Abstract:Numerical simulation and experiment studies have been conducted to investigate the effect of inclusions separation under combined magnetic field (CMF) generated by synchronous application of a rotating magnetic field (RMF) and a downward traveling magnetic field (TMF). The experimental setup is constituted by two sets of equidistant coils systems fed by out-of-phase alternating currents. The electromagnetic force field and flow field were calculated via finite-element analysis. CMF combines the rotational effect of RMF and the transport effect of TMF. Volume fraction and particle trajectories were simulated to examine the mechanism of particle separating. Good agreement between experimental and numerical results has been achieved. The flow field and the Archimedes electromagnetic force are the two main factors responsible for particle motion. This type of CMF provides a highly efficient approach at eliminating inclusions.

Abstract:High-purity ZrWMoO8 powder was prepared by a precursor decomposition method. To prepare ZrWMoO8/Cu composite, the blended powder of Cu and ZrWMoO8 as well as the copper-coated ZrWMoO8 powder with m(ZrWMoO8):m(Cu)=1:1 were obtained by ball-milling and chemical plating method, respectively. And then the two sorts of the powders were pressed into green specimens which were sintered in argon atmosphere at 500 °C for 3 h to get ZrWMoO8/Cu composites. The thermal expansion properties of the composites were studied, and it is found that the coated-powder is much more suitable for the preparation of ZrWMoO8/Cu material. Results show that after sintering, a part of the ZrWMoO8 is decomposed and reacted with copper in the composite obtained by the blended-powder. While the decomposition of ZrWMoO8 is not detected in the composite obtained with copper-coated ZrWMoO8 powder as raw materials and the composite displays an average thermal expansion coefficient of 3.3774×10-6 °C-1 between 25~250 °C and the relative density is as high as 90.6%.

Abstract:The effects of neodymium (Nd) and ytterbium (Yb) on the microstructures and tensile properties of Mg-5.5Zn-0.6Zr alloy were investigated. Results show that an addition of Nd or Yb both brings about the precipitation of a new γ (Mg, Nd) Zn2 or γ (Mg, Yb) Zn2 eutectic phase and results in a refinement in dendritics. However, the combination addition of Nd and Yb has an opposite effect on dendritics and leads to the formation of γ (Mg, Nd+Yb) Zn2 eutectic phases in the shape of network-like, even the lamellar eutectics are somehow thickened. After T4 solution treatment, the eutectic structure in Mg-5.5Zn-0.6Zr alloy is fully dissolved into the matrix while there are still some undissolved compounds at grain boundaries in Mg-5.5Zn-0.6Zr alloy with Nd and Yb addition. A new ternary phase Mg-Zn-Yb appears in Mg-5.5Zn-0.6Zr alloy containing Yb, which is formed at dendrite boundaries after solution treatment. The tensile test results indicate that the tensile strength, yield strength and the elongation are about 255.6 MPa, 163.6 MPa and 17.4%, respectively, at room temperature. This is mainly attributed to combined strengthening factors induced by Yb addition. At the elevated temperature, the Mg-5.5Zn-0.6Zr alloy with addition combination of Nd and Yb has a good performance in thermal stability, but inferiority in elongation.

Abstract:Superlight alloys, including Mg-7Li-3Zn, Mg-7Li-3Al and Mg-7Li-1.5Al-1.5Zn, were prepared using a resistance furnace under the protection of argon atmosphere. The microstructures and phases of the alloys were studied by optical microscopy, scanning electronic microscopy (SEM), X-ray diffraction (XRD). The mechanical properties of these alloys were measured by a tensile tester. The results show that the Zn and Al added in Mg-Li alloy mainly dissolve in α-Mg phase and β-Li phase. However, there still exists a part of the Al and Mg compound such as Mg17Al12 which is mainly distributed discontinuously at α phase boundary while the most of them in the β phase are granular. The as-extruded Mg-7Li-3Al alloy has the maximum tensile strength and yield strength of 239 MPa (34% higher than the as-cast) and 178 MPa (31% higher than the as-cast), respectively, and the maximum elongation reaches to 27% (93% higher than the as-cast).

Abstract:SiC particles reinforced Mg base composites were extruded at different temperatures and extrusion ratios. The effects of particles on dynamic recrystallization (DRX) of Mg matrix during hot extrusion were investigated. The results reveal that particle deformation zone (PDZ) is formed near a particle during hot deformation, and the PDZ is a characteristic of fine DRX grains in the composites extruded at lower temperatures. Particles promote DRX nucleation of Mg matrix during hot extrusion which may be attributed to high density dislocations and large orientation gradients in PDZ. Particles promote the growth of fine DRX grains until PDZ is consumed by DRX grains. On the contrary, at the stage when DRX grain boundaries contact with particles, particles pin grain boundaries and then retard grain growth.

Abstract:The cathode material LiNi0.5Mn0.5-xCrxO2 (x=0, 0.01, 0.02, 0.05, 0.1) was synthesized via a low temperature combustion process. The influence of the partial substitution of Cr for Mn on its electrochemical performance was investigated. Charge/discharge test results show that the partial substitution of Cr for Mn has a significant influence on the electrochemical performance of LiNi0.5Mn0.5-xCrxO2, and the proper amount substitution of Cr for Mn (x=0.02) can increase its discharge capacity and improve its cyclic stability. The X-ray diffraction (XRD) and Cycle Voltammetry (CV) analyses indicate that the proper amount substitution of Cr for Mn can suppress the cation mixing in the cathode material, reduce the electrochemical polarization of the electrode material and improve its reversibility. The discharge capacity of LiNi0.5Mn0.48Cr0.02O2 at 0.1 C between 2.5 and 4.6 V is 179.9 and 171.0 mAh/g in the 1st and the 50th cycle, respectively, with a capacity retention of 95.1%.

Abstract:The effects of the solution and aging treatment on the microstructure, the tensile properties at room-temperature and 650 oC and the stress rupture of GH4169 superalloy were investigated. The results show that after solution at 980 oC and aging at 720 oC plus 620 oC, both the yield strength and ultimate strength of the superalloy at room-temperature and 650 oC are highest; after solution at 960 oC and aging at 720 oC plus 620 oC, the stress rupture life of the superalloy tested at 650 oC and 725 MPa is the longest; the solution treatment can adjust the amount of d phase, primary strengthening g" phase precipitates upon aging at 720 oC, while assistant strengthening g ' phase precipitates at 620 oC.

Abstract:AgSnO2 is a most potential substitute contact material for AgCdO. In practice, however, it has some congenital defects. This paper, is to focus whether wetting ability of AgSnO2 contact material can be improved and its defects can be decreased when rare earth elements are added. Young’s equation has proved that the smaller the wetting angle is, the better the material wetting ability. So, rare earth elements La and Ce were selected as additives in the present experiment. And three Ag-based contact materials were prepared with different ratios of SnO2 to La or Ce. Then, wetting angles of the contact material were measured by the sessile drop method. They were compared with the wetting angle of the AgSnO2 contact material. The measurement results show that La can improve the wetting ability of AgSnO2 contact material obviously. For further proving this conclusion, the simulation arc tests for AgSnO2 and AgSnO2La2O3 contact materials were carried on. And their microstructures were analyzed. The results prove that AgSnO2La2O3 contact material has better wetting ability than AgSnO2.

Abstract:β grain growth kinetics of TC4-DT titanium alloy under two different prior processing conditions (deformed vs. undeformed) was investigated during isothermal heat treatments. Deformation was carried out in α+β two-phase field with deformation degree of 60% and air cooling. Heat treatment scheme with the temperatures above β transus temperature 10, 20, 30 °C and soaking time of 2, 5, 10, 30, 60, 120 min was used. The grain size parameters have been obtained by means of the image analysis software. Growth time exponent (n) and activation energy (Q) have been established for both conditions. For the undeformed samples, n varied in the range of 0.34~0.35 and Q in the range of 86.8~130 kJ·mol-1, while after deformation, the values of n and Q changed in the domain of 0.36~0.39 and 76.6~110 kJ·mol-1, respectively. Results show that the samples subjected to deformation exhibit higher growth time exponent and lower activation energy compared to the samples without deformation under the same heat treatment conditions. The variations of the growth time exponent with temperature and the activation energy with soaking time are ascribed to the interaction between diffusion of solute atoms and migration of grain boundaries both of which can be promoted by deformation. The influences of heating temperature, time and deformation on the uniformity of grain size were also studied and the intrinsic mechanism is attributed to the combined effect of β phase nucleation rate and β phase growth velocity under the above factors.

Abstract:The interrupted oxidation behavior of B, W and Y micro-alloyed TiAl-based alloys with high Nb content at 900 oC in static air was investigated. The results show that the combined addition of 0.2wt%B and 0.1wt%Y improves the oxidation resistance obviously with less oxidation weighting and enhanced adherence of the oxide scale, while the combined addition of 0.2wt%W and 0.1wt%Y leads to poor oxidation resistance with higher oxidation weighting and impairing adherence of the oxide scale. Besides, the oxidation resistance of the alloy with combined addition of 0.2wt%B, 0.2wt%W and 0.1wt%Y does not change significantly. Oxidized samples were examined by scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and X-ray diffraction analysis (XRD). It is found that the combined addition B and Y can promote the formation of continuous and compact Al2O3 oxide scale. The combined addition W and Y produces continuous Al2O3 layer near to the matrix and thick TiO2 layer with low Nb content in the mixed layer. Combined addition W, B and Y promotes the formation of Al2O3 oxide scale in the mixed layer.

Abstract:To investigate the hydrogen absorption properties of Zr-Nb alloys, the PCT (pressure-composition-temperature) measurements for Zr-Nb alloys with different Nb contents (1wt%~30wt%) were carried out under low pressure in the temperature range of 700~900 oC. The results indicate that the temperature affects significantly the two-phase equilibrium of β-Zr and δ zirconium hydride. β-Zr shows more stable characters than δ zirconium hydride in the system under the high temperature condition. Nb decreases the binding stability between the system and H, and the equilibrium hydrogen content of the zirconium alloy decreases apparently with the Nb content increasing. The main reason for the decreasing of hydrogen absorption is that δ NbH2 with high hydrogen content cannot exist under the condition of low pressure.

Abstract:The phase transitions of the Al-B system were systematically explored by means of DSC and traditional solid-state reaction. Phase and microstructures were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM), respectively. The results show that the sintering temperature plays a decisive part in the decomposition of AlB2. At the same time, holding time also has an important influence on the decomposition of AlB2. AlB2 can decompose completely at 1050 oC for 3 h using the vacuum sintering method. The formation reaction of AlB12 is a complete reaction. The reaction between Al and AlB12 can’t take place regardless of stoichiometric Al/B heated in the range of 900 to 1150 oC for 3 h.

Abstract:Nano-sized TiO2 prepared by a sol-gel method was used as photoelectrocatalyst and characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) and Brunaue-Emmett-Teller (BET). Electric field assisted photocatalytic properties of TiO2 were characterized by the degradation of methylene blue. Results show that TiO2 possesses small particle size and high effective degradation rate on the degradation of methylene blue. But the photo-degradation performance of TiO2 decreases with the synergy of electric field. It should be resulted from the loss of photocarrier that are neutralized with the positive and negative charge of the electric field before forming over oxidation groups. It could be deduced that the electric field inhibits the photocatalytic performance of TiO2 catalyst. It is also found that the degradation of methylene blue are in accordance with the Langmuir-Chinshelwood function mode.

Abstract:Isothermal compression tests of Ti555211 titanium alloy has been conducted on a Gleebe-3800 hot-simulator at the strain rate ranging from 0.001 to 1 s-1 and the deformation temperature ranging from 750 to 950 oC. A constitutive model using dislocation density rate as an internal state variable has been proposed for hot working of Ti555211 titanium alloy. According to the isothermal compression test curves, the influence of deformation temperature and stain rate on stress has been investigated. The results show that the correlation coefficient (R) and the average absolute relative error (AARE) for the constitutive model using dislocation density rate as an internal state variable are found to be 0.94277 and 15.25%, respectively, which provide a guide for process optimization and control of near β deformation of Ti555211 titanium alloy.

Abstract:Solution treated Ti-2.5Cu alloy was aged under a compressive stress of ~200 MPa. TEM investigations show that three variants of precipitated Ti2Cu plates are observed in conventionally aged samples without compressive stress. However, in the stress-aged samples, for most grains, one or two variants of Ti2Cu plates could be observed, which indicate the variant selection effect of precipitated Ti2Cu plates resulting from external compressive elastic stress. Lower yield strength and higher elongation is observed during subsequent tensile tests due to the variant selection effect.

Abstract:With adding various contents of combined grain growth inhibitors (GGI) VC and Cr3C2 into the ultrafine WC-Co composite powder, the effects of the GGI addition on the phase constitution, microstructure and mechanical properties of the cemented carbides have been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), respectively. The result shows that with the content of GGI increasing in the composite powder, the abnormal grain growth disappears and homogeneous ultrafine grain structure forms. The hardness of cemented carbides can be improved effectively with increasing the addition of VC, while enhancements of the transverse rupture strength (TRS) depends more on the Cr3C2 addition.

Abstract:The influence of sampling orientation, stress ratio and microstructures on the fatigue crack propagation behavior of 2050 aluminum alloy was investigated. The results show that the effects of sampling orientation and stress ratio on the crack propagation rates are quite significant in the near-threshold region and the stable-tearing crack growth region, while their effects are relatively small in the stable growth region. The fatigue crack growth rate in L-T orientation is the lowest, followed by the rate in T-L orientation, and the rate in S-L orientation is the largest. The effect of sampling orientation on the fatigue crack growth rate mainly depends on grain orientation, texture orientation and the orientation of second phase particle. The fatigue crack growth rate of stress ratio 0.5 is bigger than that of stress ratio 0.1, which are mainly related to the crack closure effect in the near-threshold region and remarkably influenced by the maximum stress intensity factor Kmax in the stable-tearing crack growth region.

Abstract:Melt-spun amorphous Fe73.5Cu1Nb3Si13.5B9 (FINEMET, at%) ribbons were ball-milled to obtain powder. The powder was sieved and then passivated in 0.2~1.0% phosphoric acid solution to form a well-coated passivator layer, followed by cold compaction under the pressure of 1.64~1.96 GPa to prepare toroidal magnetic cores. The powder cores were annealed at 400~600 oC to relieve the internal stress and to optimize the crystalline grain size. After annealed at 500 oC for 1 h, α-Fe(Si) crystallites with an average grain size of 14.3 nm were embedded in the amorphous matrix. Combined with the insulation of each powder and the two-phase structure, the powder core exhibits excellent magnetic properties.

Abstract:VO2 films with different thicknesses were deposited on SiO2 substrate by an inorganic sol-gel method. The variation of stoichiometry, crystalline structure and surface morphology of the films with thicknesses were analyzed by X-ray photoelectron spectroscopy, X-ray diffraction and scanning electron microscopy, respectively. Furthermore, the effects of the composition and microstructure on the phase transition property of the films were studied in the mid-infrared range. The results indicate that all the films exhibit a (110) preferred orientation; the crystallinity is enhanced, and the grain size is improved with broader distribution in the thicker films. Accordingly, the thicker films show reduced transmission before and after the phase transition, narrower hysteresis loop and larger transition slope.

Abstract:Ag-9.5Sn (wt/%) and Ag-7.6Sn-0.87In (wt/%) alloy powders were synthesized by atomization. Oxidation kinetics curves of Ag-Sn-In alloy powder, Ag-Sn alloy powder, pure Sn powder and pure Indium powder were obtained by thermo gravimetric analyzer (TGA). The particle size, surface morphology and surface composition of Ag-Sn-In alloy powders before and after oxidation were investigated. The results show that rapid oxidation mass gain process of Ag-Sn-In alloy powders is divided into two periods, and the former is faster than the latter. Minor In addition could promote rapid oxidation mass gain of the first period. Uniform dense oxide film is formed after In and Sn being oxidized, which hinders the second period of rapid oxidation mass gain process.

Abstract:The intermediate frequency electromagnetic oscillation technique was used to obtain the ideal semi-solid metal slurry and billet of the aluminum alloy ZL104. In this research, the proper number of oscillation was mainly discussed when using the intermediate frequency electromagnetic oscillation technique to produce semi-solid slurry. The influence of the electromagnetic fields generated by electromagnetic stirrer on the microstructure of the semi-solid slurry and billet was also analyzed. The results indicate that the method is easy to operate with short process and low-cost equipment. The semi-solid materials obtained from this method are uniform and do not show a skin-effect caused by the electromagnetic field distribution unevenness. Minimum average equivalent diameter of primary α-Al is 28 μm, and the shape factor of primary α-Al is 0.89.

Abstract:TiO2 doped SnO2 nano powder used for Cu matrix electrical contact materials was prepared by a sol-gel method. The transformation process of the doped SnO2 precursor during heating was analyzed by TG-DSC technique. Then, phase analysis and particle size calculation of the doped SnO2 powders calcined at different temperatures were carried out by XRD, and the microscopic morphology of the doped SnO2 powder was observed by TEM. Finally, the doping result of SnO2 powder was evaluated by analyzing the change of the lattice parameter d value. The results show that nanometer SnO2 can be successfully doped by TiO2 using the present method. The doped SnO2 calcined at 500 oC is spheroidal in shape, and about 10 nm in diameter. It can entirely meet the need of Cu matrix electrical contact materials.

Abstract:Through a solid-state reaction, tungsten borides were synthesized from boron and tungsten powders under vacuum in a graphite element furnace. In particular, the effects of B/W mole ratio, the temperature and the holding time on the products were investigated. The phase composition and morphology of the product were further analyzed by XRD and SEM, respectively. The result shows that the main products are WB and WB2 when the B/W ratio is controlled to be 2; however, when the ratio is increased to 2.5 above 1400 oC WB2 of high purity can be obtained. With the B/W ratio more than 4 the main products are mixed by both WB2 and WB4. The relative content of WB4 is increased with prolonging the annealing time. The model of WB4 formation process has been discussed.

Abstract:Thermomechanical fatigue of SnAgCu/Cu solder joints subjected to thermal cycling was investigated. Based upon an analysis of displacements for flip-chip solder joints subjected to temperature cycling, a special bimetallic loading frame with single solder joints has been designed, which allows for the strain measurements of an individual solder joint during thermal cycling. The strain-stress relationship for the solder joint, characterized by hysteresis loops, was determined by strain gauge measurement during thermal cycling from –40 to 125 oC. The failure process was characterized by resistance change of the solder joints, and the number of cycles to failure was determined when the variable D=1-R0/R approximately reached 0.5. The results show that the failure process of solder joints is accelerated with the increase of strain range applied. Coffin-Masson law was applied to characterize the relationship between solder joint life and inelastic strain range, and the model parameters were determined for SnAgCu/Cu solder joint. In addition, the microstructure evolution of the solder joints during thermal cycling was analyzed by Scanning Electron Microscopy, which gave the microscopic explanation for the failure mechanism of SnAgCu/Cu solder joints.

Abstract:ZrN/Zr/ZrN diffusion barrier was grown on Si (100) substrates under different substrate bias in a RF magnetron sputtering system. The effect of insertion of a thin Zr interlayer between Zr-N films on Zr-N diffusion barrier performance in Cu metallization was investigated. The results reveal that an increase in negative substrate bias results in a decrease in the resistivity together with a higher ZrN (111) preferred orientation. The barrier breakdown temperature of ZrN/Zr/ZrN film is about 100 °C higher than that of ZrN. It can effectively prevent the diffusion of Cu after annealing at 750 °C. The improvement of diffusion barrier performance is due to that the production of ZrO2 blocks the diffusion paths of Cu when annealing at high temperature.

Abstract:Cr3C2-NiCr/NiAl coating on the CuCo2Be alloy was prepared by a plasma spraying technique. The high temperature dry sliding friction and wear characteristics of Cr3C2-NiCr/NiAl coating and CuCo2Be were investigated at UMT-2 tribometer using Al2O3 ceramic ball as dual material. The formation mechanism, the microstructure and the high temperature friction and wear behavior of the Cr3C2-NiCr/NiAl coating were studied by Olympus confocal laser scanning microscope, SEM, EDS, and XRD. The results show that the coating is layered and compact. Nickel-aluminum compounds are angular. The phase composition of the coating is amorphous. During the friction and wear process at 500 oC, the wear mechanisms of the coating and CuCo2Be alloy are abrasive wear and adhesive wear as well as a small amount of oxidation wear. Through observing the wear volume morphology, it would find that the wear of substrate materials with the coating is significantly less than CuCo2Be before spraying, so the high-temperature wear resistance of CuCo2Be alloy is improved by plasma spraying.

Abstract:316L stainless steel fiber felt was used as raw material and the porous materials with porosity of 70%~95% were prepared by different sintering techniques. Furthermore, the effects of diameter of fiber, porosity, sintering temperature and holding time on tensile strength were investigated. The results indicate that the tensile process of the porous materials with stainless steel fiber can be divided into three stages: elastic stage, plastic deformation stage and fracture stage. Moreover, the tensile strength gradually decreases with the increasing of the diameter of fiber and porosity. In addition, the tensile strength of porous materials increases with the sintering temperature or holding time increasing.

Abstract:It is difficult to obtain a sharp cube texture through the traditional cold rolling and recrystallization annealing procedure in the non-magnetic and high yield strength Ni-9.3at%W (Ni9W) alloy due to its low stacking fault energy. In this paper, a Ni9W ingot with fine grain and homogenized tungsten distribution was prepared by the conventional metallurgy technique combined with homogenization annealing and intermediate recrystallization annealing. The rolling substrate with 80 μm thickness was obtained through intensive cold rolling and four-time intermediate recovery annealing. The total thickness reduction was 99%. A fraction of 80.2% (<10°) of cube orientation was measured for the Ni9W alloy tape through the two-step recrystallization annealing method.

Abstract:Al-12Zn-2.4Mg-1.1Cu alloy was prepared by the spray deposition method. The microstructure and mechanical properties of the spray-deposited alloy after two-step aging treatment were investigated by high-resolution electron microscopy and hardness tests. The results show that the η′ phase and GPⅡ zones are major precipitates in the alloy after the ageing treatment at 120 oC(14 h). The hardness of the alloy increases to the top and the grain boundary precipitate phases are of continuous distribution. After the two-ageing treatment at 120 oC(14 h)+160 oC(0.5 h), 120 oC(14 h)+160 oC(16 h) and 120 oC(14 h)+160 oC(24 h), the hardness of the alloy is reduced by 5.92%, 11.13% and 15%, respectively compared with those under peak-aged condition and the major precipitates are the fine η′ phase, the coarse η′ phase and the coarse η phase, respectively. The distributions of grain boundary precipitate phases are discontinuous. The grain boundary precipitate phases and the precipitate phases of grain interior have grown up obviously. After the two-ageing treatment at 120 oC (14 h)+160 oC (16 h) and 120 oC (14 h)+160 oC (24 h), the precipitation free zones are also observed. Based on the measurement of TEM images, the lattice parameter of η phase are 0.520 and 0.860 nm and those of η′ phase are 0.490 and 1.402 nm. After the deconvolution processing on η and η′ phase, the image resolution can be improved. Then, the η and η′ phase were simulated by jems, and the basic position of atoms can be determined.

Abstract:Effects of annealing time and temperature on microstructure and properties of cold-rolled Cu-Mg-Te-Y alloy have been studied. The results indicate that after cold rolling, the microstructure presents a fiber texture, the internal grain orientation changes and Vickers hardness increases while electrical conductivity decreases. After annealing treatment, Vickers hardness decreases with electrical conductivity and elongation improved. With the annealing time prolonging, the magnesium as solution atom in copper alloy escapes from copper lattice and segregates around Cu2Te phases through diffusion paths such as dislocations, so electrical conductivity goes up. In turn, electrical conductivity goes down when the grain boundaries become continuously more owing to the recrystallized new grains. Consequently, the optimum overall performance of Cu-Mg-Te-Y alloy is gained under a certain annealing process including annealing temperature of 360~390 oC and annealing time within 1 h.

Abstract:LiFePO4 is expected as the promising cathode materials for lithium-ion batteries. Chemical precipitation is an ideal method to prepare LiFePO4. From the point of view of two kinds of precursor synthesis routes, overseas and domestic research advances of LiFePO4 prepared by chemical precipitation are summarized, in which metal ion doping and carbon coating are usual modification methods. The existing problems in researches and future research directions are discussed and prospected, which provides references for researches of LiFePO4 cathode materials.