The nanostructured Al-based composites possess the combination of high yield strength and good ductility. In this paper, a micromechanical model is presented to simulate the mechanical response of bimodal nanostructur...The nanostructured Al-based composites possess the combination of high yield strength and good ductility. In this paper, a micromechanical model is presented to simulate the mechanical response of bimodal nanostructured A1 and the particle-reinforced aluminum matrix composite （PAMC）. The constitutive relations for different phases are addressed in the model, as well as the contribution of microcracks. Numerical results show that the model can successfully describe the enhanced strength and ductility of the bimodal nanostructured AI, and the predictions of the PAMC are in good agreement with the experimental data. It is worth noting that the strength and ductility are sensitive to the volume fraction of constituents and the distribution of rnicrocracks in both bimodal nanostructured A1 and PAMG. Therefore, the present theoretical results can be used to optimize the microstructure for improving the mechanical properties of nanostructured Al-based composites.展开更多
IN718 alloy was fabricated by laser powder bed fusion(PBF) for examination of microstructure, precipitates and mechanical properties in the as-built state and after different heat treatments. The as-built alloy had a ...IN718 alloy was fabricated by laser powder bed fusion(PBF) for examination of microstructure, precipitates and mechanical properties in the as-built state and after different heat treatments. The as-built alloy had a characteristic fine cellular-dendritic microstructure with Nb, Mo and Ti segregated along the interdendritic region and cellular boundary. The as-built alloys were then subjected to solution heat treatment(SHT) at 980°C or 1065°C for 1 h. SHT at 980°C led to the formation of δ-phase in the interdendritic region or cellular boundary. The segregation was completely removed by the SHT at 1065°C, but recrystallization was observed, and the carbides decorated along the grain boundaries. The as-built alloy and alloys with SHT at 980°C and 1065°C were two-step aged, which consisted of annealing at 720°C for8 h followed by annealing at 620°C for 8 h. Transmission electron microscopy revealed the precipitation of λ’ and λ" in all alloys after two-step aging, but the amount and uniformity of distribution varied. The Vickers hardness of the PBF IN718 alloy increased from 296 HV to 467 HV after direct aging. The hardness decreased to 267 HV and 235 HV after SHT at 980°C and 1065°C, respectively, but increased to 458 HV and 477 HV followed by aging. The evolution of Young’s modulus after heat treatment exhibited similar trend to that of hardness. The highest hardness was observed for IN718 after SHT at 1065°C and two-step aging due to precipitation with greater amount and uniform distribution.展开更多
Nanoparticles and microparticles reinforced Al matrix composites were fabricated by spark plasma sintering, and the microstructure and tribological properties were investigated systemically. The nano-Al2O3 particle an...Nanoparticles and microparticles reinforced Al matrix composites were fabricated by spark plasma sintering, and the microstructure and tribological properties were investigated systemically. The nano-Al2O3 particle and micro-Al2O3 particle uniformly dispersed in Al matrix composites. The introduction of nanoparticles is beneficial to the decrease of friction coefficient and wear rate, while microparticles are responsible to the high friction coefficient, resulting in the abrasive wear. With the introduction of both nanoparticles and microparticles, their synergic effect will lead to the variation of tribological behavior.展开更多
In this paper,we reported a novel method for synthesis of non-oxide porous ceramics by using random copolymers as precursors.A silazane oligomer and styrene monomer were used as starting materials,which were copolymer...In this paper,we reported a novel method for synthesis of non-oxide porous ceramics by using random copolymers as precursors.A silazane oligomer and styrene monomer were used as starting materials,which were copolymerized at 120 ℃ to form random polysilazane-polystyrene copolymers.The copolymers were then pyrolyzed at 500 ℃ to obtain porous ceramics by completely decomposing polystyrene（PS） and converting polysilazane（PSZ） into non-oxide Si-C-N ceramics.The obtained material contained a bi-model pore-structure consisting of both micro-sized and nano-sized pores with very high surface area of more than500 m;/g.We also demonstrated that the pore structure and surface area of the materials can be tailored by changing the ratio of the two blocks.Current results suggest a promising simple method for making multiscaled porous non-oxide materials.展开更多
Rheumatoid arthritis(RA)is a common autoimmune disease characterized by joint inflammation and immune dysfunction.Although various therapeutic approaches have been utilized for the treatment of RA in clinical applicat...Rheumatoid arthritis(RA)is a common autoimmune disease characterized by joint inflammation and immune dysfunction.Although various therapeutic approaches have been utilized for the treatment of RA in clinical applications,the low responsiveness of RA patients and undesired systemic toxicity are still unresolved problems.Targeting the resolution pathway of inflammation with pro-resolving mediators would evoke the protective actions of patient for combating the inflammation.Ac2–26,a 25-amino acid peptide derived from Annexin A(a pro-resolving mediator),has shown good efficacy in the treatment of inflammatory disorders.However,the low bioavailability of Ac2–26 peptides hinders their efficacy in vivo.In this paper,we formed PEGylated lipid nanoparticles(LDNPs)by the co-assembly of l-ascorbyl palmitate(L-AP)and N-(carbonyl methoxypolyethylene glycol-2000)-1,2-distearoyl-sn–glycero-3-phosphoethanolamine(DSPE-PEG 2 k)to encapsulate and deliver Ac2–26 peptides to the arthritic rats.They showed good stability and biocompatibility.After being intravenously administrated,Ac2–26 peptide-loaded PEGylated lipid nanoparticles(ADNPs)showed the prolonged in vivo circulation time and enhanced accumulation in inflamed sites.In vivo therapeutic evaluations revealed that ADNPs could attenuate synovial inflammation and improve joint pathology.Therefore,the pro-resolving therapeutic strategy using ADNPs is effective in RA treatment.展开更多
The thermal expansion behavior of aluminum matrix composites reinforced with hybrid （nanometer and micrometer） Al2O3 particles was measured between 100 and 600℃ and compared to theoretical models. The results revea...The thermal expansion behavior of aluminum matrix composites reinforced with hybrid （nanometer and micrometer） Al2O3 particles was measured between 100 and 600℃ and compared to theoretical models. The results revealed that the nanoparticle concentration had significant effect on the thermal expansion behavior of the composites. For the composites with lower nanoparticle concentration, their coefficient of thermal expansion （CTE） is determined by a stress relaxation process. While for the composites with higher nanoparticle concentration, their CTE is determined by a percolation process.展开更多
The effect of the applied electric field on the conductive behavior of zirconia ceramics is studied by measuring its initial current-voltage curve at various temperatures. The results show that when the field strength...The effect of the applied electric field on the conductive behavior of zirconia ceramics is studied by measuring its initial current-voltage curve at various temperatures. The results show that when the field strength is higher than the threshold for flash-sintering, the curves exhibit a nonlinear behavior by having an additional current on top of the linear current according to Ohm＇s law. Analyzing its transport behavior reveals that the additional current density is due to the extra oxygen vacancies induced by the electric field. The formation rate of the extra vacancies and associated current was related to the field strength.展开更多
Multi-walled carbon nanotubes（MWNTs） were incorporated into precursor-derived ceramics made from a polysilazane.A ceramic nanocomposite reinforced with about 35 vol%of carbon nanotubes（CNTs）was fabricated by infil...Multi-walled carbon nanotubes（MWNTs） were incorporated into precursor-derived ceramics made from a polysilazane.A ceramic nanocomposite reinforced with about 35 vol%of carbon nanotubes（CNTs）was fabricated by infiltrating CNT-preform with liquid-phased polymeric precursor followed by pyrolysis.The nanocomposite has a dense structure without micro-cracks.The results reveal that the nanocomposite has lower indentation hardness but higher fracture energy than non-reinforced ceramic from the microindentation tests results.The effect of the CNTs on the mechanical properties of the nanocomposite should be discussed accordingly.展开更多
The complex metallic alloy（CMA）, Al（76.8）Fe（24）, was in-situ synthesized in the Al-based hybrid composite by powder metallurgy technique. The structural analysis by X-ray diffraction, scanning electron microscop...The complex metallic alloy（CMA）, Al（76.8）Fe（24）, was in-situ synthesized in the Al-based hybrid composite by powder metallurgy technique. The structural analysis by X-ray diffraction, scanning electron microscopy,and transmission electron microscopy indicated that the Al（76.8）Fe（24） CMA phase was formed by diffusion of Fe atoms into the Al matrix during the sintering stage. The formation of the CMA phase was mainly determined by the sintering temperature which was just above the eutectic temperature of Al–Fe. Moreover,the fully dense Al-based hybrid composite was obtained and exhibited ultrahigh strength ～1100 MPa,indicating that this method is expected to be effective in producing CMA particle reinforced Al-based hybrid composite.展开更多
The conductivity of polymer-derived SiOCN ceramics exhibited an Arrhenius dependence on pyrolysis temperature, with the activation energy of ~3.95 eV. The formation and structure change of the free carbon phase were d...The conductivity of polymer-derived SiOCN ceramics exhibited an Arrhenius dependence on pyrolysis temperature, with the activation energy of ~3.95 eV. The formation and structure change of the free carbon phase were detected by means of electron spin resonance spectroscopy and X-ray photoelectron spectroscopy. It reveals that the number of dangling bonds on the free carbon is increased as pyrolysis temperature increases, with the activation energy of ~3.87 eV. So it is demonstrated that the pyrolysis-temperature induced increase in the conductivity is mainly attributed to the increase of dangling on the graphite-like carbon.展开更多
Increasing understanding of the pathogenesis of rheumatoid arthritis(RA)has remarkably promoted the development of effective therapeutic regimens of RA.Nevertheless,the inadequate response to current therapies in a pr...Increasing understanding of the pathogenesis of rheumatoid arthritis(RA)has remarkably promoted the development of effective therapeutic regimens of RA.Nevertheless,the inadequate response to current therapies in a proportion of patients,the systemic toxicity accompanied by longterm administration or distribution in non-targeted sites and the comprised efficacy caused by undesirable bioavailability,are still unsettled problems lying across the full remission of RA.So far,these existing limitations have inspired comprehensive academic researches on nanomedicines for RA treatment.A variety of versatile nanocarriers with controllable physicochemical properties,tailorable drug release pattern or active targeting ability were fabricated to enhance the drug delivery efficiency in RA treatment.This review aims to provide an up-to-date progress regarding to RA treatment using nanomedicines in the last 5 years and concisely discuss the potential application of several newly emerged therapeutic strategies such as inducing the antigen-specific tolerance,pro-resolving therapy or regulating the immunometabolism for RA treatments.展开更多
Clinically,fractures are the main cause of computer-aided design and computer-aided manufacturing(CAD/CAM)3 mol%-yttria-stabilized tetragonal zirconia polycrystal(Y-TZP)all-ceramic dental restorations failure because ...Clinically,fractures are the main cause of computer-aided design and computer-aided manufacturing(CAD/CAM)3 mol%-yttria-stabilized tetragonal zirconia polycrystal(Y-TZP)all-ceramic dental restorations failure because of repetitive occlusal loading.The goal of this work is to study the effect of test methods and specimen’s size on the flexural strength of five ceramic products.Both biaxial flexure test(BI)and uni-axial flexure tests(UNI),including three-point flexure test(3PF)and four-point flexure test(4PF),are used in this study.For all five products,the flexural strength is as follows:BI>3PF>4PF.Furthermore,specimens with smaller size(3PF-s)have higher values than the bigger ones(3PF).The difference between BI and UNI resulted from the edge flaws in ceramic specimens.The relationship between different UNI(including 3PF-s,3PF and 4PF)can be explained according to Weibull statistical fracture theory.BI is recommended to evaluate the flexural strength of CAD/CAM Y-TZP dental ceramics.展开更多
Lead-free(K0.5-x/2Na0.5-x/2Lix)(Nb0.8Ta0.2)O3(KNLNT)and(K0.49-x/2Na0.49-x/2-LixCa0.01)(Nb0.8Ta0.2)O3(KNLNT-Ca)ceramics were prepared by a conventional ceramic processing.Structural analysis shows that the Ca^2+ doping...Lead-free(K0.5-x/2Na0.5-x/2Lix)(Nb0.8Ta0.2)O3(KNLNT)and(K0.49-x/2Na0.49-x/2-LixCa0.01)(Nb0.8Ta0.2)O3(KNLNT-Ca)ceramics were prepared by a conventional ceramic processing.Structural analysis shows that the Ca^2+ doping takes the A site of ABO3 perovskite and decreases the phase transition temperature.Property measurements reveal that as a donor dopant,the Ca^2+ doping results in higher room-temperature dielectric constant,lower dielectric loss,and lower mechanical quality factor.In addition,the Ca^2+ doping does not change the positive piezoelectric coefficient d33,but increases the converse piezoelectric coefficient d 33*significantly.This is likely due to the increase in the relaxation,as well as the appearance of(CaNa/K·-VNa/K’)defect dipoles.展开更多
基金financially supported by State Key Laboratory of Traction Power (Grant No.2015TPL_Z01)Fundamental Research Funds for the Central Universities (Grant No.2682015RC07)+1 种基金support received from the National Natural Science Foundation of China (Grant Nos.11472243,and 11621062)Doctoral Fund of Ministry of Education of China (20130101120175)
文摘The nanostructured Al-based composites possess the combination of high yield strength and good ductility. In this paper, a micromechanical model is presented to simulate the mechanical response of bimodal nanostructured A1 and the particle-reinforced aluminum matrix composite （PAMC）. The constitutive relations for different phases are addressed in the model, as well as the contribution of microcracks. Numerical results show that the model can successfully describe the enhanced strength and ductility of the bimodal nanostructured AI, and the predictions of the PAMC are in good agreement with the experimental data. It is worth noting that the strength and ductility are sensitive to the volume fraction of constituents and the distribution of rnicrocracks in both bimodal nanostructured A1 and PAMG. Therefore, the present theoretical results can be used to optimize the microstructure for improving the mechanical properties of nanostructured Al-based composites.
基金sponsored, in part by the Office of Naval Research (No. N00014-17-1-2559)in part by the U.S. Army Research Laboratory (No. W911NF1720172)
文摘IN718 alloy was fabricated by laser powder bed fusion(PBF) for examination of microstructure, precipitates and mechanical properties in the as-built state and after different heat treatments. The as-built alloy had a characteristic fine cellular-dendritic microstructure with Nb, Mo and Ti segregated along the interdendritic region and cellular boundary. The as-built alloys were then subjected to solution heat treatment(SHT) at 980°C or 1065°C for 1 h. SHT at 980°C led to the formation of δ-phase in the interdendritic region or cellular boundary. The segregation was completely removed by the SHT at 1065°C, but recrystallization was observed, and the carbides decorated along the grain boundaries. The as-built alloy and alloys with SHT at 980°C and 1065°C were two-step aged, which consisted of annealing at 720°C for8 h followed by annealing at 620°C for 8 h. Transmission electron microscopy revealed the precipitation of λ’ and λ" in all alloys after two-step aging, but the amount and uniformity of distribution varied. The Vickers hardness of the PBF IN718 alloy increased from 296 HV to 467 HV after direct aging. The hardness decreased to 267 HV and 235 HV after SHT at 980°C and 1065°C, respectively, but increased to 458 HV and 477 HV followed by aging. The evolution of Young’s modulus after heat treatment exhibited similar trend to that of hardness. The highest hardness was observed for IN718 after SHT at 1065°C and two-step aging due to precipitation with greater amount and uniform distribution.
基金Funded by the National Key R&D Program of China(No.2017YFB1103500)National Science and Technology Major Project(No.2017-VI-0007-0077)the National Natural Science Foundation of China(Nos.51632007,51672218)
文摘Nanoparticles and microparticles reinforced Al matrix composites were fabricated by spark plasma sintering, and the microstructure and tribological properties were investigated systemically. The nano-Al2O3 particle and micro-Al2O3 particle uniformly dispersed in Al matrix composites. The introduction of nanoparticles is beneficial to the decrease of friction coefficient and wear rate, while microparticles are responsible to the high friction coefficient, resulting in the abrasive wear. With the introduction of both nanoparticles and microparticles, their synergic effect will lead to the variation of tribological behavior.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.21174112 and 51242009)the Research Fund of State Key Laboratory of Solidification Processing(Grant No.82-TZ-2013)+1 种基金the project "111"(B08040)the grant of the New Century Excellent Talents of Education Ministry of China(NCET-110817)
文摘In this paper,we reported a novel method for synthesis of non-oxide porous ceramics by using random copolymers as precursors.A silazane oligomer and styrene monomer were used as starting materials,which were copolymerized at 120 ℃ to form random polysilazane-polystyrene copolymers.The copolymers were then pyrolyzed at 500 ℃ to obtain porous ceramics by completely decomposing polystyrene（PS） and converting polysilazane（PSZ） into non-oxide Si-C-N ceramics.The obtained material contained a bi-model pore-structure consisting of both micro-sized and nano-sized pores with very high surface area of more than500 m;/g.We also demonstrated that the pore structure and surface area of the materials can be tailored by changing the ratio of the two blocks.Current results suggest a promising simple method for making multiscaled porous non-oxide materials.
基金supported by the National Natural Science Foundation of China(No.82003661)。
文摘Rheumatoid arthritis(RA)is a common autoimmune disease characterized by joint inflammation and immune dysfunction.Although various therapeutic approaches have been utilized for the treatment of RA in clinical applications,the low responsiveness of RA patients and undesired systemic toxicity are still unresolved problems.Targeting the resolution pathway of inflammation with pro-resolving mediators would evoke the protective actions of patient for combating the inflammation.Ac2–26,a 25-amino acid peptide derived from Annexin A(a pro-resolving mediator),has shown good efficacy in the treatment of inflammatory disorders.However,the low bioavailability of Ac2–26 peptides hinders their efficacy in vivo.In this paper,we formed PEGylated lipid nanoparticles(LDNPs)by the co-assembly of l-ascorbyl palmitate(L-AP)and N-(carbonyl methoxypolyethylene glycol-2000)-1,2-distearoyl-sn–glycero-3-phosphoethanolamine(DSPE-PEG 2 k)to encapsulate and deliver Ac2–26 peptides to the arthritic rats.They showed good stability and biocompatibility.After being intravenously administrated,Ac2–26 peptide-loaded PEGylated lipid nanoparticles(ADNPs)showed the prolonged in vivo circulation time and enhanced accumulation in inflamed sites.In vivo therapeutic evaluations revealed that ADNPs could attenuate synovial inflammation and improve joint pathology.Therefore,the pro-resolving therapeutic strategy using ADNPs is effective in RA treatment.
文摘The thermal expansion behavior of aluminum matrix composites reinforced with hybrid （nanometer and micrometer） Al2O3 particles was measured between 100 and 600℃ and compared to theoretical models. The results revealed that the nanoparticle concentration had significant effect on the thermal expansion behavior of the composites. For the composites with lower nanoparticle concentration, their coefficient of thermal expansion （CTE） is determined by a stress relaxation process. While for the composites with higher nanoparticle concentration, their CTE is determined by a percolation process.
基金financially supported by National Natural Science Foundation of China(Grant Nos.51372202,51402237,51532003,51602264)State Key Laboratory of Traction Power(Grand No.2015TPL Z01)
文摘The effect of the applied electric field on the conductive behavior of zirconia ceramics is studied by measuring its initial current-voltage curve at various temperatures. The results show that when the field strength is higher than the threshold for flash-sintering, the curves exhibit a nonlinear behavior by having an additional current on top of the linear current according to Ohm＇s law. Analyzing its transport behavior reveals that the additional current density is due to the extra oxygen vacancies induced by the electric field. The formation rate of the extra vacancies and associated current was related to the field strength.
文摘Multi-walled carbon nanotubes（MWNTs） were incorporated into precursor-derived ceramics made from a polysilazane.A ceramic nanocomposite reinforced with about 35 vol%of carbon nanotubes（CNTs）was fabricated by infiltrating CNT-preform with liquid-phased polymeric precursor followed by pyrolysis.The nanocomposite has a dense structure without micro-cracks.The results reveal that the nanocomposite has lower indentation hardness but higher fracture energy than non-reinforced ceramic from the microindentation tests results.The effect of the CNTs on the mechanical properties of the nanocomposite should be discussed accordingly.
基金the financial support from the State Key Laboratory of Traction Power (Grant No. 2015TPL Z01)the State Key Laboratory of Solidification Processing (Grant Nos. 82TZ-2013 and SKLSP201609)+1 种基金the Fundamental Research Funds for the Central Universities (Grant No. 2682015RC07)the “111” Project (Grant No. B08040)
文摘The complex metallic alloy（CMA）, Al（76.8）Fe（24）, was in-situ synthesized in the Al-based hybrid composite by powder metallurgy technique. The structural analysis by X-ray diffraction, scanning electron microscopy,and transmission electron microscopy indicated that the Al（76.8）Fe（24） CMA phase was formed by diffusion of Fe atoms into the Al matrix during the sintering stage. The formation of the CMA phase was mainly determined by the sintering temperature which was just above the eutectic temperature of Al–Fe. Moreover,the fully dense Al-based hybrid composite was obtained and exhibited ultrahigh strength ～1100 MPa,indicating that this method is expected to be effective in producing CMA particle reinforced Al-based hybrid composite.
文摘The conductivity of polymer-derived SiOCN ceramics exhibited an Arrhenius dependence on pyrolysis temperature, with the activation energy of ~3.95 eV. The formation and structure change of the free carbon phase were detected by means of electron spin resonance spectroscopy and X-ray photoelectron spectroscopy. It reveals that the number of dangling bonds on the free carbon is increased as pyrolysis temperature increases, with the activation energy of ~3.87 eV. So it is demonstrated that the pyrolysis-temperature induced increase in the conductivity is mainly attributed to the increase of dangling on the graphite-like carbon.
基金supported by the National Natural Science Foundation of China(No.82003661)。
文摘Increasing understanding of the pathogenesis of rheumatoid arthritis(RA)has remarkably promoted the development of effective therapeutic regimens of RA.Nevertheless,the inadequate response to current therapies in a proportion of patients,the systemic toxicity accompanied by longterm administration or distribution in non-targeted sites and the comprised efficacy caused by undesirable bioavailability,are still unsettled problems lying across the full remission of RA.So far,these existing limitations have inspired comprehensive academic researches on nanomedicines for RA treatment.A variety of versatile nanocarriers with controllable physicochemical properties,tailorable drug release pattern or active targeting ability were fabricated to enhance the drug delivery efficiency in RA treatment.This review aims to provide an up-to-date progress regarding to RA treatment using nanomedicines in the last 5 years and concisely discuss the potential application of several newly emerged therapeutic strategies such as inducing the antigen-specific tolerance,pro-resolving therapy or regulating the immunometabolism for RA treatments.
基金This work was supported by grants from Natural Science Foundation of China(81200814)National Key Technology R&D Program of China(no.2012BAI22B03).
文摘Clinically,fractures are the main cause of computer-aided design and computer-aided manufacturing(CAD/CAM)3 mol%-yttria-stabilized tetragonal zirconia polycrystal(Y-TZP)all-ceramic dental restorations failure because of repetitive occlusal loading.The goal of this work is to study the effect of test methods and specimen’s size on the flexural strength of five ceramic products.Both biaxial flexure test(BI)and uni-axial flexure tests(UNI),including three-point flexure test(3PF)and four-point flexure test(4PF),are used in this study.For all five products,the flexural strength is as follows:BI>3PF>4PF.Furthermore,specimens with smaller size(3PF-s)have higher values than the bigger ones(3PF).The difference between BI and UNI resulted from the edge flaws in ceramic specimens.The relationship between different UNI(including 3PF-s,3PF and 4PF)can be explained according to Weibull statistical fracture theory.BI is recommended to evaluate the flexural strength of CAD/CAM Y-TZP dental ceramics.
文摘Lead-free(K0.5-x/2Na0.5-x/2Lix)(Nb0.8Ta0.2)O3(KNLNT)and(K0.49-x/2Na0.49-x/2-LixCa0.01)(Nb0.8Ta0.2)O3(KNLNT-Ca)ceramics were prepared by a conventional ceramic processing.Structural analysis shows that the Ca^2+ doping takes the A site of ABO3 perovskite and decreases the phase transition temperature.Property measurements reveal that as a donor dopant,the Ca^2+ doping results in higher room-temperature dielectric constant,lower dielectric loss,and lower mechanical quality factor.In addition,the Ca^2+ doping does not change the positive piezoelectric coefficient d33,but increases the converse piezoelectric coefficient d 33*significantly.This is likely due to the increase in the relaxation,as well as the appearance of(CaNa/K·-VNa/K’)defect dipoles.
