复掺水泥/纤维改性路基粉质黏土力学性质研究

文章通过室内对不同水泥和聚丙烯纤维(PF)掺量条件下的粉质黏土展开单轴抗压力学试验和微观电镜扫描试验,研究复掺水泥/纤维改性路基粉质黏土的工程力学性质。研究发现:(1)粉质黏土的承载能力随水泥掺量的提高而逐渐提高,不掺水泥的粉质黏土的抗压强度为0.72 MPa,掺3%水泥-粉质黏土的抗压强度较原粉质黏土提高76.39%;(2)随着PF掺量的提高,3%水泥-粉质黏土的抗压强度呈现出先提高后减小的变化趋势,当水泥掺量为3%、PF掺量为0.5%时其抗压强度最大,达到1.61 MPa;(3)微观电镜扫描结果显示,0.25%纤维+3%水泥的粉质黏土内部结构完整性较好,土颗粒的分布较为均匀,PF起到了很好的连接作用,因此其抗压强度较大。研究成果可为软土路基的加固与改良工作提供借鉴。

Effects of Yb addition on microstructures and mechanical properties of 2519A aluminum alloy plate

The effects of Yb content on the microstructures and mechanical properties of 2519A aluminum alloy plate were investigated by means of tensile test,optical microscopy,transmission electron microscopy,scanning electron microscopy and X-ray diffractometer.The results show that addition of 0.17% (mass fraction) Yb increases the density of θ' particles of the 2519A alloy plate and reduces the coarsening speed rate of θ' phase at 300 ℃.Therefore,tensile strength is enhanced from 483.2 MPa to 501.0 MPa at room temperature and is improved from 139.5 MPa to 169.4 MPa at 300 ℃.The results also show that with the addition of 0.30% (mass fraction) Yb,the mechanical properties increase at 300 ℃ and decrease at room temperature.With Yb additions,the Al7.4Cu9.6Yb2 phase is found whilst the segregated phases of as-cast alloys along grain boundaries become discontinuous,thin and spheroidized.

Microstructure and phase forming process of Al-3Ti-0.2C-1RE grain refiner

An Al-3Ti-0.2C-1RE grain refiner was prepared by in-situ reaction method.The microstructure was investigated by optical microscopy(OM),scanning electron microscopy(SEM) equipped with energy-dispersive spectrometry(EDS) and X-ray diffraction(XRD).The results show that the Al-3Ti-0.2C-1RE grain refiner is composed of α-Al,TiAl3,TiC and Ti2 Al20 Ce phases.Compared with Al-3Ti-0.2C refiner,the morphology of TiAl3 phase is changed and Ti2 Al20 Ce phases form with the addition of RE.Accordingly,the refining performance is improved.The phase forming process of the refiner is as follows: Blocky Ti2 Al20 Ce and fine blocky TiAl3 form in the melt at the initial stage of reaction,then the fine blocky TiAl3 gradually disappears,and the blocky Ti2 Al20 Ce grows bigger with the increase of holding time.The predominant mechanism to synthesize TiC particles is the reaction between high concentration of solute Ti atoms and graphite particles.

Effect of ball milling time on microstructures and mechanical properties of mechanically-alloyed iron-based materials

The microstructures and mechanical properties of an iron-based alloy (Fe-13Cr-3W-0.4Ti-0.25Y-0.30O) prepared by mechanical alloying were investigated with scanning electron microscope,optical microscope,X-ray diffractometer and hardness tester.The results show that the particle size does not decrease with milling time because serious welding occurs at 144 h.The density of the alloy sintered at 1 523 K is affected by the particle size of the powder.Finer particles lead to a high sintered density,while the bulk density by using particles milled for 144 h is as low as 70%.In the microstructures of the annealed alloy,large elongated particles and fine equiaxed grains can be detected.The elongated particle zone has a higher microhardness than the equiaxed grain area in the annealed alloys due to the larger residual strain and higher density of the precipitated phase.

Effects of whisker surface treatment on microstructure and properties of Al_(18)B_4O_(33w)/6061Al composites

6061Al matrix composites reinforced by ZnO-coated Al18B4O33 whiskers were fabricated by a semi-solid mechanical stirring technique.The effects of ZnO coating on interfacial reaction between whiskers and matrix and the tensile properties of the composites were investigated.Tensile tests on composites were performed at room temperature,and microstructures were observed by scanning electron microscopy(SEM).The results show that the surface treatment of whiskers could reduce interfacial reaction effectively,improve the wettability between whiskers and matrix and enhance the tensile properties of the composites obviously.In addition,semi-solid stirring parameters were also under preliminary study.The stirring parameters were determined by the distribution of whiskers in the composites.The composites with homogeneously distributed whiskers were fabricated by semi-solid stirring at 610 ℃ for 30 min.

Microstructural insight into permeability and water retention property of compacted binary silty clay

The durability of silty clay embankments is partially controlled by the moisture migration, which depends on soil hydraulic properties. This paper presents an experimental study of hydraulic properties of compacted binary silty clay. Specimens with different mixing ratios and dry densities were prepared. Scanning electron microscopy and mercury intrusion porosimetry were used to characterise the microstructure of silty clay. Thereafter, falling-head permeability tests and water retention tests were conducted to study the permeability and water retention property, respectively. The results demonstrate that clay particles are dispersed and show preferred arrangements after compaction when the clay content is 100%. As the clay content decreases, the arrangement of clay particles is gradually disturbed because of the existence of silt particles, causing the formation of large pores around silt particles. When the dry density increases, the pores around silt particles significantly decrease. Moreover, the permeability of silty clay decreases but the water retention capacity increases with increasing clay content and dry density. This is because the silty clay with larger clay content and dry density has fewer large pores, which greatly restrains the flow of water. Both the permeability and water retention property of silty clay can be predicted from pore size distribution parameters.

Characteristics of coal re-oxidation based on microstructural and spectral observation

In order to investigate the characteristics of re-oxidation of residual coal in goafs in close coal seam mining,scanning electron microscope and infrared spectrometer are used to study the changes of coal microstructure and chemical reaction of functional groups of eight coal samples at different ranks.Result shows that after initial oxidation,the surface morphology of pore are different,and the porosity of coal is increased and the oxygen adsorption capacity of coal is improved.The change of coal molecular structure and presence of a large amount of active oxygen-containing functional groups lead to increasing tendency of coal to further oxidation.In addition,the higher lever of the initial oxidation is,the easier the re-oxidation occurs.

Effect of rare earth additions on microstructure and mechanical properties of AZ91 magnesium alloys

In order to meet the demands of high temperature components in automobile, the microstructure and mechanical properties of several new die-casting AZ91-rare earth (RE) magnesium alloys were studied. The alloys were characterized by optical microscopy (OM), scan electron microscopy (SEM), energy dispersive X-ray spectrometry (EDX), tensile and creep tests. The results show that Ce addition has little effect on the mechanical properties of AZ91 alloy at high temperature, while Y and Nd addition play important role in the improvement of creep resistance. New alloys containing Y or Nd with excellent high temperature performance are selected to produce cylinder head cover of high power diesel engine of Red Flag car and oil pan of Besturn car. The new magnesium alloys with RE addition for die-casting have potential to produce power-train parts, and can greatly decrease weight.

Effect of low temperature thermo-mechanical treatment on microstructures and mechanical properties of TC4 alloy

The effects of low temperature thermo-mechanical treatment （LTTMT） on microstructures and mechanical properties of Ti-6Al-4V （TC4） alloy were studied by optical microscopy （OM）, tensile test, scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. The experimental results confirm that the strength of TC4 alloy can be improved obviously by LTTMT processing, which combines strain strengthening with aging strengthening. The effect of LTTMT on the alloy depends on the microstructure of the refined and dispersed a＋fl phase on the basis of high dislocation density by pre-deformation below recrystallization temperature. The tensile strength decreases with the increase of pre-deformation reduction. The optimal processing parameters of LTTMT for TC4 alloy are as follows： solution treatment at 900 ℃ for 15 min, pre-deformation in the range of 600-700 ℃ with a reduction of 35%, finally aging at 540 ℃ for 4 h followed by air-cooling.

Effects of pre-precipitation of Cr_2N on microstructures and properties of high nitrogen stainless steel

Aging precipitation and solid solution heat treatment were carried out on three steels which have chromium content of 18%, manganese content of 12%, 15%, 18%, and nitrogen content of 0.43%, 0.53%, 0.67%, respectively. The mechanisms of precipitation and solid solution of high nitrogen anstenitic stainless steel were studied using the scanning electron microscopy, transmission electron microscopy, electron probe micro analysis and mechanical testing. The results show that, Cr2N is the primary precipitate in the tested stainless steels instead of Cr23C6. Cr2N nucleates at austenitic grain boundaries and grows towards inner grains with a lameUar morphology. By means of pre-precipitation of Cr2N at 800 ~C, the microstructure of the steels at solid solution state can be refined, thus improving the strength and plasticity. After the proposed treatment, the tensile strength, the proof strength and the elongation of the tested steel reach 881 MPa, 542 MPa and 54%, respectively.

Micro-and macro-fractures of coarse granite under true-triaxial unloading conditions

We studied the mechanical behavior of rock under different boundary conditions, based on the fractal characteristics of fractures in terms of microscopic and macroscopic investigations. Three rectangular granite specimens of similar dimensions were tested by a triaxial rock testing machine under uniaxial compression （UC）, confined compression （CC） and true-triaxial unloading conditions （RB） under rock burst boundary conditions. The failure processes of these specimens were investigated via examinations of their fracture behavior on a macro-scale by laser profilometers and on a micro-scale by a scanning electron microscopic （SEM） imaging technique. The SEM images, showing the spailing features of RB frag- ments, are compared with the grain dislocations under UC and CC conditions. Based on a variogram method, two fractal parameters, i.e., fractal dimensions （Dr^d） and the scale dependent fractal parameter Kv, were induced to present the surface roughness of scanning profiles in all directions. The fitted ellipses of Dr^d distribution show that RB surface has the smallest eccentricity, followed by the CC surface, while the UC surface had the largest eccentricity. As a result of this assessment, we conclude that rocks are affected by shear traction in an intermediate stress direction, which will cause fractures generated during rock bursts to twist rather than to tilt as shown in the uniaxial compression and the confined compres- sion tests.

Effects of sintering temperature on microstructure and performance of Ti-based Ti-Mn alloy anodic material

A novel Ti-based Ti-Mn composite anode used for electrolytic manganese dioxide(EMD) fabrication was developed by a two-step heating manganizing technique.The effects of sintering temperature on the manganized microstructure and the performance of the composite anode were studied by scanning electron microscopy(SEM),mechanical properties tests at room temperature and electrochemical methods.The results show that the thickness of the diffusion layer increases with the increase of sintering temperature up to 1 100 °C;whereas,the surface Mn content increases and reaches the maximum at 1 000 °C and then decreases thereafter.Lower surface Mn content is beneficial for the enhanced corrosion resistance and lowered open cell voltage in electrolytic process.The new anode prepared under the optimized conditions has been applied in industry and exhibits superior economic benefits to conventional Ti anodic materials.

Fabrication of Titanate Barium Films by Electrophoretic Deposition Technique

EPD （electrophoretic deposition） technique has been shown as an effective method to produce thin ore thick layers at voltage 5-100 V onto Ni conductive substrate. The aim of this study is to use the EPD method to fabricate films from suspensions BaTiO3. The effects of the EPD process parameters such as the suspension concentration, deposition time, electrical field strength on the specific EPD deposited weight, morphology particles were used. The surface microstructures of the as-deposited films were investigated by SEM （scanning electron microscopy）. A homogeneous microstructure was obtained at applied electric field of 100 V and I min of deposition time at an electrode distance of 1.0 cm.

Realization of a novel Ag/SnO_2 electrical contact material with microscopic fiber-like structure

According to the principle that fiber-like arrangement of reinforcing particles SnO2 paralleling to the direction of current is propitious to the electrical and mechanical performance of the electrical contact materials, we proposed and reported a novel precursor route used to prepare Ag/SnO,. electrical contact material with fiber- like arrangement of reinforcing nanoparticles. The mechanism for the formation of fiber-like arrangement of rein- forcing nanoparticles in Ag/SnO2 electrical contact material was also discussed. The as-prepared samples were char- acterized by means of scanning electron microscope （SEM）, optical microscope （OM）, energy-dispersive X-ray spectroscopy （EDX）, MHV2000 microhardness test, and double bridge tester. The analysis showed that the as-prepared Ag/SnO,, electrical contact material with fiber-like arrangement of reinforcing nanoparticles exhibits a high elongation of 24 %, a particularly low electrical resistivity of 2.08 μΩ. cm, and low arcing energy, and thus has considerable technical, economical and environmental benefits.

Effects of KMnO_4 on microstructure and corrosion resistance of microarc oxidation coatings on 2024 aluminum alloy

Microarc oxidation （MAO） coatings were prepared on 2024 aluminum alloy in a Na2SiO3-KOH electrolyte with KNinO4 addition varying from 0 to 4 g/L. The microstructure and phases of the coatings were characterized by scanning electron microscopy （SEM） and X-ray diffractometry （XRD）, respectively. The corrosion resistance of MAO coatings was evaluated by electrochemical potentiodynamic polarization in 5% （mass fraction） NaCl solution. The results show that when KMnO4 is added into base electrolyte, the growth speed of oxide coatings is increased obviously. The main phase of oxide coatings is Al2O3, and the contents of MnO2 and MnEA104 phases are increased at the top of oxide coatings with increasing the concentration of KMnO4. The solute elements participate in forming the oxide coatings. When a proper concentration of KMnO4 （2.5 g/L） is added into the base solution, the micropores of the MAO coatings are small and compact, and the corrosion resistance of oxide coatings is increased largely.

Promising Graphene Modified Electrode Using Layer-by-Layer Method for Microbial Biofilm Connection

In order to enhance the power output of microbial fuel cell as well as its stability, the development of a new type of anode is essential. The purpose of this work is to modify a stainless steel foam, using the layer-by-layer self-assembly technique, with rGO （reduced grapbene oxide） and PEI （polyethyleneimine）. The efficiency of this kind of modification has been investigated to determine the supply of graphene in term of electricity generation and stability. Under an applied voltage, which is used to form an electroactive biofilm, the modified stainless steel foam （SSF/（PE1/rGO）5） exhibited a current 50 times higher than the blank anode. The roughness of the SSF/（PEI/rGO）5 observed by SEM （scanning electron microscopy） is more favorable to attach more bacteria on it. Also, graphene improved the stability of the electrode as no response where observed for the blank anode after 18 days meanwhile the SSF/（PEI/rGO）5 was still running after 54 days.

Correlation between microstructural features and tensile strength for friction welded joints of AA-7005 aluminum alloy

Similar friction welded joints of AA-7005 aluminum rods were fabricated using different combinations of process parameters such as friction pressure(1.0, 1.5 and 2.0 MPa) and friction time(10, 15 and 20 s). Interfacial microstructure and formation of intermetallic compounds at the joint interface were evaluated via scanning electron microscopy(SEM) equipped with energy dispersive spectrum(EDS), and optical microscopy(OM). Microstructural observations reveal the formation of intermetallic phases during the welding process which cannot be extruded from the interface. Theses phases influence the tensile strength of the resultant joints. From the tensile characteristics viewpoint, the greatest tensile strength value of 365 MPa is obtained at 1.5 MPa and 15 s. Finally, the role of microstructural features on tensile strength of resultant joints is discussed.

Ultrastructural observation on sterilization of melittin

The effects of melittin on growth and bacteriostasis of four pathogens were extensively investigated using scanning electron microscopy(SEM) and transmission electron microscopy(TEM).The results indicated that the melittin had a marked bacteriostatic effect on the four pathogenic bacteria.Among these,E.cacotowora was influenced most powerfully and quickly,the yeast and F.fulva were the second,and the S.aureus was inhibited by a low concentration but was killed by a high concentration.It was observed in the experiments that melittin killed pathogenic bacteria in three ways.One was by pore formation.After integrating melittin into the plasma membrane,a vacuole was formed then penetrated,resulting in bacterial content leakage.The vacuole also experienced plasmolysis and the growing cavity destroyed the membrane.A third effect was the formation of vacuoles in the cells which induced the pycnosis of the cytoplasm resulting in a cell death.The mechanism of melittin bacteriostasis was the result of integrating melittin with phospholipod double layers of the plasmalemma and the endomembranes.

Electron backscatter diffraction investigation of duplex-phase microstructure in a forged Zr-2.5Nb alloy

Microstructural features of a duplex-phase Zr-2.5Nb alloy were investigated in detail using electron channeling contrast （ECC） imaging and electron backscatter diffraction （EBSD） technique in an emission gun scanning electron microscope （FEGSEM）. The excellent resolution provided by the FEGSEM promises the combined utilization of both techniques to be quite adequate for characterizing the duplex-phase microstructures. Results show that the microstructure of the Zr-2.5Nb alloy is composed of bulk a grains （majority） in equiaxed or plate shape and thin 13 films （minority） surrounding the bulk grains, with their average grain size and thickness measured to be 1.4 prn and 72 nm, respectively. Analyses on a-grain boundaries reveal a number of low angle boundaries, most of which belong to deformation-induced dislocation boundaries. Measurements on relative propor- tions of various Burgers boundaries suggest very weak （if any） variant selection during 13 ~ a cooling, which should be re- lated to deformation-induced higher nucleation rate of a phases. Compared to earlier attempts, more satisfactory indexing of fine β phases （down to nanoscale） is attained by the FEGSEM-based EBSD. Examples are presented to clearly reveal well-obeyed Burgers orientation relationships between adjacent α and β phases. Finally, it is deduced that continuing applica- tion of the FEGSEM-based EBSD to duplex-phase Zr alloys could help clarify controversies like the deformation priority of the two phases.