and ingrowth of new bone tissues into the Ti scaffold to form mechanical interlocking between them;in this process,the Ti scaffold provides constant support and Young’s modulus adaptively decreases toward that of bone.Despite the accelerated corrosion than pure Mg,the composite remains non-cytotoxic and does not cause obvious adverse reactions after implantation as revealed by in vitro and in vivo experiments.This study may offer a new possibility for combining mechanical durability and bioactivity in implant materials,and allow for customized and targeted design of the implant.
基金financially supported by the National Natural Science Foundation of China(NSFC)(Nos.51771205 and 52271072)the Natural Science Foundation of Liaoning Province(No.2020-MS-011)the Start-up Program by Northwestern Polytechnical Uni-versity.
文摘“Brittle”metallic glass(MG)usually fractures catastrophically in a shattering mode under macroscopic compression,because cleavage cracking of splitting that originates from extrinsic flaws dominates the failure of such alloys,which brings challenges for studying yield strength.Here we show that the plastic yielding behavior in a brittle Fe-based MG can be successfully activated by decreasing the sample size to micrometer scale to avoid the possible large tensile stress concentrators.The yield strength was found to be at least 33%higher than the fracture strength measured with bulk samples for the present brittle MG.The results further demonstrate that the critical stresses for shear band initiation and propagation are size-independent,while the required stress for cleavage cracking increases with decreasing sample size.The competition of thermodynamic driving forces between the two processes of shear banding and cleavage cracking hence leads to the size-induced brittle-to ductile-transition.These findings clarify the physical nature of the strength of“brittle”MG,implying the great opportunity for using high-strength brittle MGs in devices with small dimensions.
基金This work is supported by the National Natural Science Foundation of China(NSFC)under Grant Nos.51871224 and 52130002.
文摘Conventional fatigue tests on complex components are difficult to sample,time-consuming and expensive.To avoid such problems,several popular machine learning(ML)algorithms were used and compared to predict fatigue life of gray cast iron(GCI)with the complex microstructures.The feature analysis shows that the fatigue life of GCI is mainly influenced by the external environment such as the stress amplitude,and the internal microstructure parameters such as the percentage of graphite,graphite length,stress concentration factor at the graphite tip,matrix microhardness and Brinell hardness.For simplicity,collected datasets with some of the above features were used to train ML models including back-propagation neural network(BPNN),random forest(RF)and eXtreme gradient boosting(XGBoost).The comparison results suggest that the three models could predict the fatigue lives of GCI,while the implemented RF algorithm is the best performing model.Moreover,the S–N curves fitted by the Basquin relation in the predicted data have a mean relative error of 15%compared to the measured data.The results have demonstrated the advantages of ML,which provides a generic way to predict the fatigue life of GCI for reducing time and cost.
基金the National Natural Science Foundation of China(Grant Nos.51871216 and 51501190)the Opening Project of Jiangsu Province Key Laboratory of High-end Structural Materials(Grant No.hsm1801)provided by the U.S.Air Force Office of Scientific Research,under MURI grant AFSOR-FA9550-15-1-0009 to the University of California Riverside through a subcontract to the University of California Berkeley。
文摘The structures of tungsten and tungsten carbide scaffolds play a key role in determining the properties of their infiltrated composites for multifunctional applications.However,it is challenging to construct and control the architectures by means of self-assembly in W/WC systems because of their large densities.Here we present the development of unidirectionally porous architectures,with high porosities exceeding 65 vol.%,for W and WC scaffolds which in many respects reproduce the design motif of natural wood using a direct ice-templating technique.This was achieved by adjusting the viscosities of suspensions to retard sedimentation during freezing.The processing,structural characteristics and mechanical properties of the resulting scaffolds were investigated with the correlations between them explored.Quantitative relationships were established to describe their strengths based on the mechanics of cellular solids by taking into account both inter-and intra-lamellar pores.The fracture mechanisms were also identified,especially in light of the porosity.This study extends the effectiveness of the ice-templating technique for systems with large densities or particle sizes.It further provides preforms for developing new natureinspired multifunctional materials,as represented by W/WC-Cu composites.
基金financially supported by the National Natural Science Foundation of China(NSFC)under Grant(No.51771205)the Youth Innovation Promotion Association of Chinese Academy of Sciences and the LiaoNing Revitalization Talents Program under Grant(No.XLYC1808027)。
文摘High-entropy alloys(HEAs)are composed of multiple principal elements and exhibit not only remarkable mechanical properties,but also promising potentials for developing numerous new compositions.To fully realize such potentials,highthroughput preparation and characterization technologies are especially useful;thereby,the fast evaluations of mechanical properties will be urgently required.Revealing the relation between strength and hardness is of significance for quickly predicting the strength of materials through simple hardness testing.However,up to now the strength-hardness relation for HEAs is still a puzzle.In this work,the relations between tensile or compressive strength and Vickers hardness of various HEAs with hundreds of compositions at room temperature are investigated,and finally,the solution for estimating the strengths of HEAs from their hardness values is achieved.Data for hundreds of different HEAs were extracted from studies reported in the period from 2010 to 2020.The results suggested that the well-known three-time relation(i.e.,hardness equals to three times the magnitude of strength)works for nearly all HEAs,except for a few brittle HEAs which show quite high hardness but low strength due to early fracture.However,for HEAs with different phase structures,different strengths should be applied in using the 3-time relation,i.e.,yield strength for low ductility body-centered cubic(BCC)HEAs and ultimate strength for highly plastic and work-hardenable face-centered cubic(FCC)HEAs.As for dual-phase or multi-phase HEAs,similar 3-time relations can be also found.The present approach sheds light on the mechanisms of hardness and also provides useful guidelines for quick estimation of strength from hardness for various HEAs.
基金financially supported by the National Natural Science Foundation of China under Grant Nos. 51331007 and 51301174
文摘Notch is a very important geometry with widespread applications in engineering structural components. Finding a universal equation to predict the effect of notch on strength of materials is of much significance for structural design and materials selection. In the present work, we tried to find this universal equation from experimental results of metallic glasses (MGs) and other materials as well as theoretical derivations based on a universal fracture criterion (Qu and Zhang, Sci. Rep. 3 (2013) 1117). Experimental results showed that the notch effect of the studied MG was affected by the notch geometry characterized by the stress concentration factor Kt. As Kt becomes smaller, the notch strength ratio (NSR, which is the ratio of nominal ultimate tensile strength (UTS) of the notched sample to UTS of the unnotched sample) increases. By comparing MGs with other materials like brittle ceramics and ductile for ductile metals but smaller for brittle effect on strength of materials: NSR = equation was found to be consistent with crystalline metals, we find that when Kt is same, the NSR is larger ceramics. Theoretically, we derived a universal equation for notch M/Kt, where M is a constant related to materials. This universal the experimental results.
基金the financial support by the National Key R&D Program of China under grant number 2020YFA0710404the National Natural Science Foundation of China under grant number 51871216+5 种基金the KC Wong Education Foundation(GJTD-2020-09)the Liao Ning Revitalization Talents Programthe State Key Laboratory for Modification of Chemical Fibers and Polymer Materials at Donghua Universitythe Opening Project of Jiangsu Province Key Laboratory of High-End Structural Materials under grant number hsm1801the Youth Innovation Promotion Association CASsupport from the Multidisciplinary University Research Initiative to University of California Riverside,funded by the Air Force Office of Scientific Research(AFOSR-FA9550–15–1–0009)and subcontracted to the University of California Berkeley。
文摘The microscopic Bouligand-type architectures of fish scales demonstrate a notable efficiency in enhancing the damage tolerance of materials;nevertheless,it is challenging to reproduce in metals.Here bioinspired tungsten-copper composites with different Bouligand-type architectures mimicking fish scales were fabricated by infiltrating a copper melt into woven contextures of tungsten fibers.These composites exhibit a synergetic enhancement in both strength and ductility at room temperature along with an improved resistance to high-temperature oxidization.The strengths were interpreted by adapting the classical laminate theory to incorporate the characteristics of Bouligand-type architectures.In particular,under load the tungsten fibers can reorient adaptively within the copper matrix by their straightening,stretching,interfacial sliding with the matrix,and the cooperative kinking deformation of fiber grids,representing a successful implementation of the optimizing mechanisms of the Bouligand-type architectures to enhance strength and toughness.This study may serve to promote the development of new high-performance tungsten-copper composites for applications,e.g.,as electrical contacts or heat sinks,and offer a viable approach for constructing bioinspired architectures in metallic materials.
基金the National Magnetic Confinement Fusion Science Program of China(No.2014GB117000)the Joint Funds of the National Natural Science Foundation of China(No.U1605243)。
文摘The microstructures and stress-controlled fatigue behavior of austenitic stainless steel(AISI 316 L stainless steel)fabricated via laser-powder bed fusion(L-PBF)technique were investigated.For L-PBF process,zigzag laser scanning strategy(scan rotation between successive layer was 0°,ZZ sample)and crosshatching layer scanning strategy(scan rotation between successive layer was 67°,CH sample)were employed.By inducing different thermal history,it is found that the scan strategies of laser beam have a significant impact on grain size and morphology.Fatigue cracks generally initiated from persistent slip bands(PSBs)or grain boundaries(GBs).It is observed that PSBs could transfer the melt pool boundaries(MPBs)continuously.The MPBs have better strain compatibility compared with grain boundaries(GBs),thus MPBs would not be the initiation site of fatigue cracks.A higher fatigue limit strength could be achieved by employing a crosshatching scanning strategy.For the CH sample,fatigue cracks also initiated from GBs and PSBs.However,fatigue crack initiated from process-induced defects were observed in ZZ sample in high-cycle regions.Solidification microstructures and defects characteristics are important factors affecting the fatigue performance of L-PBF 316 L stainless.Process-induced defects originated from fluid instability can be effectively reduced by adjusting the laser scan strategy.
基金financially supported by the National Magnetic Confinement Fusion Science Program of China under Grant 2014GB117000the Joint Funds of the National Natural Science Foundation of China under Grant U1605243.
文摘The microstructure and fatigue and tensile properties of 316 L stainless steel fabricated via laser powder bed fusion(L-PBF)were investigated.Two 316 L stainless steel specimens with different loading directions which are either perpendicular to or parallel to building direction were prepared by L-PBF process.The results of X-ray diffraction tomography showed that there was no significant difference in morphology and size/distribution of the defects in the HB and VB samples.Since long axis of columnar grains is generally parallel to the build direction,the fatigue crack encounters more grain boundaries in VB samples under cyclic loading,which led to enhanced fatigue resistance of VB samples compared with HB sample.In contrast to HB sample,the VB sample has a higher fatigue strength due to a higher resistance to localized plastic deformation under cyclic loading.The differences in fatigue properties of L-PBF 316 L SS with different build directions were predominantly controlled by solidification microstructures.
基金supported by the National Natural Science Foundation of China (NSFC) under Grant Nos. 51471170, 51501197 and 51571198
文摘Twin boundaries(TBs) are key factors influencing the mechanical properties of crystalline materials. We have investigated the intrinsic fatigue cracking mechanisms of TBs during the past decade. The effects of TB orientations on the fatigue cracking mechanisms were revealed via cyclic deformation of a series of grown Cu bicrystals with a sole TB. Furthermore, the combined effects of crystallographic orientation and stacking fault energy(SFE) on the fatigue cracking mechanisms were clarified through cyclic deformation of polycrystalline Cu and Cu alloys. Both developments were reviewed in this report which will provide implications to optimize the interfacial design for the improvement of fatigue performance of metallic materials.
基金financially supported by the National Key R&D Program of China(No.2020YFA0710404)the National Natural Science Foundation of China(Nos.52173269 and 51871216)+1 种基金the Liaoning Revitalization Talents Programthe Youth Innovation Promotion Association CAS。
文摘Friction and wear performance is critical for dental materials which are inevitably subject to reciprocating friction against opposing teeth in applications.Here in-vitro friction and wear behavior of bioinspired ceramic-polymer composites,which possess nacre-like lamellar and brick-and-mortar architectures and resemble human teeth in their stiffness and hardness,against human tooth enamel were quantitatively investigated to imitate actual service conditions in line with standardized testing configuration.The composites were revealed to exhibit different wear mechanisms and lead to differing extents of wear to the opposing tooth enamel depending on their specific architectural types and orientations.In particular,the brick-and-mortar architecture displayed much less wear than the lamellar one,without obviously roughening the contact surfaces with enamel owing to its high ceramic content,and as such did not accelerate the wear of enamel as compared to smooth ceramics.Such characteristics,combined with its unique stiffness and hardness matching those of human enamel as well as the good fracture toughness and machinability,endow the composite with a promising potential for dental applications.This work may provide an experimental basis to this end and may also give insights towards designing new bioinspired wear-resistant materials for reducing friction and wear.
基金The authors are grateful for the financial support by National Key R&D Program of China under Grant Number 2020YFA0710404the National Natural Science Foundation of China under grant number 51871216+1 种基金the LiaoNing Revitalization Talents Program,the State Key Laboratory for Modification of Chemical Fibers and Polymer Materials at Donghua Universitythe Opening Project of Jiangsu Province Key Laboratory of High-End Structural Materials under grant number hsm 1801,the Lu Jiaxi International Team Program supported by the K.C.Wong Education Foundation and CAS,and the Youth Innovation Promotion Association CAS.
文摘The replacement of synthetic foam materials using natural biological ones is of great significance for saving energy/resources and reducing environmental pollutions.Here we characterized the microstructure and mechanical properties of natural cornstalk pith,which has a large annual output yet lacks an effective exploitation,and evaluated its feasibility for applications as a substitute for synthetic foam materials.The cornstalk pith was revealed to be a cellular material composed of closed cells elongated along the growth direction of com plant and reinforced by well-aligned vascular bundles penetrating the foam matrix.The compressive behavior is featured by a stable stress plateau which is favorable for energy absorption with its mechanical properties largely dependent on the hydration state and loading configuration.In particular,the initial dimension and mechanical properties of cornstalk pith can be effectively recovered after deformation simply by hydration treatment owing to swelling effect caused by the turgor pressure from osmosis.The cornstalk pith demonstrates an outstanding combination of low density and high energy absorption efficiency among various foam materials,specifically with its plateau stress and energy absorption comparable or even superior to those of some typical synthetic foam materials.These along with the huge resources and good biodegradability make it a promising natural energy absorbing cellular material for replacing synthetic counterparts.