Abstract:Biodegradable magnesium alloy stents (MAS) could improve the long-term clinical results of commercial bare metal or drug-eluting stents. MAS have shown a limited mechanical support for diseased vessels due to fast degradation. Protective polymer coating is a reasonable way to reduce the degradation rate of MAS. However, peeling of the coating during stent expansion is the main obstacle in stent application. In this study, experimental and computational methods were used to study the peeling problem of an optimized MAS design. The 90o peeling test provided the critical energy release rate with cohesive zone method to be used in the simulation study; the 90o peeling modeling had good agreement with the experimental test. Using reliable cohesive element material parameters, the simulation could verify whether the peeling happened when the coated MAS was expanded. The aim of this study is to provide an easy and reliable method to approach peeling problem of MAS, giving the instructions for the improvement of MAS coatings.

Abstract:The present work focuses on the surface of Ti6Al4V titanium alloy to improve its microstructure and hydrophilic property using micro-arc oxidation (MAO) in a mixed electrolyte system with different concentrations of calcium salt and phosphate salt. The morphology, the crystalline structure, the thickness and the hydrophilic property of the MAO film were detected by scanning electron microscopy(SEM), X-ray diffraction(XRD), eddy current thickness meter and electrochemical work station. Results show that the MAO film surface is porous and composed of anatase, rutile and a small amount of hydroxyapatite. The amount of hydroxyapatite phase increases with increasing of potassium dihydrogen phosphate concentration. The thickness of MAO film will not change until it increases to a certain value. The ratio of the surface loose zone to the inner compact zone changes with increasing of the potassium dihydrogen phosphate concentration. The thicker loose layer surface is porous and has the hydroxyapatite phase with more Ca and P, which can improve the hydrophilic property and biological compatibility of MAO ceramic film.

Abstract:The sessile drop method was used in the present experiment to study the spreading wetting principle. It is found that 700 K is an important point for the spreading mechanism of the alloy. DTA (Differential Thermal Analysis) was used to analyze the interfacial reaction and the Kissinger method was used to calculate the reaction thermo-kinetics parameters. In addition, it was investigated that element Cu improved the activation energy of Sn-Ag-Cu/Cu system, and suppressed interface reaction rate.

Abstract:The first principles calculations based on density functional theory (DFT) were performed to investigate the stability, the chemical bonding, the elastic constants, the hardness and the Debye temperatures of M3B2 (M=V, Nb and Ta). The structures of these borides were optimized, and the lattice parameters are in good agreement with the experimental values. The calculated cohesive energy and the formation enthalpy indicate that they are thermodynamically stable structure. The mechanical properties including elastic constants Cij, bulk modulus, young’s modulus, shear modulus and Poisson’s ratio were calculated. The Debye temperatures of M3B2 (M= V, Nb and Ta) were calculated. The results show that the values of M3B2 range from 299 to 526 K. The hardness of M-B bonds was calculated using a semi empirical hardness theory.

Abstract:The effects of 0.1wt% boron addition on microstructures and properties of as-cast Ti-6Al-4V alloy were studied. The results show that TiB phase forms in the original β grain boundaries of Ti-6Al-4V alloy due to 0.1% boron addition. Compared with boron-free Ti-6Al-4V alloy, boron added alloy is refined with uniform β grains. In addition, boron addition results in an improved strength, ductility and a changed fracture mechanism. The fracture mechanism of Ti-6Al-4V alloy is as follows: dislocation slip and pile up in the alpha colonies results in stress concentration and then voids growing until cracks forming. However, the fracture of the boron added Ti-6Al-4V alloy is as follows: a stress concentration occurs around the TiB phase and then micro-voids are formed. TiB phase breaks and is separated with the matrix and then cracks nucleate.

Abstract:The hot deformation behavior of 30%SiCp/2024 aluminum alloy composites was studied by hot compression tests using Gleeble-1500D thermo-mechanical simulator at the temperatures ranging from 350~500 ℃ under strain rates of 0.01~10 s-1. The true stress-true strain curves were obtained in the tests. Constitutive equation and processing map were established. The results show that the flow stress decreases with the increase of deformation temperature at a constant strain rate, and increases with the increase of strain rate at constant temperature, indicating that composite is a positive strain rate sensitive material. The flow stress behavior of composite during hot compression deformation can be represented by a Zener-Hollomon parameter in the hyperbolic sine form. Its activation energy for hot deformation Q is 153.251 kJ/mol. To demonstrate the potential workability, the stable zones and the instability zones in processing map were identified and verified through micrographs. Considering processing map and microstructure, the hot deformation should be carried out at the temperature of 450 ℃ and the strain rate of 1 s-1.

Abstract:Copper nitrate and sodium tungstate were employed to prepare nano-sized cupric tungstate (Ⅵ) dihydrate (CuWO4·2H2O) by hydrothermal method. Formation processes of Cu2WO4(OH)2 precursors were discussed, and the synthesis mechanism of CuWO4·2H2O precipitates from Cu2WO4(OH)2 precursors during the process of hydrothermal reaction was established. Morphological and microstructural investigations of precursors and precipitates were carried out using high resolution transmission electron microscopy (HRTEM) and X-ray diffractometer (XRD). Results show that the synthetic products CuWO4·2H2O particles are mostly spherical in the size range from 20 to 30 nm. Transmission electron microscopy (TEM) observations indicate that the formation of CuWO4·2H2O follows in situ crystallization mechanism in the process of hydrothermal reaction. In the long term hydrothermal environment of high pressure and temperature, Cu2WO4(OH)2 precursors are surrounded by WO42- ions, which are adsorbed and diffused on the surface of Cu2WO4(OH)2. By dehydrations and molecular rearrangement, CuWO4·2H2O precipitates heterogeneously nucleate here. WO42- ions react with Cu2WO4(OH)2 through CuWO4·2H2O layer until WO42- ions have been depleted.

Abstract:The morphology and the hardness of 7075 Al alloy during oscillating twin-roll casting (TRC) process at 670 °C were investigated. It was observed that compared with that by traditional process, the dendritic grains of the strips by oscillation field TRC process were severely broken, refined and equiaxed. Segregation bands at the surface and the center of 7075 strips were dramatically reduced in electromagnetic oscillatory field conditions, even completely disappeared in alternating oscillatory condition. The transverse and the rolling direction HV hardness of 7075 strips manufactured by traditional process were 1104 and 1356 MPa, respectively. Upon applying the electromagnetic field, the maximum hardness of 1615 MPa was obtained in alternating oscillating TRC process. Besides, the properties of strips will be further improved with increasing of magnetic field. No matter in what conditions, the refinement of electromagnetic field to strips will increase at elevated temperature.

Abstract:Self-assembled micronsized flower silver (Ag) particles were synthesized using AgNO3 as starting material by a stainless steel assisted vitamin C (Vc) reduction method. X-ray diffractometer (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were employed to characterize the phases and the morphologies of the products. The results show that the micronsized flower Ag particles with 1~ 6 μm size can be rapidly and routinely produced on relatively large scales, which are composed of nanoplates or nanorods with the thickness of around 200 nm. The growth process of the micronsized flower Ag particles was investigated and their growth mechanism was proposed. It is revealed that the micronsized flower Ag particles might be assembled from small particles step by step. The presence of stainless steel and temperature plays an important role in determining the geometric shape and the size of micronsized flower Ag particles.

Abstract:Cr0.82Al0.18N coating was deposited on the surface of a Ti3Al base alloy by a reactive magnetron sputtering method and the hot corrosion behaviors of this coating in Na2SO4 +25 wt% K2SO4 and Na2SO4 +25 wt% NaCl molten salt were investigated. XRD and SEM were used to analyze the phase constituents and the morphologies of the corrosion products. The results show that the sample loses its mass when corroded in sulfate and chlorate mixture molten salts while the mass increases when corroded in sulfate molten salt and the corrosion products formed in both two kinds of molten salts are mainly composed of Cr2O3 and q-Al2O3. The mass loss of the sample tested in sulfate and chlorate mixture molten salts can be explained by the easy evaporation of the chlorate molten salt and the corrosion products. The accelerated dissolution of Cr2O3 oxide scale will occur in the chlorate containing molten salt owing to the increase of the oxygen ion activity by the reaction between water vapor in the air and gas chlorine formed during the hot corrosion process. The gas chlorine will also react with the coating to form volatility metal chlorides to increase the consumption of the coating.

Abstract:YAl2p/Mg-14Li-1Al composite was made by a stir-casting technique. The aging behavior of the composite was investigated using hardness test, differential scanning calorimetry, and X-ray diffraction. The results show that the microhardness variations of both the matrix alloy and its composite are related to the precipitation and decomposition of θ-MgLi2Al phase. The strengthening of the composite is from the addition of YAl2 particulates and the precipitation in matrix alloy. The former contribution is stable, but the latter is unstable and depends on the aging behavior. The addition of YAl2 particulates delays occurring of the aging behavior of composite.

Abstract:Laser peening (LP) also known as laser shock processing (LSP), is a surface enhancement technique that induces intensive plastic deformation, high dislocation density and deeper compressive residual stress to improve the surface performance of materials. The microhardness, surface profiles, roughness, and the residual stress of TC21 alloy were tested by LSP with high energy laser. The results show that the microhardness of the shocked area is improved apparently compared with that of unshocked area. The magnitude of dent is related with the diameter and the distribution of laser spot. The roughness Ra of shocked area is less than 0.8 μm. The compressive residual stress is enhanced greatly. The investigations show that the technology of LSP could further improve the performance of TC21 alloy.

Abstract:The direct electroplating of Fe-Ni alloy films onto (100) n-type Si substrates were conducted. The electrodeposition phases, the film structure and the performance were investigated. The results show that when the current density is above 1.0 A/dm2, continuous films are formed and show an anomalous co-deposition progress occurs. When films are prepared with the current density from 1.0 to 4.0 A/dm2 the nickel composition can be adjusted from 45% to 78% (mass fraction), and the corresponding current efficiencies are from about 60% to 66%. The films consisting of 10~30 nm nanocrystallites show the fcc structure of solid solution of Fe-Ni. The magnetic hystersis loops of the alloy films exhibit a higher saturation magnetization and a very low coercive filed approaching zero, indicating that nanosized alloy films have very good soft magnetic performance.

Abstract:The hot ductility of Fe-36Ni invar alloy was studied by a Gleeble-3800 thermal-mechanical simulator and a microcomputer control universal material testing machine. The results show that the alloy has a good hot ductility (RA above 70%) at 1050~1200 °C, which illustrates that the alloy might be suitable for the rolling provided the finish rolling temperature does not go below 1050 °C. Dynamic recrystallization occurred and was found to be responsible for the better hot ductility. However, the alloy exhibits a hot ductility drop (RA below 50%) at 800~1000 °C, which is mainly attributed to the presence of the grain boundary sliding. Serious subscales, which had a typical substructure of the intragranular subscale and the intergranular subscale, occurred in the matrix after oxidation. The compression test indicates that the intergranular subscale will lead to the cracks and significantly deteriorate the hot ductility during deformation process.

Abstract:Superior bone repairing materials can shorten bone healing periods and lower the incidence of nonunion. Strontium ions are known for enhancing a bone forming effect. Doping of strontium into bone powder will be able to make an attractive bone repairing material. In this study an ion exchange method was tried to dope strontium into bone powder in vitro. The capability to dope strontium into bone tissue was also observed. The cytotoxicity of novel material was investigated by MTT (Methyl thiazolyl tetrazolium assay) method. And further primarily cultured osteoblast was used to evaluate the biocompatibility of novel strontium doped bone sample. It is found that more than 10% exchange ratio of Sr/Ca can be achieved in bone powder. The Sr-doped bone shows no cytotoxicity. Compared with untreated bone samples, osteoblasts show higher proliferation rate (129%) on Sr-doped bone samples. And ALP (Alkaline phosphatase) is 132% higher on Sr-doped bone samples. Thus it is feasible to develop a Sr-doped allograft bone graft by this method.

Abstract:Effects of of Mn and Ce addition on hydrogen-storage microstructure and properties of (Ti0.27Cr0.33V0.4)100-xMnxCey alloy have been investigated by XRD, SEM/EDS and P-C isotherm measurements. The results show that the addition of Mn enhances the precipitation of Ti-rich phases. With the increase of Mn addition, the lattice parameters of bcc main phase are reduced, the plateau pressure of alloys is increased, and the amount of residual hydrogen in alloys is decreased. The maximum capacity of effective hydrogen storage is obtained at 8at% of Mn content in alloys. Based on this alloy, the addition of Ce inhibits the precipitation of Ti-rich phases and facilitates homogeneous distribution of composition in the bulks. With the increase of Ce addition, the lattice parameters of alloys are increased, plateau pressure of alloys is improved, and the maximum capacity and effective capacity of hydrogen storage are raised.

Abstract:0.7BiFeO3-0.3PbTiO3 thin films with 0%, 1%, 5%, 10 % Mn doping (BFMPT7030/x, x=0, 0.01, 0.05, 0.1) were prepared on LaNiO3/SiO2/Si substrates by a sol-gel process. XRD results indicate that the films are completely crystallized and present highly (100) preferred orientation. Crystalline structure analyses of the thin films reveal that BFMPT7030/0.05 thin film has the smallest grain size (258 nm) and the smallest cell volume (61.25×10-3 nm3). SEM results show that the crystalline grains are fully grown up and the grain size is between 150~300 nm. The BFMPT7030 thin film with 5% Mn doping demonstrates good ferroelectric properties and a saturated hysteresis loop is observed. The leakage current tests show that with increasing of Mn content, the increasing tendency of the leakage current becomes slow as electric field increases.

Abstract:Microstructure and mechanical properties of solution strengthened Ni-20Cr-18W rolled superalloy were investigated. Microstructure features and phase composition investigations indicate the average equiaxed grain size of the as-rolled alloy is 20~30 μm (ASTM 7). Significant annealing twins can be observed within the microstructure and most M6C-type carbides mainly disperse on the grain boundary. As-rolled Ni-20Cr-18W superalloy maintains a high tensile strength due to the small grain size. Low ductility of the as-rolled superalloy can be ascribed to M6C-type carbides, which act as crack source on the grain boundary, and the transgranular fracture features with typical dimple-ductile characteristics are observed.

Abstract:Applying a composition design method of “element substitution” and based on the Slater-Pauling curve, multi-component amorphous alloy ribbons with compositions of Fe69Co8Nb7-xVxB15Cu1 (x=0, 2, 5, 7, at%) were prepared by a single roller melt-spinning method. The glass forming ability, thermal stability and soft magnetic property were investigated by XRD, TEM, DSC, PPMS and B-H loop tracer. The results show that increasing V content can reduce glass forming ability, thermal stability and coercivity, but increase saturation magnetic flux density and Curie temperature of amorphous phase. The widest heat treatment temperature range of 225.9 oC appears in these amorphous alloys with V content of x=2. The desirable soft magnetic property is obtained when x=7, with saturation magnetic flux density of 0.96 T, coercivity of only 8.95 A/m, and Curie temperature up to 349.42 oC.

Abstract:The microstructural evolution of 617B Ni-base superalloy at different strain rates were studied by Gleeble3800 thermal simulation testing machine, optical microscope and electron backscatter diffraction. The results show that for the 617B alloy, when the strain rate≤1 s-1, the deformation temperature rise is negligible. When the strain rate≥10 s-1, the temperature rise is significant. As the strain rate increases, the peak strain of dynamic recrystallization tends to increase when in the same deformation temperature condition. In the range of strain rate of 0.1~20 s-1, the dynamic recrystallized grain size trend at first decreases and then increases as the strain rate increases.

Abstract:The electromigration behavior of Cu/SAC305/Cu joints was investigated. Current stressing tests were conducted at a certain temperature and current density for various hours. The diffusion characteristics of the elements near the soldering interface and IMC (intermetallic compound) growth mechanism were studied. Results indicate that the growth of IMC presents a parabola dependence on time under thermal-electrical coupling at the anode. The thickness of IMC increases at first and then decreases. Meanwhile, the morphology of IMC changes obviously at the cathode. The diffusion of the elements at the soldering interface could be divided into two stages. At the initial stage, the high element concentration gradient in the soldering interface plays a leading role to the element diffusion. The IMC shows a similar growth trend at the anode and cathode. At the second stage, the concentration gradient in the soldering interface decreases. The electron-wind force plays a crucial role to the element diffusion. Accordingly, the thickness of IMC decreases at the cathode but increases at the anode.

Abstract:Based on?the?fundamental?principle?of?classical mechanics?and?hydromechanics,?a particle-trajectory?model?was?established to simulate transport process?of?particles?in?J/E?chamber?during the?preparation?of?micropowder with a combination of jet milling and electrostatic dispersion techniques,?and?the law of kinetic?of the particles during?J/E?process?was revealed?as well.?When the charging voltage is?20 kV, the?grain flows?of micropowder present?laminar?flows of?quasi-steady-state?as?the?velocity of jet is low.?With the increase of jet velocity, the distribution of particles?transforms?into?dispersive?state,?and?the dispersion enhances to a certain extent. While when the charging voltage increases to 60 kV,?the dispersion of particles in the chamber?is further improved, which presents?a better evenly dispersed state.?The simulation of flow dynamics of the particles shows that?increasing the jet velocity and the charging voltage can improve?the dispersiveness of the powder during the transport process in?the?J/E?chamber, and the effect of the charging voltage is more?substantial.

Abstract:2A12-T3 and 2A11-O aluminum alloy were welded by ultrasonic welding (USW), and then ultrasonic deep rolling (UDR) treating was performed on the welded layer. Macromorphology and microstructure of the USW layers before and after UDR were investigated by scanning electron microscope (SEM), electron backscatter diffraction (EBSD) and transmission electron microscope (TEM). Results show that UDR can eliminate the surface welded indents, decrease surface roughness and make microstructure more homogenous at the welded interface. Recrystallization occurs in the USW layer after UDR to form recrystallization texture and strain-induced grain growth, which could reduce welding residual stress at the welded interface. Therefore, UDR is favorable to improve microstructure and properties of the USW layer.

Abstract:Metallurgical quality of high Nb containing TiAl ingots prepared by vacuum levitation melting (VLM) has been investigated from respects of macroscopic defects, composition distribution, oxygen content and microstructure. After twice melting and pouring the melting into properly designed mould, crack-free ingots with small shrinkage defects could be obtained. There are Al macrosegregation (>1at%) at different positions of ingots. Oxygen content is decreased to 300 mg/kg by using high quality raw materials and a optimized melting process. There are not phases and microstructures induced by high melting point raw materials in the ingot, and the as-cast microstructures of the ingots are typically nearly lamellar microstructure.

Abstract:The effect of trace boron on phase transition temperature, specific heat, surface tension, fluidity and microporosity of K4169 superalloy has been investigated. The influence of different contents of minor element boron on liquidity of K4169 superalloy and quantitative measurement of the area percentage of microporosity were also studied by two different fluidity models of superalloy designed by ourselves. The results show that when the content of boron increases from 26 mg/kg to 59 mg/kg, the fluidity of K4169 superalloy can be greatly improved; however, the percentage of microporosity decreases and then increases. When the content of boron reaches 59 mg/kg, the microporosity is the smallest. Solidification parameters were measured by differential scanning calorimeter (DSC). The results indicate that with the increasing of boron content the solidification range becomes narrow, while when the content of boron exceeds 59 mg/kg, the solidification range increases. JMatPro software calculation results show that with the increasing of boron content, the surface tension of the alloy is gradually reduced. EDS analysis reveals that when the content of boron reaches 70 mg/kg, boride will precipitate in the superalloy.

Abstract:The residual stress is one of the main factors to cause the failure of thermal barrier coatings. In this paper, a sinusoid curve with different amplitudes was used to model the roughness of interface between ceramic top coat (TBC) and bond coat (BC) in thermal barrier coatings and the effect of interface roughness on residual stress distribution was analyzed. Besides, the effect of roughness on interfacial crack nucleation and propagation under load was simulated with cohesive zone model. Results show that the interface roughness has a significant effect on residual stress distribution and crack nucleation and propagation. With the increase of interfacial roughness, the maximum tensile/compressive stress near the interface also increases in the TBC/BC. When applying a certain tensile displacement load, the maximum damage and crack firstly take place in the peak and valley of minimum amplitude.

Abstract:The initial growth of diamond coated on Cu-diamond inlay structure interlayer deposited by composite electroplating was investigated using a hot filament chemical vapor deposition method. The results show that with the increase of the growth time, the growth rate of diamond particles decreases and the irregular diamond particles protruding out of the Cu-diamond composite interlayer change into facet particles gradually. Second diamond grains preferentially nucleate at dihedral angle formed by homoepitaxial growth diamond particles and electroplating copper and the new dihedral angle between second crystal and copper promotes new second nuclei. This type of multiplying of second nucleation growth finally fills in the gaps of the large homoepitaxial diamond particles and forms continuously diamond film.

Abstract:Fine grain 93W-4.9Ni-2.1Fe-0.03Y% alloy was strengthened by rapid hot extrusion. The dynamic mechanical properties and failure behavior were investigated for the rapid hot extruded fine grain tungsten heavy alloy at high strain rates. The results show that the flow stresses of the as-extruded fine-grained tungsten alloy at relatively lower strain rates are equivalent, of the order of 2000 MPa. Tungsten particles on the fracture surfaces are severely deformed and fracture into fine pieces which adhere to the soften matrix phase. This phenomenon is enhanced with the strain rate increasing. Observation of the sectioned surfaces reveals that the tungsten particles are heavily shear deformed along the fracture surface, but no plastic deformation is observed when it gets into the interior, indicating the localized shearing marks. The experimental results have proved that the failure of the extruded fine-grained tungsten heavy alloy is adiabatic shearing failure.

Abstract:CeO2-ZrO2 composite oxides (CZ) were prepared through a co-precipitation method using magnesium hydrogen carbonate as the precipitating agent which was prepared from the cheap dolomite ores. The effects of peroxide oxidation time on the properties of CZs were studied. The crystal structures, surface areas, surface micromorphologies, redox performances and oxygen storage capacities of the as-synthesized CZs were studied by XRD, BET, SEM, TPR and oxygen pulse adsorption techniques, respectively. The results show that the addition of peroxide increases CZ’s surface area, improves thermal stability, suppresses phase separation, and also increases the active surface oxygen amount. The surface area, aging property and oxygen storage capacity increase with prolonging the oxidation time and they reach to the maximum values at 30 min, when the sample’s 600 oC calcined fresh specific surface area, 1000 oC aged specific surface area as well as 500 oC oxygen storage capacity could reach 111.3 m2/g, 32.9 m2/g and 315 μmol O2/g, respectively. However, their values change little when prolonging the oxidation time further.

Abstract:TC21 titanium alloy specimens after pretreatment were carburized in a vacuum carburizing furnace. The microstructure, phases, hardness and wearability of the carburized coating were analyzed by SEM, XRD, HV hardness tester and friction-wear test machine, respectively. Results show that after carburization, no hydride can be determined by carburized layer tissue, no hybrids or H-containing phase are observed in the coating, while TiC and other carbide phases appear. The hardness of the alloy surface after carburizing increases by 2.66 times. The friction coefficient of Ti/Ti is 0.6, after carburization that of TiC/TiC is 0.23, and that of Ti/TiC is between Ti/Ti and TiC/TiC. After carburizing treatment, frictional properties of TC21 titanium alloy are improved. When Ti/Ti part is grinding each other, the carburized part can improve the wear resistance. Wear of noncarburized part becomes serious when it is grinding with a carburized part. Carburizing also changes the friction state between TC21 titanium alloy components, i.e. from adhesion wear between Ti substrate and Ti ball, to grain wear and delamination wear between Ti substrate and TiC ball.

Abstract:The effect of concentrations of hydrogen peroxide (H2O2) and salicylic acid (SA) on the material removal rate (MRR) in slurries was investigated. The influence of H2O2 and SA on the corrosion behavior was studied by electrochemical methods and X-ray photoelectron spectroscopy (XPS). The surface roughness of the polished Ru disk was characterized by atomic force microscopy (AFM). The results show that the increase of SA promotes formation of passive film, and increases the MRR of Ru. MRR increases with the increasing of H2O2 at the beginning, but it would decrease when the concentration of H2O2 is higher than 3%. The surface roughness Ra of the polished Ru surface could reach 7.2 nm.

Abstract:A ternary defect compound CuGa3Te5 was synthesized by a spark plasma sintering technique and its structures and thermoelectric properties were evaluated at 318~717 K. The XRD analysis indicates that the compound is single phase CuGa3Te5 with a direct band gap (Eg) of ~1.0 eV. The maximum thermoelectric figure of merit ZT is 0.3 at 717 K.

Abstract:The layered LiNi0.4Co0.2Mn0.4O1.97X0.03 (X=O, F, Cl) samples were prepared by a sol-gel method. The crystal structure, apparent morphology and electrochemical performance were characterized by XRD, SEM, cyclic voltammograms (CV), electrochemical impedance spectroscopy (EIS) and charge-discharge tests. The results show that LiNi0.4Co0.2Mn0.4O1.97X0.03 (X=O, F, Cl) samples remain a well-layered structure with single phase of hexagonal after fluorine or chlorine doping. The reversibility of the cathode materials is enhanced by fluorine or chlorine doping. The discharge capacity is increased and cycling property improved. The increase of electrochemical reaction impedance of cathode is restrained after fluorine or chlorine doping during cycling.

Abstract:The current Kroll method used to produce sponge titanium utilizes a process cycle of magnesium metal and chlorine gas via the electrolysis of magnesium chloride. The main issues are the high capital cost of the electrolysis process and the environmental regulations limiting high chloride concentrations. Thus, the authors have developed a conceptual method involving the pyrolysis of magnesium chloride as well as a reduction process which allows for a cycle of magnesium and chloride. The magnesia obtained in this process can be used to prepare magnesium metal through a thermal reduction method. This paper has studied the pyrolysis of magnesium chloride in detail, which is the key part of this new Mg-Ti cycle method. By plotting Mg-O-Cl predominance diagram, the conditions in which MgO stably exists can be found. The experiments show that the optimum reaction conditions are as follows: pyrolysis temperature 1200 oC, pyrolysis oxygen partial pressure 0.1 MPa and pyrolysis time 50 min. The pyrolysis rate of molten MgCl2 can reach 99.99% and the chlorine content in the product is 0.00262% under the optimum conditions. The obtained MgO powder was analyzed by XRD and SEM. These MgO powders, showing an irregular hexahedral shape, have an average diameter of 1 μm with uniform size distribution, good dispersity and high crystallinity and purity.

Abstract:Porosity characteristics of wire arc additive manufactured (WAAM) Al-Cu alloy using different pure argon flow rates and CMT process were investigated. It is observed that the porosity of aluminium alloy deposition can be significantly influenced by pure argon flow rate and CMT process. It is beneficial to reduce the porosity with the increase of pure argon flow rate. CMT-PADV is the most applicable process for aluminium alloy WAAM process. The porosity reduction using CMT-PADV process is due to its low heat input and effective oxide cleanliness of aluminium alloy filler wire. With a proper shielding flow rate of 25 L/min, CMT-PADV process can produce aluminium alloy demonstration with no porosity.

Abstract:The effect of different homogenization treatments on hot compression ductility for MX246A alloy was investigated on MTS test machine. The results show that hot compression ductility and uniformity of MX246A alloy increase with elevating homogenization temperature and prolonging homogenization time; homogenized at 1160 oC for 24 h + 1230 oC for 48 h, MX246A alloy could be compressed for 80% reduction with uniform deformation and good surface quality. The microstructure observation reveals that the compression destabilization of MX246A alloy is caused by adiabatic shear band, and the enhancement of hot compression ductility is mainly contributed to the alleviated segregation and the strengthening of carbides enveloped by γ′ phase.

Abstract:Fe-10%Ni alloys were synthesized in a high energy horizontal rotary ball mill from pure element Fe and Ni powders. Phase constitution, shape and thermal stability of the milled powders were characterized using X-ray diffractometry (XRD), scanning electron microscopy (SEM) and differential thermal analysis (DTA), respectively. And microstructure and properties of bulks prepared by hot-press sintering with milled powders as starting materials were analyzed and tested. Results indicate that under the condition of a milling speed of 400 r/min and a ball-to-powder mass ratio of 20:1, Ni fully solubilizes in Fe, which forms a supersaturate solid solution of Fe(Ni) with a body-centered cubic structure. Particles of the powder milled up to 16 h are more homogeneous and finer than those of the powder milled for 8 h, but phase of the powder is still Fe(Ni) solid solution. The alloy powder milled for 16 h were annealed in the temperature range between 500 and 800 oC. It is found that structure of the powder after annealing is stable and no phase transformation occurs in the powder. Phase of the powder is still Fe(Ni) solid solution. When the alloy powders milled for 16 h were treated by hot pressed sintering at 950 oC, a little Fe(Ni) solid solution with a face-centered cubic structure is found in the bulks. If the bulks that previously were treated by hot-press sintering at 950 oC and cooled to room temperature were subsequently sintered at 970 oC again, the phase of the powders completely transforms to Fe(Ni) solid solution with a face-centered cubic structure. However, the strength and ductility of bulks treated by hot-press sintering at 950 oC are superior to those of bulks by subsequent sintering at 970 oC, because oxide and holes are produced in resintered bulks without pressure.

Abstract:Powder is the key factor for the preparation of?thermal barrier coatings?by plasma spray. This paper introduces the?methods?of preparing?zirconia hollow sphere powder and the performance of its coating. Plasma atomization and spray drying are two ways for the preparation of zirconia hollow sphere powder. Zirconia hollow sphere powder is easy to be melted and it forms?hollow?droplets after melted; the hollow droplet has a unique counter liquid jetting along with longer solidification?time during impacting onto the substrate, which thus leads to form smaller splat with uniform thickness and less defects after solidified. Coatings sprayed from zirconia hollow sphere powder have promising properties such as moderate porosity, low thermal conductivity, low module and high sintering resistance; it can meet the requirements of high performance thermal barrier coatings.

Abstract:As current study emphases of zirconium alloys, Nb-contained zirconium alloys have excellent corrosion resistance, good mechanical properties and deformable properties. Recent research situation on Nb-contained zirconium alloys is summarized in the present paper, including the effects of chemical composition, deformation and heating treatment process on precipitation behavior of SPPs (second phase particles). Research progress of corrosion theory in zircaloy is also introduced, and lots of research problems are discussed. This paper can provide valuable references for microstructure control and corrosion resistance improvement in Nb-contained zirconium alloys.