BeO nanoparticles were synthesized by polyacrylamide gel route.The effects of the processing parameters on the morphology and size of the synthesized BeO nanoparticles were investigated.The calcination temperature of ...BeO nanoparticles were synthesized by polyacrylamide gel route.The effects of the processing parameters on the morphology and size of the synthesized BeO nanoparticles were investigated.The calcination temperature of the gel precursor containing beryllium sulfate was determined by thermogravimetry and differential scanning calorimetry（TG-DSC）,which is around 690 C and 160 C lower than the general temperature.Xray diffractometry（XRD）,transmission electron microscopy（TEM）,and specific surface area measurements（BET） showed that the synthesized nanoparticles under 700 C were pure,globular and about ～5-20 nm with narrow distribution.Interestingly,the nanograins coalesced and grew under higher calcination temperatures and longer calcination time.The influence of calcination temperature on the morphology and growth behavior is greater than that of its duration.The activation energy for grain growth was estimated to be 24.53 kJ/mol,and the dominant growth mechanism was most likely to be related to the vapor transport in pore control mode and grain-rotation-induced grain coalescence（GRIGC） mechanism.展开更多
Grain refinement into nanoscale significantly enhances the strength and hardness of metallic materials but generally reduces the thermal stability by the introduced strong tendency for grain boundary(GB)migration.Stab...Grain refinement into nanoscale significantly enhances the strength and hardness of metallic materials but generally reduces the thermal stability by the introduced strong tendency for grain boundary(GB)migration.Stabilizing nanograins through GB relaxation had been proven as an effective way in several metals recently when the grain size is below a critical value.Here,we discovered that the abnormally enhanced thermal stability induced by GB relaxation can be realized in 0.5%Sb or Fe doped Cu,similar to that in pure Cu.The observed critical grain sizes for GB relaxation in the two Cu alloys are almost the same as pure Cu.However,the GB relaxation effect on thermal stability is kind of suppressed compared to pure Cu with similar grain sizes because of the segregation/precipitation of Sb/Fe during the annealing process,which accelerates the detwinning and the failure of relaxed GBs.展开更多
Surface mechanical attrition treatment(SMAT)method is an effective way to generate nanograined(NG)surface on Ti-25 Nb-3 Mo-2 Sn-3 Zr(wt.%)(named as TLM),a kind ofβ-type titanium alloy,and the achieved nanocrystalline...Surface mechanical attrition treatment(SMAT)method is an effective way to generate nanograined(NG)surface on Ti-25 Nb-3 Mo-2 Sn-3 Zr(wt.%)(named as TLM),a kind ofβ-type titanium alloy,and the achieved nanocrystalline surface was proved to promote positive functions of osteoblastic cells.In this work,to further endow the NG TLM alloy with both good osteogenic and antibacterial properties,magnesium(Mg),silver(Ag)ion or both were introduced onto the NG TLM surface by ion implantation process,as a comparison,the Mg and Ag ions were also co-implanted onto coarsegrained(CG)TLM surface.The obtained results show that subsequent ion implantation does not remarkably induce the surface roughness and topography alteration of the SMAT-treated layers,and it also has little impact on the microstructure of the SMAT-derivedβ-Ti nanograins.In addition,the implanted Mg and Ag ions are observed to exist as MgO and metallic Ag na noparticles(NPs)embedding tightly in theβ-Ti matrix with grain size of about 15 and 7 nm,respectively.Initial cell adhesion and functions(including proliferation,osteo-differentiation and extracellular matrix mineralization)of rabbit bone marrow mesenchymal stem cells(rBMMSCs)and the bacterial colonization of Staphylococcus aureus(S.aureus)on the different surfaces were investigated.The in-vitro experimental results reveal that the Mg and Ag single-ion implanted NG surface either significantly promotes the rBMMSCs response or inhibits the growth ofS.aureus,whereas the Mg/Ag coimplanted NG surface could concurrently enhance the rBMMSCs functions as well as inhibit the bacterial growth compared to the NG surface,and this efficacy is more pronounced as compared to the Mg/Ag co-implantation in the CG surface.The SMAT-achieved nanograins in the TLM surface layer are identified to not only play a leading role in determining the fate of rBMMSCs but also facilitate fabricating dualfunctio nal surface with both good osteogenic and antibacterial activities through co-implantation of Mg and Ag ions.Our investigation provides a new strategy to develop high-performance Ti-based implants for clinical application.展开更多
Cryogenic rolling impacts on microstructure and mechanical properties of spray-formed 7055(SF-7055)Al alloy were investigated.Results show that with the increase of the reduction from 20%to 80%,the grain of cryogenic ...Cryogenic rolling impacts on microstructure and mechanical properties of spray-formed 7055(SF-7055)Al alloy were investigated.Results show that with the increase of the reduction from 20%to 80%,the grain of cryogenic rolled SF-7055 Al alloy is elongated to form a fiber texture.Numerous proliferating dislocations in the microstructure accumulate into dislocation walls and cells,and eventually form subgrains.These subgrain boundaries divide the original grain,thereby reducing the grain size.Under severe deformation conditions,they even enable the formation of nanograins.Meanwhile,the Cu-rich precipitates in the matrix are also broken and refined under the action of large rolling stress.In the process of cryogenic rolling,the tensile strength and hardness of SF-7055 Al alloy gradually increase,while the plasticity decreases.Moreover,the fracture morphology of cryogenic rolled SF-7055 Al alloy gradually transforms to the ductile and quasi-cleavage hybrid fracture characteristics with increased reduction.展开更多
Beads free polyvinyl alcohol(PVA)/NiO nanofibers with an average diameter of 400 nm were successfully prepared through the electrospinning method.NiO nanograins were formed along the axis of the nanofiber due to the c...Beads free polyvinyl alcohol(PVA)/NiO nanofibers with an average diameter of 400 nm were successfully prepared through the electrospinning method.NiO nanograins were formed along the axis of the nanofiber due to the calcination of asspun fibers for 24 h at 450℃ and their presence was confirmed by FESEM.NiO nanograins were characterized by XRD,XPS and FTIR.The characterization results showed the presence of NiO in nanograins and its polycrystalline nature with ionic states.The sensing studies of NiO nanograins were performed towards the pulmonary disease breath markers and they showed better response towards formaldehyde vapour at 350℃.Calcined NiO grains showed a good response towards the 11-1145 ppm of formaldehyde vapour at the operating temperature of 350℃.NiO nanograins also showed quick response time(37 s)and recovery time(14 s)towards 46 ppm of formaldehyde.A sensing mechanism was proposed for the formaldehyde vapour interaction at 350℃ with NiO nanograins.展开更多
The step edges and intrinsic atomic structure of single-crystal substrate play a critical role in determining the growth pathways of transition metal dichalcogenide(TMD)grains,particularly whether the TMDs will grow i...The step edges and intrinsic atomic structure of single-crystal substrate play a critical role in determining the growth pathways of transition metal dichalcogenide(TMD)grains,particularly whether the TMDs will grow into wafer-scale single-crystal or anisotropic nanoribbons.Hereby,we investigate the growth behaviours of the MoS_(2)nanograins on(0001)and()sapphire substrates.On one hand,the step edges formed on the(0001)surface after thermal treatment are found to promote the macroscopic aggregation of MoS_(2)nanograins and to form unidirectional large triangular islands along with the<>steps in the annealing process,while on the pristine(0001)surface,the MoS_(2)nanograins grow into a random network-like pattern.Moreover,oxygen treatment on the substrate can further enhance the growth of MoS_(2)nanograins.Transmission electron microscopy and fast Fourier transform patterns reveal that the substrate could modulate the orientation of MoS_(2)nanograins during their growing process.On the other hand,the MoS_(2)nanograins on the surface could self-assemble into one-dimensional nanoribbons due to the strong structural anisotropy of the substrate.In addition,the ratio of Raman intensities for peaks that correspond to the and A1g phonon modes shows a linear relationship with the grain size due to the change of the“phonon confinement”.Moreover,new peaks located at 226 and 280 cm−1 can be observed in the off-resonant and resonant Raman spectra for the MoS_(2)nanograin samples,respectively,which can be attributed to the scatterings from the edges of as-fabricated MoS_(2)nanostructures.展开更多
Copper(Cu)has been regarded as a highly efficient electrocatalyst for the conversion of CO_(2) into a multicarbon product.However,the catalytic mechanism and the active sites of Cu catalysts under operating conditions...Copper(Cu)has been regarded as a highly efficient electrocatalyst for the conversion of CO_(2) into a multicarbon product.However,the catalytic mechanism and the active sites of Cu catalysts under operating conditions still remain elusive.Yang's team applied systematic operando characterization techniques to provide a quantitative analysis of the valence states and the chemical environment of Cu nanocatalysts under electrochemical reaction conditions,which clearly reveal the evolution of Cu nanocatalysts before and after the entire electrochemical CO_(2) reduction.展开更多
Realizing the greater potential for precipitation strengthening in nanograined alloys is highly desirable but often challenging.In this study,an Fe-Ni based alloy was subjected to plastic deformation followed by aging...Realizing the greater potential for precipitation strengthening in nanograined alloys is highly desirable but often challenging.In this study,an Fe-Ni based alloy was subjected to plastic deformation followed by aging treatment to further strengthen nanograins through high-density precipitates.Microstructural characterization showed that nanograins account for∼64%of the volume,with an average size of 44 nm.Notably,the nanoprecipitates in the nanograins exhibit utterly different characteristics from those in the coarse grains.As a result,the sample has an ultra-high yield strength of 1677 MPa.Further analyses indicated that the D0_(24)-structured nanoprecipitates at the nanograin boundaries provide a greater precipitation strengthening than conventional L1_(2)-structured nanoprecipitates within the coarse grains,the reason of which is that the precipitates inhibit partial dislocation emission and grain boundary migration of the nanograins.This work deepens the understanding of precipitation strengthening in nanograined materials and proposes a novel strategy to further strengthen nanograined alloys.展开更多
Nano-sized CaMoO4 phosphors tri-doped with Er3＋, Yb3＋and Tm3＋ions were successfully synthesized by sol-gel method. Intense blue emission from Tm3＋ions was observed upon excitation of 1532 nm infrared light in Er-Y...Nano-sized CaMoO4 phosphors tri-doped with Er3＋, Yb3＋and Tm3＋ions were successfully synthesized by sol-gel method. Intense blue emission from Tm3＋ions was observed upon excitation of 1532 nm infrared light in Er-Yb-Tm system, while this blue upconversion could not be achieved with the absence of Yb3＋ions in Er-Tm co-doped sample. In order to understand this upconver-sion process, the upconversion spectra in these samples were investigated, and the possible mechanism was proposed based on ex-perimental results. It showed that two different energy transfer from Er3＋to Tm3＋existed simultaneously in Er-Yb-Tm system, the one-step direct energy transfer from Er3＋to Tm3＋, and the two-step Er3＋→Yb3＋→Tm3＋energy transfer. In particular, the 1G4 state of Tm3＋could only be populated from the 3H4 state by cross-relaxation with an excited Yb3＋ion, producing blue emission of Tm3＋. In this upconversion process, Yb3＋ions acted as an energy transfer bridge between Er3＋and Tm3＋, which also meant that the upconver-sion of other rare-earth ions under the excitation of 1532 nm was possible with the presence of Er3＋and Yb3＋.展开更多
The stability of Cu with different average grain sizes prepared by surface mechanical grinding treatment were investigated under the conditions of isothermal annealing and uniaxial tension.In both conditions,experimen...The stability of Cu with different average grain sizes prepared by surface mechanical grinding treatment were investigated under the conditions of isothermal annealing and uniaxial tension.In both conditions,experimental results revealed that the stability of the grains decreased with the decrease of grain size when the grain size was above 70–75 nm,while the stability of the grains increased with the decrease of grain size when the grain size was below 70–75 nm.The grains of about 70–75 nm in size showed the worst stability in both thermal and mechanical conditions due to having the highest level of average atom free energy and their large amount of high energy grain boundary with large curvature.This size was very close to the calculated smallest size achievable by severe plastic deformation based on the grain refinement mechanism of dislocation evolution under present processing condition,at which both the highest density of dislocation and highest energy should be produced and induces poor stability.Below 70 nm,the deformation mechanism of nanograined Cu was transformed into a partial dislocation motion,which activated mechanically induced grain boundary(GB)relaxation accompanied by GB flattening and GB energy decrease and resulted in enhanced stability.This discovery offers the potential for developing nanograined metals with high strength and high stability.展开更多
Ultrasonic fatigue tests are performed on a magnesium alloy with and without ultrasonic peening treatment(UPT).Surface enhancement layer leads to the complete change of crack initiation sites.However,crack initiation ...Ultrasonic fatigue tests are performed on a magnesium alloy with and without ultrasonic peening treatment(UPT).Surface enhancement layer leads to the complete change of crack initiation sites.However,crack initiation mechanism keeps the same and results in a single-faceted morphology at crack initiation site.Microcracks initiate as Mode Ⅱ crack within the original grain,but deflect to Mode I crack outside of the original cracked grain.A threshold SIF value is proposed to evaluate the retarding effect of grain boundary on microcrack propagation.Outside of the original cracked grain,Mode I crack propagation below the threshold ΔK_(σ-th) is responsible for the formation of fine granular area(FGA,a nano-grain layer).Based on the Numerous Cyclic Pressing(NCP) model,it is proposed that crack type should be another necessary condition for the formation of FGA.展开更多
Fatigue failure can still occur beyond 107 cycles,i.e.very-high-cycle fatigue(VHCF),in many metallic materials,such as aluminium alloys and high-strength steels.For VHCF of high-strength steels,a fine granular area(FG...Fatigue failure can still occur beyond 107 cycles,i.e.very-high-cycle fatigue(VHCF),in many metallic materials,such as aluminium alloys and high-strength steels.For VHCF of high-strength steels,a fine granular area(FGA)surrounding an inclusion is commonly identified as the characteristic region of crack initiation on the fracture surface.However,no such FGA feature and related crack initiation behaviour were observed in VHCF of conventionally cast or wrought aluminium alloys.Here,we first reported the distinct mechanisms of crack initiation and early growth,namely the microstructure feature and the role of FGA in VHCF performance for an additively manufactured(AM)AlSi10Mg alloy.The AM pores play a key role in fatigue crack initiation similar to that of the inclusions in high-strength steels,resulting in almost identical FGA behaviour for different materials under a range of mean stress with a stress ratio at R<0 or R>0.The profile microstructure of FGA is identified as a nanograin layer with Si rearrangement and grain boundary transition.This process consumes a large amount of cyclic plastic energy making FGA undertake a vast majority of VHCF life.These results will deepen the understanding of VHCF nature and shed light on crack initiation mechanism of other aluminium and AM alloys.展开更多
The relationship between the microstructure and mechanical properties of the spark plasma sintered AA2024 Y composites subjected to cryo-rolling was investigated. Yttrium addition enhances the mechanical properties of...The relationship between the microstructure and mechanical properties of the spark plasma sintered AA2024 Y composites subjected to cryo-rolling was investigated. Yttrium addition enhances the mechanical properties of the composites by promoting grain refinement and precipitation. However, there is a clear trend of initial increase and later decrease in the properties. Also, it is observed that 0.3 wt.% of yttrium is the optimum amount of reinforcement content to obtain the highest mechanical properties. To further improve the tensile strength of the composites, cryo-rolling was performed on the composites under standard cryogenic conditions by several passes up to a reduction of 25%. The mechanical properties and the corresponding microstructures of composites after cryo-rolling were correlated. The SEM and TEM microstructures reveal that the samples exhibit dual size grains, i.e., nanograins are formed as sub-grains within the actual grain. Due to the grain size reduction and the increase in the dislocation density, the tensile properties are remarkably improved compared to those of the composites before cryo-rolling. The highest mechanical properties like hardness, YS and UTS are found to be 153 HV, 539 MPa and 572 MPa, respectively, with a reasonable ductility in the composite with 0.3 wt.% Y.展开更多
Nanoporous Ag-Pt bi-metallic alloy was fabricated by free dealloying of amorphous Ag-based precursor with the nominal composition of Ag38.25Pt0.5Cu38.75Si22.5.The noble Ag and Pt were left after the less noble Cu and ...Nanoporous Ag-Pt bi-metallic alloy was fabricated by free dealloying of amorphous Ag-based precursor with the nominal composition of Ag38.25Pt0.5Cu38.75Si22.5.The noble Ag and Pt were left after the less noble Cu and Si dissolved in a certain acid solution.Bi-continuous nanoporous microstructure was formed with asymmetric ligaments and pores with typically 30-200 nm in width.The trace addition of Pt has refined the grains of the ligaments to the average size of less than 20 nm in the substrate and induced the formation of rods with nanopores.The morphologies of the rods were observed by scanning electron microscopy(SEM)and transmission electron microscopy(TEM)both in the form of clusters and as scattered individuals with characteristic length of several micrometers and diameter of tens of nanometers.The grains sizes in the rods were finer than those in the ligaments.The good mechanical integrity might be due to the combination of continuous ligaments and clusters of rods.展开更多
To provide insight into the effect of grain size on the precipitation behavior ofγstrengthening super-alloy Inconel 718,a gradient nanostructure with a large grain size span(from 9 nm to tens of microns)along the dep...To provide insight into the effect of grain size on the precipitation behavior ofγstrengthening super-alloy Inconel 718,a gradient nanostructure with a large grain size span(from 9 nm to tens of microns)along the depth direction was achieved by mean of surface mechanical grinding treatment,followed by annealing upon 700-1000℃ for 1 h.The results reveal significant differences in the type and size of precipitates in samples with different grain sizes.Noγprecipitate was detected inside the grains as the grain size was refined down to 40 nm(NG-40)and 9 nm(NG-9).Forδphase,a significantly accelerated precipitation along grain boundary was observed in NG-40 upon 700℃ annealing.Interestingly,with the grain size drops to 9 nm,the precipitation ofδwas suppressed,with some nanosized MC carbides appearing upon annealing.The grain size effect of precipitation behavior endows NG-9 an ultra-high RT-hardness(5.2 GPa)after 1000℃ thermal exposure and an ultra-high hot-hardness(3.2 GPa)at 800℃.展开更多
Nanocrystalline Magnesium ferrite has been prepared by chemical co-precipitation technique. Structural characterization has been performed by X-ray diffraction. Formation of ferrites has also been studied by using FTI...Nanocrystalline Magnesium ferrite has been prepared by chemical co-precipitation technique. Structural characterization has been performed by X-ray diffraction. Formation of ferrites has also been studied by using FTIR. Frequency dependence of real and imaginary part of initial permeability has been presented for the samples sintered at different temperatures. Real part of initial permeability, increases with the increase of grain growth. The loss component repre- sented by imaginary part of initial permeability decreases with frequency up to the measured frequency of this study of 13 MHz. Curie temperatures have been determined from the temperature dependence of permeability. Curie temperatures for the samples of this composition do not vary significantly with the variation of sintering temperatures. B-H loop measurements have been carried out by B-H loop tracer. Transport property measurements haven been carried out by electrometer and impedance analyzer.展开更多
Ag-Cu bimetallic nanoalloy,integrating the advantages of reducing migration and cost of nano-Ag and alleviating oxidation of nano-Cu,is a prospective bonding material for power electronic packaging.The Ag-coated Cu na...Ag-Cu bimetallic nanoalloy,integrating the advantages of reducing migration and cost of nano-Ag and alleviating oxidation of nano-Cu,is a prospective bonding material for power electronic packaging.The Ag-coated Cu nanoparticles(Cu@Ag NPs)paste can execute bonding with high quality at 250℃,and the achieved supersaturated Ag-Cu nanoalloy joint with ultrahigh shear strength(152 MPa)dramatically exceeds most nano-paste joints.The interstitial solid solutions with atomic-level metallurgical bonds at the interface dominantly promoted the shear strength.Besides,the numerous ultrafine nanograin,high proportion of low angle grain boundaries(7.44%)without deformation,and the Cu nanoprecipitates in the joint would improve subordinately.Furthermore,the high content(16.8%)of∑3 twin boundaries would contribute to the electrical and thermal conductivity.Thus,the multiple strengthening mechanisms with the solid solution,the second precipitated phase,and ultrafine nanograin can dramatically enhance shear strength and electro-thermal conductivity of joints for high-temperature device packaging.展开更多
This paper reports the chemical synthesis of tungsten carbide/cobalt (WC/Co) nanocomposite powders via a unique chemical processing technique, involving the using of all water soluble solution of W-, Co- and C-precurs...This paper reports the chemical synthesis of tungsten carbide/cobalt (WC/Co) nanocomposite powders via a unique chemical processing technique, involving the using of all water soluble solution of W-, Co- and C-precursors. In the actual synthesis, large quantities of commercial-scale WC-Co nanocomposite powders are made by an unique combination of converting a molecularly mixed W-, Co-, and C-containing solutions into a complex inorganic polymeric powder precursor, conversion of the inorganic polymeric precursor powder into a W-Co-C-O containing powder intermediates using a belt furnace with temperature at about 500°C - 600°C in an inert atmosphere, followed by carburization in a rotary furnace at temperature less than 1000°C in nitrogen. Liquid phase sintering technique is used to consolidate the WC/Co nanocomposite powder into sintered bulk parts. The sintered parts have excellent hardness in excess of 93 HRA, with WC grains in the order of 200 - 300 nm, while Co phase is uniformly distributed on the grain boundaries of the WC nanoparticles. We also report the presence of cobalt Co precipitates inside tungsten carbide WC nanograins in the composites of the consolidated bulk parts. EDS is used to identify the presence of these precipitates and micro-micro-diffraction technique is employed to determine the nature of these precipitates.展开更多
Deformation mechanisms of nanograined and submicron-grained pure cobalt processed by means of high strain rate shear deformation at cryogenic temperatures were studied.Microstructural analysis revealed a transition of...Deformation mechanisms of nanograined and submicron-grained pure cobalt processed by means of high strain rate shear deformation at cryogenic temperatures were studied.Microstructural analysis revealed a transition of governing deformation mechanism from deformation twinning and dislocation slip in submicron-grains to and dislocations slip in nanograins.Microhardness tests illustrated that the Hall-Petch relation slope changes consequently with the transition of deformation mechanism.展开更多
The thermal features of the nanograin boundary were described by a developed thermodynamic model. Using the nanocrystalline Cu as an example, the pressure, the bulk modulus, and the volume thermal expansion coef- fici...The thermal features of the nanograin boundary were described by a developed thermodynamic model. Using the nanocrystalline Cu as an example, the pressure, the bulk modulus, and the volume thermal expansion coef- ficient were calculated to characterize the thermodynamic properties of the grain boundaries on the nanoscale. Based on the parabola-type relationship between the excess free energy and the excess volume of the nanograin boundary, the thermal stability, as well as its evolution characteristics, was analyzed. The experimental re- sults of the temperature-varying grain growth in the nanocrystalline Cu, which exhibited the discontinuous nanograin growth behavior, verified the thermodynamic predictions. In addition, the quantitative relationships correlating the excess volume and the lattice expansion with the nanograin size were discussed.展开更多
文摘BeO nanoparticles were synthesized by polyacrylamide gel route.The effects of the processing parameters on the morphology and size of the synthesized BeO nanoparticles were investigated.The calcination temperature of the gel precursor containing beryllium sulfate was determined by thermogravimetry and differential scanning calorimetry（TG-DSC）,which is around 690 C and 160 C lower than the general temperature.Xray diffractometry（XRD）,transmission electron microscopy（TEM）,and specific surface area measurements（BET） showed that the synthesized nanoparticles under 700 C were pure,globular and about ～5-20 nm with narrow distribution.Interestingly,the nanograins coalesced and grew under higher calcination temperatures and longer calcination time.The influence of calcination temperature on the morphology and growth behavior is greater than that of its duration.The activation energy for grain growth was estimated to be 24.53 kJ/mol,and the dominant growth mechanism was most likely to be related to the vapor transport in pore control mode and grain-rotation-induced grain coalescence（GRIGC） mechanism.
基金financially supported by the Ministry of Science&Technology of China(Nos.2017YFA0204401 and 2017YFA0700700)the National Natural Science Foundation of China(No.52001315).
文摘Grain refinement into nanoscale significantly enhances the strength and hardness of metallic materials but generally reduces the thermal stability by the introduced strong tendency for grain boundary(GB)migration.Stabilizing nanograins through GB relaxation had been proven as an effective way in several metals recently when the grain size is below a critical value.Here,we discovered that the abnormally enhanced thermal stability induced by GB relaxation can be realized in 0.5%Sb or Fe doped Cu,similar to that in pure Cu.The observed critical grain sizes for GB relaxation in the two Cu alloys are almost the same as pure Cu.However,the GB relaxation effect on thermal stability is kind of suppressed compared to pure Cu with similar grain sizes because of the segregation/precipitation of Sb/Fe during the annealing process,which accelerates the detwinning and the failure of relaxed GBs.
基金financially supported by the National Natural Science Foundation of China(Nos.81501598,51631007 and 31700860)the China Postdoctoral Science Foundation(No.2017M612052)+1 种基金the Postdoctoral Foundation of Anhui Province(No.2017B211)the General Research Fund of Research Grant Council of Hong Kong(Nos.N HKU725-16,17207719 and 17214516)。
文摘Surface mechanical attrition treatment(SMAT)method is an effective way to generate nanograined(NG)surface on Ti-25 Nb-3 Mo-2 Sn-3 Zr(wt.%)(named as TLM),a kind ofβ-type titanium alloy,and the achieved nanocrystalline surface was proved to promote positive functions of osteoblastic cells.In this work,to further endow the NG TLM alloy with both good osteogenic and antibacterial properties,magnesium(Mg),silver(Ag)ion or both were introduced onto the NG TLM surface by ion implantation process,as a comparison,the Mg and Ag ions were also co-implanted onto coarsegrained(CG)TLM surface.The obtained results show that subsequent ion implantation does not remarkably induce the surface roughness and topography alteration of the SMAT-treated layers,and it also has little impact on the microstructure of the SMAT-derivedβ-Ti nanograins.In addition,the implanted Mg and Ag ions are observed to exist as MgO and metallic Ag na noparticles(NPs)embedding tightly in theβ-Ti matrix with grain size of about 15 and 7 nm,respectively.Initial cell adhesion and functions(including proliferation,osteo-differentiation and extracellular matrix mineralization)of rabbit bone marrow mesenchymal stem cells(rBMMSCs)and the bacterial colonization of Staphylococcus aureus(S.aureus)on the different surfaces were investigated.The in-vitro experimental results reveal that the Mg and Ag single-ion implanted NG surface either significantly promotes the rBMMSCs response or inhibits the growth ofS.aureus,whereas the Mg/Ag coimplanted NG surface could concurrently enhance the rBMMSCs functions as well as inhibit the bacterial growth compared to the NG surface,and this efficacy is more pronounced as compared to the Mg/Ag co-implantation in the CG surface.The SMAT-achieved nanograins in the TLM surface layer are identified to not only play a leading role in determining the fate of rBMMSCs but also facilitate fabricating dualfunctio nal surface with both good osteogenic and antibacterial activities through co-implantation of Mg and Ag ions.Our investigation provides a new strategy to develop high-performance Ti-based implants for clinical application.
基金financially and technically supported by the National Key Laboratory Foundation of Science and Technology on Materials under Shock and Impact,Beijing Institute of Technology,China(No.WDZC2024-1)。
文摘Cryogenic rolling impacts on microstructure and mechanical properties of spray-formed 7055(SF-7055)Al alloy were investigated.Results show that with the increase of the reduction from 20%to 80%,the grain of cryogenic rolled SF-7055 Al alloy is elongated to form a fiber texture.Numerous proliferating dislocations in the microstructure accumulate into dislocation walls and cells,and eventually form subgrains.These subgrain boundaries divide the original grain,thereby reducing the grain size.Under severe deformation conditions,they even enable the formation of nanograins.Meanwhile,the Cu-rich precipitates in the matrix are also broken and refined under the action of large rolling stress.In the process of cryogenic rolling,the tensile strength and hardness of SF-7055 Al alloy gradually increase,while the plasticity decreases.Moreover,the fracture morphology of cryogenic rolled SF-7055 Al alloy gradually transforms to the ductile and quasi-cleavage hybrid fracture characteristics with increased reduction.
基金K.R.K thank Council of Scientific and Industrial Research(CSIR)India for the financial support(09/1095/0017/2016-EMRI)the authors extend to thank the SASTRA Deemed to be University for providing the infrastructural facility to carry out the research work.
文摘Beads free polyvinyl alcohol(PVA)/NiO nanofibers with an average diameter of 400 nm were successfully prepared through the electrospinning method.NiO nanograins were formed along the axis of the nanofiber due to the calcination of asspun fibers for 24 h at 450℃ and their presence was confirmed by FESEM.NiO nanograins were characterized by XRD,XPS and FTIR.The characterization results showed the presence of NiO in nanograins and its polycrystalline nature with ionic states.The sensing studies of NiO nanograins were performed towards the pulmonary disease breath markers and they showed better response towards formaldehyde vapour at 350℃.Calcined NiO grains showed a good response towards the 11-1145 ppm of formaldehyde vapour at the operating temperature of 350℃.NiO nanograins also showed quick response time(37 s)and recovery time(14 s)towards 46 ppm of formaldehyde.A sensing mechanism was proposed for the formaldehyde vapour interaction at 350℃ with NiO nanograins.
基金the financial support from the Australian Research Council Discovery Program(No.DP190103661).
文摘The step edges and intrinsic atomic structure of single-crystal substrate play a critical role in determining the growth pathways of transition metal dichalcogenide(TMD)grains,particularly whether the TMDs will grow into wafer-scale single-crystal or anisotropic nanoribbons.Hereby,we investigate the growth behaviours of the MoS_(2)nanograins on(0001)and()sapphire substrates.On one hand,the step edges formed on the(0001)surface after thermal treatment are found to promote the macroscopic aggregation of MoS_(2)nanograins and to form unidirectional large triangular islands along with the<>steps in the annealing process,while on the pristine(0001)surface,the MoS_(2)nanograins grow into a random network-like pattern.Moreover,oxygen treatment on the substrate can further enhance the growth of MoS_(2)nanograins.Transmission electron microscopy and fast Fourier transform patterns reveal that the substrate could modulate the orientation of MoS_(2)nanograins during their growing process.On the other hand,the MoS_(2)nanograins on the surface could self-assemble into one-dimensional nanoribbons due to the strong structural anisotropy of the substrate.In addition,the ratio of Raman intensities for peaks that correspond to the and A1g phonon modes shows a linear relationship with the grain size due to the change of the“phonon confinement”.Moreover,new peaks located at 226 and 280 cm−1 can be observed in the off-resonant and resonant Raman spectra for the MoS_(2)nanograin samples,respectively,which can be attributed to the scatterings from the edges of as-fabricated MoS_(2)nanostructures.
基金supported by the National Natural Science Foundation of China(No.22071172).
文摘Copper(Cu)has been regarded as a highly efficient electrocatalyst for the conversion of CO_(2) into a multicarbon product.However,the catalytic mechanism and the active sites of Cu catalysts under operating conditions still remain elusive.Yang's team applied systematic operando characterization techniques to provide a quantitative analysis of the valence states and the chemical environment of Cu nanocatalysts under electrochemical reaction conditions,which clearly reveal the evolution of Cu nanocatalysts before and after the entire electrochemical CO_(2) reduction.
基金support from the National Natural Science Foundation(No.52473339).
文摘Realizing the greater potential for precipitation strengthening in nanograined alloys is highly desirable but often challenging.In this study,an Fe-Ni based alloy was subjected to plastic deformation followed by aging treatment to further strengthen nanograins through high-density precipitates.Microstructural characterization showed that nanograins account for∼64%of the volume,with an average size of 44 nm.Notably,the nanoprecipitates in the nanograins exhibit utterly different characteristics from those in the coarse grains.As a result,the sample has an ultra-high yield strength of 1677 MPa.Further analyses indicated that the D0_(24)-structured nanoprecipitates at the nanograin boundaries provide a greater precipitation strengthening than conventional L1_(2)-structured nanoprecipitates within the coarse grains,the reason of which is that the precipitates inhibit partial dislocation emission and grain boundary migration of the nanograins.This work deepens the understanding of precipitation strengthening in nanograined materials and proposes a novel strategy to further strengthen nanograined alloys.
基金Project supported by the National Natural Science Foundation of China(11204292,11274299,11311120047,11374291,11404321)Anhui Provincial Natural Science Foundation(1308085QE75)
文摘Nano-sized CaMoO4 phosphors tri-doped with Er3＋, Yb3＋and Tm3＋ions were successfully synthesized by sol-gel method. Intense blue emission from Tm3＋ions was observed upon excitation of 1532 nm infrared light in Er-Yb-Tm system, while this blue upconversion could not be achieved with the absence of Yb3＋ions in Er-Tm co-doped sample. In order to understand this upconver-sion process, the upconversion spectra in these samples were investigated, and the possible mechanism was proposed based on ex-perimental results. It showed that two different energy transfer from Er3＋to Tm3＋existed simultaneously in Er-Yb-Tm system, the one-step direct energy transfer from Er3＋to Tm3＋, and the two-step Er3＋→Yb3＋→Tm3＋energy transfer. In particular, the 1G4 state of Tm3＋could only be populated from the 3H4 state by cross-relaxation with an excited Yb3＋ion, producing blue emission of Tm3＋. In this upconversion process, Yb3＋ions acted as an energy transfer bridge between Er3＋and Tm3＋, which also meant that the upconver-sion of other rare-earth ions under the excitation of 1532 nm was possible with the presence of Er3＋and Yb3＋.
基金supported by the Ministry of Science and Technology of China(Grant Nos.2017YFA0204401 and No.2017YFA0700700)the Chinese Academy of Sciences(Grant No.ZDYZ201701)the Liaoning Revitalization Talents Program(Grant No.XLYC1808008).
文摘The stability of Cu with different average grain sizes prepared by surface mechanical grinding treatment were investigated under the conditions of isothermal annealing and uniaxial tension.In both conditions,experimental results revealed that the stability of the grains decreased with the decrease of grain size when the grain size was above 70–75 nm,while the stability of the grains increased with the decrease of grain size when the grain size was below 70–75 nm.The grains of about 70–75 nm in size showed the worst stability in both thermal and mechanical conditions due to having the highest level of average atom free energy and their large amount of high energy grain boundary with large curvature.This size was very close to the calculated smallest size achievable by severe plastic deformation based on the grain refinement mechanism of dislocation evolution under present processing condition,at which both the highest density of dislocation and highest energy should be produced and induces poor stability.Below 70 nm,the deformation mechanism of nanograined Cu was transformed into a partial dislocation motion,which activated mechanically induced grain boundary(GB)relaxation accompanied by GB flattening and GB energy decrease and resulted in enhanced stability.This discovery offers the potential for developing nanograined metals with high strength and high stability.
基金supported by the National Natural Science Foundation of China (Nos. 12102280, 12172238, 11832007, 12022208, 12072212, and 52003181)the Science & Technology Support Program of Sichuan Province (Nos. 2020YJ0230, and 2021YJ0555)the Fundamental Research Funds for the Central Universities of China (No.2021SCU12129)
文摘Ultrasonic fatigue tests are performed on a magnesium alloy with and without ultrasonic peening treatment(UPT).Surface enhancement layer leads to the complete change of crack initiation sites.However,crack initiation mechanism keeps the same and results in a single-faceted morphology at crack initiation site.Microcracks initiate as Mode Ⅱ crack within the original grain,but deflect to Mode I crack outside of the original cracked grain.A threshold SIF value is proposed to evaluate the retarding effect of grain boundary on microcrack propagation.Outside of the original cracked grain,Mode I crack propagation below the threshold ΔK_(σ-th) is responsible for the formation of fine granular area(FGA,a nano-grain layer).Based on the Numerous Cyclic Pressing(NCP) model,it is proposed that crack type should be another necessary condition for the formation of FGA.
基金financially supported by the National Natural Science Foundation of China(No.11932020).
文摘Fatigue failure can still occur beyond 107 cycles,i.e.very-high-cycle fatigue(VHCF),in many metallic materials,such as aluminium alloys and high-strength steels.For VHCF of high-strength steels,a fine granular area(FGA)surrounding an inclusion is commonly identified as the characteristic region of crack initiation on the fracture surface.However,no such FGA feature and related crack initiation behaviour were observed in VHCF of conventionally cast or wrought aluminium alloys.Here,we first reported the distinct mechanisms of crack initiation and early growth,namely the microstructure feature and the role of FGA in VHCF performance for an additively manufactured(AM)AlSi10Mg alloy.The AM pores play a key role in fatigue crack initiation similar to that of the inclusions in high-strength steels,resulting in almost identical FGA behaviour for different materials under a range of mean stress with a stress ratio at R<0 or R>0.The profile microstructure of FGA is identified as a nanograin layer with Si rearrangement and grain boundary transition.This process consumes a large amount of cyclic plastic energy making FGA undertake a vast majority of VHCF life.These results will deepen the understanding of VHCF nature and shed light on crack initiation mechanism of other aluminium and AM alloys.
基金the Indian Institute of Technology Roorkee and MHRD for providing financial support
文摘The relationship between the microstructure and mechanical properties of the spark plasma sintered AA2024 Y composites subjected to cryo-rolling was investigated. Yttrium addition enhances the mechanical properties of the composites by promoting grain refinement and precipitation. However, there is a clear trend of initial increase and later decrease in the properties. Also, it is observed that 0.3 wt.% of yttrium is the optimum amount of reinforcement content to obtain the highest mechanical properties. To further improve the tensile strength of the composites, cryo-rolling was performed on the composites under standard cryogenic conditions by several passes up to a reduction of 25%. The mechanical properties and the corresponding microstructures of composites after cryo-rolling were correlated. The SEM and TEM microstructures reveal that the samples exhibit dual size grains, i.e., nanograins are formed as sub-grains within the actual grain. Due to the grain size reduction and the increase in the dislocation density, the tensile properties are remarkably improved compared to those of the composites before cryo-rolling. The highest mechanical properties like hardness, YS and UTS are found to be 153 HV, 539 MPa and 572 MPa, respectively, with a reasonable ductility in the composite with 0.3 wt.% Y.
基金financially supported by the China Postdoctoral Science Foundation(No.2015M570964)the National Key Research and Development Program of China(No.2017YFB0304504)。
文摘Nanoporous Ag-Pt bi-metallic alloy was fabricated by free dealloying of amorphous Ag-based precursor with the nominal composition of Ag38.25Pt0.5Cu38.75Si22.5.The noble Ag and Pt were left after the less noble Cu and Si dissolved in a certain acid solution.Bi-continuous nanoporous microstructure was formed with asymmetric ligaments and pores with typically 30-200 nm in width.The trace addition of Pt has refined the grains of the ligaments to the average size of less than 20 nm in the substrate and induced the formation of rods with nanopores.The morphologies of the rods were observed by scanning electron microscopy(SEM)and transmission electron microscopy(TEM)both in the form of clusters and as scattered individuals with characteristic length of several micrometers and diameter of tens of nanometers.The grains sizes in the rods were finer than those in the ligaments.The good mechanical integrity might be due to the combination of continuous ligaments and clusters of rods.
基金supported by the Strategic Pri-ority Research Program of the Chinese Academy of Sciences(No.XDB0510400)the National Natural Science Foundation of China(No.52225102)the Youth Innovation Promotion Association CAS(No.2023201).
文摘To provide insight into the effect of grain size on the precipitation behavior ofγstrengthening super-alloy Inconel 718,a gradient nanostructure with a large grain size span(from 9 nm to tens of microns)along the depth direction was achieved by mean of surface mechanical grinding treatment,followed by annealing upon 700-1000℃ for 1 h.The results reveal significant differences in the type and size of precipitates in samples with different grain sizes.Noγprecipitate was detected inside the grains as the grain size was refined down to 40 nm(NG-40)and 9 nm(NG-9).Forδphase,a significantly accelerated precipitation along grain boundary was observed in NG-40 upon 700℃ annealing.Interestingly,with the grain size drops to 9 nm,the precipitation ofδwas suppressed,with some nanosized MC carbides appearing upon annealing.The grain size effect of precipitation behavior endows NG-9 an ultra-high RT-hardness(5.2 GPa)after 1000℃ thermal exposure and an ultra-high hot-hardness(3.2 GPa)at 800℃.
文摘Nanocrystalline Magnesium ferrite has been prepared by chemical co-precipitation technique. Structural characterization has been performed by X-ray diffraction. Formation of ferrites has also been studied by using FTIR. Frequency dependence of real and imaginary part of initial permeability has been presented for the samples sintered at different temperatures. Real part of initial permeability, increases with the increase of grain growth. The loss component repre- sented by imaginary part of initial permeability decreases with frequency up to the measured frequency of this study of 13 MHz. Curie temperatures have been determined from the temperature dependence of permeability. Curie temperatures for the samples of this composition do not vary significantly with the variation of sintering temperatures. B-H loop measurements have been carried out by B-H loop tracer. Transport property measurements haven been carried out by electrometer and impedance analyzer.
基金This work was financially supported by the National Natu-ral Science Foundation of China(No.NSFC 51775140)A part of the work was also supported by the National Science and Technology Major Project(No.2017-VI-0009-0080)+2 种基金the Guangdong Province key research and development program(No.2019B010935001)the Shenzhen Science and Technology Plan(No.JCYJ20180507183511908)Bureau of Industry and Information Technology of Shenzhen through the Innovation Chain and Industry Chain(No.201806071354163490).
文摘Ag-Cu bimetallic nanoalloy,integrating the advantages of reducing migration and cost of nano-Ag and alleviating oxidation of nano-Cu,is a prospective bonding material for power electronic packaging.The Ag-coated Cu nanoparticles(Cu@Ag NPs)paste can execute bonding with high quality at 250℃,and the achieved supersaturated Ag-Cu nanoalloy joint with ultrahigh shear strength(152 MPa)dramatically exceeds most nano-paste joints.The interstitial solid solutions with atomic-level metallurgical bonds at the interface dominantly promoted the shear strength.Besides,the numerous ultrafine nanograin,high proportion of low angle grain boundaries(7.44%)without deformation,and the Cu nanoprecipitates in the joint would improve subordinately.Furthermore,the high content(16.8%)of∑3 twin boundaries would contribute to the electrical and thermal conductivity.Thus,the multiple strengthening mechanisms with the solid solution,the second precipitated phase,and ultrafine nanograin can dramatically enhance shear strength and electro-thermal conductivity of joints for high-temperature device packaging.
文摘This paper reports the chemical synthesis of tungsten carbide/cobalt (WC/Co) nanocomposite powders via a unique chemical processing technique, involving the using of all water soluble solution of W-, Co- and C-precursors. In the actual synthesis, large quantities of commercial-scale WC-Co nanocomposite powders are made by an unique combination of converting a molecularly mixed W-, Co-, and C-containing solutions into a complex inorganic polymeric powder precursor, conversion of the inorganic polymeric precursor powder into a W-Co-C-O containing powder intermediates using a belt furnace with temperature at about 500°C - 600°C in an inert atmosphere, followed by carburization in a rotary furnace at temperature less than 1000°C in nitrogen. Liquid phase sintering technique is used to consolidate the WC/Co nanocomposite powder into sintered bulk parts. The sintered parts have excellent hardness in excess of 93 HRA, with WC grains in the order of 200 - 300 nm, while Co phase is uniformly distributed on the grain boundaries of the WC nanoparticles. We also report the presence of cobalt Co precipitates inside tungsten carbide WC nanograins in the composites of the consolidated bulk parts. EDS is used to identify the presence of these precipitates and micro-micro-diffraction technique is employed to determine the nature of these precipitates.
基金the Ministry of Science&Technology of China(Nos.2017YFA0204401 and 2017YFA0700700)the Chinese Academy of Sciences(No.zdyz201701)Science and Technology on Surface Physics and Chemistry Laboratory(No.6142A020303)。
文摘Deformation mechanisms of nanograined and submicron-grained pure cobalt processed by means of high strain rate shear deformation at cryogenic temperatures were studied.Microstructural analysis revealed a transition of governing deformation mechanism from deformation twinning and dislocation slip in submicron-grains to and dislocations slip in nanograins.Microhardness tests illustrated that the Hall-Petch relation slope changes consequently with the transition of deformation mechanism.
基金supported by the National Natural Science Foundation of China (Nos.50401001 and 50671001)the Program for New Century Excellent Talents in University,China (NCET 2006)the Doctorate Foundation of Chinese Education Ministry,China (No.20070005010)
文摘The thermal features of the nanograin boundary were described by a developed thermodynamic model. Using the nanocrystalline Cu as an example, the pressure, the bulk modulus, and the volume thermal expansion coef- ficient were calculated to characterize the thermodynamic properties of the grain boundaries on the nanoscale. Based on the parabola-type relationship between the excess free energy and the excess volume of the nanograin boundary, the thermal stability, as well as its evolution characteristics, was analyzed. The experimental re- sults of the temperature-varying grain growth in the nanocrystalline Cu, which exhibited the discontinuous nanograin growth behavior, verified the thermodynamic predictions. In addition, the quantitative relationships correlating the excess volume and the lattice expansion with the nanograin size were discussed.
