Abstract:Abstract: Numerical simulation and analysis of the influence of electrode shrinkage cavity on electroslag remelting (ESR) process of a 430mm diameter ingot of IN718 alloy were carried out using the self-developed ESR process model. Electromagnetic fields of ESR system were simulated with specially designed various shape and size of cavity in the electrode. The results show that the changed contacting area between the electrode and the slag, owing to the cavity, plays the predominant role on the distributions of the Joule heat and electromagnetic force in the slag, while the effect of axial dimension change of the shrinkage cavity is negligible. Constant melt rate ESR processes were simulated for the different radius cavity situations. It is shown that, at a constant melt rate, no effect of shrinkage cavity on the ESR process can be seen as its radius is less than 0.025 m, and only minute influence on the slag flow when the radius reaches 0.05 m. As the radius increases over 0.05 m, increasingly evident influence on the slag zone appears with the center downward flow weakened and temperature risen. Nevertheless, there is no obvious influence of the cavity on the ingot including the melt pool and mush zone. There are nonlinear relations between the shrinkage cavity radius and the ESR melting parameters including current and power, with a critical value about 0.05 m for the radius. Below the critical value, faint or even no change of the parameters appears, while, above the value, the parameters of power and current soon turn into high speed increase, approximately in a linear manner. From the standpoint of process control stability, the shrinkage cavity radius should be controlled less than 0.05 m.

Abstract:In this study, Al₂O₃-Pt/YSZ-Pt double layer composite coatings were prepared by cathode plasma electrolytic deposition (CPED) on the high-temperature alloy with a NiCoCrAlY bond-coat. The composite coatings were consisted of a Al₂O₃-Pt film and a YSZ-Pt top-coat, and showed a good adhesion with the metallic bond-coat. It is demonstrated, from the cyclic oxidation test and mechanical properties test, that such coatings possess good oxidation and spallation resistances. These beneficial results can be attributed to the effects: such coatings can inhibit further oxidation of the bond-coat owing to the extremely low oxygen diffusion rate of Al₂O₃-Pt film; the mechanical properties of Al₂O₃-Pt/YSZ-Pt composite coating are improved by the toughening effects of Pt particles.

Abstract:This study combined anodic oxidation with chemical impregnation method to prepare Al2O3/cerium oxide composite films. First, the aluminum was anodized in 49 g/L sulfuric acid, then the anodized aluminum alloys were impregnated in the solution which contained 2g/L Ce(NO3)3?6H2O, 20mL/L H2O2 at 50℃ for 30min. And the effect of different concentrations (0 g/L, 0.25 g/L, 0.5 g/L, 1 g/L, 1.5 g/L) of 1H-Benzotriazole (BTA) on corrosion resistance of Al2O3/cerium oxide composite films was researched. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), electrochemical workstation was used to characterize the properties of the composite films. The results showed that when the concentration of BTA was 0.5g/L, the deposition effect of cerium ions was best. At the same time the surface uniformity and smoothness of composite films were both enhanced. And the resistance corrosion of composite films was increased mostly.

Abstract:Atomization is an effective approach to obtain fine and spherical alloy powders. Undercooling is a important factor that can affect the property of powders during atomization. In this paper, the effects of powder size and cooling rate on the undercooling and microstructure of powders were investigated in the paper, and the relation between powder size, cooling rate and the undercooling was obtain through DSC. The result show that a small powder size and a low cooling rate will result in a large undercooling. Meanwhile, it was found that when the undercooling is large, the dendrite arm spacing of particles decrease. The smaller the powder size, the proportion of cellular grains increase, and the grain size of the powders will be even fine.

Abstract:Gas burner is the key component of coal-water slurry gasifier system. However, due to the sulfidation at high temperature, gas burner often fails in advance, which affects the stable operation of the system. In this work, Al-Mo coatings are deposited by plasma spraying with a Mo bonding layer. The sulfidation and oxidation behavior of the Al-Mo coatings is studied and compared with those of Mo coatings and Inconel 600 alloy at 973 K, 1073 K and 1173 K. It is found that both the high-temperature sulfidation resistance and the high-temperature oxidation resistance of Al-Mo coatings are superior to those of Mo coatings. The high temperature sulfidation resistance of coatings is better than that of Inconel 600 alloy. Plasma-sprayed Al-Mo coatings with a Mo bonding layer are promising candidates for the corrosion protection of steels in a sulfur/oxide-rich atmosphere.

Abstract:In this work the microstructures and high temperature oxidation behaviors of Co-Cr-Y modified pack aluminide coatings on Ni-based superalloy GH586 were investigated. The results indicated that the specific Co-Cr-Y-modified aluminide coating had a mass gain of only 0.36 mg/cm₂ after oxidation at 1000 °C for 100 h, it was much less than that of the substrate at 1000 °C. From the X ray diffraction the phases of the coatings were mainly AlNi, and after oxidation for 100h at 1000 °C the denser oxidation scale was composed of Al₂O₃, Cr₂O₃, and CoCr₂O₄. The surface and cross sectional morphologies were characterized by scanning electron microscope (SEM). The coating exhibited the better high temperature oxidation resistance, compared to the oxidation film of GH586 without coating. Moreover, the growing Cr (w) rich phase was gradually gathered in the grain boundaries during the oxidation, it is beneficial to provide more Cr element for the dense oxidation film, which is mainly attributed to the excellent high temperature oxidation resistance.

Abstract:(TiC+TiB)/Ti6Al4V composites with different TiC and TiB contents were prepared by in situ synthesis. The influence of load on dry sliding friction and wear performance of in-situ (TiC+TiB)/Ti6Al4V composites (designated as TMC) was studied by HT-1000 friction and wear testing machine, and the wear behaviors of the composites were also investigated by scanning electron microscopy (SEM) and Bruker 3D profilometer. The results show that the wear resistance of TMC was improved by the formation of TiC and TiB phases compared with Ti6Al4V matrix. For the composites with different volume fraction reinforcing phases, the wear rate and wear depth were increased with the increasing of the applied load, and the friction coefficient decreased and fluctuated within a small range. At low loads, the worn surface was covered with grooves and a small amount of wear debris; under heavy loads, the worn surface was covered with narrow and shallow grooves and large amount of wear debris. Wear mechanisms were abrasive wear and oxidation wear. With the increasing of the load, the size of the debris was increased.

Abstract:Pd-based metallic glasses have potential applications in hydrogen-related industry. In the present study, we synthesized Pd_71.5Cu₁₂Si_16.5 metallic glass as wide ribbons by arc melting and copper roller spinning. Their structures were determined by X-ray diffraction spectra using the conventional X-ray diffractometer and also short wavelength X-ray stress analyzer. Fully glassy state of the ribbons is confirmed. Multiple hydrogen absorption and desorption cycles at room temperature under 100kPa were carried out on the samples. No destruction after more than 10 cycles is observed, which demonstrates good hydrogen embrittlement resistance. The hydrogen permeation properties of the Pd_71.5Cu₁₂Si_16.5 metallic glass and its crystallized counterpart were further tested using direct permeation method. In the supercooled liquid region, the hydrogen permeation rate is obviously higher for the metallic glass form, which could be explained by the increasing free volumes introduced during isothermal stage in this range.

Abstract:In this paper, boron-doped nanodiamond was prepared by high temperature vacuum diffusion methodat in a vacuum container. Thermogravimetric analyzer(TGA), X ray photoelectron spectroscopy(XPS), X ray diffraction(XRD), Fourier transform infrared spectroscopy(FTIR), Raman spectroscopy, transmission electron microscope (TEM)were used for characterization of the prepared work. The results show that the products mainly contain C, O and B, and the mass fraction is 92.08%, 7.14%, 0.78%. In addition to diamond (111) _D and (220) _D diffraction peaks, there is also hexagonal diamond (1 0 0)_D diffraction peaks in XRD picture of boron-doped product. The introduction of B atoms results in an increase in the defects of nanodiamond, causing the G peak to move to 1620cm_-1. Boron atoms mainly exist in two forms of substitutional carbon atoms (C-B) bonds and bonds with the impurity elements (B-O) in the diamond lattice. The shape and morphology of boron-doped nano diamond particles have no obvious change. The particle size is 2~ 10nm and a small amount of cubic diamond exist. In conclusion, the initial oxidation temperature of boron-doped nano diamond increases by 175℃, the oxidation rate is slow and the thermal stability is improved.

Abstract:Mg-5Li-1Al magnesium alloy sheets processed by hot rolling were annealed at 150℃ and 300℃ for 30 min, respectively. The microstructure, mechanical properties, and texture of rolled and annealed Mg-5Li-1Al alloy sheet were investigated. The plastic deformation mechanism was also discussed. The results show that the annealed sheet possesses weak basal texture and homogenous recrystallized structure with grain size of ~ 15 μm. Increasing annealing temperature results in an increase in tensile elongation and a decrease in tensile strength and yield ratio, which are generally favored for the improvement of sheet formability. The rolled LA51 sheet after annealing at 300℃ exhibits improved mechanical properties due to Li addition and high annealing temperature.

Abstract:The LaxHo2-xFe17 (x=0.0, 0.2, 0.4, 0.6, 0.8) powders were prepared by arc melting and high energy ball milling method. The influence of the La substitution on phase structure, morphology, magnetic properties and electromagnetic parameters were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), vibrating-sample magnetometry (VSM) and vector network analyzer (VNA), respectively. The results show that the saturation magnetization increases and the average particle size increases with the increase of La content. The minimum absorption peak frequency shifts towards a lower frequency region with the increase of La content. The minimum RL of La0.2Ho1.8Fe17 reaches -28.72 dB at 8.72 GHz, and the frequency bandwidth of R<-10 dB reaches about 2.32 GHz with the best matching condition d=1.8 mm. The reflection loss with the thickness ranging of 1.2-2.4 mm could reach -10 dB, which indicates the particles be considered as the promising microwave absorbing materials with better absorption properties.

Abstract:The influence of temperature and pressure on the electronic, elastic, structural, and thermodynamic properties of Ni3Al alloy was investigated by performing a first-principles study. The calculated elastic constants, equilibrium lattice constants, and elastic modulus agree well with the recorded theoretical and experimental data. The calculated elastic constants indicate that C11 is more sensitive than C12 and C44 to pressure. The Young’s modulus, bulk modulus, and shear modulus increase with an increase in pressure. The ratio of bulk to shear modulus (B/G) and anisotropy factor A were also analyzed. The Debye temperature was obtained by calculating the elastic constants, and it changed with the change in the pressure. The thermal expansion coefficient, normalized volume, heat capacity, bulk modulus, and Debye temperature Θ were determined and analyzed by using the quasi-harmonic Debye model at pressures of 0–60 GPa and temperatures of 0–1600 K. Finally, the density of states and Mulliken population were investigated and the effect of pressure on these was analyzed.

Abstract:A comprehensive performance of formed parts is studied in Friction Stir Incremental Forming (FSIF). In this paper, various tool rotation speeds are set to form two typical parts (truncated funnel and pyramid frustum). Specifically, formability, surface quality, tensile strength, micro-hardness and thickness distribution are investigated and analyzed. Experimental results show that the formability generally increases as tool rotation speeds increase. On the contact surface, variation trends of the surface roughness are different in horizontal direction (parallel to tool path) and vertical direction (perpendicular to tool path). However, the surface roughness on the non-contact surface is almost not affected by tool rotation speed. Furthermore, mechanical properties including tensile strength and surface micro-hardness in formed parts are obviously enhanced compared to the initial sheet, of which the hardness values begin to fall down gradually after rotation speed reaches 3000 rpm. As for thickness measurement, more uniform thickness distribution of formed parts can be obtained at relative high tool rotation speeds. In general, parts formed at high rotation speed have a better comprehensive performance except the mechanical property.

Abstract:Under different stress concentration factors K_t and stress ratios R, the high cycle fatigue (HCF) properties and fracture morphologies of Ti–5Al–5Mo–5V–1Cr–1Fe (Ti-55511) forgings and bars in longitudinal orientation were studied at room temperature. The results show that stress ratio R and stress concentration factor K_t are two important factors that affect the fatigue properties. Both the fatigue strength of forgings and bars increases with increasing stress ratio and decreases with increasing stress concentration factor. The fatigue properties of forgings are better than bars, and the fatigue strength of forgings is 1.08~1.57 times greater than that of bars.

Abstract:The saturated vapor oxidation behaviors of GH2984 alloys at 750 °C were investigated by oxidation weight increasing method, X-ray diffraction and scanning electronic microscopy in different dissolved oxygen concentrations. The results showed that the oxide film of GH2984 alloys in different dissolved oxygen concentrations was of a single layer consisting of continuous Cr2O3 and disperse or local clustered internal oxidation products of Al2O3 and TiO2. The oxidation weight gain of GH2984 alloys slightly increased with increment of the dissolved oxygen concentrations in water vapor. Oxygenated treatment could accelerate the internal oxidation phenomenon, enhance the oxidation film thickness and make the scattered nodular bulges of Fe2O3 disappear and more Cr-rich nodular bulges form. Moreover, high dissolved oxygen concentrations did not affect the stabilization of Cr2O3 but decrease TiO2 content in the oxide film.

Abstract:In this work, a novel magnetic-field-driving approach is proposed and utilized to efficiently enhance the mechanical properties of selective laser melting Ti-6Al-4V. The microstructures of the as-built and the SLM specimens annealed at 400°C, 800°C below the β transus, and 1200°C above the β transus for 30 minutes in the high magnetic field of 7 T are comprehensively characterized in terms of X-ray diffraction, optical microscope, scanning electron microscope, and atomic force microscope. Lattice distortion induced by Al and V atoms are characterized by bonding charge density, providing an insight into the atomic and electronic basis for the solid solution strengthening mechanism and the martensitic transformation mechanism. Referring to the as-built speciments, the ultimate tensile strength and the elongation of annealed specimens at 400 °C and 1200°C in 7T high magnetic field were increased due to the short annealing time. Based on the coupling effect of force field induced by the heat and magnetic, it is expected that the microstructures of SLM Ti-6Al-4V would be conventionally optimized through changing the phase transformation thermodynamics. The validation of this hypothesis will pave a path to develop a novel magnetic-field-driving approach efficiently enhancing the mechanical properties of additive manufactured materials.

Abstract:The use of carbon fiber-reinforced polymer (CFRP) in aviation, automobile, marine and offshore, etc. increases sharply. The metals such as aluminum alloy are still widely used in these industries. Then, the joining technology of CFRP-metal is one of the key problems urgently to be solved and developed in these industries, especially in aviation industries. Thus, this paper gives a review on the joining processes of carbon fiber-reinforced polymer and metal. The implementation processes and joining material types of adhesive bonding, bolt connection, riveting, welding, “z-pin” (pin inserts), and joining (such as self-pierce riveting, hot riveting, mechanical clinching, friction welding) by plastic deformation, were summarized. Some future researches and developments of high-performance, light-weight, and high-reliability CFRP-metal hybrid joint were highlighted.

Abstract:Gas-tight perovskite La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ(LSCF)oxygen transport membranes were prepared by supersonic air-gas plasma spraying (SAPS) and low pressure plasma spraying-physical vapor deposition (PS-PVD). Surface exchange and bulk diffusion of the oxygen species of the two membranes were compared by the use of O₂-TPD and XPS. The O₂-TPD result shows the desorptions of the physical, chemical adsorbed oxygen and the lattic oxygen of the SAPS membrane were 2, 3 and 6 times respectively more than those of the PS-PVD membrane. The XPS result also shows a higher proportion of adsorbed oxygen of the SAPS membrane than that of the PS-PVD membrane. All the above results demonstrate that the SAPS membrane should has better adsorption and dissocation abilities on oxygen, and should also possesses more intrinsic oxygen vacancies and higher capacity of vancancy formation.

Abstract:The effect of the thickness ratio between La2Ce2O7(LC) layer and YSZ layer on the thermal shock performance of La2Ce2O7/YSZ double-ceramic-layer thermal barrier coatings was studied by experimental and numerical method. The thermal cycling test indicates that with the decrease of the thickness ratio, the lifetime of double-ceramic-layer thermal barrier coatings is improved obviously and the failure region is gradually transferred to the sample center. Meanwhile the separation position is transferred from the LC/YSZ interface to the inner LC near the upper surface. The numerical results show that the lager axial tensile stress and shear stress of the interface of LC layer and YSZ layer at the edge leads to the spallation failure at the coating edge. The larger radial tensile stress at the central area of the LC surface leads to the initiation of vertical cracks accompanied by the interface deflection, which is the reason why the coating is peeled off from the inside of the LC layer.

Abstract:The constitutive relations between the deformation energy, Young’s modulus, strength and the relative density of sintered 316L stainless steel fiber felt were studied. The in-plane tensile fracture energy varies linearly with relative density, while the in-plane compressive energy varies nonlinearly. The in-plane Young’s modulus and strength of sintered metal fiber felt show linear dependence on relative density. The linear in-plane property scaling of sintered metal fiber felt suggest that the in-plane deformation of the fiber-ligaments is stretching-dominated.

Abstract:Immiscible alloys have been investigated as a kind of alloys with special metallurgy characteristics. Liquid phase separation of Al-Bi immiscible alloys has been investigated for decades. In this work, the microstructure and the wear resistance of Al-Bi-Ce-Cu alloys were investigated. The intermetallic compounds Bi₂Ce form and act as heterogeneous nucleation sites of Bi-rich droplets, which promote the nucleation of Bi phase and obtain a dispersed microstructure. The intermetallic compound Al₂Cu locate in the Al-rich matrix and enhance the hardness of matrix. The wear resistance of alloys is not only dependent on the size of Bi-rich droplets but also dependent on the hardness of matrix. The refined microstructure and the strengthened hardness improve the wear resistance of Al-Bi alloys. Therefore, Al-Bi-Ce-Cu immiscible alloys is useful as a wear resistance material.

Abstract:Atomistic cracks have been the subject of material intensive research in recent years due to the fast development of nanomaterials. In order to have a better understanding of the fracture mechanisms of body-centered-cubic (BCC) metal, the multiscale quasi-continuum method (QC) is employed to analyze the nano-sized crack of BCC tungsten. The mode Ⅱ crack of Tungsten(W) in {110} planes along the [111] direction is simulated. The load-displacement curve and atom displacement images for each loading step are presented. The generation of partial dislocations, the nucleation and emission of perfect dislocations and the movement of dislocations in crack tip have been observed. Simulation results show that partial dislocations will produce before perfect dislocation nucleation; each drop point of the load-displacement curve corresponds to the nucleation and emission of a perfect dislocation; dislocation nucleation happens several times along with the dislocation launching; the increasing number and rapid movement of dislocations eventually lead to mode Ⅱ fracture. According to the simulation results, the curve of dislocation position vs. displacement is presented, and the movement characteristics of dislocations are analyzed. The results show that all the dislocations will launch after a new dislocation nucleation, indicating that a new dislocation nucleation will promote dislocation movement, and dislocation movement will speed up with the increase in the number of dislocations. In addition, the phenomenon and mechanism of dislocation in BCC metal is analyzed according to the theory of crystallology and Rice’ theory of unstable stacking fault energy. Finally, the forces on and between dislocation are discussed. By calculating the force balance equation in microscale, the initial equilibrium position of the dislocation is forecasted, and the movement mechanism of dislocations near the crack tip is explained, which coincides well with the simulation results.

Abstract:The effects of metal calcium and CaO crucible on deep deoxidation and desulfurization of cast superalloy K417G were studied by vacuum induction melting.Results showed that Ca can achieve the effect of deep deoxidation and desulfurization, the oxygen content decreased from 0.0013% to 0.0006%, the sulfur content decreased from 0.0007% to 0.0002%.The equilibrium relationship between measured w [Ca] -w [S] in the alloy is basically the same as that of the thermodynamic calculation.In addition, the effect of deoxidation and desulfurization of CaO crucible is obvious, oxygen content can be reduced to 0.0006%, sulfur content can be reduced to less than 0.0002%, the reduction of sulfur content is related to the formation of mCaO.nAl2O3slag in the inner wall of CaO crucible, thus realizing deep desulfurization.

Abstract:Tungsten (W) is one of the primary plasma-facing materials candidate for fusion reactor in the future. It is very significant to carry out a quantitative study on the movement and retention behavior of hydrogen isotopes in W, since it can be used to evaluate the service performance of tungsten and the material balance of fusion reactor fuel. In this work, polycrystalline W was irradiated with 100 eV D⁺ ions to the fluence of 3.8 × 10²⁴ D/m². And the subsequent thermal desorption characteristics of polycrystalline W at different heating rates were investigated by thermal desorption spectroscopy. The tota amount of deuterium desorption is about 10²² D₂/m² orders of magnitude. In particular, the thermal desorption peaks can shift to higher temperature side as the increase of heating rate. The thermal desorption behavior of deuterium in polycrystalline W is in accord with the first order reaction. The vacancies formation is the main trapping state of deuterium, and the thermal desorption energy of D atom is 1.04 eV.

Abstract:Three typical microstructures for TC17 titanium alloy, i.e. equiaxed microstructure, basket-waved microstructure and globularized microstructure, are obtained by conventional forging, beta forging and “beta pre-forging+subtransus forging”, and Fatigue crack growth rates of TC17 samples with the three microstructures are tested in order to evaluate the influence of different microstructures. The results reveal a significant dependence of microstructure on fatigue crack growth rate for this material. Basket-waved microstructure has an excellent fatigue crack growth resistance, followed by globularized microstructure, while the equiaxed microstructure shows the poorest propagation resistance. On the basis of fracture mechanics, prediction models for fatigue crack growth life based on Paris equation are developed respectively for the three different microstructures. The models suggest that the propagation life for the large crack in the three microstructure accounts for only a very small proportion of the total fatigue life, hence the control of crack initiation is more important. Superior propagation resistance means a longer critical crack length, which is easily testable in practice.

Abstract:A hydrophobic Ti6Al4V (TC4) titanium alloy with muti-level roughness surface was fabricated with micro-arc oxidation and hydrothermal reaction, combined with fluorination treatment. Fourier transform infrared spectroscopy, energy dispersive spectroscopy, and field emission scanning electron microscopy (FESEM) were used to characterize the surface structures and compositions of the materials. Water contact angle measurement was used to measure the surface wetting property of the modified TC4 as well. Therefore, the construction of a superhydrogphobic surface was successfully achieved by multilevel roughness structures and low surface energy treatment. Furthermore, the platelets adhesion and hemolysis assays suggested superior hemocompatibility of the TC4 surface after modification. Corrosion resistance tests before and after surface modification of the material indicated that the superhydrophobic structures on the TC4 surface could effectively reduce the contacting space between the interface of materials and the corrosive fluid and blood components, thereby weaken the interaction between material surface and the blood cells, such as platelets and red blood cells, and meanwhile could greatly improve the corrosion resistance of TC4.

Abstract:In order to improve the anti-corrosion and anti-wear properties of titanium alloy, a microarc oxidation (MAO) coating was fabricated on the surface of TA2 alloy. The influences of SiC nanoparticles on the microstructure and corrosion behavior of MAO coatings were investigated. The results showed that the introduction of SiC nanoparticles into the base electrolyte increased the coating thickness of MAO coating. The thickness, surface roughness and micropore size of the coating increased with the increasing applied voltage. The microcracks in the coating was decreased by SiC particles. The phase composition of coatings consisted of rutile phase, anatase phase, SiC and SiO2. The OCP and corrosion potential was increased by MAO treatment. The introduction of SiC nanoparticles decreased the anodic current density, and thus increased the corrosion property of the alloy.

Abstract:The material undergoes the complex uneven plastic deformation and microstructure evolution process coupled with multi-fields and multi-factor, during the multi-path roll forming process of the thin-walled super alloy (GH4169) ring with complex section. Especially for the uneven plastic deformation which usually leads to defects of the ring, such as wrinkling, ellipse and crack. Friction is the main parameter to describe the contact between ring and roller, which largely determines the inhomogeneity of plastic deformation during the multi-path rolling process of the thin-walled high temperature alloy (GH4169) ring with w section. And it seriously affects the improvement of roll forming quality. To predict and control the nonuniform plastic deformation, a 3D FE model of the process was built under the ABAQUS/Explicit environment. And the representation method of the nonuniform deformation is proposed.Then the nonuniform deformation behavior in the process was analyzed systematically using FE method combined with experiment and theory. The results show that the maximum value of the equivalent stress increases gradually with the progress of the multi-pass rolling process. And the deformation degree slightly decreases firstly, and then increases gradually with the increase of the friction coefficients between the thin-walled ring and slave roller, drive roller. While the effection of the friction coefficient between guide roller and the ring on the deformation degree can be neglected.

Abstract:By heating up the T_β temperature and then holding 25-90s, the semi- equiaxed structure, which is a transition structure between the equiaxed structure and the lamellar structure,is shaped. The influence of the change of heat holding time on the semi-equiaxed structure evolution law and mechanical properties is studied. Experimental results indicate that the formation of the semi-equiaxed structure is mainly because the element Mo into the β matrix diffused inhomogeneous into primary equiaxed α phase when specimens was kept above the T_β temperature for a short time,And in the cooling process,the β transformain structure grow through the primary equiaxed α phase.With the prolongation of holding time,the semi-equiaxed structure are gradually replaced by lameller structure.When heated to 1015℃,hold 45s,the tensile strength is 1219MPa,the reduction of area is 29%,and the elongation is 14%,which has a better strength and plasticity.

Abstract:The critical extrusion process of the fully dynamic recrystallization of the 690 alloy was analyzed by the Gleeble thermal compression experiment. The microstructure evolution model of 690 alloy was taken into the finite element (FE) software DEFORM-2D, and the secondary development of the FE software was carried based on the microstructure evolution during extrusion process. Then the influence of extrusion ratio, billet temperature and extrusion speed on the microstructure of 690 alloy were studied. The extrusion process control method for the microstructure o f 690 pipe according to the capacity of the extruder and the microstructure requirement. And further performing actual extrusion vertification based on the FE results. The results show that the grian size of the extrusion pipe decreases firstly and then increases with the increasing of extrusion ratio. The grain size of 690 extrusion pipe derceases with the decrease of billet temperature and extrusion speed. The grain size of the extruded pipe can bu controlled bellow 62.7μm when the billet temperature is 1200 ℃ and extrusion ratio is 15.3. The relative error between the simulation results and the extruded pipe is only 4.5%.

Abstract:In order to improve the anti-electron-bombing performance of the cathode applied in high-power magnetron tube. A method of Y2O3-Gd2O3-HfO2(Y-Gd-Hf-O) doping metallic W powders was used to prepare direct-heated cathode. The thermionic emission and anti-electron-bombing characteristics of different mass percent Y-Gd-Hf-O doping cathode were researched. Experimental results show that the 50 wt% Y-Gd-Hf-O doping cathode has large thermionic emission, which can provide 1.0 A/cm2 knee-point emitted current at 1500 ℃. The 10 wt% Y-Gd-Hf-O doping cathode has good anti-electron-bombing capability, whose thermionic emission current density has merely fell by 0.1 A/cm2 after 200 h continuous 14 W/cm2 electron bombing. At last, the thermionic emission and anti-electron-bombing mechanisms of the Y-Gd-Hf-O doping cathode were discussed reasonably.

Abstract:The stress-induced martensite transformation in β solution treated 47Zr-45Ti-5Al-3V alloy was investigated using Gleeble 3500 thermomechanical simulator and D/MAX-2500/PC X-ray diffractometer. The amount of stress-induced martensite in compressive deformation increased with decreasing strain rate and initial β grain size. The triggering stress increased with increasing strain rate and initial β grain size, while the ultimate compressive strength decreased. The curve of work-hardening rate vs. true stress was divided into three stages. The work-hardening rate at stage ΙΙ or ΙΙΙ increased with decreasing strain rate and initial β grain size.

Abstract:The thermodynamics of magnesiothermic reduction of TiO₂ was studied in order to decrease the oxygen content in reduction product. The Gibbs free energy and adiabatic temperature of reaction system were calculated, and the reaction predominance diagram was drawn. The results show that TiO cannot be reduced by magnesium when the reaction temperature is higher than 1681 K. In order to solve this problem, we put forward a new concept to restrain the reaction temperature by adding diluents. The adiabatic temperatures were calculated at different NaCl, MgCl₂ addition amount and initial temperatures, and the thermodynamic condition for complete reduction of titanium oxide was pointed out. Finally, the experiments were carried out by using NaCl and NaCl-MgCl₂ eutectic salt as diluents, and the titanium oxide was reduced completely.

Abstract:Based on the finite element software,the performance of the hydraulic expanded joint of heat exchanger was analyzed.The effect of expansion pressure,material and initial clearance on the capacity and tightness of expanded joints was investigated.Results show that the capacity and tightness of expanded joints will be apparently enhanced with increasing pressures.Under the same pressure,the capacity and tightness of the joint of TA2 tube and TA2 tubesheet is better than the performance of the TA2-Q345R material combination.As the initial clearance is smaller,the residual contact pressure and pull-out force will decrease with the increasing initial clearance.As the initial clearance is larger,the residual contact pressure and pull-out force will retain a constant value regardless of the initial clearance.

Abstract:The laws of the crystal orientation in the annealing process of Ni5W long tapes by the reel-to-reel method and Ni5W short tapes by the static method in laboratory are obvious differences. It finds that, with higher heating rate of dynamic annealing process, the formation of Cube nuclei is insufficient and growth of Cube nuclei is slow. Meanwhile, Cube orientation fraction stops growing and S orientation fraction doesn’t decrease at some point, and Cube orientation fraction growths rapidly with further increase of temperature. With the insulation heat treatment, Cube orientation nucleation and growth advantage are show in static annealing process. In the nucleation stage, many Cube nuclei are obtained, and Cube nuclei grow rapidly with the increase of temperature. The relationship between the reel-to-reel method and the static method were studied for guiding the recrystallization annealing of long tapes which helps the transformation of the study of the short tapes to the industrialization of the long tapes.

Abstract:As the most promising aerospace high temperature structural materials, Ti2AlNb alloys have high specific strength and good high temperature creep properties. The high temperature mechanical behavior and recrystallization behavior of Ti-22Al-26Nb alloy were studied. A high temperature constitutive model of the alloy was established .The dynamic recrystallization multi-stress peak curve was analyzed by fitting the experimental results. The results show that it is feasible to establish the high temperature constitutive model of Ti-22Al-26Nb alloy based on the hyperbolic sine function, which can describe the high nonlinearity of the thermodynamic parameters of Ti-22Al-26Nb alloy at high temperature complex relationship, the maximum error is 2.6%. From the modified Avrami equation, it is predicted that the recrystallization volume fraction and the strain show a recrystallization kinetics growth trend, and the complex softening behavior of the alloy during high temperature deformation is revealed.

Abstract:Solidification characteristics and segregation behavior of a Ni-Fe-Cr based alloy with planar interface and dendritic growth, which was obtained through quenching experiments during directional solidification, were investigated in this paper. The major precipitates are γ, γ′ and MC. The phase transition route is determined as follows: L→L+γ→L+γ+MC→γ+γˊ+MC. The solution distribution coefficients of Ti, Nb and Mo are less than unity. The solution distribution coefficients of Fe is greater than unity and, Al and Cr are close to 1. The solute boundary layer forms ahead of the liquid/solid interface when the steady-state growth begins. The solute is carried away mainly by diffusion in the solute boundary layer, but carried away mainly by flow out of the solute boundary layer. The solute distribution in solid phase with dendritic growth is similar to that with planar interface growth. However, the solute concentration in the quenched liquid in the interdendritic area is obviously higher than that ahead of the liquid/solid interface. The solidification segregation of the mushy zone is more serious than that of the solid region. It indicates that the back-diffusion in solid phase and the precipitation of MC carbide would reduce the solidification segregation during the dendritic growth.

Abstract:The reddish-orange phosphors YPO₄:Gd₃₊,Eu₃₊ were synthesized with the high temperature solid-state method at 1100 ℃, and discussions were conducted in respect of the influences of Eu₃₊ ion doping concentration, alkali carbonate,flux and sensitizers on the luminescence properties of YPO₄:Eu₃₊. XRD analysis shows that the synthesized principal phosphor is of the single phase YPO₄. Eu3 + ions have a better doping concentration of 2.5%. Alkali carbonate Na₂CO₃ can effectively improve the photoluminescence intensity of the phosphor. The addition of flux NH₄F can reduce the phosphor calcination temperature from 1100 ℃ to 800 ℃ and facilitate the luminescence center into the crystal lattice. Gd₃₊ ion can effectively transfer the absorption energy to Eu₃₊ ions at the luminescent center, enhancing the luminescence intensity of the phosphor. The chromaticity coordinate analysis shows that the chromaticity coordinate of the phosphor YPO₄:0.025Eu₃₊is (0.61,0.39) which locates within the scope of the chromaticity coordinate of the standard reddish-orange point．

Abstract:_{: (Ni+La2O3)/Al composites were fabricated by means of adding the mixed powder of (Ni+La2O3) with different La2O3 content to the Al substrate in the Friction Stir Processing (FSP) period. The microstructures of the composite zone were analyzed by SEM and EDS, the element distribution of the composite zone were analyzed by EPMA, the phase composition was examined by XRD, the mechanical properties of the composites were tested by tensile test at room temperature. Results show that: The microstructure and properties of (Ni+La2O3)/Al composites trend to be better firstly and then worse with increasing of La2O3 contents. When the contents of La2O3 are 5%, the contents of Al3Ni particles increase and the distribution of particles becomes uniform,the massive Ni agglomerates are decreased, so the tensile strength of the composites is the highest with 215MPa, which is increased by 22% than that of Ni/Al composites(The tensile strength is 176MPa); When the contents of La2O3 are 7%, the contents of Al3Ni particles decrease and the massive Ni agglomerates reappear, the tensile strength of the composites decreased to 201MPa.}

Abstract:Samples of Li_3-2xB_1-xN_xO₃(x=0.1,0.2,0.3)compound with pure phase were obtained by coprecipitation method at the first time.Lithium nitrate, lithium carbonate and boron oxide were as the raw materials.The Li_3-2xB_1-xN_xO₃(x=0.1,0.2,0.3)precursor powders were sintered via pressureless sintering.And Li_3-2xB_1-xN_xO₃(x=0.1,0.2,0.3)solid electrolytes were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). The results show that samples Li_2.6B_0.8N_0.2O₃ sintered at 600℃ by the non pressure sintering showed the highest total conductivity of 6.37×10_-6S/cm.The activation energy is 0.48 eV at 250~390K. And its density is the reaching 90.07% of theoretical density.

Abstract:Samples of flash butt welded GH4169 alloy were investigated in this research. Experimental results indicate that redissolution happened to the strengthening phase γ″ and γ′ under the welding heat, so that the strength and microhardness of the weldingSzone are lower than that of the base metal (BM). After solid solution treatment, the strength of the BM is reduced to the same as that of the weldents, the uniform deformation between the welding zone and the BM can be realized during tensile deformation. The 1.2% tensile plastic deformation was carried out before or after solid solution on the weldments respectively, after completing aging heat treatment (720 ℃8 h(60 ℃/h)-620 ℃8 h AC (air cooling)), the tensile results show that a small amount of plastic deformation has little effect on its mechanical properties. After solution-ageingStreatment, the tensile strength of the pre-deformation weldments is similar to that of the BM, but the plastic index is lower, this is related to the coarse grains in the welding zone.

Abstract:_{:According to different sintering conditions and TiC/WC composition ratio, three-layer biomimetic composite ceramic tool materials were prepared by hot pressing sintering process. The mechanical properties of the biomi-metic composite ceramic materials were tested, and the fracture surface morphology and crack propagation were analyzed. The flexural strength, Vickers hardness and fracture toughness are 870 MPa, 21.83 GPa, and 7.56 MPa?m1/2, which is higher than that of SG4 homogeneous ceramic cutting tool material. Section morpholo-gies show that the bioimimetic composite ceramic material has finer microstructure than that of SG4 ceramic cuttin tool material, and the grain size shows multi-scale characteristic. Fracture surfaces demonstrate a trans-granular/intergranular mode. The crack propagation path of the surface layer shows crack deflection and bifur-cation of the crack tip.The crack is also deflected as crack passing through the bi-material interface.}

Abstract:In this study, spherical TC4 alloy powders were prepared by gas atomization. The surface and internal pore defects of TC4 alloy powders with different particle sizes were characterized by SEM, synchrotron radiation CT scanning and three-dimensional reconstruction. The experimental results show that the surface of the powder gradually changes from the condensed shrinkage trace to smooth surface with the decrease of particle size. The number and size of pores in powders also gradually decrease with decreasing the particle size. The formation of anomalous powders with the morphologies of wrapping, conjoined, ellipsoid and satellite is resulted from the difference of coagulation and spheroidization time and the different flight trajectories during the atomization process. The results of three-dimensional reconstruction by synchrotron radiation CT scanning show that the porosity and pore size of the powder increase with the increase of its particle size. The authors propose that if the metal droplet could be completely broken into tiny droplets during atomizing prior to its solidification by tailoring the atomizing parameters, internal porosity defects would be effectively minimized.

Abstract:Nanoporous CuAg bimetal/manganese dioxide (NP-CuAg/MnO₂) composites as electrode materials have been successfully synthesized by chemically depositing manganese dioxide (MnO₂) on nanoporous CuAg bimetal (NP-CuAg). NP-CuAg can be produced by chemical dealloying the Cu-Zr-Ag metallic glasses. The phases and microstructures of NP-CuAg and NP-CuAg/MnO₂ composite materials were examined by XRD and SEM. The electrochemical properties of the NP-CuAg/MnO₂ composite electrode materials were investigated by cyclic voltammetry and galvanostatic charge-discharge measurements. For the NP-CuAg-supported MnO₂ composites, the MnO₂ nanoflakes are deposited on the surface of the NP-CuAg substrate. Owing to the three dimensional continuous nanoporous structure and excellent electrical conductivity of NP-CuAg, the MnO₂ nanoflakes can produce much larger surface area as compared to its aggregate particles. Moreover, the NP-CuAg/MnO₂ composite materials exhibit higher electrical conductivity than the NPC/MnO₂ composite materials. Thus, the utilization of MnO₂ surface active sites is improved, which leads to the higher specific capacitance. The specific capacitance increases with the increase of the Ag content in the precursor alloy. Cu₄₅Zr₄₅Ag₁₀ ribbon after dealloying in 0.1 M HF for 10 h, the specific capacitance reaches to 392.86 F/g. The button type energy storage device encapsulated by the NP-CuAg/MnO₂ composite electrode materials, is able to light on the LED.

Abstract:Cu-3.2Ni-0.7Si (wt%) alloy ribbons were prepared by single roller melt-spinning at different rotating speeds. The influences of cooling rate and aging on the electronic conductivity and mechanical properties of Cu-3.2Ni-0.7Si (wt%) alloy were investigated. The refinement of the solidified microstructures is distinctly observed with increasing of the cooling rate, which is responsible for the decrease of the electronic conductivity and increase of the microhardness and the tensile strength. During aging of the as-quenched alloy at a temperature, the electronic conductivity increases with lengthening of the aging time. However, the tensile strength and the microhardness first increase with lengthening of the aging time, and then decrease after reaching peak values. The considerable decrease of the electronic conductivity with increasing of cooling rate is due to the severe lattice distortion. However, the electronic conductivity considerably increases due to aging, which is attributed to the recovery of the distorted lattices. The increases of the microhardness and the tensile strength of the as-quenched alloy are due to the strengthening effect of refinement. The increases of the microhardness and the tensile strength due to aging are attributed to the strengthening effect of the randomly distributed second phase in the matrix. However, the microhardness and the tensile strength tend to decrease after reaching peak values with lengthening of the aging time, which is due to the growth and agglomeration of the precipitated second phase.

Abstract:Nanoporous Nickel/Nickel Oxide (np-Ni/NiO) composite electrodes were fabricated with a “free dealloying - natural oxidation” method by dealloying a high ductile amorphous Ni₄₀Ti₆₀ precursor alloy in 0.25 M HF solution. The structure, morphologies and electrochemical properties of the composite electrodes were studied by XRD, SEM and Electrochemical measurements. The results indicate that the np-Ni/NiO composites exhibit a sandwich-type structure with "dealloyed layer︱amorphous alloy core︱dealloyed layer ". Due to the good connection between layers, the electrode material performs an excellent flexibility and structural integration. The thickness of the dealloyed layer and the content of NiO increase with extending the dealloying time. The volume capacitance of np-Ni/NiO by dealloying Ni₄₀Ti₆₀ ribbons in 0.25 M HF for 2 h can reach to 491.1 F/cm₃ at a discharge current density of 0.5 A/cm₃. After 6000 cycles, the volume capacitance remains at 472 F/cm₃, indicating an excellent cycle stability of np-Ni/NiO composite electrodes.

Abstract:The silicon modification was prepared by adding Te and Sb elements in the smelting process. The chemical composition of the material was determined by inductively coupled method, the mechanical properties, morphology and microstructural evolution of silicon under different T6 states were analyzed by DSC, OM, SEM, EDS, TEM and Universal testing machine. The results show that the number and density of Te, Sb and Si, Mg elements dissolve in the primary α-Al matrix and the endothermic peak among from 520℃ to 530℃ rises with the increase of the solid solution and aging temperature, together with an increased solution supersaturation of silicon in the quenching moment. Whereas, the quantity of Al₄(Te,Sb) eutectic phase reduces continuously, the morphology of silicon particles change from pin-like, polygonal and long-rod to short-rod like, oval and spherical, the average size is merely 9 μm. The average tensile strength, yield strength, elongation, reduction of area and Vickers hardness after solidifing at 545℃ for 20h and aging at 170℃ for 10h with the polyethylene glycol quenching medium are 360MPa, 307MPa, 10.4%, 13.8% and 122, dimple morphology is the dominated fracture surface, accompanied by some intergranular fracture zone, and the average length of Mg₂Si phase is about 224nm.

Abstract:In the present work, the premature rupture of the chromium carbide coating on a freewheel used in a helicopter main reducer was analyzed by stereomicroscope visual examination, scanning electron microscopy examination, structure analysis, hardness test and X-ray diffraction analysis(XRD). The results showed that the fracture of the coating was a mechanical contact fatigue mechanism, the main cause of the flaking of the coating were the microcracks caused by micro porosities under the condition of cyclic loading. With the development of the microcracks, the lightly flaking area initiated on the surface, which causes stress concentration in the adjacent area and the through coating crack in the border of flaking area. The flaking of the coating reduced the loading area which increased the stress and new flaking areas initiated, at last, with the extension of different flaking areas, the throughout flaking formed.

Abstract:Abstract: In this work, PdxCoy/rGO nanocomposite catalysts with different Pd:Co ratios were prepared by electrodeposition. The structure and morphology of the prepared catalysts were characterized by Field emission scanning electron microscope, X-ray energy dispersive spectroscopy and Fourier transform infrared. The results indicate that the compositions of the as-synthesized electrocatalysts are close to the metal ion concentration ratios in the precursors. The metal particle sizes of the PdxCoy/rGO binary electrocatalys are smaller than the particle sizes of Pd/rGO and Co/rGO monometallic electrocatalysts. The size distributions of the PdxCoy/rGO binary electrocatalys are more even in comparison with those of the Pd/rGO and Co/rGO monometallic electrocatalysts. The Pd1Co3/rGO nanocomposite catalyst exhibits the largest electrochemical active surface area in 0.5 M H2SO4 electrolyte, and demonstrates the highest electrocatalytic activity and the best stability for formic acid electrooxidation. The results indicates that the as prepared Pd1Co3/rGO nanocomposite catalyst by electrodeposition is very promising for application in direct formic acid fuel cell.

Abstract:Self-assembly is a process to form the highly ordered spatial structure consisted by the basic structure unit without manual intervention. Due to large specific surface area, the 3D self-assembled nano-function materials have excellent catalytic and photoeletrochemical performance. It has been one of the research hotspots of nanomaterial preparation. Therefore, the main preparation methods of 3D self-assembled nano-function material have been reviewed, including the hydrothermal/solvothermal method, template method, external-field-induced method and so on.