is a kind of porous material. becomes the first choice of electrode,because of its pore structure and low price.In this paper,the main results and significant achievements about the preparation of activated carbon and as electrode of were summarized as follows.1.Influence of specific capacitance of activated carbonThe CFAC had higher specific capacitance than ARMPAC.Carbon foam was prepared in high pressure and high temperature,had better crystal structure,so the product of activation had higher specific capacitance.When AMCMB as activated agent content 80%and acetylene black as electric agent content 10%,the AMCMB had the highest specific capacitance.Electrode dipped in the electrolyte in vacuum,can raising the specific capacitance.2.Preparation of spherical activated carbon from mesophase pitchCarbonized the mixture of mesophase pitch and SiO2 at 300℃～600℃,after milling.The product was carbon beads.AC was prepared from carbon beads and KOH as activator.HFAC was prepared AC was prepared from carbon beads and KOH as activator,after dipped in HF.The effect of carbonization temperature,activation temperature and the carbon/alkali ratio on specific capacitance was investigated. found that carbon beads had good sharp after carbonization;propriety carbonization temperature was good for rising specific capacitance,no effect for the sharp of carbon beads.The specific capacitance of HFAC was lower than AC;when the carbonization temperature at 500℃,carbon/alkali ratio was 1:5,the AC had the highest specific capacitance,when the carbonization temperature at 550℃,carbon/alkali ratio was 1:7,the HFAC had the highest specific capacitance.3.Preparation of activated carbon from mesophase pitch with silicon compoundsMesophase pitch was prepared from MTCP at 450℃for 1h.MPAC was prepared from mesophase pitch and KOH as activator at 900℃.The other activated carbon was prepared in the same condition with different compounds. The specific capacitance of the products was reviewed.It found that the specific capacitance of products were obviously rising.The products prepared from mesophase pitch,C8H20O4Si and H2O,carbon/alkali ratio was 1:5.Its specific surface area was 3132m2/g,pore volume was 1.699cm3/g,average pore width was2.190nm,specific capacitance was 269.3F/g.4.Formation of nanocarbons during activation of MCMB with KOHMCMB/Co was prepared by pyrolyzing the mixture of coal tar pitch and cobalt acetate at 410℃for 0.5h under nitrogen atmosphere.MCMB/Co carbonized at 1000℃for 1h under nitrogen atmosphere.The product was MCMB/Co-1000.AMCMB/Co was prepared from the mixture of MCMB/Co and KOH activated at 900℃.Compare the of the products,it found that two kinds of structure nanocarbons are produced during activation of MCMB/Co with KOH,one was nanotube,the other one was nano carbonfiber.These nanocarbons had not been activated.
Post about "microstructure"
Ni-coated carbon nanotubes（Ni-CCNTs）/AM60 composites and Ni-CCNTs/Mg-1 Zn-0.25Mn-xAl（0,1,3,5,8,10）composites were fabricated by stirring casting method under the protection of Ar.Theproperties of the composites which were under the state of as-cast and high temperature were tested.The was investigated with optical microscopy and tested by x-ray diffraction.The fractography characteristics of the composites were observed by scanning electron microscopy（SEM） and energy spectrum analysis（EDS）.The effect rules of room-temperature properties and elevated temperature properties of composites when enhancing the mass fraction of Ni-coated CNTs addition were investigated emphatically. At the same time, the change of was studied.The results showed that: the addition of Ni-coated CNTs could significantly enha- nce the mechanical properties of Ni-CCNTs/AM60 composites, the rules of which were always enhancing, then reaching the maximum, and dropping at last.Under the state of as-cast, when the addition of Ni-coated CNTs was 1.0wt%, the tensile strength, micro- hardness and the ductility reached the maximum,while the addition of Ni-coated CNTs were 1.2wt%, the elastic modulus reached the peak value respectively.Under the state of high temperature, the tensile strength declined remarkably, and the ductility enhanced. When the addition of Ni-coated CNTs were 1.2wt% and 0.8%, the tensile strength and the ductility all reached the maximum, which is 34.90% and 76.73% more than the value of the matrix respectively. Ni-coated CNTs could not only refine the grains of the composites, but also overlap the grains and bear the load of resistance to deformation. The fracture mode of composites mainly consisted of the dimple and the tear edge, which showed the feature of gliding fracture. When the addition of Ni-coated CNTs and Zn was 1.0%, At ordinary temperature, the tensile strength of the Ni-CCNTs/Mg -1Zn-xAl composites increased with the increase of the content of Al first, then reaching the maximum, and dropping at last, but the microhardness increased all the time. At high temperature the rule of tensile strength to the aluminum addition are similar to that of room-temperature, while the ductility declined all the time.With the increase of Al content, the Initial Phaseα-Mg declined, while the strengthening phase Al12Mg17 incr- eased and distributed more continuously, and also, the grain size decreeases obviously.
Surface Nanocrystallization Induced by High-speed Rotation Wire-brushing Deformation and Its Effect on Plasma Nitriding
Based on the grain refinement mechanism induced by severe plastic deformation, a novel technique of high-speed rotation wire-brushing deformation (HRWD) was used to treat the surface ofand commercially pure titanium(TA2) with the purpose of exploring the feasibilities of realizing by HRWD. The experimental set-up was designed and rebuilt. The refined features were systematically characterized by means of X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations. The microhardness variation along the depth of the treated sample was examined by microhardness tester. Experimental evidences showed that after the HRWD treatment with ordinary coppered steel wire, a nanostructured surface layer of about 10-15μm in thickness was formed on . The mean grain size in the top surface layer was approximately 8nm. was found that a gradient with grain size from nanoscale to microscale was obtained along the depth of its surface layer. The microhardness of nanostructured surface layer was enhanced significantly after HRWD, compared with that of the original sample, and reached 491 HV0.05. The microstructure of the surface layer was refined into the nanoscale on TA2 by HRWD. Its mean grain size in the top surface layer was up to 15nm. In the top surface nanostructured layer, the microhardness reached 489HV0.05, which was about three times that of the coarse-grained matrix. And along the depth from the top surface, the microhardness in the surface layer gradually decreased to that of the matrix.Plasma-nitriding behavior of and commercially pure titanium after the HRWD treatment was investigated in comparison with that in the original materials. Experimental results showed that improved nitrogen transport could be obtained by plasma nitriding after the samples were subjected to HRWD. For low carbon steel nitrided below 500℃, the surface nanocrystallized samples could produce thicker compound layer than untreated samples. With the same nitriding treatment parameters, the surface microhardness of the samples treated by HRWD, increased significantly, which nearly doubled the value of plasma-nitrided coarse-grained ones. However, after 5 hours’ nitridation at 600℃, the surface nanostructured samples began to lose their good effects on the nitridation speed during the plasma nitriding. The compound layer came into existence on HRWD commercially pure titaniun nitrided at 480℃for 8 hours. Furthermore, nitrided below 600℃, the surface nanostructured TA2 could form thicker compound layer than untreated samples and raised the surface microhardness from 703HV0.05 (of nitrided coarse-grained TA2) to 909HV0.05.
The Investigation of Microstructure and Properties of Titanium Alloys with Low Elastic Modulus for Biomedical Applications
s for biomedical applications have been widely used as hard tissue repairing and replacing materials,such as human body skeletons and teeth,due to its excellent combination of properties and corrosion resistance.However,there are many shortages in titanium alloys used in clinical applications,high elastic modulus,and toxicity of alloying elements such as Al and V etc.In the article,to get low elastic modulus titanium alloy biomaterials,selecting Nb and Zr as additional elements for their good biocompatibility, the compositons of Ti-Nb-Zr alloys are designed by means of cluster line criterion method and component matching method respectively.Studies on phase constitutions and under different processing technologies and heat treatment conditions are completed by optical microscope（OM）,scanning electron microscope（SEM）and X-ray diffraction（XRD）;elastic modulus of the alloys are measured by supersonic method and tensile method respectively,and effects of different chemical compositions and heat treatments on elastic modulus are studied mainly,and properties are also investigated.The X-ray diffraction analyses of Ti14-xNb1Zrx（at.）series skull casting and suction-casting alloys designed by cluster line criterion method revealβ+α’ microstucture,the dynamic elastic modulus are from 71 to 76GPa,and increase with increasing content of Zr. The method of suction-casting fails to retain the bcc structure with Nb as centeral atom in liquid alloys from high temperatue to room temperature,not getting the alloys with onlyβphase.Ti-xNb-7Zr（wt.%）series alloys designed by component matching method made up ofβ, acicularα” and tenticularα’ phases after solution treatment lead to low dynamic elastic modulus,which are the 60～70%of the modulus of Ti-6Al-4V alloy（about 110GPa）. Ti-18Nb-7Zr alloy has the lowest modulus,about 67.2GPa.The microstucture of Ti-18Nb-7Zr alloy after aging treatment consists ofβ+αphases,and shows lamellar pattern aged at 350～450℃,growing up with the increase of aging temperature;shows needle pattern aged at 500℃.The elastic modulus and compressive strength increase with increased aging temperature.Ti-27Nb-8Zr（wt.%）alloy subjected to solution treatment at 800℃after hot rolling is comprised ofβand acicularα” phases,and has occurred recrystallization with average grain size about 55μm.The alloy has lower elastic modulus（72GPa）,tensile strength and better plasticity.The yield strength is 348MPa,tensile strength is 505MPa,elongation is 58%and reduction of area is 69%.The metastableα” andβphases have decomposed after aging treatment,the microstmcture of the alloys are comprised of free dispersed precipitatedωandβphase aged at 350～400℃,and comprised of granularω,a few thin-needleαandβphases aged at 450℃.When aging temperature is 500℃,the of the alloy is made up of free dispersed distributed thin-needleαandβphases.While the micostucture of the alloys include the hard and brittleωprecipitation phase,the elastic modulus and tensile strength of the alloys are higher,but the plasticity is lower,a better combined properties could be obtained aged at 500℃.Meanwhile,the alloy possesses preferable fatigue resistance under 500℃aging temperature,its fatigue limitσmax≥400MPa,as high as twice than fatigue limit of commercially pure titanium.
Influence of Metal Underlayers on Low-temperature Deposition of Poly-silicon Thin Films by Hot-wire CVD
High qualitywere deposited on silver- and copper-coated glass substrates by hot-wire chemical vapor deposition （HWCVD） at low temperature. The influence of the on the crystallographic growth orientation, the crystalline fraction and the grain sizes of poly-Si films deposited at the different distance between the filament and the substrate （5-10mm）, the filament temperature range of 1800～1300℃and corresponding the substrate temperature range of 320～200℃were characterized by means of X-ray diffraction （XRD）, Raman spectrum, scanning electron microscopy （SEM） and atomic force microscopy （AFM）. Information about Cu cross-section distribution of the sample was given by Electro Probe Microanalysis（EPMA）. is speculated that the presence of Cu in the amorphous silicon layer which consequently results in the formation of poly-Si indicates a diffusion of Cu atoms through a-Si.Experimental results showed that when the Ag underlayer thickness was 700nm, polycrystalline silicon films with micrometre-size grains and high crystalline fraction were obtained at the filament temperature range of 1800～1700℃（corresponding substrate temperature range of 295～270℃） for the df-s=5mm or at the filament temperature range of 1700～1600℃（corresponding substrate temperature range of 265～240℃） for the df-s=1.5 mm. The crystalline fraction of the poly-Si films increased to a maximum value and then rapidly reduced with decreasing filament temperature.Especially,the crystalline fraction deposited at the filament temperature of 1700℃（corresponding substrate temperature range of 270℃） for the df-s=5mm was 98.7%. The crystallographic growth orientation of poly-Si films deposited on silver-coated glass substrates did not vary with various parameters: intensity peak ratios of three strong diffraction peaks at （111）, （220）, and （311） planes for all samples are similar to those of Si powder, suggesting that there is no preferential orientation of crystallites. When the Ag underlayer thickness was decreased to 30nm, the crystallographic growth orientation had not any changes for the df-s of 7.5mm. The crystalline fraction increased to a maximum value and then rapidly reduced and the grain sizes continuously decreased with decreasing filament temperature at the filament temperature range of 1700～1300℃（corresponding substrate temperature range of 265～180℃）. Polycrystalline silicon films composed of large and uniform columnar grains with a moderate lateral grain size of～1μm, vertical grain size over 15μm have been fabricated on copper-coated glass substrates at the df-s of 5mm. Influence of Cu underlayer on grain growth process appeared to be more visible at the filament temperature range of 1800～1700℃,which is consistent with the results obtained from the films deposited on silver-coated glass substrates under the same conditions. Owing to the presence of Cu underlayer, the crystalline fraction of poly-Si films was increased (the crystalline fraction of poly-Si films deposited on Cu-coated glass substrate was over 90% at the df-s of 5mm or 8mm) and the crystallographic growth orientation was changed in certain experimental conditions. Moreover, the grain size and the crystalline fraction of poly-Si films notablely decreased with the increasing distance between the filament and the substrate. Larger df-s and lower filament temperature have passitive effect on the nucleation and growth of poly-Si films. Cu atoms in the underlayer had diffused through a-Si layer which resulted in the formation of a silicon-copper solid solution.
Lightweight is a critical factor that decides the whole performance of high-speed railway. Although aluminum rolling stock produces effective lightweight, the strength of the welding joint will considerably reduce due to fusion welding. This will seriously influences the safety of high-speed railway. The friction stir welding is characterized with the excellent properties of the welding joint and low welding stress and distortion, and has been applied in the aluminum alloy rolling stock of high-speed railway. Aiming to the fabricating of the aluminum alloy rolling stock, in this paper theand properties of friction stir welded was investigated, and the rule and mechanism of the post welding aging on the welding joint was discussed so as to provide the theory and experiment basement for the application of friction stir welding in the high-speed train.With the different heating temperature and stir on the welding joint of FSWed , the various base and Mg2Si were obtained. The welding nugget happened to dynamically recrystallize and the refined crystal grains were obtained and the majority of Mg2Si particles dissoluted due to the intensive stir and higher high temperature. In the thermal-mechanical affect zone that was heated under the recrystallized temperature, the crystal grains were elongated due to the mechanical stir and Mg2Si particles partly dissoluted and the others grew. In the heat affect heat without the mechanical stir, to some extent, both of the crystal grains and the majority of Mg2Si particles grew. prompted that Mg2Si precipitated again. However, with the different aging temperature and time, and with the different supersaturation in the welding nugget, TMAZ and HAZ, the aging proceed at the different extent and rate and as a result the different aging effectiveness appeared at the various zone of the welding joint. The aging increased the strength and hardness, but decreased the plastics. Because the base microstructure deformed and Mg2Si grew irreversibly, the natural and artificial aged joint strength respectively reached to 75% and 88% of parent metal. The tensile specimens all fractured ductile at the retreated side of the heat effect zone with the lowest microhardness.The various zones of the welding joint showed the difference in the . The ranking of the was welding nugget, parent metal, and heat affect zone. The corrosion mechanism was pin corrosion and the influencing factor was mainly heterogeneous in the microstructure. The artificial aging prompted Mg2Si precipitated and grew, consequently the corrosion resistance of the welding joint decreased. On the other hand, the difference of the various zones in the also reduced as a result of the reduced heterogeneous microstructure.
7050 and 7055 aluminium alloy which have high strength and high toughness are used as principal structural materials in carrier rocket,space vehicle and space base industry et al.So the researches and application of 7050 and 7055 aluminium alloy are atteached more attentions.Because of high element content of 7050 and 7055 aluminium alloy,cracks and element segregation exist in conventional semi-continuous casting,which badly affect the yield andproperties.In recent years,special technics are used such as powder metallurgy,adding minor element Ag,Mg and Zr,and new technics are applied such as high intensity spraying deposit and hot extrusion to produce higher element content,higher strength and higher toughness aluminium alloy which always increase the cost.In this thesis,according to the cracks and element segregation defects,effects of current intensity and electromagnetic frequency on magnetic distribution of electromagnetic coil of one circle,five circles and one hundred circles are tested.Static pouring experiments are done to investigate the effects of electromagnetic parameters on solidification structure and element distribution of 7050 and 7055 aluminium alloy.The result shows that the average grain sizes are refined obviously and element segregation are restrained effectively with electromagnetic field.Electromagnetic frequency has a great effect on the shaping property of the melt.The height of meniscus increases with the electromagnetic frequency enhances.By increasing the circles of electromagnetic coil,the current intensity can be reduced and the intensity of electromagnetic field can be enhanced to increase the electromagnetic stirring force and constraining force.Effects of casting parameters such as casting speed,casting temperature,cooling water intensity,element content and casting liquid level on the quality of semi-continuous casting of are studied. technics are explored to get high quality s.The result shows that,when the current intensity is 2500A,electromagnetic frequency is 1700Hz,casting speed is 85 mm/min, casting temperature is 710℃,cooling water intensity is 3 m~3/h and casting liquid level is in the half height of the graphite mould, whose size is 420mm×130mm×1000mm is cast successfully.The casting defects such as crack,element segregation,cold shut,remelt and surface segregation knots are restrained effectively by electromagnetic field.The average grain size is refined from 71.4μm to 62.9μm with the application of electromagnetic field.The tensile strength is increased by 15.6%and the elongation is improved by 76.8%compared to those without electromagnetic field.The action mechanism of electromagnetic field on semi-continuous casting of 7050 aluminiurn alloy slab is discussed.
Magnesium alloy is the lightest metal among practical metal material. Magnesium alloy has the high relative intensity, the high relative stiffness, the better diamagnetism, the higher electronegativity and thermal conductivity, good property of shock absorption and good machinability. But the strength of Magnesium alloy is rather low, which has been the main reason in hindering the development of Magnesium alloy. So improving the strength of magnesium alloy and having a good comprehensive performance, which becomes one of the focuses of the current study on the materials. In this paper the method ofelements alloying is used for improving the strength of magnesium alloy. With the pure magnesium being the raw material, adding zincification and the different proportional mixed to which, the different component of casting and extruding(the heat ratio is 17.5:1) of the deformation magnesium alloy are prepared out . This paper studies the effects of zinc and rare earth elements on the and the properties of the alloy, and explores the strengthening mechanism.The results showed that, the organization of casting states of Mg-5Zn alloy was refined by adding the RE, but with the contents of the RE increasing the refining effects decreased. After heat extruding deformation at 350oC, the cast structure of all the casting states magnesium alloy has become deformation : the grains get refined significantly and the second phases distributs homogeneously. The higher content of RE,the finer the grains, the more significant the fiber-texture microstructure. But the increasing of the number of the second phases leads to enhance the brittleness of the alloy. The performance test showed that with the increasing of the content of the RE, the strength of the deformed magnesium alloy present curved change. The highest strength at room temperature and high-temperature is obtained when the content of the RE is 4%. The deformed magnesium alloys are aged treatment, but the organization and the performance are not change significantly. is determination that the alloy is not strengthened by heat treatment. is analysis that the adding of the rare earth and the treatment of has a great effect on the comprehensive properties of the Mg-Zn alloy. It can fine the grains and purify the grain boundary, which improve the strength and the plasticity of the alloy.
Gradient Bioceremics Composite Coating Produced by Wide-Band Laser Cladding on Surface of Ti Alloy and Its Cell Biocompatibility
Hydroxyapatite（HA） has excellent biocompatibility and bioactivity, however, theproperties of HA is not satisfied, because its flexural strength and fracture toughness are lower than that of bone. is restricted to be applied on the human body. Although Ti and its alloy has excellent properties, they belong to biological implanting material, there is little bio activity. Due to its favorable biocompatibility and mechanical properties, hydroxyapatite-coated Ti alloy has been accepted as one of the most promising implanting materials for orthopaedic and dental applications.In this paper, as to problem on preparing bioceramic coating, wide-band laser cladding and gradient design thought are adopted, biocompatibility and bioactivity of HA coating is increased by adding different kinds of rare earths（RE） class and contents, the bioceramic coating with HA andβ-TCP is fabricated on the Ti alloy, the of gradient coating with bioactivity was studied with the help of SEM , XRD and microhardness analysis. At last, the biocompatibility of bioceramic coating was estimated from the cytobiology level. The experimental results show that the gradient bioceramic coatings which have excellent chemical metallurgy bonding on the interface consist of metal base, alloy coating and bioceramic coating. The rare earth oxide（CeO2 and Y2O3） can reduce crack susceptibility of coating and refine grainsize during wide-laser cladding. Secondly, CeO2 and Y2O3 plays an important role in inducing to synthesize HA andP-TCP during laser cladding . Thirdly, When Ca/P is 1.5, the ceramic structure is smaller than the 1.4 of Ca/P, and its crystalline state is good. And different CeO2 contents lead to different amounts of synthesizing HA+β-TCP. When Ca/P is 1.4 and the addition of CeO2 reaches to 0.4wt.%, the amount of synthesizing HA andβ-TCP is the most; when Ca/P is 1.5 and the amount of CeO2 is between 0.2wt.% and 0.4wt.%, the the amount of synthesizing HA and P-TCP is also the most.the .fourthly, the coating containing CeO2 and Y2O3 has no toxic effect. The active ceramic phase amounts of calcium（Ca） and phosphorus（P） base on the surface of bioceramic coating effect the appreciation of osteoblastic cell. The bioceramic coating containing CeO2 and Y2O3 has better cell biocompatibility than Ti alloy. When Ca/P is 1.4 and the addition of CeO2 reach to 0.4wt.%, the amount of osteoblastic cells is the most, and the cell amount on coating withCeO2 is more than that of coating with Y2O3.
Owning excellentproperties from ambient to elevated temperature, s are considered as promising materials with their application in cutting-tools, bearing and engine components, et al. Components with complex shape can be made of by taking advantages of its superplasticity, which is an important way in near-net shape forming. ZrO2 （3Y）-CaO-SiO2-TiO2 nanocomposite ceramic was studied under the route of”powders synthesis–composite sintering–performance testing”. The s and properties of ZrO2（3Y）-CaO-SiO2-TiO2 nanocomposite ceramic have been investigated systematically.ZrO2（3Y）-CaO-SiO2-TiO2 powders with excellent chemical homogeneity were synthesized by heating of ethanol-aqueous salt solutions combined co-precipitation method. The influences of sintering temperature on compositions, phase composition, particle size and sintering activity were studied. TEM, SEM, XRD, BET and other instruments were used to test the whole process and identify the powder’s characteristic. Nano-scaled ZrO2（3Y）-CaO-SiO2-TiO2 powders with particle size of 1520nm,specific surface area of 69.15m2·g-1 can be obtained. The powders also showed uniform grain size, less agglomeration and good sintering activity.ZrO2（3Y）-CaO-SiO2-TiO2 ceramic composite was obtained by vacuum hot- pressing sintering. The and the mechanical properties of the ceramics under different sintering temperature were investigated. After hot-pressing sintering at 1300℃, the average grain size of the ceramic material is about 230nm, the relative density is up to 97.8% and the hardness is 1400.58kgf·mm-2.Superplastic compressive tests demonstrate that the material behaves good deformability in temperature range of 1400℃to 1450℃. During the compression tests, the material did not show any strain softening, which was quite different from the results obtained in the tensile tests of this kind of material.