Abstract:In order to clarify the effect of TiB2 particle size on the arc erosion behavior of Ag-TiB2 composite, Ag-4wt%TiB2 composite reinforced by different grain-sized TiB2 particles was prepared by mechanical milling and powder metallurgy. The microstructures of Ag-4wt%TiB2 composites were analyzed, and the global distribution of TiB2 particles was quantitatively evaluated by the enumeration method. The vacuum arc erosion of Ag-4wt%TiB2 composite was tested in a modified TDR240A single crystal furnace. The surface morphology of the Ag-4wt%TiB2 composite after arc erosion was characterized. The mass losses before and after arc erosion were measured. The arc duration was determined by the discharged waveform recorded by a Tektronix TDS-2014 dual channel digital memory oscilloscope, and the arc erosion mechanism was discussed as well. The results show that with the decrease of TiB2 particle size, the TiB2 particles are more uniformly dispersed in the Ag matrix, and Ag-4wt%TiB2 composite presents less mass loss, shorter arc duration, larger arc erosion area and shallower erosion pits. It suggests that fine TiB2 particle can effectively improve the arc erosion resistance of the Ag-4wt%TiB2 composite.

Abstract:The Ti-based components were synthesized via electron beam selective melting (EBSM) using blended pre-alloyed powders of Ti6Al4V and Ti45Al7Nb with a mass ratio of about 1:1. The microstructures and the chemical compositions of EBSM component samples were investigated by optical microscopy (OM), scanning electronic microscopy (SEM), electron probe micro-analyzer (EPMA) and X-ray diffraction (XRD). The results indicate that an increase of energy density leads to a decrease of fusion defects and an increase of density of the samples. The macro-structure consists of two regions, the martensite phase region and α2+β phase region. The martensite phase is formed due to the rapid solidification, while the reheating cycles have a remarkable effect on the formation of α2+β phase. The micro-hardness of martensite region is significantly higher than that of α2+β phase region. Due to the discontinuous distribution of thick platelet α2 phase along grain boundaries and the high coordinating deformation capability of equiaxial α2 phase, the samples have a tensile strength up to 1214.3 MPa, and a large elongation of 18%.

Abstract:Two aluminide coatings were produced on Ni substrate via a conventional pack-cementation at 600 oC for 10 h using Y2O3 or CeO2 particles instead of part of Al2O3 as filler. For comparison, aluminizing was also performed under the same condition using pure Al2O3 as filler. The results of isothermal-oxidation at 1000 oC indicate that Y2O3 can suppress the growth of q-alumina and improve the oxidation resistance, while CeO2 accelerates the q to a-alumina transformation and significantly improves the oxidation resistance. Besides, the effects of Y2O3 or CeO2 filler on the coating oxidation behavior were discussed.

Abstract:The silver-coated Al-Mg alloy powders were prepared by electroless plating using glucose and sodium potassium tartrate tetrahydrate as reducing agents. The main salt Tollens’ reagent were added into the reducing agent at different rates to get the composite powders with different microscopic morphologies. The results show that the alloy powders are coated best at the adding rates of 2~3 mL/min of the main salt Tollens’ reagent and have a satisfied electrical resistivity of 5.13×10-6 Ω·m. The analysis of microstructure and deposition process indicates that the reduced silver particles are first nucleation-deposited along alloy powder grain boundaries, and then act as catalytic nucleation centers to promote the silver reduction deposition. The coating grows up continuously, and finally a complete and homogeneous silver coating is formed on the surface of Al-Mg alloy powder.

Abstract:A high damping Mg-Zn-Y alloy containing LPSO phase and I phase was investigated. The microstructure of a high damping Mg80Y4Zn16 (at%) alloy was examined by optical microscopy (OM) and SEM. Furthermore, the differential thermal analysis (DTA) was used to analyze its phase transformation. Microstructure evolution and damping properties under the conditions of the different solid solution time (3, 6, 9 h) were studied. The results show that the main phase component of the Mg80Y4Zn16 alloy is α-Mg, Mg12ZnY (X phase), Mg3Zn6Y (I phase) and Mg10ZnY2 phase (LPSO phase), in which I phase and LPSO phase coexistence is firstly reported. The average damping value of the alloy is 0.03, indicating that it is a high damping alloy. The damping is strain amplitude dependent. The high damping mechanism was also discussed.

Abstract:Thermal properties of CdSiP2 polycrystalline were studied by differential thermal analysis (DTA) technique with a quartz capillary column. It is found that the melting point and crystallization temperature of CdSiP2 are 1139 and 1126 °C, respectively, and the supercooling degree of CdSiP2 melt is evaluated to be 13 °C. According to the results of DTA, the structure of a furnace and the temperature profile of the crystal growth for CdSiP2 were optimized. A crack-free CdSiP2 crystal with 15 mm in diameter and 40 mm in length was grown by the modified vertical Bridgman (VB) method. The X-ray diffractionmeter (XRD), X-ray energy dispersive microanalysis (EDX) and infrared spectrophotometer?(IR) were employed to characterize the properties of as-grown crystal. A new cleavage face of (112) was identified in XRD spectrum. The results of EDX indicate that the crystal is of good stoichiometry. The infrared transmission is up to 55% in the infrared region from 7000 to 1500 cm-1. All the characterization results show that the obtained crystal is integrated in structure and good in optical quality which can be used in devices fabrication.

Abstract:The metal foams are a novel kind of structural and functional composite materials, which have attracted a wide attention due to their particular structure and characteristics. In order to promote the research and the application of metal foams, six kinds of simulation models about the metal foams were summed up, including cubic cell model, Gibson-Ashby model, octahedron model, tetrakaidecahedron model, Voronoi model and 3D random spheres model. The structure?characteristics of each model were described, and the merits and faults of each model?were also analyzed synthetically.

Abstract:Semiconductor nanowires are attracting intense interest as a promising substrate material for surface enhanced Raman spectroscopy (SERS). Based on vapor-liquid-solid (VLS) procedure using Au as a catalyst, silicon nanowires (SiNWs) with controllable diameters were developed by the plasma enhanced chemical vapor deposition (PECVD) system. Inspired by the fact that the morphology of SiNWs can be effectively modulated by tuning the size of catalyst droplets, we designed a needle-like SiNWs owing to the shrink and consumption of Si-Au catalyst droplets. Transmission electron microscopy(TEM) and X-ray diffraction (XRD) analyses reveal that crystalline Si phase is possessed of amorphous SiO2 in the as-prepared coaxial nanowires. The morphology of the prepared SiNWs was examined by scanning electron microscope (SEM). As SERS active substrates, Ag nanoparticles were synthesized on surface of SiNWs by galvanic displacement. Results show that enhancement factor (EF) of SERS achieved on the prepared needle-like SiNWs/Ag is more than 10 times than that of cylindrical-shaped SiNWs/Ag for R6G molecules detection. It is supposed that needle-like SiNWs composited with Ag nanoparticles can be exploited as a new type nanosensor, environmental?monitoring or biomedical diagnostics. In addition, many other needle-like semiconductor nanowires such as germanium needle-like nanowires also can be prepared by similar method in the present study.

Abstract:We theoretically investigate the optoelectronic properties of graphene driven by an external DC electric field caused via in-plane source-drain voltage. It is found that the Drude part dominates the optical conductivity in the low-frequency region, whereas the plasmon effect can give rise to a relatively weak but observable the optical conductivity in the high-frequency region. Both the Drude and plasmon-induced parts of optical conductivity can be observed in the terahertz (THz) bandwidth. Drude part decreases monotonously with increasing of the photon frequency, the plasmon-induced part exhibits a peak at about ω~1 THz due to resonant plasmon-photon interaction in graphene. Moreover, we examined the dependence of plasmon-induced optical conductivity on the driving electric field and electron density and find that it depends sensitively on these parameters. It is indicated that the optical conductivity resulted from Drude and plasmon-induced parts in graphene can be tuned efficiently not only by electric gating but also by source-drain voltage.

Abstract:The changes of the crystal orientation and lattice defects have a considerable impact on the electrochemical performances of lithium ion electrodes. Here, a new method of controlling the crystal growth of the LiFePO4 films by helium permeation was developed. The helium-permeated LiFePO4 thin film cathodes were prepared by radio frequency (RF) magnetron sputtering deposition. The morphologies of the helium-permeated LiFePO4 samples characterized by scanning electron microscope (SEM) presented pore structure. The X-ray diffraction (XRD) results of the LiFePO4 thin film cathodes indicate that the permeation of helium results in a noticeable increase of peak intensity at the 29.81o, which is normal to the pathway for lithium ion conduction (the [010] direction). It is concluded that there exists a preferential crystal growth orientation of (010) face which is in favor for the reversible insertion/de-insertion of Li ions, and therefore leading to the improvement in electrochemical performance of LiFePO4 samples.

Abstract:Chrysanthemum-like ZnO nanowire clusters were prepared by hydrothermal process, then were transferred to Ti substrate by electrophoresis method, and uniform ZnO nano-film with certain thickness was formed. Finally ZnO field emission cathode sample was fabricated after vacuum heat treatment. The microstructure and the morphology of chrysanthemum-like ZnO nanowire clusters were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM), respectively. Field emission tests were conducted for cathode samples after heat treatment, results reveal that the low turn-on field is 2.0 V/mm for the chrysanthemum-like ZnO, and the threshold field is 5.5 V/mm. Moreover, the field emission current density is 200 mA/cm2 under the condition of electric field of 7.5 V/mm, and the field emission current density and its stability can be effectively improved by appropriate enlarging the thickness of the ZnO coating. The field emission mechanism was also explored.

Abstract:Porous Ti-Al intermetallics materials were prepared form titanium and aluminum powders by pressureless sintering route, and the macro-morphology, phase composition, porosity, microstructure and formation mechanism of porous Ti-Al intermetallics were investigated. The results show that the volume expansion of the Ti-Al compacts is observed in all samples. The porosities of Ti-Al intermetallics are within the range of 49.88%~57.53%, and the open porosities are within the range of 47.60%~56.15%. The porous materials are made of interconnected skeleton, big pores among skeleton and small pores in the interior of skeleton. The interstitial pores in green powder compacts are the most important source of big pores of porous Ti-Al intermetallics, and the in-situ pores from the melting and flowing of aluminum powders is also significant to the formation of big pores. Small pores are from the precipitation of Ti-Al intermetallics particles in pressureless reactive sintering, and TiAl3 is the main phase of porous materials, and porous Ti-Al intermetallics are formed by thermal explosion mechanism.

Abstract:The dynamic mechanical properties and ballistic impact property of α+β region and β region forged TC21 titanium alloy were studied using Split Hopkinson Pressure Bar and ballistic impact experiment. The results show that in the dynamic compression tests, the α+β region forged TC21 alloy has higher dynamic strength but lower dynamic failure strain than the β region forged TC21 alloy; in the ballistic impact experiment, both the α+β region and β region forged TC21 alloy do not demonstrate improved ballistic impact property as compared to the mill-annealed TC4 alloy, which is considered to be attributed to the similar failure mechanism analyzed. In the bimodal microstructure, spall fragments induced by ductile hole formation is the failure mode; while in the lamellar microstructures, the TC21 targets fail by the type of brittle fragmentation. Further post ballistic metallurgical observations find that failure mechanism involved in TC21 alloy is facilitated by the initiation and propagation of adiabatic shear bands and cracks induced by adiabatic shear bands.

Abstract:Dynamic compression experiments have been conducted for TC6 titanium alloy, ATI425 titanium alloy and TC3 titanium alloy by a split Hopkinson Bar process. These titanium alloys were prepared by different heat treatment processes, and the size of cylindrical standard samples was Φ5 mm×5 mm. On the basis of the dynamic compression experiments, the dynamic strength, plasticity and impact absorbed energy under the strain rate of 3000 s-1 were obtained. Meanwhile, the ballistic performance test was carried out. The armor targets were made up of a titanium panel and a A3 steel backplane. Therefore, the relationship between dynamic mechanical properties and ballistic performance of titanium alloys can be revealed. The results show that the ballistic performance of titanium panel is closely related to its dynamic strength and plasticity. Noticeably, the influence of dynamic strength on ballistic performance is more significant than that of dynamic plasticity; the ballistic performance is mainly determined by dynamic strength. Meanwhile, the impact absorbed energy cannot directly reflect ballistic performance of titanium alloy, and a large front crater and smaller plugging destroy can significantly improve the ballistic performance of titanium panel.

Abstract:The influence of Mo doping on the mechanical properties of TiAl alloy has been studied by the first-principles method based on density functional theory. According to the calculated lattice parameters, elastic constants, bulk modulus and shear modulus of the systems with different doping concentrations, we find that Mo doping can improve the ductility of TiAl alloy. The strong s-s, p-p and d-d electron interactions happen among all the s-, p- and d-electrons of Ti atom and near Mo atom, which astrict effectively the migration of Ti and Al atom and is beneficial to enhance the stability and strength of the alloy.

Abstract:Elevated-temperature flow behavior of TC4-DT titanium alloy was investigated by conducting isothermal hot compression tests at strain rate from 0.01 to 10 s-1 and in the temperature range of 1181~1341 K on Gleeble-3500 simulator. The Arrhenius constitutive equation considering the strain was established based on the experiment data with the material constants expressed by a polynomial fitting of strain. The results show that all the true stress-strain curves exhibit the characteristics of strain hardening followed by flow softening and it is particularly significant at higher strain rates and lower temperatures. The flow stress values predicted by the developed constitutive model demonstrate a well agreement with the experimental results at the strain rates under 1 s-1. The correlation coefficient (R) and average absolute relative error (AARE) are 0.9952 and 5.78%, respectively, which con?rm that the modi?ed constitutive equation could give an accurate and precise estimate of the ?ow stress of TC4-DT titanium alloy.

Abstract:By the first-principles plane-wave pseudopotential method based on the density functional theory, the effects of pressure on the electronic structure and mechanical properties of γ'-Ni3Pt were studied. The first-principles calculations have been carried out on γ'-Ni3Pt as a function of pressure from 0 to 50 GPa with a step 5 GPa. The results indicate that the equilibrium lattice parameters under zero pressure are consistent with other experimental and theoretical data. The calculated total density of states and partial density of states under different pressures show that the compound exhibits metallic properties, and the stability of system increases first and then decreases with the increase of pressure. In addition, the bulk modulus (B), shear modulus (G), Young's modulus (E) and Poisson's ratio (υ) of Ni3Pt were calculated by the Voigt-Reuss-Hill method (VRH). It's found that the hardness and ductility of crystal are improved as the pressure increases. In short, it's calculated that the pressure has a marked impact on the electronic structure and mechanical properties of Ni3Pt.

Abstract:The composite alloy ingot with Cu60Ni40 alloy as the outer layer and Ni9W alloy as the inner layer was obtained using the Spark Plasma Sintering (SPS) method. Then the Cu60Ni40-Ni9W-Cu60Ni40 composite substrate with non-magnetic, high strength and strong cube texture were prepared by RABiTS technology. The rolling texture and the micro-orientation of composite substrates processed by heavy cold rolling and recrystallization annealing was analyzed by EBSD technique. The results show that a typical copper-type rolling texture is obtained in the surface of the Cu60Ni40-Ni9W-Cu60Ni40 composite substrate after heavy cold rolling; meanwhile the texture gradient is rendered in the section direction in the sample. The cube texture (<10°) in the surface of the composite substrate reaches 97.6%. In the recrystallization process, the cube grains have the tendency to nucleate and grow up in the outer layer rather than in the inner layer, and the cube grains in the outer layer gradually merge the non-cubic grains in the inner layer. Moreover, through the analyses of mechanical properties, the yield strength σ0.2 of the tapes approaches to 170 MPa, which is similar to the level of the commercial Ni5W tapes.

Abstract:The microstructure and orientation of directionally solidified Al-40%Cu hypereutectic alloy were investigated, and the different microstructures were formed because of the growth competition between eutectic phase and the primary Al2Cu phase. By X-ray diffraction techniques, the pole figures of Al2Cu phase were tested within the macro-orientations and the orientation distribution function (ODF) was calculated. Meanwhile the micro-orientations of directional solidification samples were determined by EBSD. At the directional solidification rate 2 μm/s, the microstructure is all eutectic (Al/Al2Cu) phase, in which Al2Cu phase has the orientation of (001) direction; however, at 10 μm/s the primary Al2Cu phase dendrite with faceted characteristic grows ahead of eutectic phase, which has mainly (001) orientation. When the solidification rate reaches 100 μm/s, Al2Cu phase with non-faceted characteristic grow into complex morphology, and its orientation focuses on the (100), (110) and (001) directions. Al2Cu phase grows along with the direction of?heat flux. The results of XRD analysis show that dendritic morphology and orientation can be well controlled under directional solidification with relatively lower rate.

Abstract:The structural stability, electronic structures and elastic properties of Mg17Al12, Mg2Sn and Al2Y phases in Mg-Al-Sn-Y alloy have been investigated by CASTEP program based on the density functional theory. The calculated results of heats of formation and cohesive energies show that Al2Y phase has the strongest alloying ability and structural stability. The structural stability mechanism and the brittle behavior were obtained from the electronic structure of these three intermetallic compounds. The three independent crystal elastic constants of Mg17Al12, Mg2Sn and Al2Y phases were calculated; bulk modulus, shear modulus, Young’s modulus, and Poisson’s ratio were predicted. Further analysis shows that Mg17Al12, Mg2Sn and Al2Y phases are all brittle phases, and Al2Y are the brittlest and stiffest.

Abstract:The compressive creep behavior of as-cast AgInCd alloy was investigated by special modified apparatus on RDL-50 creep tester at 300~400 °C and compressive stress was in the range of 12~24 MPa. The relationship between temperature, stress and steady strain rate has been analyzed. The stress exponent n and apparent activation energy Qa of the creep process were calculated and based on the TEM images of microstructure the mechanisms of compressive creep behavior were discussed as well. The results show that the steady strain rate of the alloy increases with the increase of temperature and compressive stress. Compared with the exponential function, the relation between stress and rate seem to coincide with power function better. The stress exponent n are 3.31, 4.09 and 5.77 at the temperatures of 300 °C, 350 °C and 400 °C, respectively. The apparent activation energy Qa of the creep process are 68.1 kJ/mol, 103.7 kJ/mol and 131.6 kJ/mol under the compressive stress of 12 MPa, 18 MPa and 24 MPa, respectively. There are lots of stacking faults in the TEM images under each creep condition, which play a critical role in the creep mechanisms. Mechanical twinning is the main mechanism at 300 °C while dislocation climbing is the dominant mechanism at 400 °C.

Abstract:A carrier method was used to measure the dissolution equilibrium of iron vapour over liquid U-Fe alloys from 1500 to 1600 °C, and then the activities as well as activity coefficients of iron in liquid U-Fe alloys were calculated from the results for iron. It is found that iron shows strong negative deviation from Raoult’s law, and the relationship between the standard free energy of dissolution reaction Fe(g)=[Fe]Y and temperature is DG0=–448682+125.4T. At 1500 and 1600 °C, the activity coefficients g of iron at infinite dilution are 0.344 and 0.485, respectively.

Abstract:To describe the fracture toughness of bimodal nanocrystalline (BNC) materials which are composed of nanocrystalline (NC) matrix and coarse grains, we have developed a theoretical model to study the critical stress intensity factor (which characterizes toughness) of BNC materials. A typical case has been considered where crack lies at the interface of two neighboring NC grains and the crack tip intersect at the grain boundary of the coarse grain, while the cohesive zone size is assumed to be equal to the grain size d of the NC matrix. Blunting and propagating processes of the crack is controlled by a combined effect of dislocation and cohesive zone. Edge dislocations emit from the cohesive crack tip and make a shielding effect on the crack. It is found that the critical stress intensity factor increases with the increasing of grain size d of the NC matrix as well as the coarse grain size D. Moreover, the fracture toughness is relatively more sensitive to the coarse grain size than that of NC matrix.

Abstract:Ansoft software was used to simulate the electromagnetic force of the cylindrical thin-walled casts under the action of traveling magnetic field, and the influence of excitation currents on mold-filling capacity of different alloys and surface depression of thin-walled casts were investigated. The results show that the magnetic field remarkably influences the mold-filling capacity of alloys and the casting surface depression simultaneously. The mold-filling capacity and the possibility of the surface depression are increased with the square of the excitation current intensity increasing. Under the same excitation current intensity, the excitation current frequency has the optimal value to the mold-filling capacity; the possibility of the casting surface depression decreases along with its decrease below 1000 Hz.

Abstract:Cu-based TiB2/Cu electrodes reinforced by conductive ceramic TiB2 particles with a particle size of about 3 mm were prepared by electroforming in acid H2SO4 solution. Their structure was observed by scanning electron microscopy and metallographic microscope, hardness was measured by Vickers hardness tester, the corrosion resistance was measured by salt spray tests, and the electric erosion resistance was evaluated by brittle-hard materials. The results show that the reinforcing TiB2 particles are uniformly distributed in the matrix. The particle size of the electroformed Cu and TiB2/Cu is 30 and 10 mm, the hardness is 984 and 1235 MPa, and the corrosion is 47.8 and 40.3 mg, respectively. Compared with Cu electricity deposit, TiB2/Cu composites have preferable surface, small grains and higher hardness, and this kind of composite material as an EDM tool electrode material show good corrosion resistance and electrical erosion resistance.

Abstract:La3+ doped TiO2 powder was prepared by chemical precipitation and the technique was optimized by an orthogonal experiment. The morphology, structure and light absorption properties of TiO2 powders were characterized by SEM, XRD, XPS and UV-Vis. The results show that the effect of the calcinating temperature and the amount of La3+ on optical absorption properties of TiO2 is significant. The main crystal structure of La3+ doped TiO2 powder at different calcinating temperatures is anatase. Higher calcinating temperature can enhance the absorption intensity of La3+ doped TiO2 in the UV band. Doping La3+ can improve agglomeration of TiO2 powder and narrow the band gap of TiO2. In addition, a certain amount of hydroxyls are also adsorbed on the surface of TiO2 due to La3+ doping. The optimal preparation conditions of La3+ doped TiO2 powder are as follows: the calcinating temperature 800 °C, the amount of La3+ 0. 6 mol%, the solution temperature 90°C, and the pH value 8.0. TiO2 powder prepared under the above conditions has the optimal visible light property.

Abstract:(Cu0.46Zr0.44Al0.08Dy0.02)100-xFex amorphous alloys with x=0, 1, 3, 5, 7 were prepared by a copper mold casting method. Amorphous structure and mechanical properties of the alloys were studied by X-ray diffraction (XRD), differential scanning calorimetry (DSC), Transmission electron microscopy (TEM), universal testing machine and scanning electron microscope (SEM). The results show that appropriate Fe addition can enhance structure of the amorphous alloys. The structure of the bulk alloy is completely amorphous when the Fe content is x=1 or 3, and apparent nanoscale phase separation occurs in the as-prepared alloys. When x=3 the alloy possesses large compression strength (1835 MPa) and plastic deformation (0.5%).

Abstract:The corrosion behavior of two nanocrystalline bulk Cu-50Ag alloys prepared from hot pressing powders which were synthesized by liquid phase reduction or mechanical alloying was investigated in acidic solutions as compared with the corresponding coarse grained Cu-50Ag alloy. Results show that the corrosion rates of the three alloys become faster after H2SO4 is added to Na2SO4 solutions. The corrosion rates of PMCu-50Ag and LPRCu-50Ag alloys remain unchanged, but those of MACu-50Ag alloy become faster with the increment of H2SO4 solution concentrations. In Na2SO4 solutions, there are no passivation phenomena for three Cu-50Ag alloys. On the contrary, there are passivation phenomena after H2SO4 is added to Na2SO4 solutions. The corrosion rates of three Cu-50Ag alloys increase in the order of PMCu-50Ag, LPRCu-50Ag and MACu-50Ag alloys. The rates of LPRCu-50Ag alloy are slightly higher than those of PMCu-50Ag alloy, but are evidently lower than those of MACu-50Ag alloy. In Na2SO4 solutions, EIS of three alloys are composed of single capacitive loops. There are diffusion tails after H2SO4 is added to Na2SO4 solutions. This indicates the corrosion processes are controlled by diffusion.

Abstract:The corrosion and hydrogen embrittlement behavior as well as their influence on the tensile properties of 7050 aluminum in EXCO solution have been investigated by means of metallographic microscope, slow strain rate testing (SSRT), hydrogen determinator and transmission electron microscope. The results show that the corrosion characteristic develops from pitting to exfoliation with immersion time increasing, and the hydrogen embrittlement effect occurs, too. The combined action of corrosion and hydrogen embrittlement reduces the tensile properties of the alloy to a large degree. The alloy’s residual strength and elongation affected by hydrogen embrittlement have been quantitatively analyzed by tensile tests after removing the corrosion layer. When the immersion time reaches 64 h, the residual strength and elongation influenced only by hydrogen embrittlement decrease to 68.2% and 60.2%, respectively.

Abstract:The effects of the content of Cu and Si elements as well as heat treatment on the lattice constant and electrical properties of Al-Si alloys were investigated by Wheatstone bridge conductivity measurement, optical microscope, scanning electron microscope and X-ray diffraction analysis. The results indicate that increasing the content of Si and Cu can decrease the conductivity of Al-Si alloy. When Si content is larger than its solubility in Al, variation of Si content has less influence on the lattice constant, and the resistivity of Al-Si alloy is determined by the volume percentage of Si. When Cu content is within its solubility in Al, the increase of Cu content would increase the distortion of aluminum lattice; consequently, the influence of Cu can be estimated according to Al lattice constant deviation. After heat treatment (450 °C×5 h+250 °C×2 h), the distortion of the matrix lattice decreases significantly, and the electrical conductivity of Al-Si alloys improves obviously with the increment up to 32%.

Abstract:The microstructure and properties of the welded joint were studied based on the tungsten argon arc welding of 2 mm thick alloy 800H. The characteristics of microstructure, mico-hardness, room-temperature and high-temperature tensile strength, fractography and intergranular corrosion of samples were analyzed. Results show that the crystallizing morphology on the weld seam is of columnar crystals and equiaxed grains, the grains of heat-affected zone (HAZ) grows bigger, and a small amount of TiN and (Fe,Cr)23C6 phases precipitate in the welded joint. The average hardness of base metal, HAZ and welding seam is 1730, 1526 and 1590 MPa, respectively. Moreover, room temperature tensile strength and elongation for alloy 800H is 565.0 MPa and 31.8%, respectively, which are both higher than the ASME standard requirement (tensile strength 450.0 MPa and elongation 30.0%), and ductile fracture happens at room temperature. The high temperature (650 °C) tensile strength and elongation of alloy 800H welding joints is 394.5 MPa and 15.5%, respectively, and the fracture is mixed mode at 650 °C. In comparison with welded joint of alloy 800H, the corrosion of base metal are much severer, with intercrystalline fracture of base metal and a few corrosion pits on the surface. The TiN precipitates in the base metal could result in pitting.

Abstract:The effects of organic-inorganic cage-type polyhedral oligomeric silsesquioxane (POSS) on the whisker formation behavior of Sn-based lead-free solders were investigated. Pure Sn and Sn3.0Ag0.5Cu (SAC305) solders were used as solder matrix, and the composite solder was fabricated with 3 wt% POSS trisilanol addition. The samples were tested under thermal cycling to accelerate whisker growth, and the temperature range varied between –40 °C and 85 °C. The surficial evolution and interfacial microstructure were observed. The results indicate that POSS would stabilize solder matrix under thermal cycling condition. Meanwhile, the strength and microhardness of solders are improved by POSS significantly, which consequently reduce the deformations in the solders caused by deformations, and inhibit whisker formation eventually.

Abstract:A dense and continuous coating with less cracks and holes was obtained by micro-arc oxidation (MAO) process in an electrolyte composed of Na5P3O10+NaOH+Na2EDTA under the constant voltage mode. The surface and cross-sectional morphologies, phase structures and chemical composition of the coatings were characterized by scanning election microscopy (SEM), X-ray diffraction (XRD) and energy disperse spectroscopy (EDS), respectively. The hydrogen permeation performance of the oxide films was evaluated by vacuum dehydrogenation experiment and XRD. The results show that the obtained coating with an average thickness of 78 μm contains a transition layer, a dense layer and a loose layer. The coating is mainly composed of M-ZrO2, T-ZrO2 and C-ZrO2, and M-ZrO2 accounts for about 90%. The PRF (permeation reduction factor) value of the oxide film reaches up to 11.7, which indicates that the ZrO2 ceramic coating formed on the surface of ZrH1.8 has a superior hydrogen anti-permeation effect.

Abstract:TiO2 nanorod composites were prepared on the flyash hollow microsphere substrates by a C2H5OH/H2O mixed solvothermal method. The morphology of TiO2 nanorod with different preparation conditions and the growth process was studied. The results reveal that the crystal form of TiO2 nanorods is rutile phase. The morphology and the size of TiO2 nanorod depend on the volume ratio of C2H5OH/H2O, titanium precursor concentration and reaction time. The crystallinity of TiO2 nanorod increases with appropriate ethanol, and also the tetragonal rodlike crystal morphology becomes distinct. The size of TiO2 nanorods gradually increases with the increase of concentration and reaction time. In addition, TiO2 nanorod composites show a better photocatalytic activity in degrading rhodamine B.

Abstract:The solution treatment and thermal treatment (TT) processes of GH690 tube made in China were investigated with different processing parameters including temperature and time. The microstructural features, consisting of the grain size, carbide morphology along grain boundary and chromium-depleted zone of the investigated GH690 tube, were characterized through OM, SEM and TEM and evaluated based on Inconel 690 commercial tube. The results indicate that the proportion of large grains in the investigated GH690 tube increases gradually with increasing the solution temperature. The activation energy of grain growth is 265 kJ/mol. The influence of time on grain size becomes significant once the solution treatment is above 1100 °C. Thermal treatment processes for promoting the formation of fine semi-continuous carbides along grain boundaries are 680 °C/10~20 h, 715 °C/10~20 h and 750 °C/5~15 h. Similar microstructural features, including grain size, carbide morphology along grain boundaries and chromium depletion profile, are observed in both the investigated GH690 tube and the Inconel 690 commercial tube after solution treatment at 1090~1110 °C for 5 min followed by thermal treatment at 715 °C for 10 h or 15 h. Nonetheless, the size and density of TiN are lower and the minimum chromium content is higher in the investigated GH690 tube than those in the Inconel 690 commercial tube. Overall, microstructural features in GH690 tube made in China are superior to those in Inconel 690 commercial tube. The optimized heat treatment process is suggested based on microstructure analyses as well as the consideration of economic cost in production.

Abstract:High-k hafnium oxide films were deposited by atomic layer deposition (ALD) on p-type Si (100) substrates. Tetrakis-diethylamino-hafnium (TDEAH) and water were used as hafnium precursor and the oxidant, respectively. Effects of deposition parameters, e.g., flow of precursors, pressure of the reactor, and temperature of the reactor and precursors on the growth of HfO2 films were investigated. By the adjustment of deposition parameters, two growth models of HfO2 films, chemical vapour deposition (CVD) liked growth model and ALD growth model were found. Results indicate that the growth model mainly depends on Q and M. There exists a transition from CVD-liked growth model to ALD growth model by the optimization of deposition parameters. The optimal deposition parameters with a GPC (growth per cycle) of 0.1 nm /cycle were obtained. Moreover, the results show that the crystallization of HfO2 film is under the control of temperature and thickness of the film.

Abstract:TiO2 thin films were prepared by a magnetron sputtering technique and then annealed at different temperatures. The crystal quality, surface morphology, optical absorption and photocatalytic performance of the as deposited and annealed films were characterized and compared by XRD, AFM and ultraviolet-visible spectrometer. The results show that with the increase of annealing temperature, the TiO2 phase turns from anatase to rutile, while at 600 oC, two kinds of phase coexist. During the annealing process, the grain sizes of the TiO2 films change simutaneously. Compared with rutile, anatase phase presents better photocatalytic performance.

Abstract:With silicon substrates and arrays of optical fiber cores as assembly fixtures, 3×3 arrays of Au microspheres produced by melting and condensing Au fibers were manually arranged. ZnO nanowires were hydrothermally synthesized on Au microspheres, and glucose oxidase was immobilized on ZnO nanowires, obtaining the spherically hierarchical structure array-based working electrodes. The surface morphologies and the glucose oxidase immobilization effects of the spherically hierarchical structures as well as the electrochemical performance of the working electrodes were quantitatively characterized. The linear range, sensitivity, low detection limit and Michaelis-Menten constant of this glucose sensor are 0~2.5 mmol/L, 17.24 μA·(mmol/L)-1·cm-2, 3.44 μmol/L, and 1.85 mmol/L respectively.

Abstract:The basic features of phosphorescent emission from Ir(ppy)3 (ppy=2-phenylpyridinate), dissolved in THF, were investigated by a magneto-luminescence technique. It is found that there are two peaks in the phosphorescent spectra in visible region from 2.2~77 K. They are located at 547.70 nm and 515.70 nm wavelength. This is due to radiative electronic transition from two substates in 3MLCT structure to the ground state of Ir(ppy)3. Changing temperature can vary electron distribution and life-time on different substates in the 3MLCT structure of Ir(ppy)3. Thus, we can observe a strong dependence of the phosphorescent spectrum on temperature. Furthermore, we find that the intensity of phosphorescent emission from Ir(ppy)3 increases with magnetic field at 2.2 K. The presence of the high magnetic field can alter the electronic states and, thus, modulate the electron distribution and transition possibility for substates in 3MLCT. As a result, the phosphorescence emission from Ir(ppy)3 can be enhanced by the presence of the magnetic field.