Abstract:The cerium oxide films with high refractive index and good UV irradiation shielding performance were synthesized on the glass substrates by a hydrothermal method using Ce(NO3)3·6H2O and CO(NH2)2 as raw materials. The films and the powders prepared at the same time were characterized by SEM, XRD, FT-IR, ellipsometer and UV-vis. The influences of original Ce(Ⅲ) concentration and urea dosage on cerium oxide films were researched. The results show that the films are smooth and the particles are small at low Ce(Ⅲ) concentration and urea dose. The sediments are cerium oxide and Ce(CO3)2O·H2O crystal, and silicon of substrate is involved in hydrothermal reaction. Meanwhile, the film refractive indexes are affected by film compact and chemical composition. Both of absorbance and absorption wavelength edge become big with increasing of Ce(Ⅲ) concentration and urea dose, and the main influence factors are the film thickness and composite semiconductors. The optimal Ce(Ⅲ) concentration is 0.008 mol/L, and the optimal urea dosage is 0.06 g.

Abstract:Oxygen enriched α composite layer with 82 μm thickness was formed on the surface of Ti-10V-2Fe-3Al alloy by the heat treatment at 830 oC for 1 h in air and water quenching. The effects of α composite layer on the microstructure and mechanical properties of Ti-10V-2Fe-3Al alloy were investigated. The microstructure, the hardness and the elements distribution of α composite layer were studied. The results show that the hardness variation of α composite layer does not always display a decreasing trend from the edge to the matrix, but shows the law of high-low-high to stable trend, which is related with the distribution of elements (especially V and Fe) and microstructure evolution. The surface hardness of Ti-10V-2Fe-3Al alloy with α composite layer increases by 45%; meanwhile, the tensile strength and yield strength decrease by 5% only. Cracks will be generated firstly on the sample surface along the direction perpendicular to the tensile stress in tensile procedure, then expand in α composite layer and cross up to the matrix material. Fracture morphologies show the characters of ductility in matrix zone and brittle fracture in α composite layer zone. Stress induced phase transformation from β phase to α″ phase will take place during the tensile deformation.

Abstract:The numerical simulation was implemented using FEM software DEFORM-2D to study the influence on deforming quality caused by sheath wall thickness and sheath bottom thickness. The results show that when the deformation degree is the same, the density distribution uniformity of the billet becomes better along with the increase of sheath wall thickness, but poor with the increase of sheath bottom thickness. Under the conditions of different sheath wall thicknesses, the billet density distribution uniformity first gets worse and then gets improved with the increase of deformation degree, and the uniformity becomes the best when the deformation degree is 80%. Under the conditions of different sheath bottom thicknesses, when the deformation degree is less than 62%, the density distribution uniformity of the billet gets worse first, and then gets improved; when the deformation degree is over 62%, it becomes better as sheath wall thickness increases.

Abstract:The functional coating with high microhardness, high wear resistance and low friction coefficient on metal surface can reduce friction power consumption effectively and prolong the service life of mechanical equipments. In this study, Ni-P-SiC-WS2 composite coating was deposited on the stainless steel substrate by electroless composite plating. The surface morphology, microstructure, the composition, the microhardness, the tribological properties and the corrosion resistance of the coating were tested and analyzed. The results indicate that the surface of Ni-P-SiC-WS2 coating is compact. Extrinsic insoluble SiC and WS2 are entrenched in the coating and dispersed uniformly. Compared with other nickel coatings obtained under the same experiment condition such as Ni-P-SiC and Ni-P-SiC-MoS2, the tribological properties and the corrosion resistance of Ni-P-SiC-WS2 are improved effectively due to hard-particle-dispersion-strengthening and soft-particle-lubrication of SiC and WS2 in the composite coating.

Abstract:A europium (Eu)-doped nanohydroxyapatite (Eu-nHA) photoluminescent material was synthesized through a wet chemical precipitation method. The prepared Eu-nHA nanomaterial was then characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), spectral analysis of elements, spectrofluorometry and luminescence test. Results show that the Eu-nHA nanoparticles exhibit a tiny rod-like morphology with the particle size of 5~15 nm (width) × 15~30 nm (length). Besides, the nano-crystal pattern of Eu-nHA and successful doping of Eu ions into nHA have also been revealed. Meanwhile, the present study shows that the Eu-nHA agent actually displays functional red fluorescence under proper ultraviolet (UV) irradiation. It is evident that 5D0-7F1 and 5D0-7F2 transition of Eu ions play key roles in the photoluminescence activity. In conclusion, the synthesized Eu-nHA agent holds promise as a novel nano-fluorescence agent for biomedical applications.

Abstract:The effects of Ca on the microstructures and the corrosion resistance of as-cast AZ91 alloys with contents of 0.5 wt%, 1.0 wt% and 1.5 wt% Ca were investigated. Constant immersion technique, potentiodynamic polarization and salt spray test were employed to determine the corrosion resistance of AZ91 alloys. Morphological characterization by optical microscope (OM), microanalysis by scanning electron microscopy (SEM)/energy dispersed spectroscopy (EDS) and phase identification by X-ray diffractometry (XRD) indicate that the presence of 0.5 wt% Ca does not form any new intermetallic phase but restrains the discontinuous precipitation of the β-Mg17Al12 phase through dissolution in both the second phase and magnesium matrix. The AZ91 alloy with the addition of 1.0 wt% Ca exhibits the optimal corrosion resistance. Al4Ca phase in bone-like morphology appears in the alloys with a larger quantity of Ca (1.0 wt% and 1.5 wt%), in line with a marked size reduction of the β-Mg17Al12 phase. The β-Mg17Al12 phase is distributed uniformly among the matrix of the AZ91-1.0Ca alloy. The variation of the corrosion resistance of the as-cast AZ91 alloys with the addition of Ca is attributed to the change of the microstructure.

Abstract:In order to study the effects of the structures of HTS current leads on AC losses, two different structure HTS current leads were fabricated. Based on the Clem model, the effects of external magnetic field on AC losses were taken into account. The coordinate system on the cross section of the current leads was established. By taking the advantage of coordinate translation and coordinate rotation, the distributions of the magnetic field in HTS current leads were obtained. On the basis, AC loss calculation models for the two different structure HTS current leads, rectangular skeleton current lead (RSCL) and dodecagon skeleton current lead (DSCL) were built. Then, calculation programs were compiled using MATLAB and AC losses of the two different structure HTS current leads were calculated. Finally, the experiments of AC losses of HTS current leads were carried out by an electrical method in liquid nitrogen environment. AC losses of the two different structure current leads were measured at different currents and different frequencies. The theoretical results and measured data were compared and the effects of the structures of HTS current leads on AC losses were analyzed. The calculation results of AC losses show the coordinate transformation model is more accurate than the Norris model. The results also show AC loss of DSCL is smaller than that of RSCL.

Abstract:Pd-based multicomponent nanoporous metals were fabricated by electrochemically dealloying Pd20Ni60P20 metallic glass in an acid solution. The compositions and the pore size of the nanoporous metals were controlled by tuning the dealloying overpotential. The Pd-based nanoporous metal dealloyed at the critical potential presents superior electrocatalytic performances in formic acid electro-oxidation in comparison with the commercial Pd/C catalyst.

Abstract:Using experimental data gained from hot compression tests in the temperature range of 750~950 °C and strain rate range of 0.001~1 s-1, the constitutive relationship of Ti-555211 titanium alloy was investigated based on the back propagation artificial neural network constitutive model (ANN model). The capability of the model was measured by the average absolute relative error (AARE), and correlation coefficient (R). The simulated values were compared with experimental values. The results show that the R and AARE for the ANN model are 0.99938 and 1.60%, respectively, indicating that the hot deformation behavior of Ti-555211 titanium alloy can be predicted by the ANN model efficiently and accurately. Furthermore, the back propagation artificial neural network model is a more efficient quantitative way to predict the deformation behavior of the Ti-555211 titanium alloy compared to the mathematical equation. The results show that the peak stress of the alloy decreases with increasing of temperature and decreasing of strain rate, and the phenomenon of discontinuous yielding is more obvious with the increase of deformation temperature and strain rate. The flow curve characteristics under different deformation parameters show obvious differences.

Abstract:The sandblasting-acid-etched (SLA) technique and hydroxyapatite (HA) deposition are the two methods widely used to improve surface characteristics of titanium implants. In the current study, a layer of HA was deposited on SLA-treated titanium (SLA-Ti) by a simple deposition method. The surface topography and surface roughness of SLA-Ti and HA-coated titanium (HA-Ti) were evaluated using scanning electron microscope (SEM) and atomic force microscope (AFM). Protein adsorption, osteoblast chemotaxis as well as osteoblast attachment on both Ti surfaces were additionally analyzed. The results show that SLA-Ti surface is covered with uniform, multiple micropores, whereas HA-Ti surface is covered with a large number of uniform microparticles under multiple microporous background. In comparison to SLA-Ti, the surface roughness of HA-Ti surface is lower. The protein adsorption on SLA-Ti and HA-Ti surfaces is generally even, and the chemotaxis of osteoblast have no differences. After 12 and 24 h of incubation, more osteoblasts are adhered to the HA-Ti surface and more osteoblast-osteoblast connection is observed on HA-Ti surface compared to SLA-Ti surface. These findings demonstrate that HA coating deposited on SLA-Ti surface improves SLA-Ti surface morphology and promotes osteoblast attachment in vitro.

Abstract:The microstructure and tensile binding strength of Ni-based self-lubricating coatings PS304 by plasma spraying and PM304 by powder metallurgy were studied. The result shows that the PS304 coating prepared by plasma-spraying has a coarse microstructure and high porosity. The lubricant phase fluoride and strengthening phase Cr2O3 are distributed unevenly. However, the microstructure of PM304 coating prepared by mechanical milling and vacuum sintering is uniform and dense, and the size of particles is much finer. The tensile test shows that the PS304 coating has a low tensile binding strength. The tensile fracture occurs not only in the interface of coating and substrate, but also appears in the internal of the coating. The PM304 coating has a higher tensile binding strength, and a good metallurgical bonding can be obtained between coating and substrate. The tensile fracture mainly appears in the internal of the coating. The higher tensile binding strength of PM304 coating is mainly due to 4 reasons, including the increase of density, the decrease of the sharp pores number, a metallurgical bonding formed between Ag and NiCr, and the dispersion hardening effect of fine particles precipitated from the NiCr substrate which increases the strength of the NiCr substrate.

Abstract:The cold rolling texture and recrystallization texture of the 99 % reduced Cu-45Ni alloy substrates with thickness of 80 and 40 μm were investigated by XRD. The recrystallization evolution of those two Cu-45Ni alloy substrates were also investigated by electron backscattered diffraction (EBSD). The cube texture formation of Cu-45Ni alloy substrates with different thicknesses were demonstrated from the fraction of cube texture, low angle grain boundaries, and the average grain size. The results show that a “Copper” type rolling texture is obtained after 99% deformation reduction for both two tapes, and the rolling texture causes little impact on the cube texture formation. The substrates with 40 μm in thickness have a stronger cube texture and a high fraction of low angle grain boundaries. It is because the probability is higher that two cube grains meet and grow up fast to form a strong cube texture in the substrate with small thickness during partial recrystallization.

Abstract:The microstructure, tensile property and fracture toughness of 2397-T87 Al-Li alloy plate were investigated by optical microscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, tensile and plane-strain fracture toughness tests. The results show that a pronounced texture variation through the plate thickness is found. Near the surface, Goss texture is dominating. While in the center of the plate, typical β fiber texture and a scattering of cube texture are observed. And the subsurface layer exhibits a very weak texture. From the center to the subsurface, the fraction of β fiber texture and cube texture decreases; in contrast, the fraction of shear type texture reaches the maximum in subsurface layer. The tensile properties in different layers along the thickness direction are inhomogeneous. The strength near the surface is lower than that in the center. And the through-thickness strength properties variation in the rolling direction is more remarkable than that in the long transverse direction. In the same thickness layer, the fracture toughness and the strength are anisotropic. The strength in the rolling direction is higher than that in the long transverse direction and the short transverse direction, and the strength in the short transverse direction is the lowest. The fracture toughness in L-T orientation is the highest, followed by that in T-L orientation, and the fracture toughness in S-L orientation is the lowest.

Abstract:The corrosion behavior and mechanism of friction stir weld (FSW) joint of 2219 aluminum alloy was investigated by in-situ corrosion test, static mass loss test and immersion test. The results show that the corrosion rate of the weld is less than that of the parent material and the corrosion resistance of the weld improves greatly. The local pitting corrosion initially originates in dissolving of the adjacent matrix around the second phases and the second phase particles act as cathode. The intergranular corrosion happens in the weld nugget zone (WNZ) and thermo-mechanically affected zone (TMAZ) after in-situ corrosion test for 2 h and pitting corrosion occurs in base materials. The homogeneous second phase particles and fine equiaxed grains in the WNZ are the main reasons for the high resistance of exfoliation corrosion.

Abstract:The removal of typical impurity from tungsten using electron beam melting was studied. The feasibility of electron beam melting purification of tungsten was investigated. The impurity removal kinetics of electron beam melting was analyzed, and the removal rate control mechanism of Fe, Si and Ti at the power of 110, 130, and 250 kW was obtained. The results show that various impurities can be removed from the tungsten matrix by electron beam melting except Mo, and the removal efficiency and saturated vapor pressure difference are closely related. Kinetics analysis of removal of impurities and electron beam melting experiment indicate that Si, Fe and Ti is controlled by liquid-gas interface mass transfer with the mass transfer coefficient of 0.21, 0.56, 0.11×10-4m/s at 110 kW, and 0.83, 3.04, 1.78×10-4 m/s at 130 kW, whereas 0.36, 2.37, 1.48×10-4 m/s at 250 kW, respectively.

Abstract:The electronic structure, vibrational and dielectric properties of MoS2 were studied by first-principles based on density functional theory (DFT). The band structure, density of states, the dielectric function spectrum and the infrared reflectivity spectrum were presented. The results indicate that MoS2 is a semiconductor with indirect band gap. The dielectric tensors are highly anisotropic. It is found that lattice vibration makes less contribution to the dielectric constant than that of electronic screening. Due to the existence of Infrared active modes over the range of 300~500 cm-1, there is a strong interaction between the material and electromagnetic wave, impairing the wave-transparent properties of MoS2.

Abstract:To study the effect of S on the second phase particles (SPPs) of zirconium alloys, alloy samples were prepared by adding different contents of S (26~570 μg/g) into Zr-0.70Sn-0.35Nb-0.30Fe alloys. SEM and TEM with EDS were used to investigate the composition and crystalline structure of SPPs. The results show that in Zr-0.70Sn-0.35Nb-0.30Fe alloy, there exists Zr(Nb,Fe)2 SPPs with hexagonal close packed structure, while in the alloys containing S, orthogonal Zr3Fe SPPs appear besides Zr(Nb,Fe)2 SPPs and the Zr3Fe SPPs increase in amount with increasing S content. Zr9S2 SPPs occur when the S content reaches 190 μg/g, and also increase in amount with further increasing S content. The ratio of Nb/Fe decreases with the increase of SPPs’ size in the same zirconium alloy. It is indicated that the S content dissolving in α-Zr matrix is between 26 mg/g and 190 mg/g for the alloys in this study and the excess S dissolving in α-Zr matrix is precipitated as Zr9S2 SPPs rather than entering into other SPPs.

Abstract:The influence of thermo-mechanical treatment on microstructure and mechanical property of Ti-25Nb-2Mo-4Sn alloy was systematically investigated by X-ray diffraction, transmission electron microscopy and tensile test. Results show that the high-temperature β phase cannot be fully stabilized and a large amount of α" martensites forms after a solution treatment at 800 °C for 1 h followed by water quenching, which is caused by the low content of β-stabilizers (Nb and Mo) in Ti-25Nb-2Mo-4Sn alloy. In this case, the alloy exhibits low yield stress. It is also found that even under the same aging treatment of 400 °C for 2 h, the aging products for the solution treated specimen and the cold-rolled specimen are β + ω and β+α, respectively. Cold rolling deformation induces a mass of dislocations and grain boundaries could suppress the formation of ω and alternatively promote α phase precipitation. Upon a cold rolling and aging at 475 °C for 15 min, superior mechanical properties are achieved in Ti-25Nb-2Mo-4Sn alloy, with yield strength of 1033 MPa and tensile strength of 1113 MPa, combining with a low elastic modulus of 65 GPa.

Abstract:The stress and strain fields of AA7050 aluminum alloy billets during direct-chilling (DC) casting process from an aluminum production company were simulated by directly coupling thermal, fluid and stress fields for three different start-up casting speeds. The results show that the center of the billet is subjected to large tri-axial tensile stress whereas the periphery demonstrates obvious compressive stress. According to the relatively higher circumferential and radial stress and strain combined with lower axial stress and strain in the mushy zone, it can be predicted that hot tears tend to propagate along the axial direction while hot tears perpendicular to axial direction are not likely to occur. It is necessary to apply a lower casting speed at start-up phase in the casting process to decrease thermal stress and strain in the mushy zone in order to reduce cracking tendency.

Abstract:Mg nanoparticles were prepared by an inert gas condensation method using magnesium powder of 99.9% purity, and the effect of evaporating temperature and deposition location on the morphology and size of Mg nanoparticles were studied. Result shows that chain-like Mg nanoparticles with size of 10~50 nm are prepared in the front tip of the cold trap at the evaporation temperature of 600 oC. Some Mg nanowires are observed among the nanoparticles. Smaller size Mg nanoparticles are obtained at lower evaporation temperature in the front and back tips of the cold trap. According to collision and coagulation mechanism in the gas-solid phase transition theory, the formation process of Mg nanoparticles was explained and the corresponding model was established.

Abstract:High corrosion resistance Zn-Fe alloy coatings were electroplated onto NdFeB sintered magnet from a weak acid chloride solution. The influences of the main electroplating technological parameters on Fe content in the coating were investigated to optimize the process conditions. Meanwhile, the corrosion resistance and its mechanism were investigated by NSS, SEM and electrochemical tests. The result shows that the optimized Zn-Fe alloy (Fe content 0.92%) coated NdFeB can stand for 196 h against neutral 3.5wt% NaCl salt spray without any white rust. The function of the coating for NdFeB substrate is anodic protection. The coating with dense crystal can fill intrinsic defects of NdFeB substrate and provide favorable conditions for getting compact passivation film. The better corrosion resistance is attributed to the less surface defects and high electric resistance.

Abstract:An extrusion directly following vacuum pressure infiltration technique was used to fabricate 2D-Cf/Al composite. When the specific pressure is 60~90 MPa, vacuum level is maintained at 10~30 kPa, squeeze infiltration temperature is 580~620 oC and keeping pressure time is 60~120 s, 2D-Cf/Al composite with ideal infiltration quality could be fabricated. Through microstructure observation, it is shown that the aluminum alloy is filled uniformly, and defects could be seldom found in composite. The experiment results indicate that the density of the composite is 17.9% lower than that of the matrix. Ultimate tensile strength of composite is satisfied, which is improved by 100% compared with that of matrix alloy. Heat treatment tests reveal the ultimate tensile strength is improved by 41%, because the microstructure is improved and the internal stress and defects are controlled effectively after heat treatment. On the contrary, the adverse stress would appear in the composite because of the difference of thermal expansion coefficient between carbon fiber and matrix alloy in the process of heat treatment, so the mechanical properties of the composite is decreased by 16%.

Abstract:Micro-arc oxidation (MAO) process was conducted on ZrH1.8 in an electrolyte composed of Na5P3O10 under the constant voltage mode. The influence of frequency on thickness, phase structure, cross-section morphology and the hydrogen resistance performance of coatings were investigated. The surface and cross-sectional morphologies, phase structure of the coatings and film thickness were characterized by scanning election microscopy (SEM) and X-ray diffraction (XRD). Hydrogen resistance performance was evaluated by vacuum dehydrogenation. The results show that the thickness of coatings on ZrH1.8 decreases from about 50 mm to 45 μm with the increase of frequency. The increase of frequency can enhance the density of coating effectively. Besides, the change of frequency has no obvious influence on the coating phase structure, and the coating is mainly composed of M-ZrO2 and T-ZrO1.88, and the amount of M-ZrO2 accounts for more than 80%. The increase of frequency can improve the hydrogen resistance of the ceramic coating, and the PRF (permeation reduction factor) value reaches up to 10.8 when the frequency increases to 300 Hz.

Abstract:In order to improve the laser deposition repair quality of BT20 titanium alloy, an electromagnetic stirring device was introduced to assist laser deposition repair, and the effects of rotating magnetic field on the macromorphologies, microstructures and micro-hardness of the laser repair layer were studied by changing the magnetic field intensity and magnetic stirring speed. The results show that under the effect of the electromagnetic field, the surface is flat. Meanwhile, the lamellar α/β in laser repaired zone is mechanically broken, the length of intra-crystalline α layers is reduced, but the thickness of α lamellar is almost the same, 0.4~0.5 μm, so the grains are refined and the microhardness increases. As the field intensity and the stirring speed increase, the micro-hardness of repaired parts also increases, while the micro-hardness of the repaired zone tends to be homogenization with certain parameters.

Abstract:Pd thin film was deposited by radio frequency magnetron sputtering on the Zr70Fe5.4V24.6 (wt%) alloy substrate. The growth characteristics and microstructure of the Pd membrane were researched. The influence of Pd on the hydrogen absorption/desorption properties of Zr70Fe5.4V24.6 alloy was also investigated. The results indicate that the sputter deposited Pd film of fcc structure grows with the (111) preferred orientation. The results of hydrogen absorption/desorption properties test show that Pd film has no significant effect on activation properties of Zr70Fe5.4V24.6 alloy, as well as hydriding kinetics. The length of plateau area of P-C-T curves increases by about 90% after Pd membrane deposition; meanwhile, the reversible hydrogen storage capacity H/A increases from 0.63 to 1.20. After Pd film deposition, the absolute value of hydride formation enthalpy and the average value of formation entropy increase by 77% and 56%, respectively, indicating the formation of the more stable hydride.

Abstract:The effects of two fabrication methods, foil-fiber-foil (FFF) and matrix coated fiber (MCF), on the texture in the matrix of SiCf/Ti composites were investigated by electron back-scatter diffraction (EBSD). The results show that the texture is different between different zones in the matrix of SiCf/Ti-6Al-4V composite fabricated by FFF. However, there is some fiber texture in the matrix of SiCf/Super α2 composite fabricated by MCF, which is in accordance with the characteristic of anisotropy for composites. This will be beneficial to obtain the high performance composite.

Abstract:Mn-ferrite composite hollow microspheres were prepared by a self-reactive quenching method. The effect of Zn adding on morphology, phase structure and electromagnetic parameters of the hollow microspheres were analyzed. The results show that most of the prepared powders are spherical hollow microspheres, and the particle size is in the micron range. A small amount of agglomerated particles fail to spheroidize but form irregular particles because the self-propagating reaction is not complete. The Mn0.5Zn0.5Fe2O4 ferrite composite hollow microspheres are obtained by adding metal Zn powders, and the properties of microwave electromagnetic loss are improved. The microwave absorption peaks move to higher frequency.

Abstract:Microstructure and thermal expansion coefficient of LaFe11.2Si1.8 alloy in different annealing processes were investigated by X-ray diffraction, scanning electron microscope and thermo-dilatometer. The results show that the sample annealed at 1200 oC for 5 h contains a certain amount of α-Fe phase, while the samples annealed at 1050 oC for 15 d and at 1100 oC for 2 d form a single La(Fe,Si)13 phase with the NaZn13 structure. The magnitude of the negative thermal expansion is linear with the La(Fe,Si)13 phase content. Typically, the magnitude of the negative thermal expansion and thermal expansion coefficient of the samples annealed at 1050 oC for 15 d are 3.22×10-3 and –39.31×10-6 K-1, respectively.

Abstract:Ag coated Ni composite nanopowder was prepared by an electroless plating method. Conductive paste was prepared using the composite nanopowder as conductive phase. The phase structure, morphology, size distribution as well as electrical conductivity of the nanoparticles were studied using X-ray diffraction (XRD), transmission electron microscopy (TEM), and resistivity analysis. The results show that the composite nanoparticles possess a core-shell structure with nano Ni as the core and Ag as the shell. The size of the composite nanoparticles ranges from 20 nm to 100 nm. The thickness of Ag layer is about 4 nm. A thick film with resistivity of (1.26~2.83)×10-4 Ω·cm can be obtained by sintering Ag coated Ni composite nanopowder conductive paste at 200 oC for 60 min under 1.33 Pa, and the conductivity of the film is superior to that of the Ni nanopowder, Cu nanopowder and Ag-Cu nanopowder conductive paste.

Abstract:N-type Bi2Te2.7Se0.3 thermoelectric materials with Ga and K dual doping were synthesized by vacuum melting and hot pressing. XRD results indicate that Ga and K elements have been completely dissolved into the crystal structure of Bi2Te2.7Se0.3. The single-phase solid solution alloy has been formed. SEM results show that the bulk samples are compact with the laminated structure. Ga and K dual doping increases the Seebeck coefficient of Bi2Te2.7Se0.3 through Ga and K partial substitution of Bi in the most range of 300~500 K, while the electrical conductivity of the dual doped samples is improved. The thermal conductivity of the dual doped samples is higher than that of Bi2Te2.7Se0.3. The maximum ZT value reaches 1.05 at 500 K for Ga0.02Bi1.94K0.04Te3Se0.3 sample.

Abstract:The formation, morphology, size, distribution, growth and structure of Nd-rich rare earth (RE) phases in powder metallurgy (PM) high temperature titanium alloy were investigated. The results show that the RE-rich phases in as-rapidly-solidified high temperature titanium alloy powder precipitate in the process of powder droplet solidification, and the particle size is 50~250 nm in diameter. The majority of the particles are uniformly distributed in the alloy matrix. The particles are nearly spherical within the grains and ellipsoidal along the grain boundary. The major axes of the ellipsoidal particles are lying nearly parallel to the grain boundary. The calculated size and distribution of the second phase particles are in agreement with the TEM experimental results. The diameters of RE-rich phases are largely smaller than 50 nm precipitated from the supersaturated matrix after hot isostatic pressing (HIP) between 700 and 1000 oC in a short time. The size variation of the original RE-rich phases is minimal. However, the particle size including the original and the precipitated is 150~500 nm in diameter after HIP at 1200 oC for 3 h. The HRTEM image and SAED pattern of the RE-rich phases indicate that they are composed of many nanocrystallines while they are still composed of nanocrystallines whose size grows up minutely after HIP at high temperature. Maybe the later nanocrystalline is different from the former one because the tin-rich phases appear on the RE-rich phases “matrix”, resulting in the complex microstructure of the RE-rich phases.

Abstract:Laser surface treatment is an effective way to improve the hardness, and resistance to wear and corrosion. Laser surface treatment (laser surface alloying, laser cladding and laser surface melting) for titanium and titanium alloys have received more attention for it can expand their application. Combining with recent studies, this paper comprehensively overviewed the factors affecting two kinds of laser surface treatment methods, laser surface gas nitriding and laser surface powder alloying. The surface microstructure, performance, defect control after laser surface treatment and the optimization of laser parameters were also summarized. On this basis, current problems and future development were described.

Abstract:At present, the lithium-ion battery is mainly limited by safety, high-power performance and cost. These problems are expected to be solved by new high-performance anode material of lithium titanate oxides. Based on the recent research progress, several representative lithium-titanium-oxygen species lithium intercalation compounds such as Li4Ti5O12, LiTi2O4, Li2Ti3O7, and Li2Ti6O13 are selected. The important achievements of their crystal structures, electrochemical properties, preparation methods, chemical modifications and application researches are comprehensively elaborated. Finally, the direction of future research and development for such anode materials are pointed out.