Abstract:The TiSi-C:H films were deposited on the silicon and the stainless steel substrates by middle-frequency magnetron sputtering Ti80Si20 targets using the methane gas as the precursor. The effects of the methane flow rate on the deposition rate, the structure, the mechanical and tribological properties were investigated. The results demonstrate that the structure, the mechanical and tribological properties of the films strongly depend on the methane flow rate. The deposited films exhibit a transition from a tapered columnar nanocomposite structure consisting of ~10 nm nanocrystallites and amorphous phases to an amorphous structure with increasing of methane flow rate. The films deposited at a low methane flow rate show high hardness, high internal stress and high wear rates, whereas the films deposited at high methane flow rate show a decrease in hardness and internal stress but an improvement in tribological performance. The variations on the mechanical and tribological properties may be attributed to the evolution of the microstructures of the films with increasing of methane flow rate.

Abstract:The core-shell structured Al2O3/YAG:Ce phosphor was prepared by a spray drying method. The obtained samples show cubic Y3Al5O12 structure, have a spherical shape with the size in the range of 1~8 μm and exhibit higher internal quantum yield compared to the samples prepared by co-precipitation. Based on the fact that the spray drying method can be employed to fabricate microencapsulate particles, the formation mechanism of the core-shell structured Al2O3/YAG:Ce phosphor was formulated. The slurry, which was mixed with micrometer Al2O3 particles and polycations consisting of Y3+, Al3+ and Ce3+, was atomized and shaped by the evaporation of droplets. In the process of solvent evaporation, the interparticle capillary forces make the self-assembly of polycations into the close-packed shell surrounding the Al2O3 particles, because the polycations have a bigger diffusion rate than Al2O3 particles. At last, the precursor was calcined at the temperature from 850 oC to 1250 oC for 2 h and then the core-shell structured phosphor was produced. Therefore, a novel idea for preparing core-shell structured phosphor is proposed.

Abstract:The luminescent properties of phosphors are sensitive to their morphologies, particularly to the sizes of phosphor particles. The optimal morphology of the phosphor for the field emission display (FED) is the microsized sphere-like particles. However, less attention has been paid to the phosphors with micron-size controlled particles. In this paper, we reported an improved co-precipitation method to synthesize the red-emitting Y2O3:Eu3+ phosphor with the particle sizes controlled in several microns. The optimum phosphors were obtained at the calcination temperature of 1050 °C and pH=5.5, showing the sphere-like particles with the size distribution from 0.9 μm to 3.1 μm. Compared with the commercial phosphors, such optimum phosphors greatly enhance the cathodoluminescent properties and the corresponding luminescence intensity under the low excitation voltage of 1 kV is increased by 50%. Results indicate an effective way to develop the high-quality FED phosphors.

Abstract:Based on the density functional theory (DFT) and using the plane waves ultra-soft pseudo-potential technique, some basic properties of Nb3AlN were simulated, such as ground electronic states and thermodynamic performances. The simulation results show that the properties of Nb3AlN were similar to those of metals, with good electrical conductivity and thermal conductivity. The heat capacity increases with increasing of temperature and decreasing of pressure. The Grüneisen parameter γ increases with increasing of temperature, and decreases non-linearly as the pressure climbs up. The Debye temperature is influenced by temperature and pressure, which decreases sharply with increasing of temperature and climbs up with the increasing of pressure rapidly. The simulation results of the relationship between Gibbs free energy and temperature show that Nb3AlN can be synthesized through an appropriate process.

Abstract:Ferroferric oxide nanotubes were prepared by calcining and reducing the composite nanofiber precursors fabricated by electrospinning. Influences of the electrospun parameters (PVA concentration of solution, applied voltage and collector distance) on the preparation of the composite nanofiber precursors were discussed. The structural properties of the obtained nanotubes were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The formation mechanism of the Fe3O4 nanotubes was investigated through the nonequilibrium heat-treatment procedure. Furthermore, the magnetic property of Fe3O4 was measured using a vibrating sample magnetometer. Results reveal that the tubes show a uniform and continuous morphology, whose outer and inner diameters are about 100 nm and 50 nm, respectively. Fe3O4 possesses saturation magnetization (Ms) of 54.2 A·m2/kg, coercivity (Hc) of 215×79.6 A/m and remanent magnetization (Mr) of 12.8 A·m2/kg, respectively.

Abstract:High temperature magnetic properties of the SmCo7 films deposited on Si(100) substrate with Mo underlayer were investigated. The results show that the effects of high temperature aging treatment on the crystal structure and the magnetic properties of the films are not obvious. According to the law of approach to the saturation and high temperature magnetization curves of the films, the temperature dependence of magnetic anisotropy constant K1 can be obtained, which clearly suggests that the preferred orientation of SmCo crystalline will be destroyed at a certain extent by elevated temperatures. Moreover, the proper temperature dependence of magnetic properties for the films, is suitable for applications in microelectromechanical system (MEMS).

Abstract:The micromorphology and the grain size of 7075 Al alloys were investigated by optical microscopy (OM). The rolled sheets were fabricated by electromagnetic field. It is found that the dendritic crystal of 7075 alloy sheet by alternating oscillating twin-roll cast (TRC) is severely broken, stretched, refined and equiaxed under the condition of pouring temperature 670 °C, compared with that of traditional TRC sheets. Meanwhile, the microstructures of the rolled sheets by static magnetic field (MF) process are also refined and stretched to some degrees with exciting current of 100 A. Segregation bands in center of TRC sheets are dramatically alleviated under the conditions of DC magnetic field and alternating oscillation field, while the influence of alternating oscillation TRC process is much more powerful. Hardness of 7075 sheets both on transverse and surfaces increases in turn along with traditional, static MF and alternating oscillation TRC. With increasing of electromagnetic intensity, the hardness and the properties of sheets are further improved. No matter wherever in the sheets, the influence of electromagnetic field will be further improved by elevated temperature.

Abstract:Four complexes Nd(C2F5COO)3Tfpy, Nd(C3F7COO)3Tfpy, Nd(C2F5COO)2(C6F5COO)Tfpy, and Nd(C2F5COO)3Phen were synthesized to investigate the effects of different ligands on fluorescent properties of Nd3+. Their structures were characterized by UV absorption spectra, FT-IR spectra and 1H NMR spectra. On the basis of testing absorption spectra, photoluminescence spectra and emission decay curves of each solution of the complexes, Judd-Ofelt(JO) analysis was carried out for each fluorescent solution. Structure analysis indicates that all ligands have successfully coordinated with central rare earth ions. Relatively small Ω2 obtained through JO analysis demonstrates that the coordination bonds between Nd3+ and the vicinity ligand are ionic for four complexes. The benzene rings of ligands are favorable for improving the fluorescence quantum efficiency of Nd3+. Compared with Phen, Tfpy is an excellent neutral second ligand because it has more asymmetric chemical structure and less hydrogen atoms. The four Nd(III)complexes all have potential to become liquid laser material because of their large stimulated emission cross sections.

Abstract:WC-17Co cermet coatings were deposited on Ni718 alloys using the high-velocity oxygen fuel (HVOF) technique. These coatings were then heat treated by different processes (150?°C, 10?h; 300?°C,?10?h; 450?°C,?10?h). The effects of heat treatment on microhardness, elasticity modulus, and fracture toughness were studied by an indentation method. The residual stresses of the coated specimens were evaluated by the Almen strip method. The results show that the phase constitution and the structure of the WC-17Co coatings exhibit no obvious change in 150, 300, and 450 °C heat-treatment. The microhardness, elasticity modulus, and fracture toughness of the WC-17Co coatings decrease with the increase of heat treatment temperature. The descent tendency of the mechanical properties is attributed to the decline in compressive residual stresses after isothermal heat treatment.

Abstract:Compressive tests of Sn-4.5Zn-2Bi-In-P, Sn-9Zn-2.5Bi-In-P and Sn-8Zn-3Bi were conducted with gleeble1500 at constant temperature and strain rate. The conditions of the tests consisted of three temperatures 20, 60, 100 oC, and five strain rates 101, 100, 10-1, 10-2, 10-3. Results show that the saturation stress of three materials rises with the strain rate increasing, and decreases with the temperature increasing. In all experimental results, the saturation stress of Sn-8Zn-3Bi is maximum, and that of Sn-4.5Zn-2Bi-In-P is minimum. Nine parameters of Anand constitutive equation were confirmed for each kind of lead-free material by nonlinear fitting. By comparison and analysis between the experimental data and model prediction data of three materials under different conditions, the results show that Anand constitutive equation can describe the mechanical behaviors of three materials accurately, and supply a strong support for the reliability simulation and efficacy losing analysis.

Abstract:Numerical simulation and experimental studies were used to analyze the effect of spiral magnetic field with different exciting currents on the solidification process of the Pb-Sn alloy. The results show that with the increase of exciting current the spiral magnetic field can reduce the cooling rate and temperature gradient of molten metal, and facilitate the transition from columnar to equiaxed structure. The axial component of the force can enhance the circulation of the melt along the axial direction, which can promote dispersive distribution of the primary β phase and eliminate the macro-segregation. However, the strong stirring at large current increases the collision probability between the grains and the grains aggregate more easily while the increasing induction heat also delays the cooling rate of the molten metal, and then the size of grains becomes bigger. At f=10 Hz, there is a suitable range of exciting current within 100~125 A for refining grains and improving the macro-segregation.

Abstract:The constitutive model for titanium alloy was researched to describe the dynamic recovery (DRV) and dynamic recrystallization (DRX) behavior during hot deformation. During this process, based on the constructing method of classical plasticity and viscoplastic unified constitutive model using internal state variables, the constitutive model was developed considering the deformation mechanism of materials by deriving the correlative relations. The proposed model is able to offer more clearly physical insight. At last, the deformation behavior of a new kind of metastable β Ti2448 titanium alloy was described by the proposed model during hot deformation. The stress-strain curves predicted by the developed constitutive model well agree with experimental results, which confirms that the developed constitutive model can give an accurate estimate of the flow stress of Ti2448 titanium alloy. The developed model is effective, the method is reasonable and it can provide an effect method to model the flow behavior of metastable β titanium alloys during hot deformation.

Abstract:Non-equilibrium solidification of AZ91 magnesium alloy containing RE elements was performed by a copper mould casting method, and the effects of category of RE (RE=Ce, Er) and its content (0.25, 0.5, 0.75, 1 wt%) on the primary grain size, solute concentration and phase structures were researched. Results show that less solute content exists in α-Mg grain for Ce addition, accompanied by the serious solute enrichment ahead of solid/liquid interface and the formation of Al11Ce3 phase with high melting point. Consequently, the refinement effect of Ce is more significant than that of Er. With increasing the amount of Ce, both the primary grain size and the ratio of β-Mg17Al12 phase decrease continuously, with the dispersive distribution of eutectic phase in the matrix. In contrast, grain coarsening appears when the Ce content is larger than 0.75 wt%. On this basis, the refinement mechanism was explained according to nucleation and growth processes, which was further verified by the differential thermal analysis experiment.

Abstract:Different nanotextured titanium surfaces were created by controlling the exposure time and temperature of titanium in a mixture of H2O2 and H2SO4. The field emission scanning electron microscopy (FE-SEM), atomic force microscope (AFM) and contact angle measurement were used to study the characteristics and mechanism of the construction of nanotextured titanium surfaces. Bioactivity was investigated by immersing the samples in a simulated body fluid (SBF) for 7 d. Results show that the difference of the nanotopographies is attributed to the increase of the concentration of H+, which speeds up the dissolution of porous titania gel and a bone-like apatite could be formed on the surface created by chemical oxidation. The method in this paper can be developed to be an intelligent nanotechnology for nano-functionalization of titanium.

Abstract:A series of polycrystalline sample SmCo1-xFexAsO (x=0, 0.05, 0.1, 0.2) was prepared by a solid-state reaction method. X-ray diffraction patterns indicate that all the samples have formed the ZrCuSiAs-type structure. The decrease of the lattice constant a and the increase of c are observed with the increased doping amount. Magnetic measurement results show that complicated magnetism consists of antiferromagnetic, ferromagnetic and paramagnetic between 5 and 300 K. Strong irreversibility in M-T curve is observed just below the Curie temperature. With Fe content increasing, antiferromagnetic order of SmCoAsO is suppressed, and its ferromagnetism is enhanced. M-H curves show that metamagnetic transition occurs below their antiferromagnetic transition temperature for samples with x<0.2, and the transition field decreases with increasing Fe content. When Fe content reaches to 0.2, no metamagnetic transition can be observed down to 5 K. All of the results are consistent with the existence of a metamagnetic critical end point at critical concentration which is close to 0.2.

Abstract:Lithium-rich cathode material was synthesized by a sol-gel method, and the product Li[Li0.2Ni0.15Mn0.55Co0.1-xCrx]O2-yCly was calcined at 900 oC for 12 h. X-ray diffraction (XRD) spectroscopy tests present the α-NaFeO2 layered structure of the material. Scanning electron microscopy (SEM) indicates that its particle size is uniform and can reach nano-range; electrochemical testing shows that for the material with Cl- and Cr3+ co-doping in 2~4.8 V voltage and 0.1 C rate, its initial discharge specific capacity reaches 239.8 mAh·g-1 and coulombic efficiency is 81.2% at 20 oC; while at 55 oC, in the same conditions, the initial discharge specific capacity and the first coulombic efficiency are 308.3 mAh·g-1 and 92.7%, respectively. After 40 cycles, at the rate of 1 C, the specific capacities retain 173.5 mAh·g-1 at 20 oC and 207.7 mAh·g-1 at 55 oC.

Abstract:To solve the problem of low charging efficiency and high self-discharge of Fe-Ni batteries, the structure and electrochemical performance of Fe3O4 anodes surface-modified by 0~1wt% Li2O-2B2O3 (LBO) were studied. The results show that the appropriate amount of LBO (0.1 wt%) can be deposited on the surface of electrode uniformly, and there is no obvious chemical reaction between LBO and Fe3O4. The Fe3O4 electrode modified by 0.1wt% LBO has an electrochemical capacity up to 315.2 mAh/g, 54.1 mAh/g higher than Fe3O4 electrode without LBO, and its charging efficiency, cycle performance and self-discharge are improved. This improvement is directly related to the reduction of charge transfer impedance, as well as the increase of hydrogen evolution overpotential and corrosion resistance.

Abstract:The effects of second phases on microstructure and mechanical properties of as-cast Mg-Ca-Sn permanent moulding magnesium alloy were investigated. The results indicate that sole addition of Ca and Sn refined grain size of as-cast magnesium alloy in a certain degree. Mg2Ca phase precipitated at grain boundaries continuously and granular Mg2Sn phase existed at grain boundaries and inside the grains. Point and needle-like CaMgSn phase can be formed after Ca and Sn combined addition. Because CaMgSn particles acted as heterogeneous nucleus of α-Mg during solidification, the grain of α-Mg was significantly refiner than sole addition one. The edge-to-edge matching model was used to analyze the crystallography mismatch relationship between CaMgSn and α-Mg. Microhardness of Mg-Ca-Sn magnesium alloy was improved remarkably with finer grain size.

Abstract:Copper-mold suction casting was employed to prepare the Cu56.4Zr31.02Ti6.58Al6 bulk metallic glass (BMGs). X-ray diffraction (XRD), transmission electron microscopy (TEM), and differential scanning calorimetry (DSC) were used to analyze their microstructure, activation energy and crystallization mechanism. The criterions y(a) and z(a) were applied to test the validity of different nucleation-growth models for the first crystallization stage of the BMGs. Results show that the primary crystallization product of Cu56.4Zr31.02Ti6.58Al6 is Cu10Zr7 and the Starink-Zahra model can describe the crystallization mechanism well. Fitting parameters show that impingement effect factor λi≠0, indicating that impingement effect can't be ignored. Avrami exponent n decreases to 2.3 from 2.5, suggesting that the BMG experienced a continuous nucleation process and diffusion controlled growth process. Furthermore, the nucleation rate has a decrease trend.

Abstract:The effects of the mold temperature and the forming speed on semi-solid 6061 alloy forging were studied by means of software DEFORM-3D. The results show that when the temperature of semi-solid slurry is kept at 650 oC, the mold temperature 400 oC, and the forming speed 50 mm/s, an excellent part can be obtained. The HV hardness value of semi-solid forging parts with T5 treatment is 2166 MPa, 170.5% higher than that of the normal low-press cast parts. The simulation results are well in agreement with the experiment.

Abstract:The corrosion behavior of microarc oxidation (MAO) coatings prepared on AZ31 Mg alloys at 50, 100, 300, 500, 1000 and 3000 Hz was studied in simulated body fluid (SBF). The microstructure, porosity, and chemical phase composition of the samples before and after corrosion were analyzed. The potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) were employed to characterize the corrosion performance. The results show that pulse frequency plays an important role on the corrosion resistance of the MAO coating. The corrosion current density decreases and electrochemical impedance increases with the increase of the pulse frequencies, which result from the dense microstructure at high frequency. The coating produced at 3000 Hz exhibits the largest corrosion resistance with the densest morphology in the present study.

Abstract:Grain size and microstructure evolution mechanisms for 2A02 aluminum alloy under different deformation and heat treatment conditions have been investigated by means of hot working simulator and OM and TEM analysis. The results show that when the hot deformation was lower than 40%, work hardening dominated the forging processes. When the hot deformation was up to 60%, work hardening and dynamic softening dominated by geometric dynamic recrystallization (GDRX) interacted and went to a balance, inducing the obvious zigzag type or the serrated grain boundary formed by the movement and merging of sub-grains. During the aging process after the solution treatment, the TEM observation indicates that the dislocation density of equal-axial grains after recrystallization was becoming lower with the increasing of the aging time, while according to the optical microscope results, the longer the aging time was, the larger the obtained equal-axial grains could be.

Abstract:High-temperature (750 oC) creep tests of smooth and notched specimens were performed, and the creep properties of GH3536 nickel-base superalloys were investigated under the tension loading of 160 MPa, 200 MPa and 240 MPa. The creep fracture mechanism was revealed with the scanning electron microscopy (SEM) analysis of the fracture surface and finite element analysis (FEM) of the stress distributions. The results show that notches reduce both of the creep deformation and the creep rate compared with the smooth specimen. The FEM analysis indicates that the axial stress redistribution and relaxation in the notch root benefit the creep properties of the specimen and lead to longer creep life. The SEM analysis shows that although the surface morphology is different, the growth and accumulation of microspores are the main factors of creep fracture for both smooth and notched specimens.

Abstract:The effect of pre-compression on the tension-compression asymmetry in a hot-rolled Mg-3Al-1Zn alloy was investigated by Electron backscattered diffraction (EBSD) and X-ray diffraction (XRD). The tensile and compressive tests of the pre-compressed materials reveal that the tension-compression asymmetry is greatly reduced via pre-compression, which results in the production of twins facilitating the grain size refinement. Yield strength and peak strength are obviously enhanced. The orientation of the grains and the intensity of the basal texture are effectively modified through the twins resulted from pre-compression. Additionally, {102}-{102} twins are found to be generated in the previously formed {102} twins. The existence of these twins modifies the deformation behavior of the materials during re-deformation, which is beneficial to the reduction of the tension-compression asymmetry.

Abstract:Aluminum oxide coating on the surface of tungsten fibers was prepared by a sol-gel method. The microstructure characteristics of Al2O3 coating with different contents of PVA additive, different drying processes and different calcination temperatures were studied by TG-DSC, XRD, SEM and EDS. The results show that coating agglomerations and cracks can be avoided via the step-by-step drying process. 5 vol% PVA addition enhances the stability of the sol greatly and the uniform and crack-free Al2O3 coating on the surface of tungsten fibers can be achieved. The best calcining temperature is 950 oC for the coating. Antioxidation temperature is increased by 120 oC and the oxidation mass is reduced by about 9% for Al2O3-coated tungsten fibers compared with tungsten fibers.

Abstract:The residual stress of Ti-3Al-2.5V tube, which was manufactured by different thermal-mechanical processes, has been investigated. XRD was applied to measure the residual stress based on the shift of the peak of diffraction profiles. The results show that the residual stress values of Ti-3Al-2.5V tube under the certain fabrication parameters are all positive, whereas the values after the process change are negative. It means that the former one is tensile stress, which is opposite to the latter’s compressive stress. There is an obvious difference in fabrication process between them. Because the compressive stress can benefit the fatigue life and stress corrosion resistance, the tensile stress should be avoided in tubing production.

Abstract:The effect of the solution treatment on the crack growth rate regularity of GH864 alloy was studied at 650 oC. The results indicated that the crack growth rate firstly decreases and then increases with increasing grain size and solution temperature. The relationship between grain size and the crack growth rate was fitted according to milt-group test data. It is predicted that the crack growth resistance may have an optical point when the grain size reaches 100 μm. The relationship between solution temperature and the crack growth rate of GH864 alloy was concluded. The crack growth rate regularity of GH864 alloy is divided into five areas by different solution temperatures. The crack growth rate is decreased with increasing the solution temperature when the solution temperature is below 1080 oC, and the lowest occurs at the solution temperature 1080 oC while the rate is increased with increasing the solution temperature when the solution temperature is higher than 1080 oC. The crack growth resistance may be obtained by precisely controlling solution temperature and grain size.

Abstract:Graphene/NiFe2O4 (Gr/NiFe2O4) nanocomposites were synthesized using a facile one-pot hydrothermal method with graphene oxide (GO), Fe2(SO4)3 and NiSO4 as starting materials. The as-prepared Gr/NiFe2O4 was characterized using X-ray diffraction (XRD), transmission electron microscope (TEM), and Raman spectra (RS). The results indicate that GO is reduced to graphene and the well-dispersed NiFe2O4 nanoparticles are simultaneously deposited onto graphene sheets under the conditions generated by the hydrothermal system. There is a strong interface interaction between the graphene and NiFe2O4 nanoparticles, which avoids their aggregation. The formation mechanism of Gr/NiFe2O4 nanocomposites was discussed. The growth kinetics of NiFe2O4 nanoparticles follows the Ostwald ripening, in which smaller particles dissolve owing to their high surface energy and are essentially consumed by larger ones.

Abstract:The surface temperature field change of AZ31B magnesium alloy was measured by infrared thermography during fatigue testing. Fatigue life of an extruded AZ31B alloy was predicted using different methods. Results show that the temperature evolution mainly undergoes five stages when the cycle loading is higher than the fatigue strength: temperature rising, the steep decrease, the constant value on temperature, abrupt temperature rise before specimen fracturing and final temperature drop. According to the temperature field change law, two methods were proposed to predict the fatigue life. The fatigue lives are obtained according to the temperature rise characteristics (?TM) in the course of fatigue test. The curve of ?TM-Nf shows that ?TM=3.89 oC is the maximum temperature increment, i.e. failure will occur when ?TM is more than 3.89 oC, and compared with the measured 3.68 oC, the error is smaller, 5.7%. Energy method is used to determine the fatigue life and draws the S-N curve. Fatigue strength is 99.3 MPa from the curve, and the error is 0.5 % compared with the measured result 99.8 MPa. The method of infrared thermography is convenient and time saving for evaluating the fatigue life of magnesium alloy.

Abstract:The paper summarizes recent investigations in producing the La(FexSi1-x)13-based magnetocaloric materials and their cooling performance. Some key issues which need further investigations are addressed.