Abstract:A series of Al-Ni reactive multilayer with different modulation periods were fabricated by DC magnetron sputtering process, and transient-liquid-phase (TLP) bonding of copper and Al2O3 ceramic was carried out by the multilayer foils. The microstructure of the as-deposited foils and the cermet joint were investigated. The reaction behaviors of Al/Ni multilayers were characterized by means of DSC and X-ray diffraction. The results show that the application of Al/Ni multilayer foils not only decreases the joining temperature of the copper and Al2O3 ceramic, but also improves the quality of the joint

Abstract:A novel high thermal conductivity joining between diamond heat sink and light emitting diode (LED) chip was investigated. AlNi nano/micro-multilayers were fabricated and used to test the bonding of copper and diamond by self-propagation. The thermal analysis results and micro structure observation show that the bilayer (one alternative sputtering period of aluminium and nickel layers) of the mulilayer will influence the heat release of propagation reaction, and hence help to control the bonding process with steady. The influence of the vanadium addition and the magneto-conductivity of nickel element on the structures of the multilyers were also discussed, which has relation with the bilayer either. The quality of the diamond-copper joint by nano-multilayer bonding is better than that of the silver glue bonding in shearing strength and thermal conductivity

Abstract:A novel method was presented to prepare Ag/SnO2 (12 wt% SnO2) electrical contact materials. First, Ag-SnO2 nano composite powder with 42 wt% SnO2 synthesized by a coprecipitation method was characterized. XRD results reveal that the synthesized composite powder is composed of cubic Ag and rutile type of SnO2. SEM and TEM images show that nano-Ag and nano-SnO2 particles are homogeneously dispersed in the composite powder. The preparation process of nano composite powder was analyzed with the help of the TG-DTA curves of the precipitation. Then, the obtained Ag-SnO2 nano composite powder was mixed with Ag powder to prepare Ag/SnO2 electrical contact materials (ECM) by powder metallurgy process and the prepared Ag/SnO2 electrical contact materials was characterized. The results demonstrate that owing to the higher dispersion of nano SnO2 particles in Ag matrix, the physical properties of ECM prepared by the new method, such as the density, hardness and conductivity are better than that by the traditional method

Abstract:First-principles calculations were performed to investigate electronic structure of orthorhombic SrHfO3 under pressure. The optimized lattice parameters of the orthorhombic SrHfO3 at zero pressure are in very good agreement with the available experimental and calculational values. The pressure dependence of band structure, density of states (DOS) and charge densities of orthorhombic SrHfO3 was obtained. When pressure is low (<20 GPa) the minimum indirect band gap of the orthorhombic SrHfO3 is Z-Γ while it is changed to be S-Γ when pressure is high (≥20 GPa). With the increase of pressure, the DOS of orthorhombic SrHfO3 shifts to the lower energy. Charge densities imply that bonding between Hf and O is mainly a covalent bonding and the bonding between Sr and O is mainly an ionic bonding. With the increasing of pressure, the covalent bonding (Hf-O) and the ionic bonding (Sr-O) are enhanced, whereas the ionic interactions (Sr-HfO3) are weakened

Abstract:Mg2Si0.487-2xSn0.5(GaSb)xSb0.013 (0.04 ≤ x ≤ 0.10) solid solutions were synthesized by a B2O3 flux method followed by hot pressing. X-ray power diffraction analysis confirms that single-phased samples are obtained. It is found that the Sb-doping effectively enhances the electrical conductivity. The Seebeck coefficients increase while the electrical conductivity decreases for Mg2Si0.487-2xSn0.5(GaSb)xSb0.013 with the increase of temperature. With increasing of GaSb content the electrical conductivity first increases and then decreases. Among all the samples, Mg2Si0.287Sn0.5(GaSb)0.1Sb0.013 sample has the lowest lattice thermal conductivity which is about 15% lower than that of Mg2Si0.5Sn0.5 [11] at room temperature. A maximum dimensionless figure of merit of 0.61 at 720 K has been obtained for Mg2Si0.327Sn0.5(GaSb)0.08Sb0.013 mainly due to its high electrical conductivity, which is obviously higher than that (0.019 at 540 K) of Mg2Si0.5Sn0.5 [11]

Abstract:The equipment of RH600 Hydrogen Analyzer (Fusion) was adopted to measure the hydrogen content of Nb47Ti alloy bars, with Φ50 mm×40 mm after different annealing processes in RX-460 electric furnace. Based on the analysis results, a dehydrogenation method was proposed. The results indicate that the main hydrogenation takes place at the annealing temperature of 1200 oC, while the hydrogenation can not occur in the subsequent annealing at 950, 930 and 900 oC. The hydrogenation phenomenon occurring in Nb47Ti alloy is mainly attributed to the joint effect of the high activity constituent elements and the rare hydrogen atmosphere. The 800 oC/3 h and 800 oC/6 h vacuum heat treatment can reduce the hydrogen content in Nb47Ti alloy effectively from 60 μg/g to 21 and 29 μg/g, respectively

Abstract:The microstructure and the shear strength of titanium explosive-rolled clad plate at different rolling temperatures and rolling reductions were analyzed. The shear strength was determined by tensile shear test, and the microstructure was observed by optical microscopy, X-ray diffraction, scanning electron microscope and transmission electron microscope. The results show that upon decreasing of starting rolled temperature and pre-heat temperature, the shear strength of the titanium explosive-rolled clad plate increases. During the pre-heat treatment process, the compounds including TiC and Ti-Fe intermetallics are formed at the interface due to diffusion of carbon and iron. These compounds are harmful to interfacial bonding strength. It is also revealed that the shear strength increases with the increasing of rolled reduction in thickness at any specific temperatures. Under the rolling pressure, the interface shape transforms from a wavy to straight, and the interfacial intermetallic compounds are broken. Big reduction leads to a higher fragmentation degree of the discontinuously distributed intermetallic compounds, which improves the shear strength of the composites.

Abstract:Many cultural relics adhered with gold leaf (e.g. gold foil) are found damaged seriously in recent years. In this paper, gold leaf was exposed in the imitating atmosphere of moisture SO2, NO2 and their mixture to investigate its corrosion possibility in environment atmosphere at ambient temperature. Following phenomena were observed. The gold leaf was corroded in all these three atmospheres, which is contrary to the common sense that gold can only be corroded in aqua regia at ambient temperature. In SO2 atmosphere, the main reason of the corrosion is the preferential oxidation of the impurity of Cu. In the atmospheres of NO2 and the mixture of SO2 and NO2, the main reason of the corrosion is the combination of the preferential oxidation of the impurity and the oxidation of gold itself caused by the high defect density stemmed from the severe cold deformation during its processing. The discovery that gold can be corroded in moisture acid atmosphere at ambient temperature expands the understanding of the character of gold, and provides beneficial guidance to the protection of culture relics and modern artworks decorated with gold foil

Abstract:A series of MgNi-ZrB composites were prepared from MgNi alloy and ZrB alloy by a mechanical alloying (MA) method. The influences of ZrB doping on the structures and the electrochemical properties of MgNi alloy were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), charge-discharge cycles, cyclic voltammetry (CV), Tafel polarization and electrochemical impedance spectroscopy (EIS). The results demonstrate that ZrB doping obviously improves the cycle life of MgNi alloy. The MgNi-ZrB (100:5) composite made from the doped powder ball milled for 15 h exhibits the best electrochemical performances. It shows high discharge capacities of 226 and 209 mAh·g-1 after 20 and 50 cycle, respectively, which are much higher than that of MgNi alloy. Potentiodynamic polarization and EIS tests show that ZrB doping improves the anticorrosion and the electrochemical kinetic properties of MgNi alloy significantly

Abstract:A three-dimensional finite element model (FEM) was developed by using ANSYS software to reveal the thermal-mechanical behaviors during the pulsed laser welding (PLW) for the fixture restraint in a Hastelloy C-276 butt-welded joint with 0.5 mm thickness. The welding temperature histories and residual distortions were measured to validate the FEM. Based on the FEM, the effects of the restraint distance on transient stresses and plastic strains, residual stresses and distortions were investigated by changing the fixture restraint conditions. The results show that the simulated temperature histories and residual distortions agree well with the experimental results; the restraint distance has a great influence on the magnitude of transient plastic strains, and then the distribution and the magnitude of residual stresses and distortions are changed. Except for the longitudinal residual tensile stresses, the peak values of the transverse residual tensile stresses and displacements and the magnitudes of the angular distortions decrease as the restraint distance decreases from 20 mm to 4 mm. A relatively smaller restraint distance can be used as a cost-effective method for mitigating the transverse residual tensile stresses and the angular distortions, but has an adverse influence on the longitudinal residual tensile stresses

Abstract:The welding process of transverse cross joints was simulated by temperature field and welding residual stress fields in AZ31B magnesium alloy. On the basis of Dang Van criterion, considering the effect of welding residual stress, the critical plane method was used to assess the fatigue properties of the transverse cross joints in AZ31B magnesium alloy, and then the results were compared with the conventional fatigue test. The results show that the parameters for steel recommended by the French Welding Institute and for aluminum alloy recommended by investigators in china are all not suitable for AZ31B magnesium alloy which need to be amended as α*=0.5, and β*=55 MPa. Furthermore, the Dang Van curve is fitted and the result is consistent with the fatigue test, and the modified Dang Van criterion could assess the transverse cross joints in AZ31B magnesium alloy reasonably. According to the stress concentration, the possible failure position of specimens could be prognosticated

Abstract:A finite element (FE) model for the extrusion process of large-scale thick-walled 304 stainless steel pipes was firstly developed based on DEFORM-2D platform, which can predict the DRX evolution behavior by coupling with a DRX model of 304 stainless steel. Secondly, the influence of the above key extrusion parameters on the average grain size and the grain uniformity of the extruded pipe were investigated by a liner orthogonal regression method. Finally, the influence laws of the key parameters on the average grain size and the grain uniformity were analyzed by a single factor method. The results show that extrusion speed V, initial billet temperature Tb and extrusion ratio λ have more obvious effects on the average grain size and the grain uniformity than other ones, and the influence sequences of these parameters to the average grain size and the grain uniformity are Tb>λ>V and Tb>V>λ, respectively. And the average grain size becomes smaller and the grain uniformity gets enhanced with the decrease of V and the increase of Tb and λ

Abstract:High-temperature TiAl pre-alloyed powder was produced by Plasma Rotating Electrode Process (PREP), and its characteristics were investigated. The results show that the as-prepared particle size mostly ranges from 46 μm to 150 μm, and its distribution is bimodal distribution. The freezing microstructure and phase of pre-alloyed powder are related to its granularity. The microstructure of powder with large particle size is usually dendritic structure, while that with small particle size shows smooth surface. The phase of as-prepared powder is mainly hexagonal α2 phase, but powder with particle size less than 46 μm contains some β phase, and powder with particle size larger than 200 μm has a small amount of γm phase. It is obvious that the powder with different phase and microstructure has an inherited effect on the densification microstructure formed by hot isostatic pressing. Powder with large particle size is prone to forming the coarsening lamellae structure and residual powder boundary in the densification microstructure.

Abstract:Based on the central composite experimental design method, the impact levels of uncertain parameters to failure assessment curve were qualitatively analyzed, such as material properties, defect dimension and operating pressure. With the sensitivity method, the impact levels of uncertain parameters to failure assessment curve were quantitatively analyzed. It is demonstrated that the qualitative results and quantitative results are consistent. Based on EPRI method, probabilistic failure assessment curves (PFAC) of commercially pure titanium TA2 were established with the probabilistic method, and non-probabilistic failure assessment curves (NPFAC) were established based on interval analysis method. Compared NPFAC with PFAC, it could be found that NPFAC for structural defect assessment is feasible and effective

Abstract:Anisotropy of mechanical properties and influencing factors of hot rolling TC4 alloy were studied through quasi-static tests, dynamic compression tests, XRD, metallographic study, and electron microscopy analysis. Results indicate that the quasi-static and dynamic compression properties of 930 oC hot rolling TC4 titanium alloy exhibit obvious anisotropy: the rolling direction shows the best ductility and lowest yielding strength, while the transverse direction shows the highest yielding strength and worse ductility. The ductility and strength of the normal direction are both between the rolling direction and the transverse direction. Microstructure analysis results show that there are four factors which are responsible for the anisotropy of the mechanical properties. Firstly, after the hot rolling process, a weak plane texture was formed; secondly, the original grains were deformed into fibrous structure; thirdly the plate-like α clusters' normal axis tended to be parallel to the transverse direction of the rolling sheet; finally, a large amount of dislocations which are distributed in the grain were being parallel to the transverse direction according to the TEM results. The anisotropy of the mechanical properties is attributed to the above four factors

Abstract:Creep tests were carried out on Ti-600 alloy at the temperature of 550, 600 and 650 oC, and with the stresses of 250, 300 and 350 MPa. Steady state creep rate, stress exponent n, activation energy Q at different temperatures and various stresses were calculated for the alloy. Threshold stress σ0 was introduced to get the true stress exponent p. Creep deformation mechanism was also investigated. The results indicate that the steady state creep rate will increase with the rise of temperature and stress, and the creep time will be shortened at the same time. The nominal creep activation energy for the alloy is 473.5 kJ/mol. At 600 and 650 oC, the threshold stress is 103.1 and 42.1 MPa, respectively; n is 6.5 and 4.9, respectively; p is 4.23 and 4.22, respectively. Constitutive equations of steady state creep rate for the alloy were established both at 600 and at 650 oC. The main creep deformation mechanism for the alloy is dislocation climbing

Abstract:The typical defects resulting in the broken wire during the preparation of NbTi superconducting alloy wires was described. The formation mechanism of forging streamline, the Ti-riched segregation resulted from solute redistribution and the mechanism of streamline and black spots were analyzed. The results indicate that the Ti-riched segregation of NbTi alloy could be described by black spots and tree ring in X-ray photograph and the essence of this segregation is channel segregation. It is aimed to provide a method to optimize the preparation technology, which can eliminate the Ti-rich segregation and improve the constituent and microstructure homogeneity of NbTi superconducting alloy.

Abstract:Laws for temperature fields and cooling rate during laser welding have been studied by numerical simulations, in order to explore the mechanism of successful laser welding of the Ti40Zr25Ni3Cu12Be20 bulk metallic glass (BMG). Taking the effect of convection and radiation on heat transfer into account, the thermophysical properties were detected as a function of temperature. Heat source model with the cylinder and Gaussian was selected. Based on the model, the temperature fields of the Ti-based BMG at different welding parameters were calculated. Combined with the results of experiment and simulation, the microstructures from welded zone and heat affected zone have been analyzed. The mechanism of successful laser welding of Ti40Zr25Ni3Cu12Be20 BMG has been discussed from heating process and cooling process. The results obtained from the microhardness tests of completely amorphous joint indicate that the heat affected zone (HAZ) has higher hardness than those of the parent metal and weld zone (WZ). The phenomenon was studied theoretically from the relationship of glass transition temperature, cooling rate and yield strength. The experiment was also done to validate the accuracy of the analysis

Abstract:A plasma surface metallurgy technique was used on the surfaces of carbon steel to form W-Mo alloying layer and W-Mo-Y alloying layer. Dynamic behavior of W, Mo and Dy was investigated by origin software, Fick’s second law and Arrhenius formula. Results show that Dy addition increases the diffusion coefficient of W and Mo by 0.94 times and 0.62 times, respectively in the diffusion layer from surface of 0~5 μm while increases the diffusion rate of W and Mo by 2.87 times and 1.07 times, respectively in the diffusion layer from surface of 80 μm. However, the Dy addition decreases the activation energy of diffusion of W by 7.13 kJ/mol and Mo by 5.19 kJ/mol from surface of 5 μm, while it decreases the activation energy of diffusion of W by 32.20 and Mo by 10.18 kJ/mol from surface of 90 μm. Under the same process condition, the main influence factor of diffusion in W-Mo-Dy co-diffusion layer is vacancy concentration. Dy decreases activation energy of diffusion of W and Mo in the subsurface

Abstract:The effects of grain boundary carbide on crack propagation behavior of GH864 alloy were studied at 650 oC after different heat-treatment. The results indicate that the pattern of grain boundary carbide of GH864 alloy is gradually evolved after different heat-treatment, i.e. little particle→discontinued→continued→necklace→closed. The precipitation of grain boundary carbide strengthens the grain boundary and decreases the crack growth rate. The change tendency was concluded between the grain boundary carbide continuous factor and the crack growth rate. When the grain boundary carbide continuous factor is below 1, the crack propagation resistance increases with increasing the size of grain boundary carbide and grain size. The comprehensive interaction effect between the grain size and grain boundary carbide was also concluded. The optimum crack propagation resistance may exist when there is the lowest point in the interaction effect between the grain size and grain boundary carbide

Abstract:The three-dimensional elastic-plastic stress fields around the notch have been analyzed by a crystallographic finite element program, which takes the effects of lattice rotation and finite deformation into consideration. The primary orientation is fixed along the [001] direction while the notch directions are parallel to [010] and []. The special attention is paid on the activating characteristic of slip systems. The numerical results show that the randomness orientations have important consequences on the activation of slip systems and the maximal resolved stress for the notch. The extreme of the maximum resolved stress appears around β=45o. The maximum resolved stress has an obvious fluctuation along the thickness direction, which is nearly constant in the midsection and tends to decrease sharply near the free surface. We can conclude that the slip (crack) is likely initiated at the midplane first. In the experiment, these regions correspond to the smooth region and the shear lip on the fracture face

Abstract:The biomedical porous NiTi alloy was prepared by atmosphere sintering process, and the effects of NH4HCO3 contents on the microstructure, bending strength, elastic modulus and corrosion resistance of the biomedical porous NiTi alloy were investigated. The results show that with increasing the NH4HCO3 content, the porosity and pore size of the porous NiTi alloy increase, while the bending strength, elastic modulus and corrosion resistance all decrease. The porosity of the porous NiTi alloy is about 36%~62%, the pore size 50~300 μm, the bending strength about 22~220 MPa and the elastic modulus about 0.7~6 GPa. All of these parameters are very close to that of human bones, indicating that these porous NiTi alloys could be used as the candidate of human hard tissue replacement materials

Abstract:The effect of the quenching-tempering process on the columnar structure in Ti-46Al-xB alloys was investigated. It is found that the columnar structures of Ti-46Al-xB alloys are evidently refined by the quenching-tempering process. The reason is that the increase of the temperature gradient and the solid state phase transformation during cooling process lead to atomic mismatch in grain boundary or phase interface, and then a large number of dislocations are formed, which can pin the grain boundary. The experimental results show that finer columnar structure of TiAl-based alloys can be obtained by addition of alloying element B and the heat treatment process. Besides, the addition of B element can impede the extension of dislocations, promoting the effect of anchoring of dislocation, and then the columnar structures are further refined in TiAl-based alloys

Abstract:Porous titanium with two different topology structures was designed and fabricated by a titanium mesh-stacking-sintering method. The microstructure and mechanical properties of the porous titanium specimens were investigated by scanning electron microscope (SEM) and electrical universal testing machine, respectively. The Young’s modulus and yield stress (σ0.2) were calculated from the stress-strain curves. The results show that the square pore distribution such as the staggered pore in the regular pore model can reduce the elastic modulus and yield stress as much as 74% and 10% at the same porosity, respectively. On the basic analysis from the analytical model, it is suggested that the bending and stress concentration are the main reasons of the elastic modulus and yield stress reduction

Abstract:The porosity in the welded seam can be generated easily during the YAG laser nonpenetration welding of zircaloy sheet, which affects the quality of welding. This research used Zr-4 and N18 as the objects for the welding experiment. The method of cutting cross-section of weld seam was used to analyze the porosity number and observe the morphology and location of porosity in the weld. The effects of process parameters including laser pulse current, pulse width, defocusing distance and laser pulse modulation on porosity generating were discussed. The results show that the generating of porosity is due to the unstable collapse of the keyhole in the process of YAG laser nonpenetration welding of zircaloy. The porosity would be formed when the speed of bubble escaping from the weld pool is lower than that of melting metal solidifying. Under the condition of 1.0 mm penetration welding, the results also show that with the increase of laser pulse current and pulse width, the porosity number presents a gradual increase. With the increase of defocusing distance, the porosity number shows a gradual decrease. Compared with non-segmented programming model, this research uses such measures as segmented programming, slowing down the current and reducing welding speed to obtain the relatively lower porosity number, and the pore size can be controlled below 0.5 mm effectively

Abstract:A kind composite of MgH2-In was prepared by ball milling the powder mixtures of MgH2 and In on a planetary mill. XRD was used to analyze the phases and phase transition during hydriding/dehydriding process of the composite. The dehydriding properties and phase transition temperature of the composite were investigated by DSC and GC (Gas Chromatograph). The thermodynamic and kinetic properties of hydrogenation/dehydrogenation of the composite were measured by the automatic gas adsorption instrument based on Sievert principle. The results indicate that the enthalpy and activation energy of hydrogen desorption of MgH2 are significantly reduced due to the formation of Mg3In and Mg(In) solid solution during the dehydriding process. Thus the dehydriding temperature of MgH2 is decreased, and the kinetics is greatly improved

Abstract:Al2O3-ZrO2(Y2O3) eutectic ceramics were produced by a laser engineered net shaping system. We preliminarily explored the law of forming morphology, internal cracks and pores of the ceramics with the change of laser power. X-ray diffractometer analysis and scanning electron microscopy observation were carried out for the sample phase composition and microstructure, respectively. The research indicates that higher laser power can get less internal cracks and pores of ceramic samples. The microstructure shows a well-ordered cellular eutectic structure made up by a homogeneous distribution of very fine submicron levels t-ZrO2(Y2O3) fibers embedded in the cellular. Periodic banded structure appears in the vertical direction of deposition due to the characteristics of layer by layer accumulation by laser engineered net shaping processing

Abstract:6013 type aluminum alloy produced by cyclic channel die compression (CCDC) process was investigated to explore whether the fine grain and elimination of anisotropy can be obtained. Microstructures and properties of 6013 type aluminum alloy were tested by optical microscopy (OM), transmission electron microscopy (TEM) and hardness tester. The results indicate that CCDC process can effectively refine the grains and eliminate the anisotropy. Different-orientation, staggered belts are observed, which is conducive to refining the microstructure when the alloy is subjected to CCDC process. Recrystallization, equiaxed grains, and homogeneous distribution are gotten when the alloy is annealed at 480 oC for 2 h. The grains are significantly refined and the microstructural anisotropy is reduced compared with the alloy without CCDC. The strength of the alloy decreases first and then increases with increasing the passes of CCDC. The hardness (HV) of the alloy is 1418.5 MPa and 1503.5 MPa compressed by 3 passes and 12 passes, respectively, when the alloy was treated by T6 solution-aging (560 oC /2 h+191 oC /4 h). It is shown that the fine grain and elimination of anisotropy can be obtained and the strength would be increased after multi-passes CCDC

Abstract:The microstructure evolution and mechanical properties of indirect-extruded Mg-8Sn-1Al-1Zn have been investigated by OM, SEM, XRD, EBSD, TEM and a stand universal testing machine. The results indicate that the high strength Mg-8Sn-1Al-1Zn alloy with ultrafine grained structure can be successfully fabricated by indirect extrusion at 250 oC. During the extrusion process, most of the coarse grains were changed into fine equiaxed grains with average sizes of 1.92 μm. In addition, some nano-sized particles were observed by TEM in the alloy. The extruded alloy reveals a type of fiber texture in which basal poles are preferentially perpendicular to the ED. The formation of the ultra-fine grained structure was ascribed to the dynamic recrystallization and second phase. The tensile yield strength and compressive yield strength of the extruded alloys are 285 and 260 MPa, respectively. The R value of the alloy equals to 0.91. The superior strength and low yield asymmetry are mainly related to the fine-grained structure and dispersive fine second phase particles

Abstract:Quasi-static tensile properties, deformation and fracture behaviors of both quenched and aged U-5.7%Nb alloys in a temperature range from room temperature to 800 oC were investigated. The results show that the second yield phenomenon of both quenched and aged U-5.7%Nb alloys occurring at room temperature disappeared at a temperature higher than 200 oC, and the embrittlement behaviors of two alloys appeared at 400 oC. Meanwhile, the superplasticity has been observed in two alloys at the temperature higher than 700 oC, and the superplasticity of the quenched alloys was more evident than that of the aged alloys. The microstructures of the aged U-5.7%Nb deformed at quasi-static tension, Hopkinson tension and expansion loadings have been analyzed. The results indicate that the dimples at the center zone of the specimens were more obvious than that at the rim zone in aged U-5.7%Nb alloys fractured at different strain rates. And the grains at the fracture of Hopkinson tension were larger than that of the quasi-static loading. Shear fracture, rim cracking and inclusion falling off were observed in the fracture of the alloys deformed at expansion loading

Abstract:Dynamic deformation and failure behavior of U-Nb alloy with different heat treatment (200 oC/2 h, 400 oC /2 h, 600 oC /2 h) were studied. Hat-shape specimens were used in an attempt to induce strain localization in U-Nb alloy. Dynamic load was applied to specimens by use of a Split Hopkinson Press Bar (SHPB) apparatus. The microstructure was examined by optical microscopy and scanning electron microscopy. Results show that the appearance of adiabatic shear bands (ASBs) is relative to the microstructure of material. Different kinds of ASBs are found in 200 oC/2 h and 600 oC/2 h specimens, while specimens (400 oC/2 h) exhibit dimple-like feature, indicating that significant melting takes place during deformation under high strain rate loading condition

Abstract:To control the surface quality of gold films electrodeposited on tungsten helix, the effects of current density, electrolytic temperature and deposition time on the electrodeposits were studied. The morphology of gold films was evaluated by means of scanning electron microscope (SEM). The results indicate that current density affects the grain size of the film. When electrodepositing at higher current density, the surface defects such as burring and sponge feature the gold film. The electrolytic temperature causes poorer stability of electrolytic solution and deposition quality. In addition, the variation of deposition time results in different electrodeposits quality. With increasing the deposition time, the edge effect is serious. The proper deposition time is about 1.5 h

Abstract:The synthesis conditions of pure phase LiFePO4 target have been studied. The synthesis process was analyzed by TG-DTA, the crystal phase was examined by XRD and the surface morphology was observed by SEM. The results indicate that the pure phase of LiFePO4 sample is obtained in solution route by calcining at 1073 K under Ar (93%) and H2 (7%) mixture gas flow, and then it is made as the target with high crystallinity and large grains. LiFePO4 film can be prepared by pulsed laser deposition. The film shows a dense structure, and the grain size is achieved at the nanometer level

Abstract:Pure nano-crystalline Co powders of nearly spherical shape have been produced using a high-energy ball mill. This method has used the mechanical force to crush solid reactant, which increased the BET specific surface area and reaction speed of reactant, and accelerated the nucleation rate. The method includes three steps. Firstly, a precursor of CoC2O4 was prepared by the mechano-chemical solid state reaction with H2C2O4·2H2O and Co(NO3)2·6H2O at ambient temperature. Secondly, the precursor CoH2C2O4 powders were dispersed by spray-drying to get the spherical precursor. Finally, Co powders were obtained by decomposition of the precursor CoH2C2O4 for about 3~3.5 h at 450~500 oC. The powders were characterized by X-ray diffractometer and scanning electron microscopy. The results show that spherical, cubic structure, 100 nm β-Co powders were synthesized

Abstract:The present review gave an overview of applications of ceria in low temperature fuel cells. The promotion effects of ceria in electrocatalysts, possible mechanism, and the impact factors were summarized. In the end the prospects of the application of ceria in low temperature fuel cells were described.