Abstract:Bi_1.76Pb_0.34Sr_1.93Ca_2.0Cu_3.06O_8+d (Bi-2223) precursor powders were fabricated with a two-powder route based on co-precipitation process. During this process, Bi_1.76Pb_0.34Sr_1.93CaCu_2.06O_8+d (Bi, Pb-2212) and CaCuO₂ (with the actual phase composition of Ca₂CuO₃ and CuO) powders were first synthesized and calcinated separately, then mixed together before packed into Ag sheath. By tuning the pH values during the co-precipitation process, CaCuO₂ powders with different average particle size of ~1.10, 0.75, and 0.60 mm were obtained, respectively. Then single filament Bi-2223/Ag tapes were fabricated by powder in tube (PIT) process with precursor powders obtained by mixing the different particle sized CaCuO₂ powders and well-calcinated Bi-2212 powders. The influences of CaCuO₂ particle size on microstructure, phase evolution dynamics and superconducting current capacity of sintered Bi-2223 tapes were systematically studied. Due to higher uniformity of Ca₂CuO₃ and CuO distribution in filaments, clustering of secondary phases and insufficiently reacted areas were effectively avoided. Therefore, higher current capacity of ~12200 Acm^_-2 was obtained on the 1# tape by further optimizing the final dimension of the tapes.

Abstract:Solid-liquid interface morphology of the titanium ingot has great influence on the microstructure during the solidification process. This paper focused on the effect of Crystallizer"s 3D dimension of the ultra-long and ultra-thin TC4 slab ingot on the solid-liquid interface morphology. The results show that when the cross-section length of TC4 slab ingot exceeds 450mm, the cooling capacity of the crystallizer does not increase. When the length exceeds the effective distance, the depth of molten pool and the width of mushy zone will not change with the increase of the length in the crystallizer. Moreover, increasing the ratio of the crystallizer’s length to width is helpful to improve the production quality. The simulation results show that it is better to choose between 4:1 and 6:1. When the height of the crystallizer is higher than 300mm, the depth of the molten pool and the width of mushy zone will not change. Therefore, the certain range theoretical basis was obtained to design the crystallizer’s three-dimension during EBCHM for the ultra-long and ultra-thin TC4 slab ingot.

Abstract:The flow pattern of materials is closely related to the formation of joint structure, has a crucial influence on the mechanical properties of joints for friction stir welding. The material flow of the joint was studied by slicing method which was adopted to observe different layer for dissimilar friction stir butt welding. The visualization of the flow material was accomplished by 3D reconstruction of the joint, which shows the flow pattern of the joint and the cause of the defect. The three-dimensional mathematical model of the flow of Al/Mg materials in FSW process is established based on computational fluid dynamics (CFD) and multiphase flow theory in this paper. The material flow patterns are analysed and predicted under different welding parameters by the distribution of tracing particles added in numerical models. The study reveals that the flow of material in the upper part of the joint is strong, the material moves to the front of tool as a whole. The magnesium alloy of the middle part in the advancing side of the joint moves forward to the front of the tool, and the temporarily cavity is filled with aluminum alloy from the retreating side. The cavity which is not completely filled will form a hole defect when the material flow is not enough due to improper process parameters. The whole joint material is mainly laminar flow. The flow mode of joint material basically does not change when the heat input is satisfied. The transfer distance and mixing mode of material will change under the condition of high rotation speed or overheat. The two materials cross the butt line for many times in mode of laminar flow around the tool and mix fully when the turbulence occurs at the retreating side.

Abstract:The compressive true stress-true strain curves of TC4 alloy with different strain rates at room temperature were investigated by the INSTRON test machine and split Hopkinson pressure bar (SHPB) device. Johnson-Cook (JC) constitutive model of TC4 alloy was established by fitting the experimentally obtained stress-strain curves. Based on the constitutive model, the impact compression experiment of TC4 alloy at high strain rate was simulated by ABAQUS. The correctness of the parameters for the constitutive model was verified by comparing the experimental results with the simulation data. In order to achieve the goal of lightweight of the mortar, a new lightweight titanium alloy mortar base plate was designed. The finite element model of the mortar base plate under impact load was established considering the strain rate effect of TC4 alloy. The strength and stiffness of the base plate were analyzed, and the variation law of the stress and displacement of the base plate was obtained. The research results of this paper provide a reference for lightweight design and development of the base plate and other equipment structures.

Abstract:Nickel-based alloys are commonly used as welding part for the primary circuit safe-end welded joints of pressurized water reactors. Due to the harsh service environment and the uneven mechanical properties of the welded joints, the nickel-based alloys are prone to produce stress corrosion cracking, which has a great impact on the safe operation of nuclear power. To understand the variation of the material macrostructural parameters (including the plastic properties of the material and the stress intensity factor K) on the SCC crack growth rate, the SCC crack propagation finite element model of nickel-base alloy 600 under different macrostructure parameters was established, and the effects of different plasticity and K on the plastic zone and tensile plastic strain around the crack tip are analyzed. Results show that the plastic zone size and tensile strain around crack tip are affected by K, yield strength and hardening exponent, among which the K at crack tip has a greater influence, and it is inversely proportional to yield strength, while the K is directly proportional to hardening exponent. The results of SCC growth rate calculated under different K were compared with the experimental results under high temperature water environment, and the range of characteristic distance r₀ of nickel-based alloy 600 was obtained. The research results can provide a scientific basis for SCC rate prediction under high temperature water environment of nickel-based alloy 600 for nuclear power.

Abstract:In order to eliminate the inhomogeneous structure of as-cast GWZK94 alloys, the homogenization with the temperature range of 505-520 ℃ and the time range of 8-20 h were conducted by using resistance heating furnace. Optical microscope (OM), differential scanning calorimeter (DSC), X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), electron backscatter diffraction (EBSD), universal mechanical tester, and Vickers hardness tester were applied to investigate the microstructure evolution and mechanical properties. The as-cast alloy mainly consisted of the dendritic α-Mg matrix, lamellae with metastable stacking faults (SFs), Mg24(Gd, Y, Zn)5 which was a eutectic phase, bulk-shaped long-period stacking ordered (LPSO) phases (Mg12(Gd, Y) Zn), and a few RE-rich phases. During the homogenization, the lamellae and Mg24(Gd, Y, Zn)5 eutectic phases gradually dissolved into the matrix, and the volume fraction of bulk-shaped LPSO phases decreased while the lamellar-shaped LPSO phases grew into grains steadily, while some precipitated particle phases formed near the grain boundaries. At 520 ℃, triangle-shaped remelting eutectic phases appeared which indicated the over burning of magnesium alloy. Both ultimate tensile strength (UTS), tensile yield strength (TYS) and fracture elongation showed a tendency to correspond to microstructure evolution, and a more uniform hardness was investigated. The homogenization condition was optimized to be 515 ℃/16 h..

Abstract:The leaching behavior and kinetics of ilmenite ore with NaOH hydrothermal method was researched in this work, and the innovative metallurgical process for leaching titanium from ilmenite ore is proposed with NaOH hydrothermal method in order to overcome the severe dilute H₂SO₄ waste water pollution of current titanium extraction process in industry. It is determined that the optimal reaction conditions is as follows: the reaction temperature 240℃, NaOH concentration 400 g.L^_-1, the mass ratio of alkali to ore 3.5:1, partial oxygen pressure 0.5 MPa, reaction time 2 h, agitation speed 600 rpm, and ore particle size <75μm, and the leaching degree of titanium can reach 95%. Based on XRD analyses and SEM microstructure examination, the decomposition behavior of ilmenite ore was investigated and the generating of sodium titanium particles were observed. The producing phenomenon of the product layer was not found during leaching. The leaching kinetics study shows that the leaching rate of ilmenite ore with NaOH hydrothermal method is controlled by the solid product layer diffusion with the apparent activation energy of 47.39 kJ/mol and an empirical rate equation is “1-2X/3-(1-X)^_2/3=[735.09exp(-47389.8/RT)]t”.

Abstract:In order to improve the efficiency of chemical preparation of YBa2Cu3O7?δ (YBCO) with long taps, the pyrolysis of traditional process preparing precursor film needs to be reduced to one step, so the crystallization process should be directly connected to the former without the cooling of pyrolysis. Replacing copper trifluoroacetate with copper isooctanate can alleviate the centralized heat release and the contraction of the precursor film during pyrolysis. A suitable amount of boric acid was added into the precursor solution with total cation concentration of 1.0 mol/L, after a continuous heat treatment YBCO superconducting film was obtained. Utilizing the flow state of boric acid at 200-500 ℃, boron oxide was doped into YBCO film which shows denser and smoother by filling some pores, compared with that one prepared by undoped precursor solution under the same conditions, the former shows higher superconductivity.

Abstract:The morphology of silver fillers, surface lubricants of silver fillers, the composition of matrix, curing procedures and so on will affect the performance of ECAs. The morphology of silver fillers is a crucial factor. Effect of the silver with different morphologies on properties of ECAs under the same condition was studied. silver flakes, silver spheres and silver wires were prepared and treated by glutaric acid to eliminate the effect of other factors. Then these silver particles were used as conductive fillers compositing with epoxy resin to prepare ECAs. The thermal degradation, electrical conductive properties, mechanical property and storage stability of ECAs were investigated. The results show ECAs filled with silver wires exhibit lowest electrical resistivity and percolation threshold, best mechanical property and good storage stability under the same condition. ECAs filled with silver flakes show better electrical conductive property and storage stability but poorer mechanical property than ECAs filled with silver spheres.

Abstract:The novel IrO2-CeO2-G/Ti composite electrodes were prepared by thermal decomposition method. The synthesized electrodes with different IrO2 content had been characterized by scanning electron microscope(SEM), transmission electron microscope(TEM), X-ray diffraction(XRD) and X-ray photoelectron spectroscopy(XPS). The electrochemical performances of the electrodes were investigated by cyclic voltammetry, galvanostatic charge–discharge and electrochemical impedance spectroscopy in 0.5 M H2SO4 solution. The results showed that the electrode with 2.5mg/cm2 IrO2 exhibited an excellent specific capacitance value of 459.5 F/g, and the specific capacitance maintained about 97.8% after 5000 charge-discharge cycles at a 5mA/cm2 current density. The electrode with 2.5mg/cm2 IrO2 was an ideal electrode for supercapacitor due to?its unique composition proportion and the excellent pseudocapacitance property.

Abstract:Phase equilibria of the Ni-Co-Sn ternary system at 700 °C and 1000 °C were experimentally determined by using electron probe microanalyzer and X-ray diffraction. No ternary compound was found at 700 °C and 1000 °C. There was an extensive region of mutual solubility existing between βCo3Sn2 phase and Ni3Sn2(h) phase. Three Ni-Sn binary compounds [Ni3Sn(l), Ni3Sn(h) and Ni3Sn4] showed absolutely different solubilities for the element Co. The maximum solubility of Co in Ni3Sn(l) and Ni3Sn4 phases at 700°C were 6.9 at.% and 25.6 at.%, and the solubility of Ni3Sn(h) phases changed into 15.5 at.% at 1000°C. The Ni-Co side presented an interconnected (αCo, Ni) phase region at both 700oC and 1000°C and its homogeneity range for Sn was from 1 at.% to 10.5 at.%. The solubility of Ni in the linear compound CoSn phase was about 15.9 at.%.

Abstract:WC-CoCr/ Fe-based amorphous alloy composite coating has been prepared by high velocity oxygen fuel (HVOF) spraying. Microstructure, hardness, wear resistance, high temperature oxidation and corrosion resistance of the composite coating are comparatively studied with WC-CoCr coating. XRD analysis and SEM observation show that the composite coating is mainly composed of WC, W₂C and a Fe-based amorphous phase. In comparison with WC-CoCr coating, the hardness of the composite coating is slightly decreased, but there is no statistically significant difference between them. As a result of hardness decrease, the wear resistance of the composite coating is a little bit inferior to that of the WC-CoCr coating. Results of high temperature oxidation at 800 ^_oC proved that the composite coating exhibits excellent thermal stability, which is mainly attributed to the formation of a dense and uniform oxide layer during the high temperature oxidation test. Moreover, electrochemical test revealed that the corrosion resistance of the composite coating is better than that of WC-CoCr coating in 3.5 wt.% NaCl solution.

Abstract:Fe-Cu composite plate has good ductility, electrical and thermal conductivity, the ferromagnetism of Fe, and the diamagnetism of Cu, so it can be widely used in power, electronics and other industries. However, it is hard to weld Fe and Cu using conventional methods due to their low mutual miscibility. The explosive welding method was adopted to prepare the Cu-Fe-Cu (with the thickness 17, 5, 17mm respectively) composite plate in this study. Firstly, the theoretical model was adopted to design explosive welding parameters. The weldability window, the detonation velocity and thickness of the charge, and the gap size were obtained. Then, a new numerical simulation method, in which the SPH, Lagrange and Euler methods are used and no equivalent treatment of the explosive welding components is taken, was used to analyze the explosive welding process. The collision velocity of the flyer plate, temperature and pressure distribution near the bonding interface as well as wavy interface are obtained, and it proved the validity of the theoretical design parameters. Finally, the Cu-Fe-Cu composite plate is successfully prepared by explosive welding method. The hardness distribution and the shear strength of the bonding interfaces are tested. The results show that parameters of the interface wave obtained experimentally and numerically are basically the same; compared with that of the original ones, the hardness of Fe and Cu near the bonding interface increased about 34.2% and 49.8% respectively; the average shear strength of the first and the second interface is 212.7 MPa and 225.3 MPa respectively.

Abstract:A series of FeZrB alloys with different nominal compositions were prepared by melt-spinning and then annealed at their first crystallization temperatures, respectively. The thermal curve, microstructure and magnetic property of alloys were investigated by simultaneous thermal analyzer (STA), X-ray diffraction (XRD), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM). The results show that the primary crystallization phases are different with the compositions of FeZrB alloys changing. Four groups of primary crystallization phases can be observed in the alloys, i.e. α-Fe phase, α-Fe+Fe23B6-type phases, α-Fe+α-Mn type phases and α-Fe+Fe2B+ZrB phases, and their morphologies are of different by TEM. The relations of saturation magnetization (Ms) and coercivity (Hc) for the alloys with different primary crystallization phases are as follows: Ms(α-Fe)>Ms(α-Fe+α-Mn type)>Ms(α-Fe+Fe2B+ZrB)>Ms(α-Fe+Fe23B6-type) and Hc (α-Fe+α-Mn type)>Hc(α-Fe+Fe2B+ZrB)>Hc(α-Fe+Fe23B6-type)>Hc(α-Fe).

Abstract:Tantalum(Ta)/Molybdenum(Mo) dissimilar joint was successfully joined by laser welding process with pure Pt filler wire. The weld surface morphology, microstructure, interface element distribution, fracture morphology, phase structure, electrical performance and environment adaptability were studied by metallography microscope, scanning electron microscopy, hardness and mechanical properties of joints, X-ray diffraction, electron micro-hardness and tensile test, vibrationStable and ultra-high high vacuum system. Laser parameters have profound effects on microstructures of the laser-welded joints. Pores were generated in the weld zone caused by the preferential vaporization of pure Pt filler metal. The weld zone mainly contained TaPt2, TaPt3 and MoPt phase, resulting higher hardness in the weld zone than that of base metal. The joint fracture surface exhibited typical brittle fracture morphology. The electrical property and vibration test had examined the joints welding quality for electron guns. Meanwhile, the reliability of laser welding process in the development, production, and application of microwave tubes had been verified.

Abstract:In this study, porous Zn-xMg alloy scaffolds (x=5,10 and 15 wt.%) were fabricated as bone tissue engineering scaffold by spark plasma sintering (SPS) using same volume content space holder (NaCl). The effect of content of Mg on the mechanical properties, microstructural characterizations of the porous Zn-xMg alloys scaffold were revealed. Results showed that with increasing content of Mg, the porosity increased from 40.3% to 54.3% and the mean open pore size increased from 289 μm to 384 μm due to the dealloying effect of Mg. Mechanical tests results showed that porous Zn-Mg alloy was a typical elastic-brittle metallic foam and porous Zn-10Mg was best among three scaffolds. The strength and elastic module of the scaffolds showed good biomechanical compatibility and had the promising to be used as a lower load-bearing implant material.

Abstract:Ti-22Al-25Nb is a high-temperature structural material which oxidation resistance will be important for further developments and applications. The oxidation behaviors of sintered Ti-22Al-25Nb alloy which was prepared by reactive sintering with element powders were investigated at the temperature range of 650~950 °C in static air. The maxima of the mass gains at different temperatures (650 °C, 750 °C, 850 °C, 950 °C) were 0.15 mg·cm?2, 0.41 mg·cm?2, 1.68 mg·cm?2 and 6.9 mg·cm?2, respectively. The Ti-22Al-25Nb sintered alloy exhibited a good oxidation resistance, especially below 750 °C (with breakaway oxidation occurring at 950 °C). According to the oxidation kinetics analyses, the oxidation behaviors approximately followed parabolic law below 750 °C. Whereas, with temperatures rising above 850 °C, the oxidation behaviors fitted linear law. Oxidation kinetics were discussed with regard to the influence of the Nb alloying element. Based on the observations and analyses of the oxidation morphologies and phases, there were proven that the oxidation resistance of the O phase (orthorhombic Ti2AlNb) was superior to others. The reason for this phenomenon was the difference of Nb content in different phases could result in a difference of oxidation resistance.

Abstract:The tensile behavior of γ-TiAl alloys with vacancy defects has been studied by molecular dynamics simulation (MD) considering different lattice orientation. A succession of simulations were performed to analyze the effect of vacancy and lattice orientation on mechanical properties and micro-defect evolution. The results indicate that the orientation has evidently impacts on critical stress with Ti and Al vacancy. The yield stress of the model with Ti vacancy is higher than containing Al vacancy model along three crystal directions. During the deformation of single crystal γ-TiAl alloys, it is found that the dislocation density has the same changeable trend as the number of stacking faults. In addition, the influence of temperature on yield strength also was discussed. When the temperature increases, the ultimate stress declines non-linearly, and elastic modulus of the material decrease obviously. The higher temperature, the less influence of crystal orientation and vacancy defect on the ultimate stress.

Abstract:The stress corrosion cracking and hydrogen embrittlement of the Al-xMg-3.1Zn aluminum alloys were studied by slow strain rate tensile tests and dynamic electrolytic hydrogen charging experiments, respectively. The effect of Mg on the stress corrosion cracking behaviors was indicated combining with transmission electron microscopy and fracture analysis. The results showed that the stress corrosion cracking was happened in the studied alloys, and the corrosion susceptibility decreased with a decrease of Mg content due to the decrease of the grain boundary precipitates continuity. This was result from the decrease in the anodic dissolution of grain boundary precipitates and hydrogen embrittlement behaviors with a decrease of Mg content.

Abstract:In the present study, Effect of Al element addition (1~3wt.%) and heat treatment on microstructure evolution and mechanical property of one new alloy Ti-xAl-3.5Fe-0.1B was studied. Results indicated that Ti-xAl-3.5Fe-0.1B is α+β two-phase titanium alloy. Yield strength of the alloy increased from 590MPa to 900MPa and tensile strength increased from 808MPa to 1074 MPa with the variation of Al element from 1% to 3% due to solid solution strengthening effect, at the same time, the elongation to failure reduced to 15.4%. Microstructure observation revealed that the thickness of the lamellar primary α phase reduced and the grain size remarkably refined as the increasing Al element content. Meanwhile, It was found that yield strength continuously increased to 1000 MPa, tensile strength increased to 1144 MPa and the elongation to failure increased to 17.5% separately after double annealing, which indicated unique mechanical property. The metastable β phase formed in the microstructure decomposed to secondary α phase with fine grain size during the double annealing in the alloy, which blocked the movement of dislocation and induced enhancement of strength, at the same time, the dispersion of secondary α phase on β substrate was also beneficial to the strength. On the other hand, the present of equiaxed α phase was considered favorable to the improvement of elongation to failure.

Abstract:Scanning Electron Microscopy, Energy Dispersive Spectroscopy, Metallographic Microscope and Low Cycle Fatigue testing machine were used to study the relationship between the Low Cycle Fatigue performance of 650 °C/ maximum stress 980MPa and the size, area ,distribution of fracture inclusions of a nickel-based FGH97 superalloy. The results show that the low-cycle fatigue fracture is mainly casued by non-metallic inclusions. If the size or area of the non-metallic inclusions is less than a critical value（about 80μm）, there is no significant effect on the low cycle fatigue life of 650 ℃/ maximum stress 980MPa , and the average life value reaches 190,992 cycles. The distribution of inclusions has no significant influence on the low cycle fatigue life when the size is less than the critical value of 80μm.When the size exceeds the critical value, the larger size of inclusion and the closer to surface result in the lower the low cycle fatigue life.

Abstract:Low cycle fatigue behavior of TC4 ELI titanium alloy with bimodal and lamellar microstructure had been investigated by analyzation of strain-cycles curve with different stress amplitudes. Results indicated that the volume fraction of equiaxed α phase is about ~ 26.6% for the bimodal microstructure, the average grain size is approximate 7.8 μm. At the same time, the thickness of α phase layer is about 0.5 ~ 2.0 μm for lamellar microstructure. Cyclic softening phenomenon was observed for all the samples of TC4 ELI alloys with different microstructure at the maximum stress. Sample with bimodal microstructure exhibited higher low cycle fatigue life, which could be attributed to the shorter effective slip path than the one with lamellar microstructure. More than that, the presence of equiaxed α-phase with high dislocation density also could hinder the initiation and propagation of fatigue cracks for the bimodal microstructure. Fracture morphology shown flat and smooth for the sample with bimodal microstructure, however, some geometric facets associated with the original coarse-grained β were found for the sample with lamellar microstructure.

Abstract:The interfacial reactions and diffusion behaviors of Zn atoms in Cu/Sn-9Zn/Ni interconnects during liquid-solid electromigration (L-S EM) under a current density of 5.0×103 A/cm2, 1.0 × 104 A/cm2 and 2.0 × 104 A/cm2 at 230 oC have been in situ studied using synchrotron radiation real-time imaging technology. Zn atoms would directionally diffuse towards the Cu interface under both flowing directions of electrons with the current density of 5.0×103 A/cm2, then taken part in the interfacial reaction, resulting in the thickness of intermetallic compounds (IMC) at Cu interface thicker than that at Ni interface. While when the current density rise to 1.0 × 104 A/cm2 and 2.0 × 104 A/cm2, the reverse polarity effect, evidenced by the continuous growth of intermetallic compound (IMC) layer at the cathode and the thinning of the IMC layer at the anode, was resulted from the abnormal directional migration of Zn atoms toward the cathode in electric field, which was more significant at high current density. Irrespective of the flowing direction of electrons, the consumption of Cu film was obvious while that of Ni film was limited. The dissolution of anode Cu followed a linear relationship with time with current density of 1.0 × 104 A/cm2 and 2.0 × 104 A/cm2 and electrons flowed from the Ni to the Cu, and the consumption rate was magnitude higher at high current density. It is more damaging with electrons flowing from the Ni to the Cu than that from the Cu to the Ni. In addition, based on the electromigration flux Jem and chemical potential gradient flux Jchem the diffusion behavior of Zn and Cu atoms were analyzed.

Abstract:Effective thermal conductivity is a key parameter to characterize the thermal property of closed-cell aluminum foam. It is of great significance to predict the effective thermal conductivity of closed-cell aluminum foam. In this paper, based on the existing models for effective thermal conductivity of closed-cell aluminum foam, an improved model was proposed. Furthermore, the numerical simulation method was employed to analyze the unsteady heat transfer process of closed-cell aluminum foam. And the effective thermal conductivity was obtained from the distribution of temperature field. The results show that the improved model has higher prediction accuracy compared with Lu model. Besides, the improved model has better applicability and prediction accuracy compared with the three theoretical models from literature.The number of cells in the heat transferdirection has a great influence on the accuracy of the effective thermal conductivity by the numerical simulation method. The accuracy of numerical simulation is the highest when the number of cell holes is enough. Considering cost and accuracy, the improved model has better applicability.

Abstract:Hydrogenated TiO2 nanotube arrays exhibit good electrochemical performance, which can be further improved by constructing anatase <001> preferred orientation structure within TiO2 nanotube arrays. The anatase TiO2 nanotube arrays with different degrees of <001> orientation via adjusting the Glycol-H2O ratio in anodization process and the subsequent annealing atmosphere. After electrochemical hydrogenation, the as-prepared samples with different degrees of <001> orientation were characterized by SEM, XPS, XRD, TEM and electrochemical measurements, the effects of preparation process on <001> orientated structure was investigated. The mechanism of the enhanced electrochemical properties by orientated structure orientation was discussed. The hydrogenated TiO2 nanotube arrays with highly <001> orientation delivered the charge specific capacitance as high as 17.31 mF·cm-2, which can attribute to the synergetic effects of hydrogenation and <001> oriented structure.

Abstract:In this paper, effect of Ca on hot deformation behavior and workability of Mg-Gd-Y-Zn-Zr alloy were investigated by Gleeble 3500 thermal simulation tester conducted at a temperature ranging from 573K to 723K and strain rate varying from 0.001s-1 to 1s-1. It’s indicated that the addition of Ca increased the flow stress and hot deformation active energy, widened the range of processing stable zone and the optimal processing zone, but decreased the maximum power dissipation efficient, and inhibited the dynamic recrystallization. Combined the microstructure after thermal compression which was analyzed by laser confocal microscopy, the accuracy of the processing map was verified. The optimized hot processing parameters of Mg-Gd-Y-Zn-Zr were formulated, namely strain rate ranging from 0.001s-1 to 0.01s-1, temperature ranging from 623K to 723K. Depending on the optimum processing parameters, an isothermal forged magnesium alloy with good quality and no deformation defects was fabricated.

Abstract:The effects of alloying elements on phase equilibria in Co-based bond coating alloys are predicted by CALPHAD method. The results show that Al significantly influences on the precipitation amounts of β` and γ, and Cr has a definite effect on the precipitation of σ. The appropriate contents of Al and Cr elements are determined to be around 13% and 22%, respectively. The results of calculated phase formations and phase changes as a function of temperature are extensively discussed, which indicats that γ begins to precipitate from the matrix β` at 1208 ℃ and reaches the highest content at 974 ℃, then the σ will precipitat. According to the phase transformation, the heat treatment process of the alloy was formulated, dissolved at 1300 ℃ and aged at 1 000 ℃. The alloy samples were prepared by vacuum induction melting. Segregation and the amorphous structure in as-cast alloys was eliminated after the above heat treatment, and the two-phase structure, β`+ γ, of the commercial target is obtained.

Abstract:The demand and requirements of large-size magnesium alloy profiles in the field of rail transit and other fields are increasing. The high strength tough magnesium alloy profiles have high trial mold cost, long development cycle and difficult preparation. In this paper, the HyperXtrude software is used to simulate the profile structure of the large-size high-strength and tough Mg-9Gd-4Y-1Zn-0.8Mn alloy rail transit support beam. Under the premise of ensuring the successful extrusion of large-size high-strength and tough magnesium alloy support beam profiles, the preferred process is determined. The extrusion temperature is 470 ℃, the extrusion speed is 0.3 mm/s, and the maximum pressing force required under the process is determined which is 34606 KN. The large-size high-strength and tough magnesium alloy support beam profile used in rail transit with good surface quality, uniform composition and homogeneous structure is successfully prepared. The tensile strength of each part of the profile is above 370 MPa, the elongation is above 10%, and the highest strength is 391 MPa. The strength of the aging state is obviously improved, reaching 460 MPa or more, and the elongation is slightly decreased, exceeding 8%. The highest strength reaches 475 MPa.

Abstract:The effect of Fe content on the microstructure and tensile properties of TC4 alloy manufactured by laser solid forming was investigated. The analysis of microstructure evolution of samples during heat treatment process showed that Fe didn’t affect the microstructure of as-built samples, consisting of coarse columnar β grains in the longitudinal section, while after heat treatments the coarse columnar β grains in the longitudinal section were translated into fine columnar β grains with increasing Fe content from 0.026%wt. to 0.18%wt, suggesting the occurrence of recrystallization. The tensile strength of samples at room temperature after heat treatments was higher than the standard requirements for forging. The tensile strength parallel to building direction was improved with the increasing of Fe, as for the strength perpendicular to building direction was insensitive to Fe content.

Abstract:The effects of different casting moulds on the microstructures and mechanical properties of ZTC4 titanium alloy were studied. The effects of cooling rate, solidification rate and solidification time on the microstructures and mechanical properties of ZTC4 titanium alloy were studied by numerical simulation and experimental analysis.The results show that compared with the ceramic sample, the graphite sample has better heat dissipation effect, faster cooling speed and higher solidification speed, which makes the microstructure of the sample to be fine lath martensite alpha produced by quenching, with smaller grain size, more orientation and larger solidification thickness.The yield strength, tensile strength and hardness of the mechanical properties increased by 6.7%, 2.6% and 4.2% respectively, but the elongation and section shrinkage decreased by 37% and 34.5%, respectively. At the same time, different positions of the same mold have some influence on the cooling rate. The cooling rate at different positions of the sample is in the order of middle > bottom > top.

Abstract:Effects of combined aging process on microstructure and properties of age-hardenable Cu-3Ti-0.2Fe-0.2Cr alloy foils were investigated by mean of hardness test, tensile test, conductivity test, OM and SEM. It was shown that after the optimized combined aging treatment of pre-rolling with the reduction of 50%, pre-aging at 450 ℃ for 4 h, re-rolling with the reduction of 95.6% and re-aging at 450 ℃ for 1.5 h, the hardness, tensile strength, elongation and electrical conductivity of Cu-3Ti-0.2Fe-0.2Cr alloy foil were 354.6 HV, 1062 MPa, 1.9% and 17.1 %IACS, respectively. Compared with the specimen treated with Pre-0 h+CR+Re-2 h, the alloy foil treated with optimized combined aging process possessed the similar mechanical properties and higher electrical conductivity. The fractograph of the studied alloy foil treated with optimized combined aging process was composed of flat facets resembling cleavage, river pattern and dimples, manifesting a mixed-rupture mode.

Abstract:Oriented porous superalloy was prepared by freeze-casting with GH3536 powder as raw material and guar gum/CMC-Na as stabilizers. The results show that slurries could be stabilized by adding 0.4~1wt.% of guar gum or 1~3wt.% of sodium carboxymethylcellulose; as the solid loading increases from 10vol.% to 30vol.%, the width of oriented pore decreases from 308μm to 198μm and the wall thickness increases from 81μm to 223μm, with the axial and radial compressive strength improving from 10.72MPa and 9.2MPa to 75.02MPa and 78.49MPa, respectively. The fabricated oriented porous superalloy is a plastic material with the ability of absorbing energy.

Abstract:The effects of different heat input and multi-layer thermal cycle on the crack morphology, distribution, expansion mode and microstructure and hardness of the deposition zone were analyzed by laser deposition of DZ125 single-layer multilayer experiments. The results show that as the heat input increases, the number of low-melting eutectic increases, and the formed liquefaction cracks expand along the crystal and increase in size. Optimizing the process parameters and reducing the heat input can prevent from producing the cracks; as the number of sedimentary layers increases, the heat accumulation increases, the cooling rate decreases, the thermal stress increases, and the solidification crack expands in both the horizontal and longitudinal direction. The interlayer heat is reduced by interlayer cooling to obtain a single-channel multilayer crack-free structure. In the first layer of the deposition zone, the carbides gradually become round and the number decreases, and the hardness of the first layer decreases slowly.

Abstract:The microstructures and precipitation hardening of Ti1023 and Ti5553 alloys in the same solution treatment and step-quench aging treatment (ST-SQA) have been studied. The morphology of α phase about precipitation and distribution in different aging treatment were observed carefully by using SEM and TEM, and the variation of density and width of secondary α phase were analyzed. The hardness of these two alloys was measured. The result shows that: Ti1023 alloy is more likely to precipitate α phase than Ti5553 alloy due to low stability of ? phase. Ti1023 alloy precipitates α phase at 300℃ aging and get the maximum density of precipitation at 400℃,while Ti5553 alloy precipitates α phase at 450℃, and get the maximum density of precipitation at 550℃. As for Ti1023 alloy, the peak of hardness is obtained at 400℃ aging, while as for Ti5553 alloy, double peaks of hardness are shown at 350℃ and 550℃ aging, respectively. The variation of hardness was caused by the precipitation of secondary phase in ? phase for different aging temperatures. When aging temperature is below 400℃, the hardness of Ti1023 alloy depends on both α phase and ω phase, and the hardness of Ti15553 alloy depends on only ω phase. As aging temperature is over 400℃, the hardness of both Ti1023 and Ti5553 alloys depend on the density of precipitation and the size of α phase.

Abstract:The hot tensile deformation behaviors of rolled ME20M magnesium alloy at temperatures of 623-773K and strain rates of 0.001-0.1s_^-1 were studied by INSPEKT Table 100kN universal high temperature experimental machine. The effects of deformation temperature and strain rate on the flow stress of the material were analyzed, and the constitutive model and processing map under hot deformation conditions were established. The results show that the flow stress of the rolled ME20M magnesium alloy increases with the decrease of deformation temperature or the increase of strain rate. The predicted peak stress of the constitutive model is in good agreement with the experimental results, and the average relative error is 5.19%. After considering the influence of strain on the material constant in the constitutive model, the predicted stress value is highly correlated with the experimental value, and the average relative error is 6.00%. The best hot working range is 673-773K, the strain rate of 0.001-0.01 s_^-1.

Abstract:The Ti/IrO2-SiO2 and Ti/IrO2-SiO2-CeO2 composite oxide anodes were prepared by thermal decomposition method. The apparent morphology of the electrode was characterized by SEM. The cyclic voltammetry curve and oxygen evolution polarization curve were used to characterize the electrocatalytic performance of self-made electrodes and commercial electrodes（Ir-Ru、Ir-Sn、Ir-Ta、Ir-Ta-Sn）. The cobalt was recovered from the cobalt chloride solution by a double-membrane three-compartment electrolytic reactor. The advantages and disadvantages of cell voltage, power consumption and chlorine inhibition performance of self-made electrodes and commercial electrodes were discussed. The results show that the doping of rare earth Ce is beneficial to improve the surface roughness, active surface area and electrocatalytic activity of the electrode. Compared with Ir-Si, Ir-Ru, Ir-Sn, Ir-Ta and Ir-Ta-Sn electrodes, the Ir-Si-Ce electrode has the lowest oxygen evolution potential and the highest electrocatalytic activity. In the experiment of recovering cobalt by electrodeposition method, the Ir-Si-Ce electrode cell has the lowest voltage and energy consumption and the best chlorine inhibition performance compared with other electrodes. The chlorine reduction rate of it is as high as 97.5%.

Abstract:The copper-based bulk materials were prepared by low-pressure cold spray additive manufacturing technology. The thermal conductivity and mechanical properties of the bulk materials were tested. The cross-section and tensile sections of the bulk materials were observed and analyzed by means of SEM. The results show that the thermal conductivity of copper-based bulk materials prepared from copper-based powders with a volume ratio of 10% Al₂O₃ is better. With the increase of Al₂O₃ content, the thermal conductivity decreases. After annealing, the cold-sprayed copper-based bulk material has improved thermal conductivity and mechanical properties. The thermal diffusivity and tensile strength show a trend of increasing first and then decreasing with the increase of annealing temperature. When the annealing temperature is 500℃, the thermal diffusivity of the heat-treated copper-based bulk material is 80.43% of the processed copper bulk material,the tensile strength is 125.3 MPa.

Abstract:Topology optimized porous lattice structure with different unit cell size (1~6 mm) and porosity (40~80%) were fabricated by Selective Laser Melting, and their compressive deformation behavior and elastic properties were discussed. The results shown that compressive strength and elastic modulus of lattice structure were inversely proportional to unit cell size. Their compressive strength ranged from 126 to 199 MPa and elastic modulus ranged from 3.5 to 55.47 GPa. The stress-strain curves of lattice structures with different unit cell size followed three kinds of stress-strain laws: elastic material, elastic-brittle material and brittle material. The compressive deformation process was simulated by ABAQUS and explained the reason of two 45° fracture band. The numerical results shown a good agreement with experimental results. The stability was evaluated by Gibson-Ashby model, and the stability parameter C decreased with the increase of unit cell size. Meanwhile, the fitting curves based on Gibson-Ashby model were established, and the value of n increased with the increase of unit cell size. A 3D surface mathematical model combining unit cell size, relative density and relative elastic modulus was established, and the design area satisfying mechanical properties of bone implants was proposed.

Abstract:By comparing the microstructure of hot extruded forming tube and burst tube as well as the analysis of crack and fracture of burst tube, the microstructure and crack formation mechanism of GH3625 alloy tube during hot extrusion were studied. The results show that the microstructure of the burst tube and the formed tube are equiaxed crystals, but the cracking of the burst tube causes the stress concentration at the grain boundary to be released. Besides, no deformation twins are formed in the microstructure and there is no uneven grain size in the radial direction of the tube. The root cause of crack formation is that the extrusion ratio is too high, which causes the adiabatic heat of the tube to be severely heated during the hot extrusion process, so that the low melting Laves phase melts and diffuses into the surrounding matrix. Under the action of high tensile stress at the exit of the mold, these cracks continue to propagation and eventually join together, causing the tube to burst. The higher cooling rate of the fracture surface leads to a shorter time for the passage of the microstructure through the austenite region, more recrystallized nucleation core and the grain growth process is hindered, so that a very fine recrystallized grain is formed on the fracture surface.

Abstract:The mixture of Ni, Co, Cr, Al, Y powders were prepared by mechanically mixing method for 4 hours with the ratio of 4:2:1.5:1:0.03 of Ni, Co, Cr, Al, and Y, and the deposited mixed powder coating with a thickness of 150 μm was prepared on the 310s stainless steel substrate by using the low-pressure cold spray equipment (GDU-3-15). The sample was placed to a vacuum tube furnace (TL1700) for thermal diffusion treatment. The microstructure, phase composition and microhardness of in-situ synthesis NiCoCrAlY alloy coatings were analyzed by Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffractometry (XRD) and microhardness tester, et al. The results show that the mixed powder coating of Ni, Co, Cr, Al,Y prepared by the cold spraying is mainly constituted with simple elements. However, the diffusion reaction of the elements occurs in the coating after vacuum diffusion at 1100 ℃ for 4 h. Simultaneously, there is a diffusion phenomenon between the coating and the substrate, which forms an obvious metallurgical bond. Oxidation experiments show that the NiCoCrAlY coating of in-situ synthesis exhibited significantly lower oxidation weight gain than the pure substrate, which can protects the substrate from rapid oxidation effectively.

Abstract:In order to eliminate the microstructure inhomogeneity of TA19 flash welding joint and improve the comprehensive properties of TA19 flash welding joint. Use Gleeble3500 thermal simulation testing machine on TA19 flash welding head in deformation temperature 900~ 980 ℃, the deformation were 30%, 60%, deformation rate of 0.01 ~ 1 s- 1 for isothermal constant rate under the condition of hot compression test, as to research in welding joint organization under different deformation parameters change characteristics. The experimental results showed that the rheological stress curve of the welded specimen showed a dynamic softening trend during the compression process, and the recovery and recrystallization of the flaked phase were sufficient under the condition of low deformation rate, which promoted the increase of its width and size, and the wedge of phase resulted in the disconnection of the flaked phase. With the increase of deformation amount and deformation temperature, under the action of dynamic recrystallization and element diffusion, the equiaxial ratio of sheet increases gradually. In the process of deformation, residual phases were broken and some mo-rich particles were distributed on the phase matrix. In the subsequent heat treatment process, Mo rich particles on the matrix were dissolved back into phase, which was grown to complete the segmentation of the phase, which was further axialized by static recrystallization. Flash welding specimens under 980 ℃, deformation rate 0.01 s- 1, after 60% deformation under deformation, by 930 ℃ for 1 h + 590 ℃ for 4 h air cooling annealing treatment, can fully realize the weld microstructure of transition such as axis, heat treatment after welding joint organization is given priority to with shaft such as organization, organization uniformity obviously improved.

Abstract:In this paper, uniform scandia doped tungsten powder was prepared by sol-gel method combined with reduction process, and then the scandia doped impregnated cathode was successfully prepared by microwave sintering. The characteristics of Sc-doped tungsten powder, the microstructure of cathode sponge matrix, the emission properties, and the surface behavior of the active substance were analyzed. The result shows that the scandia doped tungsten powder has the average size of around 1μm and Sc element was uniformly distributed. The morphology of the sponge skeleton have spherical shape, the pore distribution was uniform, the average pore diameter is about 0.46 μm, and scandia is evenly distributed in the matrix. The cathode prepared by the microwave sintering method exhibited good emission properties, e.g., the current density of this cathode reached 137.59 A/cm2 at 950 ℃b, and the emission slope is 1.431. The atomic ratio of Ba:Sc:O on the cathode surface is 1.8:1:2.2 after activation, and a amount of nanoparticles are present on the cathode surface , which promotes emission of the cathode.

Abstract:The thermal compression test was carried out by Gleeble 3500 thermal simulator and combined with microstructure observation and statistical analysis to study the effect of thermal deformation on the size and distribution characteristics of NbC particles in GH4169 alloy. Studies have shown that the adiabatic effect during compression leads to a further increase in the core temperature of the sample, thus providing conditions for NbC re-dissolution during the deformation process. The high dislocation density region formed by the NbC particles and the matrix during the deformation process promotes the diffusion of the elements and accelerates the remelting and passivation of the sharp corner regions with small radii of curvature. With the increase of deformation, the NbC remelting tendency increased, and the average size and volume fraction showed a decreasing trend. During the deformation process, the metal flow promotes the displacement of the NbC particles. Under the 70% deformation amount, the average spacing of the NbC particles increases significantly higher than the 30% and 50% deformation samples. Therefore, with the increase of deformation, the NbC particles have a distribution characteristic from chain→chain bending→chain direction→dispersion distribution, which promotes the fine and diffuse distribution of the original chain NbC in the matrix. The results provide a direct reference for the improvement of GH4169 flash soldering performance.

Abstract:YBCO+PVDF films had been successfully fabricated by chemical solution deposition method. The decomposition behavior of YBCO gel was influenced by the addition of PVDF. YBCO+PVDF gel was suitable for fast pyrolysis process. During the pyrolysis process, the fluorine could enter into the intermediate phase and inhibit the formation of BaCO₃. The results showed that the addition of PVDF would improve the epitaxial growth of YBCO film. It was beneficial to achieve high performance of YBCO film.

Abstract:The effects of aging treatment on the microstructure and properties of laser additive remanufactured IN718 alloy were studied. The results show that the aging treatment can not change the epitaxy growth structure of laser additive remanufactured IN718 alloy, but it will affect the content and morphology of Laves phase. With increase of the aging time, γ phase gradually grows up and changes to δ after holding for a certain time at different aging temperatures. The higher aging temperature, the shorter the time required. In addition, the microhardness and tensile strength of the repaired zone increase firstly and then decrease with holding time at different aging temperatures. The peak value of microhardness is 410 HV_0.2 at 720 ℃ for 16 h, 385 HV_0.2 and 361 HV_0.2 at 760 ℃ and 800 ℃ for 4 h, respectively. The maximum values of tensile strength corresponding to different aging time at 720 ℃, 760 ℃ and 800 ℃ are 1153 MPa, 1090 MPa and 1026 MPa, respectively.

Abstract:Deformation mechanism of magnesium alloys is complex and prone to be affected by initial process states and deformation conditions of materials during the thermal process, therefore, exhibits different stress-strain relationships. Stress-strain curves of casting and wrought magnesium alloys AZ31B were obtained by Gleeble-1500, and the constitutive models of magnesium alloys under two different initial process states were constructed based on the Arrhenius hyperbolic sine function, the effect of initial process states on stress-strain curves and deformation mechanism of magnesium alloy were analyzed. Experimental results show that wrought magnesium alloy appears shear fracture along 45° direction due to deformation texture and amounts of twins at low temperature when the strain rate is greater than 0.1s_^-1. However, The deformation mechanisms of casting and wrought magnesium alloys AZ31B keep the same at high temperatures and low strain rates, therefore, the stress-strain curves of them are basically similar. The hardening index n and activation energy Q of wrought magnesium alloys are smaller than casting magnesium alloys.

Abstract:The static and dynamic compression tests of Ti-811 alloy with acicular microstructure have been conducted by using the Instron testing machine and the split Hopkinson bar system respectively. Its deformation and fracture mechanism under various strain rates have been studied. The results show that: the yield strength of acicular microstructure exhibits positive-negative-positive strain rate sensitivity successively with increasing strain rate. The intrinsic reason is the competition between dislocation slip and twinning mechanism. The fracture mechanisms of acicular microstructure under static and dynamic compression are obviously different, which show double-shearing and single-shearing fracture mode respectively. Saw-tooth chips formed at the end faces of dynamic compression specimen, which is due to restraint of the severe relative slide of the material at the two sides of primary shearing band by incident bar and transmission bar.

Abstract:The effect of homogenization treatment on aging behavior of Al3(Sc,Zr) and homogeneity of Mg were studied in an Al-6Mg-0.4Mn-0.15Zr-0.04Sc alloy using Micro-hardness test, optical microscope, scanning electron microscope and transmission electron microscope. The peak hardness of alloy annealing at the normal homogeneous temperature of 475℃ was 83HV, much lower than those isochronally annealed at 175-550℃, demonstrated that the alloy did not obtained the sufficient aging strengthening from Al3(Sc,Zr) particle during one-stage annealing at 475℃. Therefore, two-stage homogeneous treatment was designed. The first stage annealing was selected from 275-350℃, where the 300℃ exhibited the highest peak hardness of 87HV, and the second-stage annealing were performed at 475℃ with the peak hardness of 92HV. The microstructure analyses indicated the Al3(Sc,Zr) particles in two-stage annealing were much finer than that of one step annealing. After annealing at 300℃/7h+475℃/15h, the segregation of Mg disappeared and the Al3(Sc,Zr) particles formed dispersedly at the same time.

Abstract:Along with the rapid development of portable electronic products and electric vehicles, the research on lithium-ion batteries (LIBs) with high energy density and power density has attracted more and more attention. Anode material as a necessary component of electronic device has become an important research direction. Commercial graphite anode is limited by its low theoretical capacity. Germanium-based nanomaterials have emerged as important candidates for lithium-ion battery anode materials owing to its high theoretical specific capacity and unique chemical and physical properties. This review will focus on preparation methods, current applications and future development of germanium nano materials with different morphologies and composition in LIBs.

Abstract:Zr alloy has been gradually developed and applied in nuclear industry, aerospace, biomedicine and other fields,just for its excellent characteristics, such as high hardness, high melting point, low thermal expansion coefficient, corrosion resistance and low thermal neutron absorption cross section. In this paper, the Zr alloys research status of composition design methods, including empirical/semi-empirical method, first-principles calculation method, d-electron orbital method and CALPHAD method, are introduced. Especially, the research methods and current situation of Zr alloy involved in first-principles calculation are mainly introduced. With the aid of the alloy design model and computer operation, the relationship between the mechanical behavior and microstructure of materials can be effectively and systematically understood, providing a theoretical basis for alloy composition design.Combined with the research progress and achievements of Zr alloy design methods at home and abroad, the research and development trend of Zr alloy design is briefly discussed.