An aluminum-based in-situ composites reinforced with Mg2Si and Si particles were produced by centrifugal casting A1-20Si-5Mg alloy. The microstructure of the composites was examined, and the effects of temperature on ...An aluminum-based in-situ composites reinforced with Mg2Si and Si particles were produced by centrifugal casting A1-20Si-5Mg alloy. The microstructure of the composites was examined, and the effects of temperature on fracture behavior of the composite were investigated. The results show that the average fraction of primary Si and Mg2Si particles in the composites is as high as 38%, and ultimate tensile strengths （UTS） of the composites first increase then decrease with the increase of test temperature. Microstructures of broken specimens show that both the particle fracture and the interface debonding affect the fracture behavior of the composites, and the interface debonding becomes the dominant fracture mechanism with increasing test temperature. Comparative results indicate that rich particles in the composites and excellent interface strength play great roles in enhancing tensile property by preventing the movement of dislocations.展开更多
Structures and properties of the blends of thermotropic liquid crystallinepolymer(LC70)and poly(ethylene terephthalate) (PET) were investigated by usingWAXD,DSC,SEM and mechanical test.The results revealed that Wc,x m...Structures and properties of the blends of thermotropic liquid crystallinepolymer(LC70)and poly(ethylene terephthalate) (PET) were investigated by usingWAXD,DSC,SEM and mechanical test.The results revealed that Wc,x markdly decreased withLC70/PET>30%,and at about LC70/PET=10%, this blend can yield better mechanicalproperties.In these blends LC70 can play the role of the nuclear agent for PET.SEMphoto showed that LC70/PET in in-situ composites possessed 'core-shell' structure andwas immiscible, but at LC70/PST=10%, the LC70 can be uniformly dispersed into matrix PET.展开更多
The Cu-15Cr in-situ fiber-reinforced composites sheets were prepared by cold drawing combined with cold rolling process. The evolution process of Cr fibers was studied, and when cold rolling reduction ε = 95%, the mo...The Cu-15Cr in-situ fiber-reinforced composites sheets were prepared by cold drawing combined with cold rolling process. The evolution process of Cr fibers was studied, and when cold rolling reduction ε = 95%, the morphology of Cr fiber at different annealing temperature and the thermal stability of Cu-15Cr alloy were studied. Microstructure was also studied by scanning electron microscopy（SEM）. Meanwhile, the tensile strength of the alloy was tested by means of a precision universal tester, and the resistance value of the alloy was determined by using a digital micro-Euclidean instrument. The experimental results show that, with the increase of deformation, Cr dendrites evolve into homogeneous and parallelly arranged Cr fibers, and the cross-section of Cr fibers undergoes a ＂V＂ shape transition to ＂一＂ shape. In addition, spheroidization of the Cr fibers occurs on edges and extends to the center as annealing temperature rises. Moreover, the Cr fibers remains stable when the annealing temperature is below 550 ℃. Furthermore, the tensile strength of Cu-15Cr alloy decreases gradually as the annealing temperature increases, while the electrical conductivity maximizes when annealing at 550 ℃. Our study also shows that Cu-15Cr alloy has obtained a better comprehensive performance with tensile strength of 656 MPa and electrical conductivity of 82%IACS after annealing at 450 ℃.展开更多
The morphology of PE in the in-situ CB/PE composites prepared from in-situ polymerization via a catalyst-supported approach was studied by DSC. It is found that both the melting peak temperature and crystallinity of t...The morphology of PE in the in-situ CB/PE composites prepared from in-situ polymerization via a catalyst-supported approach was studied by DSC. It is found that both the melting peak temperature and crystallinity of the PE shelldecrease as filler level increases. The unexpected phenomena are ascribed to the strong interaction between PE and CB andthe very high specific area of CB. It is suggested that the lamellar thickness should be well correlated to the PE shell thickness. A two-layer PE model is successfully used to explain the experiment results.展开更多
The corrosion behaviour of Hadfield manganese austenitic steel matrix composite reinforced with the varying amount of TiC and unreinforced Hadfield manganese austenitic steel matrix alloy has been evaluated in 3.5% Na...The corrosion behaviour of Hadfield manganese austenitic steel matrix composite reinforced with the varying amount of TiC and unreinforced Hadfield manganese austenitic steel matrix alloy has been evaluated in 3.5% NaCl aqueous solution with the pH value of 6 by the potentiodynamic polarization curves and linear polarization resistance measurements at a scan rate of 1 mV/s at room temperature (25°C ± 2°C). The corrosion rate of the composites is higher than that of their unreinforced matrix alloy and it increases with the increasing volume fraction of TiC. The poor corrosion resistance of the composites can be attributed to the galvanic effects between the matrix and reinforcement.展开更多
The effect of friction stir processing(FSP)at different rotation speeds(400,630,800,and 1000 r/min)and traverse speeds(25 and 50 mm/min)on the tribological properties of a Si particle reinforced Zn−40Al−2Cu-based in-s...The effect of friction stir processing(FSP)at different rotation speeds(400,630,800,and 1000 r/min)and traverse speeds(25 and 50 mm/min)on the tribological properties of a Si particle reinforced Zn−40Al−2Cu-based in-situ composite was investigated.After preliminary optimization,800 r/min and 25 mm/min were selected as optimum FSP parameters.According to the results,multi-pass FSP improved the tribological properties.For instance,at an applied pressure of 0.75 MPa,the wear rate and average coefficient of friction(COF)of four-pass FSPed composite were lower than those of base composite by 53%and 50%,respectively.SEM examinations of worn surfaces,wear debris,and worn subsurfaces revealed that the intensive refinement and uniform distribution of microstructural phases,especially the coarse Si particles,reduced Si particles interspacing,and elimination of casting defects were the most important factors enhancing the substrate resistance against sliding-induced deformation.This led to the formation of stable tribolayers that improved the tribological properties.展开更多
The microstructures and magnetic properties of two in-situ composites, directionally solidified Sb-9.5%Mn and Sb-50%Mn alloys, were investigated. The aligned ferromagnetic compound MuSb or Mn2Sb was embedded in Sb or ...The microstructures and magnetic properties of two in-situ composites, directionally solidified Sb-9.5%Mn and Sb-50%Mn alloys, were investigated. The aligned ferromagnetic compound MuSb or Mn2Sb was embedded in Sb or Mn matrix with varying Mn content. The magnetization curves and thermal magnetic Curves were examined along solidification direction, which reveals the magnetic behaviors of the composites.展开更多
The Nb 10Si (mole fraction, %) alloy was fabricated using the vacuum arc melting method and heat treated at 1850?℃ and 1?550?℃ for 2～100?h in Ar atmosphere. The microstructure of the alloy has been investigated usi...The Nb 10Si (mole fraction, %) alloy was fabricated using the vacuum arc melting method and heat treated at 1850?℃ and 1?550?℃ for 2～100?h in Ar atmosphere. The microstructure of the alloy has been investigated using X ray diffractometry(XRD), scanning electron microscopy (SEM) equipped with X ray energy dispersive spectrometry (EDS) and transmission electron microscopy (TEM). The results show that 1?550?℃, 100?h is an optimum heat treatment condition to acquire the equilibrium Nb+Nb 5Si 3 two phase microstructure. The microstructure of Nb 10Si alloy in the as cast condition consists of continuous Nb 3Si matrix and dispersed Nb particles, which implies that the alloy is in the metastable equilibrium state. In the case of 1?850?℃, 2?h heat treatment the Nb particles are coarsened evidently. However, in the heat treatment condition of 1?550?℃ for 25～100?h the growth of Nb particles is unconspicuous. After heat treated at 1?550?℃, Nb 3Si phase transforms into the equilibrium Nb 5Si 3 and Nb phase with the increase of heat treatment time gradually. TEM observations reveal that the interface of Nb phase and Nb 5Si 3 phase is clean and some twins with about 10?nm in width are found.展开更多
The effects of alloying elements on the mechanical properties as well as electrical conductivity in Cu-15%Cr(mass fraction) in-situ composites were systematically studied and high strength and high electrical conducti...The effects of alloying elements on the mechanical properties as well as electrical conductivity in Cu-15%Cr(mass fraction) in-situ composites were systematically studied and high strength and high electrical conductive Cu base in-situ composites have been developed. The best combination is the addition of 0.1% to 0.2% Zr, Ti, or Sn in Cu-15%Cr in-situ composite, thermomechanical treatment to refine the microstructure and optimizing the precipitation of second phase. The strength is controlled by high density of dislocations in the Cu matrix, the lamellar spacing of the second phase, and the fine Cr precipitates. The aging treatment to reduce solute atoms has a beneficial effect on the increase of electrical conductivity. The addition of Zr, or Ti of about 0.15% to 0.2% promotes the precipitation of Cr particles.展开更多
The effect of alloying elements V and Al on microstructure and room temperature fracture toughness of an experimental Nb-Si in-situ composite was investigated. The Nb-Si alloys with different amount of V and Al were p...The effect of alloying elements V and Al on microstructure and room temperature fracture toughness of an experimental Nb-Si in-situ composite was investigated. The Nb-Si alloys with different amount of V and Al were prepared by non-consumable arc-melting furnace. The experimental results showed that with the addition of V and Al, the microstructure of the Nb-Si materials transformed from Nbss+Nb3Si to Nbss+Nb5Si3 and the lattice parameters of Nbss phase decreased, and the alloying element V promoted the formation of the finer Nbss structure. It was observed that the room temperature fracture toughness was improved by the addition of V and Al, and the optimum room-temperature fracture toughness of the material appeared in the alloy with 2.6at.%V and 3.6at.%Al. The improvement of room temperature fracture toughness may be mainly attributed to the increment of the volume fraction of Nbss phase and the decrement of the silicide phase size.展开更多
Microstructure and properties of deformation processed Cu 16Fe 2Cr and Cu 18Fe in situ composite wires obtained by cold drawing combined with intermediate annealing were investigated. At lower strains( η <2.52), m...Microstructure and properties of deformation processed Cu 16Fe 2Cr and Cu 18Fe in situ composite wires obtained by cold drawing combined with intermediate annealing were investigated. At lower strains( η <2.52), most of the Fe(Cr) phases were elongated into filaments except some remain granular because of their higher hardness. The ultimate tensile strengths of Cu 16Fe 2Cr and Cu 18Fe are approximately equal at the same drawing strains, suggesting the increase of strength of Cu 16Fe 2Cr due to higher strength of Fe(Cr) filaments than that of Fe filaments which is counteracted by the somewhat coarse Fe(Cr) filaments in Cu 16Fe 2Cr at the same drawing strains. The increase of the electrical conductivity of Cu 16Fe 2Cr and Cu 18Fe after intermediate annealing is attributed to the precipitation of Fe, Cr atoms, which dissolved during melting processing. Electrical conductivity of the Cu 16Fe 2Cr in situ composites is higher than Cu 18Fe in situ composites at the same drawing strains. The addition of Cr to Cu Fe system can increase mechanical stability of the filaments in the composites.展开更多
The strength of the deformation-processed Cu-Fe in-situ composite was conducted by material test system(MTS). The results show that the strength increases with the increasing deformation strain and iron content,which ...The strength of the deformation-processed Cu-Fe in-situ composite was conducted by material test system(MTS). The results show that the strength increases with the increasing deformation strain and iron content,which is greater than that of the calculated value based on the rule of mixture. The mechanism of strengthening was analysed and evidenced by interface barrier. The correlation between the strength and the thickness of copper phase (tcu) obeys Hall-Petch relationship and can be described well by geometrical necessary dislocation model and interface as dislocation source model.展开更多
The effects of intermediate annealings on the microstructure, the strength and the electrical resistivity of deformation-processed Cu-Fe in-situ composites were studied. The results show that intermediate annealings f...The effects of intermediate annealings on the microstructure, the strength and the electrical resistivity of deformation-processed Cu-Fe in-situ composites were studied. The results show that intermediate annealings favour the formation of uniform tiny fibres from the iron dendrites but they have no obvious effect on the strength of the composite. The bigger the strain is, the higher the strength is. As the strain increases, the resistivity increases due to the increase of interface density. Intermediate annealings result in notable decreasing resistivity due to the precipitation of the iron atoms from the Cu matrix and decrease of solute scattering resistivity. The doping with Zr improves the strength of the composite slightly and the ultimate tensile strength(UTS) increases about 10%. The colligated performances of deformation-processed Cu-11.5%Fe and Cu- 11.5%Fe-Zr composites at strain η= 5.37 are 64.6% IACS/752MPa and 61.4% IACS/824MPa respectively.展开更多
It has always been challenging work to reconcile the contradiction between the strength and plasticity of titanium materials.Laser powder bed fusion(LPBF) is a convenient method to fabricate innovative composites incl...It has always been challenging work to reconcile the contradiction between the strength and plasticity of titanium materials.Laser powder bed fusion(LPBF) is a convenient method to fabricate innovative composites including those inspired by gradient layered materials.In this work,we used LPBF to selectively prepare Ti N/Ti gradient layered structure(GLSTi)composites by using different N_(2)–Ar ratios during the LPBF process.We systematically investigated the mechanisms of in-situ synthesis Ti N,high strength and ductility of GLSTi composites using microscopic analysis,TEM characterization,and tensile testing with digital image correlation.Besides,a digital correspondence was established between the N_(2) concentration and the volume fraction of LPBF in-situ synthesized Ti N.Our results show that the GLSTi composites exhibit superior mechanical properties compared to pure titanium fabricated by LPBF under pure Ar.Specifically,the tensile strength of GLSTi was more than 1.5times higher than that of LPBF-formed pure titanium,reaching up to 1100 MPa,while maintaining a high elongation at fracture of 17%.GLSTi breaks the bottleneck of high strength but low ductility exhibited by conventional nanoceramic particle-strengthened titanium matrix composites,and the hetero-deformation induced strengthening effect formed by the Ti N/Ti layered structure explained its strength-plasticity balanced principle.The microhardness exhibits a jagged variation of the relatively low hardness of 245 HV0.2 for the pure titanium layer and a high hardness of 408 HV0.2 for the N_(2) in-situ synthesis layer.Our study provides a new concept for the structure-performance digital customization of 3D-printed Ti-based composites.展开更多
Titanium matrix composites reinforced with ceramic particles are considered a promising engineering material due to their combination of high specific strength,low density,and high modulus.In this study,the TA15-based...Titanium matrix composites reinforced with ceramic particles are considered a promising engineering material due to their combination of high specific strength,low density,and high modulus.In this study,the TA15-based composites reinforced with a volume fraction of 10% to 25%(TiB+TiC)were prepared using powder metallurgy and casting technique.Microstructural characterization and phase constitution were examined using optical microscopy(OM),scanning electron microscopy(SEM),and X-ray diffraction(XRD).In addition,the microhardness,room temperature(RT)and high temperature(HT)tensile properties of the composites were evaluated.Results revealed that the reinforcements are distributed uniformly even in the composites with a high volume of TiB and TiC.However,as the volume fraction exceeds 15%,TiB and TiC particles become coarsening and exhibit rod-like and dendritic-like morphology.Microhardness increases gradually from 321.2 HV for the base alloy to a maximum of 473.3 HV as the reinforcement increases to 25vol.%.Tensile test results indicate that a reinforcement volume fraction above 20% is beneficial for enhancing tensile strength and yield strength at high temperatures,but it has an adverse effect on room temperature elongation.Conversely,if the reinforcement volume fraction is below 20%,it can improve high-temperature elongation when the temperature exceeds 600℃.展开更多
This study examines the microstructure,mechanical properties(with a focus on room-temperature toughness),and oxidation resistance of Ho-doped NbDSi based in-situ composites.The base alloy consists of the coarse primar...This study examines the microstructure,mechanical properties(with a focus on room-temperature toughness),and oxidation resistance of Ho-doped NbDSi based in-situ composites.The base alloy consists of the coarse primary Nb_(5)Si_(3)phase and the Nb_(5)Si_(3)+Nbss(Nb solid solution)eutectic cells.Ho doping influences the solidification path.When the Ho doping is higher than0.2 at%,the alloys transform into eutectic alloys.Ho can be solid-solved in trace amounts in the Nbss phase.However,most of Ho forms a stable Ho oxide phase,which alleviates oxygen contamination problem to some extent.Moreover,the interface separation between Ho oxide and other phases reduces the plastic deformation constraint.Thus,with 0.4 at%Ho doping,the K_(Q)value is18.03 MPa·m^(1/2),which is 31.1%higher than that of the base alloy.The strength of the Ho-doped alloys does not deteriorate with an increase in toughness.However,the large network-like Ho_(2)O_(3)in the 0.8Ho alloy causes a decrease in toughness and strength.In addition,the Ho oxide phase effectively blocks the inward oxygen intrusion.With 0.8 at%Ho doping,the oxidation mass gain per unit area is 10.16 mg·cm^(2),which is 39.7%lower than that of the base alloy.展开更多
MXenes are a family of two-dimensional(2D)layered transition metal carbides/nitrides that show promising potential for energy storage applications due to their high-specific surface areas,excellent electron conductivi...MXenes are a family of two-dimensional(2D)layered transition metal carbides/nitrides that show promising potential for energy storage applications due to their high-specific surface areas,excellent electron conductivity,good hydrophilicity,and tunable terminations.Among various types of MXenes,Ti_(3)C_(2)T_(x) is the most widely studied for use in capacitive energy storage applications,especially in supercapacitors(SCs).However,the stacking and oxidation of MXene sheets inevitably lead to a significant loss of electrochemically active sites.To overcome such challenges,carbon materials are frequently incorporated into MXenes to enhance their electrochemical properties.This review introduces the common strategies used for synthesizing Ti_(3)C_(2)T_(x),followed by a comprehensive overview of recent developments in Ti_(3)C_(2)T_(x)/carbon composites as electrode materials for SCs.Ti_(3)C_(2)T_(x)/carbon composites are categorized based on the dimensions of carbons,including 0D carbon dots,1D carbon nanotubes and fibers,2D graphene,and 3D carbon materials(activated carbon,polymer-derived carbon,etc.).Finally,this review also provides a perspective on developing novel MXenes/carbon composites as electrodes for application in SCs.展开更多
A novel Mg^(-1)0Li-3Al(wt.%,LA103)matrix composite reinforced by ex situ micron TiB_(2) particles was developed in the present study.The ball milling and cold pressing pretreatment of the reinforcements made it feasib...A novel Mg^(-1)0Li-3Al(wt.%,LA103)matrix composite reinforced by ex situ micron TiB_(2) particles was developed in the present study.The ball milling and cold pressing pretreatment of the reinforcements made it feasible to prepare this material under stir casting conditions with good dispersion.The microstructure and mechanical properties of the composites prepared by different pretreatment methods were analyzed in detail.The TiB_(2) particles in the Al-TiB_(2)/LA103 composite using the pretreatment process were uniformly distributed in the microstructure due to the formation of highly wettable core-shell units in the melt.Compared with the matrix alloys,the Al-TiB_(2)/LA103 composite exhibited effective strength and elastic modulus improvements while maintaining acceptable elongation.The strengthening effect in the composites was mainly attributed to the strong grain refining effect of TiB2.This work shows a balance of high specific modulus(36.1 GPa·cm^(3)·g^(-1))and elongation(8.4%)with the conventional stir casting path,which is of considerable application value.展开更多
The shear behavior of backfill-rock composites is crucial for mine safety and the management of surface subsidence.For exposing the shear failure mechanism of backfill-rock composites,we conducted shear tests on backf...The shear behavior of backfill-rock composites is crucial for mine safety and the management of surface subsidence.For exposing the shear failure mechanism of backfill-rock composites,we conducted shear tests on backfill-rock composites under three constant normal loads,compared with the unfilled rock.To investigate the macro-and meso-failure characteristics of the samples in the shear tests,the cracking behavior of samples was recorded by a high-speed camera and acoustic emission monitoring.In parallel with the experimental test,the numerical models of backfill-rock composites and unfilled rock were established using the discrete element method to analyze the continuous-discontinuous shearing process.Based on the damage mechanics and statistics,a novel shear constitutive model was proposed to describe mechanical behavior.The results show that backfill-rock composites had a special bimodal phenomenon of shearing load-deformation curve,i.e.the first shearing peak corresponded to rock break and the second shearing peak induced by the broken of aeolian sand-cement/fly ash paste backfill.Moreover,the shearing characteristic curves of the backfill-rock composites could be roughly divided into four stages,i.e.the shear failure of the specimens experienced:stage I:stress concentration;stage II:crack propagation;stage III:crack coalescence;stage IV:shearing friction.The numerical simulation shows that the existence of aeolian sand-cement/fly ash paste backfill inevitably altered the coalescence type and failure mode of the specimens and had a strengthening effect on the shear strength of backfillrock composites.Based on damage mechanics and statistics,a shear constitutive model was proposed to describe the shear fracture characteristics of specimens,especially the bimodal phenomenon.Finally,the micro-and meso-mechanisms of shear failure were discussed by combining the micro-test and numerical results.The research can advance the better understanding of the shear behavior of backfill-rock composites and contribute to the safety of mining engineering.展开更多
Polymer dielectrics capable of operating efficiently at high electric fields and elevated temperatures are urgently demanded by next-generation electronics and electrical power systems.While inorganic fillers have bee...Polymer dielectrics capable of operating efficiently at high electric fields and elevated temperatures are urgently demanded by next-generation electronics and electrical power systems.While inorganic fillers have been extensively utilized to improved high-temperature capacitive performance of dielectric polymers,the presence of thermodynamically incompatible organic and inorganic components may lead to concern about the long-term stability and also complicate film processing.Herein,zero-dimensional polymer dots with high electron affinity are introduced into photoactive allyl-containing poly(aryl ether sulfone)to form the all-organic polymer composites for hightemperature capacitive energy storage.Upon ultraviolet irradiation,the crosslinked polymer composites with polymer dots are efficient in suppressing electrical conduction at high electric fields and elevated temperatures,which significantly reduces the high-field energy loss of the composites at 200℃.Accordingly,the ultraviolet-irradiated composite film exhibits a discharged energy density of 4.2 J cm^(−3)at 200℃.Along with outstanding cyclic stability of capacitive performance at 200℃,this work provides a promising class of dielectric materials for robust high-performance all-organic dielectric nanocomposites.展开更多
基金Project(51174244) supported by the National Natural Science Foundation of ChinaProject(CDJZR11130005) supported by the Fundamental Research Funds for the Central Universities,China
文摘An aluminum-based in-situ composites reinforced with Mg2Si and Si particles were produced by centrifugal casting A1-20Si-5Mg alloy. The microstructure of the composites was examined, and the effects of temperature on fracture behavior of the composite were investigated. The results show that the average fraction of primary Si and Mg2Si particles in the composites is as high as 38%, and ultimate tensile strengths （UTS） of the composites first increase then decrease with the increase of test temperature. Microstructures of broken specimens show that both the particle fracture and the interface debonding affect the fracture behavior of the composites, and the interface debonding becomes the dominant fracture mechanism with increasing test temperature. Comparative results indicate that rich particles in the composites and excellent interface strength play great roles in enhancing tensile property by preventing the movement of dislocations.
文摘Structures and properties of the blends of thermotropic liquid crystallinepolymer(LC70)and poly(ethylene terephthalate) (PET) were investigated by usingWAXD,DSC,SEM and mechanical test.The results revealed that Wc,x markdly decreased withLC70/PET>30%,and at about LC70/PET=10%, this blend can yield better mechanicalproperties.In these blends LC70 can play the role of the nuclear agent for PET.SEMphoto showed that LC70/PET in in-situ composites possessed 'core-shell' structure andwas immiscible, but at LC70/PST=10%, the LC70 can be uniformly dispersed into matrix PET.
基金Funded by the Key Project of the Ministry of Education of China(No.109061)the National Natural Science Foundation of China(No.10874118)the“SMC Young Star”Scientist Program of Shanghai Jiao Tong University
文摘The Cu-15Cr in-situ fiber-reinforced composites sheets were prepared by cold drawing combined with cold rolling process. The evolution process of Cr fibers was studied, and when cold rolling reduction ε = 95%, the morphology of Cr fiber at different annealing temperature and the thermal stability of Cu-15Cr alloy were studied. Microstructure was also studied by scanning electron microscopy（SEM）. Meanwhile, the tensile strength of the alloy was tested by means of a precision universal tester, and the resistance value of the alloy was determined by using a digital micro-Euclidean instrument. The experimental results show that, with the increase of deformation, Cr dendrites evolve into homogeneous and parallelly arranged Cr fibers, and the cross-section of Cr fibers undergoes a ＂V＂ shape transition to ＂一＂ shape. In addition, spheroidization of the Cr fibers occurs on edges and extends to the center as annealing temperature rises. Moreover, the Cr fibers remains stable when the annealing temperature is below 550 ℃. Furthermore, the tensile strength of Cu-15Cr alloy decreases gradually as the annealing temperature increases, while the electrical conductivity maximizes when annealing at 550 ℃. Our study also shows that Cu-15Cr alloy has obtained a better comprehensive performance with tensile strength of 656 MPa and electrical conductivity of 82%IACS after annealing at 450 ℃.
文摘The morphology of PE in the in-situ CB/PE composites prepared from in-situ polymerization via a catalyst-supported approach was studied by DSC. It is found that both the melting peak temperature and crystallinity of the PE shelldecrease as filler level increases. The unexpected phenomena are ascribed to the strong interaction between PE and CB andthe very high specific area of CB. It is suggested that the lamellar thickness should be well correlated to the PE shell thickness. A two-layer PE model is successfully used to explain the experiment results.
文摘The corrosion behaviour of Hadfield manganese austenitic steel matrix composite reinforced with the varying amount of TiC and unreinforced Hadfield manganese austenitic steel matrix alloy has been evaluated in 3.5% NaCl aqueous solution with the pH value of 6 by the potentiodynamic polarization curves and linear polarization resistance measurements at a scan rate of 1 mV/s at room temperature (25°C ± 2°C). The corrosion rate of the composites is higher than that of their unreinforced matrix alloy and it increases with the increasing volume fraction of TiC. The poor corrosion resistance of the composites can be attributed to the galvanic effects between the matrix and reinforcement.
文摘The effect of friction stir processing(FSP)at different rotation speeds(400,630,800,and 1000 r/min)and traverse speeds(25 and 50 mm/min)on the tribological properties of a Si particle reinforced Zn−40Al−2Cu-based in-situ composite was investigated.After preliminary optimization,800 r/min and 25 mm/min were selected as optimum FSP parameters.According to the results,multi-pass FSP improved the tribological properties.For instance,at an applied pressure of 0.75 MPa,the wear rate and average coefficient of friction(COF)of four-pass FSPed composite were lower than those of base composite by 53%and 50%,respectively.SEM examinations of worn surfaces,wear debris,and worn subsurfaces revealed that the intensive refinement and uniform distribution of microstructural phases,especially the coarse Si particles,reduced Si particles interspacing,and elimination of casting defects were the most important factors enhancing the substrate resistance against sliding-induced deformation.This led to the formation of stable tribolayers that improved the tribological properties.
基金supported by the Doctoral Foundation of State Education Commissioll(grant No.9328605)the Applied Science Research Project of Jiangsu Province(Grant No.BJ9502),China
文摘The microstructures and magnetic properties of two in-situ composites, directionally solidified Sb-9.5%Mn and Sb-50%Mn alloys, were investigated. The aligned ferromagnetic compound MuSb or Mn2Sb was embedded in Sb or Mn matrix with varying Mn content. The magnetization curves and thermal magnetic Curves were examined along solidification direction, which reveals the magnetic behaviors of the composites.
文摘The Nb 10Si (mole fraction, %) alloy was fabricated using the vacuum arc melting method and heat treated at 1850?℃ and 1?550?℃ for 2～100?h in Ar atmosphere. The microstructure of the alloy has been investigated using X ray diffractometry(XRD), scanning electron microscopy (SEM) equipped with X ray energy dispersive spectrometry (EDS) and transmission electron microscopy (TEM). The results show that 1?550?℃, 100?h is an optimum heat treatment condition to acquire the equilibrium Nb+Nb 5Si 3 two phase microstructure. The microstructure of Nb 10Si alloy in the as cast condition consists of continuous Nb 3Si matrix and dispersed Nb particles, which implies that the alloy is in the metastable equilibrium state. In the case of 1?850?℃, 2?h heat treatment the Nb particles are coarsened evidently. However, in the heat treatment condition of 1?550?℃ for 25～100?h the growth of Nb particles is unconspicuous. After heat treated at 1?550?℃, Nb 3Si phase transforms into the equilibrium Nb 5Si 3 and Nb phase with the increase of heat treatment time gradually. TEM observations reveal that the interface of Nb phase and Nb 5Si 3 phase is clean and some twins with about 10?nm in width are found.
文摘The effects of alloying elements on the mechanical properties as well as electrical conductivity in Cu-15%Cr(mass fraction) in-situ composites were systematically studied and high strength and high electrical conductive Cu base in-situ composites have been developed. The best combination is the addition of 0.1% to 0.2% Zr, Ti, or Sn in Cu-15%Cr in-situ composite, thermomechanical treatment to refine the microstructure and optimizing the precipitation of second phase. The strength is controlled by high density of dislocations in the Cu matrix, the lamellar spacing of the second phase, and the fine Cr precipitates. The aging treatment to reduce solute atoms has a beneficial effect on the increase of electrical conductivity. The addition of Zr, or Ti of about 0.15% to 0.2% promotes the precipitation of Cr particles.
文摘The effect of alloying elements V and Al on microstructure and room temperature fracture toughness of an experimental Nb-Si in-situ composite was investigated. The Nb-Si alloys with different amount of V and Al were prepared by non-consumable arc-melting furnace. The experimental results showed that with the addition of V and Al, the microstructure of the Nb-Si materials transformed from Nbss+Nb3Si to Nbss+Nb5Si3 and the lattice parameters of Nbss phase decreased, and the alloying element V promoted the formation of the finer Nbss structure. It was observed that the room temperature fracture toughness was improved by the addition of V and Al, and the optimum room-temperature fracture toughness of the material appeared in the alloy with 2.6at.%V and 3.6at.%Al. The improvement of room temperature fracture toughness may be mainly attributed to the increment of the volume fraction of Nbss phase and the decrement of the silicide phase size.
基金Project( 5 98191)supportedbyNaturalScienceFoundationofHebeiProvince China
文摘Microstructure and properties of deformation processed Cu 16Fe 2Cr and Cu 18Fe in situ composite wires obtained by cold drawing combined with intermediate annealing were investigated. At lower strains( η <2.52), most of the Fe(Cr) phases were elongated into filaments except some remain granular because of their higher hardness. The ultimate tensile strengths of Cu 16Fe 2Cr and Cu 18Fe are approximately equal at the same drawing strains, suggesting the increase of strength of Cu 16Fe 2Cr due to higher strength of Fe(Cr) filaments than that of Fe filaments which is counteracted by the somewhat coarse Fe(Cr) filaments in Cu 16Fe 2Cr at the same drawing strains. The increase of the electrical conductivity of Cu 16Fe 2Cr and Cu 18Fe after intermediate annealing is attributed to the precipitation of Fe, Cr atoms, which dissolved during melting processing. Electrical conductivity of the Cu 16Fe 2Cr in situ composites is higher than Cu 18Fe in situ composites at the same drawing strains. The addition of Cr to Cu Fe system can increase mechanical stability of the filaments in the composites.
文摘The strength of the deformation-processed Cu-Fe in-situ composite was conducted by material test system(MTS). The results show that the strength increases with the increasing deformation strain and iron content,which is greater than that of the calculated value based on the rule of mixture. The mechanism of strengthening was analysed and evidenced by interface barrier. The correlation between the strength and the thickness of copper phase (tcu) obeys Hall-Petch relationship and can be described well by geometrical necessary dislocation model and interface as dislocation source model.
文摘The effects of intermediate annealings on the microstructure, the strength and the electrical resistivity of deformation-processed Cu-Fe in-situ composites were studied. The results show that intermediate annealings favour the formation of uniform tiny fibres from the iron dendrites but they have no obvious effect on the strength of the composite. The bigger the strain is, the higher the strength is. As the strain increases, the resistivity increases due to the increase of interface density. Intermediate annealings result in notable decreasing resistivity due to the precipitation of the iron atoms from the Cu matrix and decrease of solute scattering resistivity. The doping with Zr improves the strength of the composite slightly and the ultimate tensile strength(UTS) increases about 10%. The colligated performances of deformation-processed Cu-11.5%Fe and Cu- 11.5%Fe-Zr composites at strain η= 5.37 are 64.6% IACS/752MPa and 61.4% IACS/824MPa respectively.
基金supported by the Guangdong Basic and Applied Basic Research Foundation (2020B1515120013,2022B1515120066)National Natural Science Foundation of China (Nos.U2001218, 51875215)+1 种基金Key-Area Research and Development Program of Guangdong Province (2020B090923001)Special Support Foundation of Guangdong Province (No.2019TQ05Z110)。
文摘It has always been challenging work to reconcile the contradiction between the strength and plasticity of titanium materials.Laser powder bed fusion(LPBF) is a convenient method to fabricate innovative composites including those inspired by gradient layered materials.In this work,we used LPBF to selectively prepare Ti N/Ti gradient layered structure(GLSTi)composites by using different N_(2)–Ar ratios during the LPBF process.We systematically investigated the mechanisms of in-situ synthesis Ti N,high strength and ductility of GLSTi composites using microscopic analysis,TEM characterization,and tensile testing with digital image correlation.Besides,a digital correspondence was established between the N_(2) concentration and the volume fraction of LPBF in-situ synthesized Ti N.Our results show that the GLSTi composites exhibit superior mechanical properties compared to pure titanium fabricated by LPBF under pure Ar.Specifically,the tensile strength of GLSTi was more than 1.5times higher than that of LPBF-formed pure titanium,reaching up to 1100 MPa,while maintaining a high elongation at fracture of 17%.GLSTi breaks the bottleneck of high strength but low ductility exhibited by conventional nanoceramic particle-strengthened titanium matrix composites,and the hetero-deformation induced strengthening effect formed by the Ti N/Ti layered structure explained its strength-plasticity balanced principle.The microhardness exhibits a jagged variation of the relatively low hardness of 245 HV0.2 for the pure titanium layer and a high hardness of 408 HV0.2 for the N_(2) in-situ synthesis layer.Our study provides a new concept for the structure-performance digital customization of 3D-printed Ti-based composites.
基金financially supported by the National Key Research&Development Program of China(Nos.2020YFB2008300,2020YFB2008303)。
文摘Titanium matrix composites reinforced with ceramic particles are considered a promising engineering material due to their combination of high specific strength,low density,and high modulus.In this study,the TA15-based composites reinforced with a volume fraction of 10% to 25%(TiB+TiC)were prepared using powder metallurgy and casting technique.Microstructural characterization and phase constitution were examined using optical microscopy(OM),scanning electron microscopy(SEM),and X-ray diffraction(XRD).In addition,the microhardness,room temperature(RT)and high temperature(HT)tensile properties of the composites were evaluated.Results revealed that the reinforcements are distributed uniformly even in the composites with a high volume of TiB and TiC.However,as the volume fraction exceeds 15%,TiB and TiC particles become coarsening and exhibit rod-like and dendritic-like morphology.Microhardness increases gradually from 321.2 HV for the base alloy to a maximum of 473.3 HV as the reinforcement increases to 25vol.%.Tensile test results indicate that a reinforcement volume fraction above 20% is beneficial for enhancing tensile strength and yield strength at high temperatures,but it has an adverse effect on room temperature elongation.Conversely,if the reinforcement volume fraction is below 20%,it can improve high-temperature elongation when the temperature exceeds 600℃.
基金supported by the National Natural Science Foundation of China(Nos.51825401 and 52374384)the Fundamental Research Funds for the Central Universities(No.2023FRFK06014).
文摘This study examines the microstructure,mechanical properties(with a focus on room-temperature toughness),and oxidation resistance of Ho-doped NbDSi based in-situ composites.The base alloy consists of the coarse primary Nb_(5)Si_(3)phase and the Nb_(5)Si_(3)+Nbss(Nb solid solution)eutectic cells.Ho doping influences the solidification path.When the Ho doping is higher than0.2 at%,the alloys transform into eutectic alloys.Ho can be solid-solved in trace amounts in the Nbss phase.However,most of Ho forms a stable Ho oxide phase,which alleviates oxygen contamination problem to some extent.Moreover,the interface separation between Ho oxide and other phases reduces the plastic deformation constraint.Thus,with 0.4 at%Ho doping,the K_(Q)value is18.03 MPa·m^(1/2),which is 31.1%higher than that of the base alloy.The strength of the Ho-doped alloys does not deteriorate with an increase in toughness.However,the large network-like Ho_(2)O_(3)in the 0.8Ho alloy causes a decrease in toughness and strength.In addition,the Ho oxide phase effectively blocks the inward oxygen intrusion.With 0.8 at%Ho doping,the oxidation mass gain per unit area is 10.16 mg·cm^(2),which is 39.7%lower than that of the base alloy.
基金supported by the Basic Scientific Research Funds for Colleges and Universities affiliated to Hebei Province(JST2022005)Thanks are given to the financial support from the National Natural Science Foundation of China(22005099).
文摘MXenes are a family of two-dimensional(2D)layered transition metal carbides/nitrides that show promising potential for energy storage applications due to their high-specific surface areas,excellent electron conductivity,good hydrophilicity,and tunable terminations.Among various types of MXenes,Ti_(3)C_(2)T_(x) is the most widely studied for use in capacitive energy storage applications,especially in supercapacitors(SCs).However,the stacking and oxidation of MXene sheets inevitably lead to a significant loss of electrochemically active sites.To overcome such challenges,carbon materials are frequently incorporated into MXenes to enhance their electrochemical properties.This review introduces the common strategies used for synthesizing Ti_(3)C_(2)T_(x),followed by a comprehensive overview of recent developments in Ti_(3)C_(2)T_(x)/carbon composites as electrode materials for SCs.Ti_(3)C_(2)T_(x)/carbon composites are categorized based on the dimensions of carbons,including 0D carbon dots,1D carbon nanotubes and fibers,2D graphene,and 3D carbon materials(activated carbon,polymer-derived carbon,etc.).Finally,this review also provides a perspective on developing novel MXenes/carbon composites as electrodes for application in SCs.
基金supported by the National Natural Science Foundation of China(Nos.51821001 and U2037601)Major Scientific and Technological Inno-vation Projects in Luoyang(No.2201029A)+1 种基金Foundation Strengthening Plan Technical Field Fund(No.2021-JJ-0112)Shanghai Jiao Tong University Student Innovation Prac-tice Program(No.IPP24076).
文摘A novel Mg^(-1)0Li-3Al(wt.%,LA103)matrix composite reinforced by ex situ micron TiB_(2) particles was developed in the present study.The ball milling and cold pressing pretreatment of the reinforcements made it feasible to prepare this material under stir casting conditions with good dispersion.The microstructure and mechanical properties of the composites prepared by different pretreatment methods were analyzed in detail.The TiB_(2) particles in the Al-TiB_(2)/LA103 composite using the pretreatment process were uniformly distributed in the microstructure due to the formation of highly wettable core-shell units in the melt.Compared with the matrix alloys,the Al-TiB_(2)/LA103 composite exhibited effective strength and elastic modulus improvements while maintaining acceptable elongation.The strengthening effect in the composites was mainly attributed to the strong grain refining effect of TiB2.This work shows a balance of high specific modulus(36.1 GPa·cm^(3)·g^(-1))and elongation(8.4%)with the conventional stir casting path,which is of considerable application value.
文摘The shear behavior of backfill-rock composites is crucial for mine safety and the management of surface subsidence.For exposing the shear failure mechanism of backfill-rock composites,we conducted shear tests on backfill-rock composites under three constant normal loads,compared with the unfilled rock.To investigate the macro-and meso-failure characteristics of the samples in the shear tests,the cracking behavior of samples was recorded by a high-speed camera and acoustic emission monitoring.In parallel with the experimental test,the numerical models of backfill-rock composites and unfilled rock were established using the discrete element method to analyze the continuous-discontinuous shearing process.Based on the damage mechanics and statistics,a novel shear constitutive model was proposed to describe mechanical behavior.The results show that backfill-rock composites had a special bimodal phenomenon of shearing load-deformation curve,i.e.the first shearing peak corresponded to rock break and the second shearing peak induced by the broken of aeolian sand-cement/fly ash paste backfill.Moreover,the shearing characteristic curves of the backfill-rock composites could be roughly divided into four stages,i.e.the shear failure of the specimens experienced:stage I:stress concentration;stage II:crack propagation;stage III:crack coalescence;stage IV:shearing friction.The numerical simulation shows that the existence of aeolian sand-cement/fly ash paste backfill inevitably altered the coalescence type and failure mode of the specimens and had a strengthening effect on the shear strength of backfillrock composites.Based on damage mechanics and statistics,a shear constitutive model was proposed to describe the shear fracture characteristics of specimens,especially the bimodal phenomenon.Finally,the micro-and meso-mechanisms of shear failure were discussed by combining the micro-test and numerical results.The research can advance the better understanding of the shear behavior of backfill-rock composites and contribute to the safety of mining engineering.
基金the National Natural Science Foundation of China(No.51973080,92066104).
文摘Polymer dielectrics capable of operating efficiently at high electric fields and elevated temperatures are urgently demanded by next-generation electronics and electrical power systems.While inorganic fillers have been extensively utilized to improved high-temperature capacitive performance of dielectric polymers,the presence of thermodynamically incompatible organic and inorganic components may lead to concern about the long-term stability and also complicate film processing.Herein,zero-dimensional polymer dots with high electron affinity are introduced into photoactive allyl-containing poly(aryl ether sulfone)to form the all-organic polymer composites for hightemperature capacitive energy storage.Upon ultraviolet irradiation,the crosslinked polymer composites with polymer dots are efficient in suppressing electrical conduction at high electric fields and elevated temperatures,which significantly reduces the high-field energy loss of the composites at 200℃.Accordingly,the ultraviolet-irradiated composite film exhibits a discharged energy density of 4.2 J cm^(−3)at 200℃.Along with outstanding cyclic stability of capacitive performance at 200℃,this work provides a promising class of dielectric materials for robust high-performance all-organic dielectric nanocomposites.
