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    • >Special Issue:Lght Metal Alloy
    • Optimization of hot forming-quenching integrated process parameters for complex aluminum alloy automotive components

      2019, 48(4):1029-1035.

      Abstract (1203) HTML (150) PDF 0.00 Byte (1038) Comment (0) Favorites

      Abstract:Hot forming-quenching integrating process of aluminum alloy sheet has been developed to improve formability and overcome thermal distortion by integrating hot stamping and quenching in one operation, which is significantly beneficial for the application of aluminum alloy components in vehicle lightweight industry. In this novel technology, processing parameters are interrelated and interacted. To obtain appropriate forming parameters, thermo-mechanical finite element (FE) model using a unified viscoplastic damage model is set up to predict the formability of a complex-designed 6xxx aluminum alloy B-pillar. A Back Propagation (BP) neural-network combined with multi-objective genetic algorithm (GA) method is adopted to optimize the key process variables including blank temperature, stamping speed and die clearance during hot stamping process. After optimization, the thinning and thickening are reduced to 13.0% and 10.0% by comparing with the initial 56.5% and 14.2%, respectively. In addition, a successful hot stamping B-pillar with satisfactory mechanical performance and excellent forming accuracy is achieved experimentally by using the optimized parameters. It indicates that the finite element model can simulate the hot stamping process accurately and that the optimization method utilized in this paper is feasible and effective.

    • Influence of static magnetic field on the microstructure and properties of 7055 aluminum alloy

      2019, 48(4):1036-1045.

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      Abstract:In this paper, the mechanical properties and microstructure of 7055 alloy subjected to static magnetic fields at different magnetic induction intensities (B = 0 T, 1 T, 3 T, 5 T and 7 T) were investigated. The dislocation characteristics, phase transitions, tissue textures, tensile properties, fracture morphologies and residual stresses were researched through advanced modern techniques. The results showed that the dislocation densities in the treated samples increased with increasing B, and a transformation of cellular dislocation to the low-energy network dislocation has been observed. In addition, the magnetic field has also played a role in grain refinement due to sub-grain’s formation and facilitating the common η (MgZn2) at grain boundaries to dissolve toward internal grains and transfer into η" phase, which contributes to the enhancement of the tensile strength and toughness of materials. At B = 3 T, the magnetic field weakened the lattice distortion and made a structural adjustment, and material performance arrived at the optimal elongation value 10.5%, residual stress 38 MPa and tensile strength value 555 MPa. Besides, the fracture morphologies were analyzed by Scanning Electronic Microscopy and the fracture characteristics were in agreement with the plasticity property.

    • The Failure Assessment Curve of the Circumferential Through-wall Cracked Orthotropic TA2 Pipe

      2019, 48(4):1051-1058.

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      Abstract:This paper presents the limit loads, J integral results and failure assessment curve (FAC) for the circumferential through-wall cracked isotropic and orthotropic pipe of pure titanium TA2. Limit loads, J integral and curves were calculated based on the 3-dimensional (3-D) elastic-plastic finite element (FE) analyses. Geometric variables of pipe and crack size are systematically varied. Effects of the orthotropy on failure assessment curves are considered. Calculation results show that the limit load and J integral of isotropic pipe and the anisotropic pipe are obvious different. For failure assessment curves, when the load ratio Lr < 0.9, if the orthotropic material is evaluated as an isotropic material, the evaluation results are conservative. When the load ratio Lr > 0.9, if the orthotropic material is evaluated as an isotropic material, the evaluation result is too dangerous. And it is the most dangerous when the mechanical properties of the axial direction are stronger than those of circumferential direction. Thus the orthotropy of circumferential through-wall crack pipe cannot be neglected for defect assessment.

    • Spall of different thicknesses Al7050 alloy under ultrahigh strain rate laser shock peening

      2019, 48(4):1096-1101.

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      Abstract:The spall characteristics of different thicknesses Al7050 alloy treated by laser shock peening (LSP) with different process parameters (Process-1 and Process-2) were investigated to obtain the spall mechanism and spall threshold. The particle velocity of rear free surface and spall crater morphology in 0.33 mm thickness Al7050 induced by LSP with Process-1 were measured and analyzed by a Photonic Doppler Velocimetry (PDV) system and scanning electron microscope (SEM), respectively. Spall sizes, spall thicknesses and spall fracture morphology in 5 mm thickness Al7050 induced by LSP with Process-2 were analyzed by a C-scan ultrasonic nondestructive testing with water immersion, optical microscope (OM) and SEM, respectively. The results indicated that spall strength and LSP strain rate of 0.33 mm thickness Al7050 were calculated by PDV data. Spall crater morphology was also analyzed in detail. Spall sizes of 5 mm thickness Al7050 increased with continued multiple LSP impacts and its spall thicknesses were in range from 343 μm to 364 μm. Spall mechanism was mixture ruptures of ductile behavior with spherical voids and brittle behavior with straight cracks. Continued LSP-5 was the spall threshold of 5 mm thickness Al7050. Compared with as-received material, the micro-hardness of 5 mm thickness Al7050 with continued LSP-5 increased in the surface layer and decreased near rear free surface. The results provided not only some important insights on the spall behavior of aluminum alloy with laser shock but also fundamental research for avoiding the spall in industrial applications.

    • Effects of Al content on the mechanical properties of single crystal TiAl alloy

      2019, 48(4):1102-1108.

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      Abstract:TiAl alloy has been widely used in the aerospace and automotive industry because of its excellent properties, but the shortcomings such as brittleness and fracture toughness are still significant at room temperature, which limits its applications. The purpose of this paper is to explain the effects of Al content on the mechanical properties and to discuss the crack propagation mechanism of single crystal TiAl using molecular dynamics simulation. The stress–strain curves and evolution process of the defects were obtained under different Al contents. The results confirmed that the Al content would affect the elastic modulus and the strength of the TiAl alloy. Because of defects, such as stacking faults, dislocations and vacancies, and their migrations result in the plasticity of TiAl tended to be better when the Al content below 45at%. And the specimen implies brittleness with the Al content greater than 45at% obviously. Furthermore, the plasticity deformation dominated the main mode in the low content, while the crack fracture presented brittleness when the Al content is high. Al contents would affect the mechanical proprieties of TiAl alloy and the plasticity of TiAl would increase with decreasing Al content. In addition, the mechanism of crack propagation would vary with the change of Al content.

    • Dynamic globularization kinetics and Finite Element Analysis for the Hot Working of Ti-5Al-5Mo-5V-3Cr-1Zr with Initial Lamellar Microstructure

      2019, 48(4):1109-1115.

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      Abstract:Characteristic of α phase is an important factor affecting the mechanical properties of titanium alloys. To predict the microstructure evolution of the Ti-55531 (Ti-5Al-5Mo-5V-3Cr-1Zr) with initial lamellar α, the dynamic globularization kinetics model of Ti-55531 during hot deformation was characterized by Avrami equation. A series of thermal simulation experiments were conducted to obtain the curves of stress σ versus strain ε to determine the equation parameters. By further transforming the stress σ-strain ε curves into strain hardening rate dσ/dε-ε curve, the critical strain εc (corresponding to the minimum value of dσ/dε) and the peak strain εp (the strain at dσ/dε = 0) be obtained. The dynamic globularized fraction fg at different deformation conditions was also measured. Sequentially, the parameters in the Avrami equation were determined from the linear fitting of the relationships among strain rate, temperature, and dynamic globularized fraction. The as-obtained Avrami equation was expressed as fg =1-exp[-0.5783((ε-εc)/εc)0.907], where εc =0.6053εp and εp =1.249×10-4?0.0807exp(58580/RT). Finally, the as-obtained dynamic globularization kinetic model was implanted into finite element program to simulate dynamic globularization kinetics. By combining the dynamic globularization kinetics model with the finite element method, the dynamic globularization of the lamellar α was predicted effectively.

    • Electrochemical corrosion behavior of Ti35 alloy in 6 M nitric acid containing fluoride ions

      2019, 48(4):1124-1129.

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      Abstract:Ti35 alloy has excellent corrosion resistance and can serve in the high concentration of oxidizing boiling acid medium for a long time. It is an ideal candidate material for commercial reprocessing. In this paper, the open circuit potential (OCP), the potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS) of Ti35 alloy were tested by electrochemical test system in 6M nitric acid solution containing fluoride ions and the effect of the fluoride ion on the corrosion resistance of Ti35 alloy was investigated. The results show that the corrosion resistance of the alloy decreases with the increase of fluoride concentration while the alloy still exhibits good corrosion resistance in general. The critical concentration of fluoride ions affecting the corrosion resistance of the alloy is about 50 ppm. Further, the mixed potential theory is adopted to explain the undermined mechanism of the changing corrosion resistance of the alloy.

    • Influences of Deep Cryogenic Treatment on Precipitated Phase of 7A99Aluminium Alloy

      2019, 48(4):1155-1160.

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      Abstract:Backward extrusion 7A99 ultrahigh-strength aluminium alloy was treated by T6 peak aging treatment and peak cold-heat cycle aging treatment (T6-DCT). TEM, HRTEM and 3DAP were employed to study the influences of T6-DCT treatment on the types, distribution, size and density of the precipitated phases. The result shows that the types of the precipitated phases increase, that η" phase turn to η" phase and η phase coexistence together. The avearge equivalent radius of the precipitated phases change from 1.2 nm to 1.0 nm after T6-DCT. The density of the precipitated phases increase from 4.53×1024/m3 to 7.55×1024/m3, which lead to dispersion-strengthening. After T6-DCT, the segretion of Zn and Mg decreases, and the precipitated phases distribute more homogeneous than that of T6 treatment.

    • Galvanic corrosion behavior of T2/TC4 galvanic couple in static artificial seawater

      2019, 48(4):1161-1167.

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      Abstract:In this article, galavanic corrosion test of T2/TC4 galvanic couple in static artificial seawater was carried out. The dissolution rate of copper ion and the behaviors of T2/TC4 galvanic couple in static artificial seawater was analyzed by electrochemical workstation, ICP, SEM, EDS and XRD. The results shows that the reaction is intensively when galvanic corrosion occurs between T2 alloy and TC4 alloy, T2 alloy acts as anode and the corrosion rate is increase, TC4 alloy acts as cathode. Compared with the corrosion of T2 alloy, the dissolution rate of copper ion by T2/TC4 galvanic corrosion has been enhanced several times and maintained at around 160μg/(cm2.d), Therefore marine antifouling requirements for inhibiting the attachment of great majority can be achieved. The corrosion product is mainly cuprous oxide when corrosion occurs in T2 sample, No corrosion products are covered on the surface of T2 sample after galvanic corrosion with TC4 alloy.

    • 0.2%H facilitating the phase transformation of the Ti-22Al-25Nb

      2019, 48(4):1174-1178.

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      Abstract:Ti-22Al-25Nb alloy is a new type of Ti2AlNb alloy. Its high hot-processing temperature and large deformation resistance are always significant limitations for its wide application. Hot-hydrogen technics, as an efficient method to reduce the deformation resistance of Titanium alloys, is applied to the Ti2AlNb alloy in recent years. This paper reveals that the phase transformation process accelerates and the phase transformation point declines during the hot treatment process of the Ti-22Al-25Nb alloy after a 0.2wt.% hydrogen addition. Hydrogen facilitates the recrystallization process and the grain size refines from 135μm to 60μm at 960℃. Hydrogen facilitates the decomposition of strengthening phase O phase into B2 phase and the transformation of the α2 phase from granular shape to trip shape during the temperature increasing process. Hydrogen promotes the preferential segregation and fast growth of the O phase at grain boundaries and accelerates the transformation process of B2→O phase during the 750℃ heat preservation process.

    • Study on Fretting Corrosion Wear Behaviors of TC4 Alloy

      2019, 48(4):1183-1188.

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      Abstract:Abstract: Fretting wear test of TC4 alloy in sodium chloride solution are studied, the effects of loads on wear scars, the friction coefficient and the wear resistance are investigated under different friction counterparts. Results show that the wear mechanism attributes adhesive wear to fatigue and peeling with abrasive wear, and corrosion wear appears on the surface; The friction coefficient decreases under the sodium chloride solution and the curves keeps stable; The friction coefficient curves of Al2O3\TC4 fluctuates greatly and the wear mechanism turns fretting into reciprocating sliding under the large loads. The wear rate and wear resistance of Si3N4\TC4 is larger than that of GCr15\TC4, which means the abrasion performance of GCr15\TC4is better than that of Si3N4\TC4 and GCr15 ball performed the best wear properties under the corrosive wear. The agravity of TC4 alloy is caused by wear and the interaction of wear and corrosion in sodium chloride solution.

    • Effect of High-pressure Torsion on Microstructure and Properties of TA15 Titanium Alloy

      2019, 48(4):1189-1194.

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      Abstract:TA15 samples with different turning numbers were prepared by high-pressure torsion process. Using metallographic observation, X - ray diffraction analysis and microhardness test, the effects of high-pressure torsion on the microstructure and properties of TA15 titanium alloy were analyzed. The experimental results show that the microstructures of the specimens are not evenly distributed in the radial direction after deformation. With the increase of turning numbers, the coarse primary equiaxed α phase gradually decreases and the grain refinement effect is obvious. And the material appears preferential orientation in the (200) crystal. After the high-pressure torsional deformation, the size of the sub-crystal decreases, while the microstrain and dislocation density increase significantly. In addition, the microhardness of the deformed specimens increases remarkably. Moreover, the hardness increases with the number of torsion turns increasing. When the number of twists turns is greater than 4, the microhardness tends to a saturation value.

    • Effect of rolling mode on texture evolution of CP-Ti TA2 rolled sheets

      2019, 48(4):1195-1201.

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      Abstract:This paper reports the effect of the rolling mode on texture evolution in the commercially pure titanium (CP-Ti)TA2 sheets. For this purpose, total height reductions of 50% was imposed on the samples by three route modes: Route A is conventional rolling (CR), Route B is non-isothermal rolling(NWR) which CP-Ti sheets were rolled under a fixed temperature difference of 90-degree for the upper and lower rolls, respectively, Route C is repeated bending–unbending (RUB) where the sheets were bent by non-isothermal rolls with differential speed. Systematic analysis of the deformation characteristics refers to crystallographic orientation and texture component was performed using EBSD. The results indicate that the deformation characteristics significantly vary with the rolling modes. The texture of the CRed sheets is similar to those already reported for such rolled α-titanium, except that the center of the main peak is slightly shifted for a few degrees. And their small recrystallized grains and large deformed grains are oriented along <0001>//RD. However, prismatic texture formed in NWRed sheet and the grains’ orientation is <2-1-10>//RD. The texture and orientation changing are contributed to different temperatures for upper and lower rollers surface and thus induces intense shear strain uniformly throughout the sheet. NWR has a similar effect on shear deformation as equal channel angular extrusion. Basal texture and pyramidic texture are observed in the sheets processed by RUB, the priority was pyramidic texture. The finer grains exhibit a strong orientation of <0001>//RD, two weaker orientations of <2-1-12>//RD and<2-1-13>//RD.

    • High Performance Milling of Ti40 Alloy through Variable Feed Method

      2019, 48(4):1213-1219.

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      Abstract:This paper presents a method for improving the cutting tool life by varying the feed throughout the milling process of Ti40 burn resistant titanium alloy. In this research, the model between tool life and the feed variation amplitude, period and step duration of the milling was constructed and the optimal feed variation parameters were selected. Experimental results show that the optimal sinusoidal feed milling parameters were 11.72 percent sinusoidal feed variation amplitude, with 120 seconds one period and 5 seconds incremental steps, which increase the cutting tool life by a maximum of 33 percent. In comparison with constant feed processes, variable feed milling changes the mechanism of the tool rake face by increasing the tool-chip contact area, change the crater position and decrease the crater wear depth, thus strengthens the tool edge and increases tool life.

    • Dynamic compressive mechanical properties of TB6 titanium alloyunder high temperature and high strain rate

      2019, 48(4):1220-1224.

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      Abstract:Using high temperature Hopkinson pressure bar test system,TB6 titanium alloy reducts the quality test 3000 s - 1 strain rate respectively, which is at different temperatures (550℃-850℃) and dynamic compression mechanical properties test, and get the material in different temperature and strain rate under the coupled action of true stress-strain curve, the temperature of the material flow stress and strain rate sensitivity. The experimental results show that under the condition of high strain rate, material has a certain strain rate strengthening, plasticizing effect, with the increase of temperature, the effects of the adiabatic heating thermal softening strenghthen, shear zone length increases. materials in 750 ℃ show abnormal strain rate softening phenomenon, shear band bifurcation may be the cause of strength decreased.

    • Influence of pre-torsion and annealing heat treatment on the tensile mechanical properties of TA2

      2019, 48(4):1231-1238.

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      Abstract:The effects of pre-torsion and annealing heat treatment on the tensile mechanical properties of TA2 were studied in present paper.According to tensile test results,the pre-torsion can significantly enhance the tensile yield strength and ultimate strength of TA2.The yield strength increases with the pre-torsion angle in a certain range,and drops sharply when the pre-torsion angle exceeds a certain value(6π).The ultimate strength increases all the time with the pre-torsion angle. The elongation decreases with pre-torsion angle. Subsequent annealing heat treatment tests of pre-torsion TA2 at different temperatures(350°C-750°C) show that the strength gradually decreases with annealing temperature.When temperature is 650 °C ,the strength has been reduced to the initial value of parent metal.The elongation increases with temperature, but it can"t recover to its initial value of parent material. The observation of fracture surface shows that dimple get smaller and shallower with the increase of pre-torsion,and there are lots of cleavage striation characterized by river pattern when pre-torsion angle is 8π.The observation of SEM shows that twins and deformation tissues after the pre-rotation is the main reason for the increase of TA2 strength.

    • A Crossover Iterative Method of Controlling Machining Deformations for Pre-stretched 7075 Aluminum Alloy Thick Plates

      2019, 48(4):1239-1248.

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      Abstract:Aeronautical monolithic components are characteristic of thin wall, large size, high machining accuracy, many material removals, and so on. The pre-stretched aluminum alloy thick plates are usually selected as blanks of aeronautical monolithic components. In the following process of high speed machining, the residual stresses will release from the blanks with the removal of material. In sequence, a new equilibrium of residual stresses can be achieved by the workpiece deformations which can strongly impact the machining quality. Therefore, the effect of residual stress release on machining deformation is investigated to control the machining quality. It is very crucial for the realization of machining process with high efficiency and precise. Above all, according to separation of a blank into removed materials and formed workpiece, the initial residual stresses can be divided into released stresses and efficient stresses so that the analysis model of machining deformations is deduced by the static equilibrium conditions and bend deformation theory. And then, finite element method is employed to solve the analysis model of machining deformations. The experiment of machined workpieces, carried out in NC machining factory, shows that both the amplitude and deformation curve, the simulated results are good agreement with the measured data. However, the measurement error of residual stresses causes 10% difference of the amplitude of the simulated results with the experimental values. Finally, an optimal model with the objective of minimum machining deformation is formulated to find the proper machining position. Therefore, a crossover iterative method is next suggested for the proposed optimal model. The initial machining position is selected from the minimum value with a given step along the positive direction. According to the sign difference of machining deformations at the current position with the last one, the step and its direction can be determined for the next selection. If the sign of the current deformation is same as the previous deformation, the step and its direction for the next position is same as the current position. Otherwise, it is chosen with the decrease step along the negative direction. The search procedure for the machining position is exceeded until the absolute value of the current step is within the given threshold value. In comparison with middle position method which is usually adopted by the enterprises, the presented crossover iterative method can decrease 99.79% machining deformations.

    • Effect of the step-quenching on microstructures and mechanical properties of TC21 titanium alloy

      2019, 48(4):1260-1266.

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      Abstract:In this paper, the microstructures which were obtained through step-quenching and the mechanical properties of TC21titanium alloy were investigated systematically. The samples were solution treated at 900℃ for 0.5h, and then 9 sets of step-quenching experiments with temperature from 600℃ to 60℃ were carried out. The microstructure characteristics, hardness and tensile mechanical properties was measured and compared with different microstructures. The results show that the width of secondary α lath gradually decreased from 600℃ to 400℃, and nearly remained constant from 400℃ to 60℃. The variation of the macro-Vickers hardness is the same as that of βtrans matrix. The elongation and the reduction of area slowly increases with increasing the quenching temperature. The Vickers hardness, yield strength and tensile strength increase with decreasing the width of secondary α lath. The microstructure with a good combination of strength and ductility was obtained through the step-quenching at 300 to 400℃.


      2019, 48(4):1267-1274.

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      Abstract:The 7475 aluminum alloy backfill friction stir spot welding is studied in this paper. Firstly, the 2mm 7475 aluminum alloy is welded by different process parameters, then the surface and cross section of the joint are observed, and the hardness and tensile shear test of the sample are carried out. The results show that the joint can be divided into four parts according to the weld microstructure, and the grain size of different parts is different. Hook, holes and unjointed microstructures due to poor fluidity of the material are found in the microstructure. At the same time, the hardness of the base metal zone and stirring zone is significantly higher than that of the heat affected zone and the thermo-mechanically affected zone; in addition, the highest hardness and tensile shear strength of the joint vary with welding tool rotation speed land the depth of the sleeve. However, the effect of the stirring sleeve movement rate on the mechanical properties of the solder joint is not obvious.

    • The microstructure and mechanical properties of GH4169/TC4 joints prepared by transient liquid phase (TLP) diffusion bonding

      2019, 48(4):1275-1280.

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      Abstract:To expand titanium alloy and Ni-based superalloy application fields, the prepration of titanium alloy/Ni-based superalloy composite joints is necessary. In this study, transient liquid phase (TLP) bonding has been successfully developed to join TC4 and GH4169 using Ti/Ni composite foils as interlayer. The microstructure, mechanical properties and formation mechanism of joint were investigated. The interfaces, fracture, composition and phases of as-prepared TC4/GH4169 joints were analyzed by scanning electronic microscopy (SEM), energy disperse spectroscopy (EDS) and X-ray diffraction(XRD), as well as shear strength and microhardness of joints were tested by universal testing machine and microhardness tester, respectively. The results showed that element interdiffusions and chemical reactions took place in the joining zone and multiple interlayer gradient structure, i.e. “Ni(s,s) / TiNi<sub>3</sub>/ Ti<sub>2</sub>Ni/ Ti/ Ti<sub>2</sub>Ni/ Ni/ TiNi”, was formed between GH4169 and TC4 under the process parameters of 960℃, 5MPa, 30min. The joint was compact with continuous interfacial bonding without obvious defects except some pores and microcracks exist in the interface of “Ni/ TiNi+Ti<sub>2</sub>Ni”. Hardness of each part of the prepared joint is not uniform, among them, the residual Ti and Ni interlayers have lower hardness, which is beneficial to alleviate the internal stress, the peak value appeared in the GH4169 side as a result of the formation of Ni(s,s) and TiNi<sub>3</sub>. Combined with the shear test, fracture morphology and phase analysis, the shear strength of as-prepared TC4/GH4169 joints achieved 124.6MPa and fracture occurs in the interface of “Ni/ TiNi+ Ti<sub>2</sub>Ni”, which presented a brittle characteristic.

    • >Reviews
    • Research progress in effect of surface deformation nano-crystalline on nitriding behavior of metallic materials

      2019, 48(4):1352-1360.

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      Abstract:A gradient nano-submicro-structure was obtained in metal surface via surface deformation nano-crystalline technology, which can provide severe plastic deformation on metal surface by external force. This unique gradient structure can not only be used to promote nitriding process of metallic materials, but also significantly be beneficial to form excellent nitriding layer, which can improve the comprehensive properties and service life. Therefore, it showed good application prospect in many fields. Recently, more and more investigations were focused on improving nitriding via surface deformation nano-crystalline pre-treatment, due to the academic and industrial application value. In the present article, the effect of surface deformation nano-crystalline on nitriding behavior is summarized in detail. Finally, the problems existed on the enhancement of nitriding are pointed out and it is also predicted what should be made in the future.

    • >Materials Science
    • Improvement of the Side-Suspended High-Temperature Superconductor Maglev Rotating Systemin an evacuated tube

      2019, 48(4):1046-1050.

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      Abstract:A well-established side-suspended maglev rotating system possesses two permanent magnet guidways (PMGs) with unimodal magnetic field for every one of them. The maglev vehicle of the system can reach a speed over 80 Km/h at the suspending gap of 6 mm in an evacuated circular tube. A way to increase the maximum speed of the system without changing the whole structure greatly is discussed. Putting the two parallel PMGs together to form a single PMG with trimodal magnetic field will obviously increase levitation force of the system. This will be possible to increase the maximum speed of the system. However the mass of vehicle will increase at the same time to contract the effect of the increase of levitation force. Evaluating the effects of them generally indicates that the trimodal structure PMG (TMG) can support higher speed than that of the unimodal structure PMG (UMG). Otherwise, maximum speed for TMG augments with the increase of the number of bulks. When the number of columns of bulks is 17, the speed for TMG is 8.2 percent larger than that for UMG.

    • Design of high entropy alloys based on the phase formation criteria and the big data system

      2019, 48(4):1059-1064.

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      Abstract:The development and phase formation criteria of high entropy alloy (HEAs) are described briefly. A new alloy design form is proposed in view of the big data system of high entropy alloy, and a new high entropy alloy is designed and studied. The result shows that the design form, AxByC(100-a-b-x-y)DaEb, is more in line with the requirements of the big data system compared with the previous alloy forms such as AxBCDE. The proposed design method can screen the expected alloy composition from the big data system of high entropy alloy rapidly and visually. The designed high entropy alloy, AlCoCrFeMo0.05Ni2, agrees with the target alloy, and has a great application prospect below 700 ℃.

    • Texture evolution and strengthening behavior of single crystal copper during equal channel angular pressing

      2019, 48(4):1065-1073.

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      Abstract:Because of the excellent conductivity, single crystal copper has been widely used in many industrial fields. However, the lower strength has severely restricted its further development and application. So, ECAP was adopted in this study to reinforce the single crystal copper by route A/Bc/C and research the effect of different routes. The texture of single crystal copper during 6 passes ECAP with a die channel angle of 120°through the route A, route Bc and route C were investigated by electron backscatter diffraction (EBSD) and X-ray diffraction (XRD). At the same time, the elongation and strength of the material were tested. The results show that after 5 passes, the tensile strength and elongation of route A, route Bc and route C is 405MPa with 30%, 395 MPa with 26.7% and 385 MPa with 27.9%, respectively. After 6 passes, the texture of route A is {112}<110> and weaker {110}<112> texture, route Bc is{001}<110>, texture of route C is dispersed. In the pole figure of the samples ECAPed by route C, double texture structure firstly appeared, the next is route A. There is no other texture appeared in the pole figure by the route Bc. Meanwhile, the conductivity of the material is just had a small decrease, and all of them are above 98% IACS. It can be seen that ECAP can significantly reinforce the material without obviously decreasing the conductivity in a right strain. Simultaneously, the different extrusion routes can obvious influence the properties of the material, the sample of route A has highest strength, and the route C has best conductivity.

    • Preparation and characterization of Mg doped InxGa1-xN thin films by magnetron sputtering

      2019, 48(4):1074-1078.

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      Abstract:Being considered In2O3, Ga2O3, Mg as In, Ga and Mg sources, the InxGa1-xN and Mg doped InxGa1-xN thin films were deposited on Si substrate by magnetron sputtering. The In component in the film decreases with the doping of Mg, because Mg doped suppresses the formation of In-N bond and increases the chance of Ga into the film. The EDS analysis of Mg doped InxGa1-xN film as-prepared show that 1.4 % of Mg content was successfully doped into the InxGa1-xN film. The electrical performances of In0.84Ga0.16N and Mg doped In0.1Ga0.9N thin films reveal that the type conduction of InxGa1-xN thin films is transformed from n-type to p-type conduction, and the hole concentration and mobility of Mg doped In0.1Ga0.9N thin film are found to be 2.65×1018 cm?3 and 3.9 cm2/Vs, respectively.

    • The influence of δ phase on the microstructure and properties of Inconel 625 superalloy tubes

      2019, 48(4):1079-1086.

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      Abstract:In this paper, the amount, distribution and morphology of δ phase in the alloy were controlled by cold deformation and aging treatment without changing chemical compositions of Inconel 625 superalloy to ensure the microstructure stability and performance reliability of the alloy. The influence of cold deformation (ε) on the amount, distribution and morphology of δ phase precipitation and the precipitation of δ phase on the microstructure and properties of Inconel 625 superalloy tubes are investigated by room temperature compression tests plus aging treatment. X-ray diffraction (XRD), scanning electron microscopy (SEM) and, energy dispersive spectrdmeter (EDS) is utilized to analyze the δ phase characteristics. It is found that with the increase of cold deformation (ε), the average grain size decreases and the deformation uniformity of the grain becomes better gradually, and the hardness increases. Cold deformation (ε) promotes precipitation of δ phase. With the increase of cold deformation (ε), the δ phase first precipitates at the deformation twin and grain boundaries as well as deformation bands, and then precipitates in the grains, the precipitation of δ needle phase were oriented in two near-orthogonal directions or a lattice-like distribution within the grain and the δ phase were oriented in two parallel directions at the deformation bands. At the same time, the morphologies of δ phase change gradually from needle to spheroid or short rodlike with increasing cold deformation (ε).The average grain size of the alloy reduces with the increase of cold deformation (ε) and the extension of aging time (t). The hardness of the alloy increases with the extension of aging time (t) at ε=35 %, however, the hardness of the alloy has no obvious change ε≥50 %.

    • Corrosion behaviour of arc sprayed high Al content of Zn55Al coatings on Q235 steel in 3.5 wt% NaCl solution

      2019, 48(4):1087-1095.

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      Abstract:In this work, a Zn55Al coating was deposited on Q235 steel by arc spraying high Al content Zn55Al pseudo-alloy wires formed by multi-core canned hot extrusion and a cold drawing method. The microstructure of the Zn55Al pseudo-alloy wire was investigated by scanning electron microscopy (SEM) and micro-region X-ray diffraction (Micro-XRD). The corrosion behaviour of the Zn55Al coating and pure Al coating as well as the Zn15Al coating were investigated by an immersion corrosion test and electrochemical measurements, and the difference between the coatings was also assessed. The results indicated that Zn55Al pseudo-alloy wires were composed of pure Zn and pure Al. An alloying phenomenon did not occur in the whole formation process. The Zn55Al coating that contained Zn-rich phases and Al-rich phases exhibited an obvious lamellar structure with a few holes and gaps. After 20 days of immersion, it was found that the Zn55Al coating formed a dense passive film and had better corrosion resistance than the Zn15Al coating. The corrosion potential (Ecorr) of the Zn55Al coatings was approximately 80 mv, which is more positive than that of the Zn15Al coatings but is more negative than that of the pure Al coatings and the Q235 substrate. The results of galvanic corrosion test also showed that the Zn55Al coating can provide better electrochemical protection than Zn15Al coating to the Q235 substrate. This suggested that Zn55Al coating displays not only a better corrosion resistance but also a stronger electrochemical protection to the Q235substrate. The protective mechanisms of the Zn55Al coating were also discussed.

    • Influence of fiber size and interface morphology on the electrochemical corrosion resistance of directionally solidified NiAl-9Mo eutectic alloy

      2019, 48(4):1116-1123.

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      Abstract:As the solidified microstructures have a significant influence on the corrosion behavior, our aim is to derive the optimum microstructures and electrochemical conditions for producing Mo nanowires. Eutectic microstructures showing coupling growth of NiAl phase and Mo fibers were obtained at growth rates from 10 to 40 μm/s. The fiber size varies from 800 nm to 300 nm, and decreases with the increase of solidification rate. Potentiodynamic polarization studies indicated that NiAl-Mo alloy at a growth rate of 20 μm/s has a better corrosion resistance in 0.1 M HCl solution at room temperature. The electrochemical corrosion behavior of directionally solidfied NiAl-Mo alloys not only depends on fiber size, but also related to the interface morphology. To further analyze the influence of interface morphology on the corrosion behavior, velocity suddenly change experiments were carried out. The microstructure of directionally solidified NiAl-Mo alloy transformed from planar to cellular and dendritic structures as the value of V/V1 increased. The results of potentiodynamic polarization curves revealed that the planar structure has the highest corrosion resistance compared to other mophologies with the same fiber size of Mo-nanowires.

    • Nano-cutting temperature field distribution and the influence of anisotropy on cutting temperature of single crystal germanium

      2019, 48(4):1130-1134.

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      Abstract:In order to understand the nano-cutting properties of single crystal germanium and improve the optical surface quality of nano-germanium devices, the three-dimensional molecular dynamics (MD) method was firstly applied to investigate the temperature distribution of the material atoms during the nano-cutting process of single crystal germanium. The anisotropy effect of Ge (100)、(110)、(111) on the cutting temperature and the influence of cutting temperature on cutting force were investigated. It was found that the highest cutting temperature during the cutting process was distributed among the chips, reaching 460K. there is also a high temperature region in the friction zone of the tool back face, the highest temperature is above 400K. Among the three different crystal planes, Ge (111) has the highest cutting temperature, because the atoms between different crystal faces have different spatial structures. Ge (111) has the highest atomic density, namely, Ge(111) is the densely packed surface of the single crystal germanium, which releases the most energy. What’s more, cutting temperature has also played an impact on the cutting force, As the cutting temperature increases, the cutting force of the material atoms will be reduced.

    • Oxidation Behavior of MoSi&lt;sub&gt;2&lt;/sub&gt;-CoNiCrAlY Composite Coating Prepared by Plasma Spraying

      2019, 48(4):1135-1141.

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      Abstract:MoSi&lt;sub&gt;2&lt;/sub&gt;-CoNiCrAlY composite coatings were deposited on GH4169 alloy with ball milled nanocrystalline powders by plasma spraying technology. Cycle oxidation behavior of coated and uncoated GH4169 alloy at 900℃ in static air was investigated. The results showed that the composite coating exhibited good oxidation resistance at high temperature, and the oxidation rate was only 1.23&#215;10&lt;sub&gt;-7&lt;/sub&gt; mg&lt;sub&gt;2&lt;/sub&gt;.cm&lt;sub&gt;-4&lt;/sub&gt;.s&lt;sub&gt;-1&lt;/sub&gt;, which was attributed to a self-sealing oxide film SiO&lt;sub&gt;2&lt;/sub&gt; with excellent protective properties formed at the early stage by oxidation of MoSi&lt;sub&gt;2&lt;/sub&gt;. The oxidation resistance of the coating would be reduced by the peeling of SiO&lt;sub&gt;2&lt;/sub&gt; in the later period of oxidation and the reoxidation of Mo&lt;sub&gt;5&lt;/sub&gt;Si&lt;sub&gt;3&lt;/sub&gt; phase to generate MoO&lt;sub&gt;3&lt;/sub&gt; and MoO&lt;sub&gt;2&lt;/sub&gt; gas phase as well as the internal oxidation of MoSi&lt;sub&gt;2&lt;/sub&gt;.

    • Deformation Behavior and Mechanisms of Tensile in a Advanced High-performance Nickel-Based PM Superalloy

      2019, 48(4):1142-1147.

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      Abstract:The deformation microstructures, deformation behavior and mechanisms of FGH98 after tensile tests at room temperature(23℃) and intermediate temperatures(650℃、750℃、815℃)have been investigated by scanning electron microscopy(SEM)and transmission electron microscopy(TEM). The results show that FGH98 alloy, with multi-mode size distribution γ'phase, obtained excellent tensile properties at room temperature and intermediate temperature. The dislocations sheared γ'phase, forming stacking fault(SF) in the γ'precipitate and a dislocation loop around the γ'precipitate, which is the dominant deformation mechanism during the tensile deformation at room temperature. The dislocation loop hindered the subsequent dislocation movement. However, forming SFs and deformation twins by dislocations shearing γ'phase becomes the dominant deformation mechanisms at intermediate temperatures. With the increasing of deformation temperature, the deformation mechanisms transfer from SFs to deformation twins, and the density of twins increased. The model of a/3<112> partial shearing the γ'precipitate forming faults and twins was given. With the increase of strain, the stacking faults accumulated on the adjacent {111} planes, promoting the formation of continuous twins. The formation of continuous twins can coordinate the deformation between the γ and γ'phase and release the deformation stress, resulting in enhancement of the alloy plasticity.

    • Kinetics of δ phases precipitated at grain boundaries during aging of GH4169 superalloy

      2019, 48(4):1148-1154.

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      Abstract:GH4169 alloy is a Ni-Fe based superalloy which is used as the critical component in areoengine. The evolution of δ phase has highly influence on the hot working process, microstructure evolution and performance. In this paper, GH4169 alloy which are solution treated and deformed at high temperature were conducted on aging treatment to investigate the morphology and precipitation mechanisms of δ phases. The volume fraction of δ phases increases with the Nb element content. The peak temperature for δ phases precipitation is 920℃ which is not influenced by the content of Nb element. The nucleation rate and volume fraction of δ phases increases with the decreasing of average grain size. Otherwise, the size of δ phases decreasing with average grain size. Low angle grain boundaries within grains promote the precipitation of δ phases intergranular. The critical barrier and critical radius decreases with the radius of vurvature. Otherwise, the nucleation rate of δ phases increases with the increasing of curvature. The distribution morphologies of δ phases precipitated at grain boundary are similar to needles, sawtoothes and fish tails.

    • The study of the oxidation of the ZrB2-ceramic composite

      2019, 48(4):1168-1173.

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      Abstract:An analysis of the thermodynamics behavior of the ZrB2-glass ceramic and the phase and microstructure of the oxidation scale during the oxidation process was reported.The results indicate that the ZrB2 is oxidized to generate ZrO2,B2O3 glass phase,the oxidation product ZrO2 react with SiO2 to form ZrSiO4 during the temperature between 1000°C and 1400°C.when the temperature below 1177°C(1450K),the oxidation scale mainly contain ZrO2,B2O3 glass phase,ZrSiO4.when the temperature exceed 1177°C(1450K), the B2O3 glass phase evaporated ,at the same time,the SiO2 glass phase has good fluidity ,the oxidation Scale mainly include ZrO2,SiO2 phase ,ZrSiO4.the reaction products,B2O3phase,ZrSiO4 and fluidity SiO2 phase all have an excellent resistance for the process O2 diffuse into the matrix.

    • Synthesis, mechanical properties and thermal conductivity of GdTaO4

      2019, 48(4):1179-1182.

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      Abstract:In order to search the more excellent thermal barrier coating materials, the monoclinic GdTaO4 ceramics are synthesized by solid-phase reaction. The microstructure is analyzed. The results of first-principles calculations indicate that the Young’s modulus along [100] crystallographic orientation is triple as large as that along [010] and [001] crystallographic orientation. The measured thermal conductivity is 1.70 W.m-1.K-1at 800℃ in experiment, which is lower than the thermal conductivities of 7-8YSZ (2.37-2.47 W.m-1.K-1). The GdTaO4 is a promising thermal barrier coating material.

    • Low Cycle Fatigue Behavior of Ultrafine grained CP-Zr Processed by ECAP and RS

      2019, 48(4):1202-1207.

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      Abstract:Ultrafine grained (UFG) commercially pure Zr was prepared by Equal Channel Angular Pressing (ECAP) and Rotary swaging (RS). The Low cycle fatigue properties of the UFG pure Zr were investigated by a method under axial loading controlled by symmetric strain. The characteristics of cyclic stress and strain response and hysteresis loop of UFG pure Zr were discussed. Softing and hardening characteristics and cumulative hysteresis of the UFG pure Zr were analyzed and then the fatigue life was predicted. The results indicate that the cyclic softening and hardening properties of UFG pure Zr depend on the size of the applied total strain amplitude, and the softening ratio is most significant when the total strain amplitude is more than 1.0%. The hysteresis loop area increases with the total strain amplitude increasing, and the “ratchet phenomenon” occurs when the strain amplitude is small. Regression analysis shows that the fatigue life of UFG pure Zr matches Coffin-Manson"s empirical

    • Arrhenius properities of electrochemical performance and impedance parameters of lithium ion batteries

      2019, 48(4):1208-1212.

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      Abstract:The influence of ambient temperatures on charging capacities of 18650 type LFP and NCA batteries were investigated in this paper, and the performance in low temperature was compared. Electrochemical impedance measurements were taken in various temperatures, the values of ohm, film and charge transfer resistances were confirmed according to equivalent circuits. As for LFP batteries, ohmic resistance and film resistance are well meet the Arrhenius relations in the range of -10~25 ℃, however, in a wider range of -10~50 ℃ charge transfer resistance is well meet. However, as for NCA batteries, film resistance and charge transfer resistance are complyed with Arrhenius relations in range of 0~50 ℃. The comparison analyses of solid phase ion diffusion coefficient in different temperatures indicate that the ion diffusion rate of LFP battery is obviously affected by low temperatures, nevertheless, slightly affected for the NCA battery.

    • Microstructure and micromechanics features of Ni-Ti-Si coating deposited by laser cladding

      2019, 48(4):1225-1230.

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      Abstract:A cladding layer 55Ni-35Ti-10Si (at.%) was synthesized on copper using laser cladding in this paper. It was composed of two kinds of microstructures. The microstructures of the cladding layer were characterized by optical microscope (OM), scanning electron microscope (SEM), X-ray diffraction (XRD) and energy dispersive spectrometer (EDS). According to the analysis results, phases appeared in upper layer should be Ti solid solution+Ni3Si and the morphology was dendritic. The under layer was composed of Ti solid solution+ Cu solid solution and the morphology was cellulate. The crystal growth in solidification process was analysed using a modification model which is combined Kurz-Giovanola-Trivedi (KGT) model with Lipton-Kurz-Trivedi (LKT) model. Mechanism of cladding layer stratification was studied by thermodynamics. Microhardness of cladding layer was tested. The average hardness of upper layer and under layer were 800HV and 220HV, respectively. The synthesis of under layer increased the stability of cladding layer.

    • >Materials Technology
    • Preparation, mechanical properties and electrical conductivity of carbon nanotube reinforced Cu matrix composites

      2019, 48(4):1249-1255.

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      Abstract:The copper based composite powders containing 0.5~2wt.% CNTs were prepared by molecular-level method combined with the two-step mixing process using CNTs, electrolytic Cu powder and Cu (CH3COO) 2.H2O as raw materials, and then the Cu-CNTs composites were prepared by spark plasma sintering. The influence of preparation process and CNTs content on the microstructure, electrical conductivity and mechanical properties of Cu-CNTs composites were studied. The results show that when CNTs content is less than 1.0wt.%, Cu-CNTs composite powders prepared by two-step mixing process have good homogeneity and good dispersibility. The Cu-CNTs composites with high density and uniform CNTs were obtained after sintering. When the content of CNTs is more than 1.0wt.%, the densities and the uniformity of CNTs are obviously decreased. With the increase of the CNTs content, the strength of composites increases in initial stage and then declines, and the plasticity and electrical conductivity tend to decrease. Compared with the high-energy ball milling and molecular level method, the Cu-1.0wt.%CNTs composites prepared by two-step method exhibits the superior mechanical properties, including the electrical conductivity of 51.7 MS/m (89.1% IACS), the hardness of 113 HV, the tensile strength of 279 MPa, and the elongation of 9.3%.

    • Effect of graphene doping on the superconducting properties and microstructure of MgB2 bulks

      2019, 48(4):1256-1259.

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      Abstract:Magnesium diboride (MgB2), which has the great technology advantage at 20-25 K and 1-3 T, is a promising material compared with other metallic superconductors and high-temperature superconductors due to its low cost raw material and without liquid helium. In order to meet the requirement of pratical applications, it is necessary to increase the superconducting properties of MgB2, so the flux pinning properties and intergrain connectivities have become the focus of researchers. In this work, MgB2 bulks with graphene, graphene-acetone solution, graphene coating B doping were synthesiszed and the microstructure, critical current density, flux pinning properties were studied systematically. The critical current density by graphene doping directly got significant enhancement at low field. However, the superconduting properties for samples synthesiszed by solution process and coating method did not improved obviously due to the oxidation decreased the activity of B powders.

    • The microstructure and property evolution of the GY200 nickel base alloy for steam turbine blades after long-time aging

      2019, 48(4):1281-1287.

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      Abstract:: Thermal-calc thermodynamic software was used to calculate the precipitates in GY200 equilibrium conditions.The microstructure, performance, carbides and γ" phase evolution of GY200 nickel base alloy for the blades of an advanced super supercritical power station at 700 and 750 °C with different aging times were studied by means of metallography, scanning, and chemical phase analysis. The results show that the strength increases significantly after aging, and the impact performance decreases slightly. The carbides mainly consist of M23C6 and MC phases. The replacement of Mo in Waspaloy by W decreases the precipitation tendency of M6C. The content of M23C6 phase increased with the increase aging time, and the carbides separated out as chains and lamellae in the grain boundary. The amount of MC phase began to decrease after aging for 3000 h. The amount of γ" phase increased after aging at 700°C for 3000 h, stabilized after 5000 h, and remained basically unchanged at 750 °C. The γ′ phase has good thermal stability at 700°C with a low coarsening rate. The coarsening rate at 750°C is higher and the diameter of γ′ is about 100nm after aging at 5000h.

    • Effect of Temperature on Tensile Behavior of Nickel-Based Single Crystal Superalloy DD13

      2019, 48(4):1288-1292.

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      Abstract:Tensile behaviors of a Nickel-based single crystal superalloy DD13 were studied from room temperature to 1050 °C in this study. Results show that both of yield strength and tension strength reached the peak value, namely 1108 MPa and 1340 MPa when testing temperature reached 700 °C. However, a converse trend was observed for the temperature dependence of plastic properties. Model of dislocation overcoming the precipitation strengthening phase (γ′) takes a key role on yield strength, which changes from shearing to climbing with the rising testing temperature. After the yield point, both of tension strength and plastic property are decided by that whether dislocations could slide smoothly or not. Relational twisting of partial dislocations with stacking fault from different slipping systems was observed at 700 °C.

    • Extrusion procedure and microstructure properties of multi-filamentary MgB2 superconducting wires

      2019, 48(4):1293-1297.

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      Abstract:For improving the combine strength among filamentaries and the density of superconducting cores in multi filamentary MgB2 wire, the traditional hot-extrusion method was introduced to the MgB2 wires fabrication process. MgB2 wire with the conducting structure of 180 cores was fabricated by the extrusion method. Compound billet is extruded from Φ64 mm to Φ20 mm in diameter with one pass extrusion. The extruded wire is fabricated to the final size Φ0.8 mm in diameter with cold drawing and mid-annealing process. Superconducting filamentary is uniformly distributed and the thickness of Nb diffusion barrier is also smooth without breaking points through the microstructure analysisof the wires at each fabrication stages. The hectometer MgB2 wires is fabricated successful by this method. The extrusion technique is promising for producing long MgB2 superconducting wires.

    • The Influence of Zirconium Salt Materials on the Structure and Properties of LiZr2(PO4)3 Lithium ion Solid Electrolyte

      2019, 48(4):1298-1303.

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      Abstract:Samples of LiZr2(PO4)3 compound with pure phase , adopting the method of solid phase and liquid phase method, were obtained by pressureless sintering from different zirconium salt raw materials. And LiZr2(PO4)3Li-ion solid electrolytes were characterized through x-ray diffraction (XRD), scanning electron microscope (SEM) and electrochemical impedance (EIS) . Analyzing the results of the test, the influence of different zirconium salt raw materials on the structure and performance of LiZr2(PO4)3 solid electrolytes is studied. A room-temperature stable α- LiZr2(PO4)3phase(R-3c,a=8.8442?andc=22.264?) is prepared from zirconium acetate. While synthetic LiZr2(PO4)3 prepared from the other three kinds of zirconium salt raw materials exist in triclinic phase . Rhombohedral phase LiZr2(PO4)3 lithium ion solid state electrolyte sample prepared from different zirconium raw materials show the highest total conductivity of 2.25 × 10-5 S/cm, and the activation energy is 0.28 eV.

    • Preparation and electrochemical performance of Carbon-encapsulated NiO Nanoparticles

      2019, 48(4):1304-1309.

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      Abstract:Core shell structure carbon encapsulated NiO nanoparticles were successfully prepared by DC arc discharging plasma technology. The micstructure of the samples were studied by X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), X-ray energy dispersive spectrometry (XEDS) and Surface physical adsorption. The cyclic voltammetry, galvanostatic changing-discharging and electrochemical impedance spectroscopy were investigated to characterize the electrochemical performances of the composites as the electrode materials for super-capacitors. The experimental results indicate that the carbon encapsulated NiO nanoparticles prepared by DC arc plasma technology possess typical core shell structure, the core of the particles is NiO with face centered cubic structure, and the outer shell is disordered carbon layer. The particle morphology exhibit cube structure with uniform particle size and good dispersion. The particle size distribution is in the range of 30-70nm, the average particle size is 50nm, and the thickness of the carbon shell is about 5nm. Carbon encapsulated NiO nanoparticles has high specific capacity and good electrochemical activity.

    • Microstructure and Properties of Cu-Cr-Ag alloy fabricated by up-drawn continuous casting and continuous extrusion

      2019, 48(4):1310-1316.

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      Abstract:Effect of aging treatment on microstructure and properties of Cu-Cr-Ag alloy fabricated by up-drawn continuous casting and continuous extrusion are investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that the grains were refined significantly, with an average size of 4~5 μm, when the cast rob was processed during the continuous extrusion. The relation curve between Vickers hardness and aging time firstly rapid decrease, then quickly raise, finally slowly decrease and the electrical conductivity firstly rapid increase, then slowly raise, finally trended to stable as the aging time rise, when the Cu-Cr-Ag alloy was solutioned at 875℃ for 1h, 60% cold deformation and aged at 450℃ for different time, respectively. The precipitation sequence of Cu-Cr-Ag alloy aged at 450 ℃ is supersaturated solid sloution→G.P zones→fcc Cr phase→order fcc Cr phase→bcc Cr phase. The orientation relationship between bcc Cr precipitates and the matrix exhibit NW-OR

    • Effect of Al-Nb Content on Microstructure and Properties of GH706 Alloy for Rotor

      2019, 48(4):1317-1324.

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      Abstract:The effects of increasing Al and decreasing Nb on microstructure and mechanical properties of GH706 alloy before and after long time age heat treat were studied. Result show that increasing Al content and decreasing Nb content in alloy contribute to disappear of γ′′、Laves and δ phases in alloy, and after aged at 750℃ for 500h, γ′ and η grow up slightly and mechanical properties reduce limited. While precipitates of alloy without modification(conventional GH706) grow up rapidly and mechanical properties decrease obviously. The result indicated that the alloy can be used at higher temperature with modification of increasing Al and decreasing Nb.

    • Effect of Ni-B-C on Electrochemical Properties of La0.94Mg0.06Ni3.49Co0.73Mn0.12Al0.20 Hydrogen Storage Alloy

      2019, 48(4):1325-1329.

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      Abstract:Ni-B-C powder prepared by ball milling was introduced to improve the electrochemical properties of new AB3-type hydrogen storage alloy La0.94Mg0.06Ni3.49Co0.73Mn0.12Al0.20. X-ray diffraction(XRD) and scanning electron microscope(SEM) were adopted to investigate the phase structure and Surface morphology of the alloy. It suggests that the alloy remains the original LaNi5 and La2Ni7 phases and some little particles appear on the surface of alloy. The addition of Ni-B-C improves the maximum discharge capacity and capacity retention rate. After adding a mass fraction of 10% Ni-B-C, the maximum discharge capacity increased from 346 mAh/g to 363 mAh/g, and the capacity retention rate after 50 cycles increases from 70% to 77%. The exchange current density I0 and the limiting current density IL reach 106 mA/g and 987 mA/g, respectively. Potentiodynamic polarization indicates the corrosion resistance of the electrodes is enhanced. The results show that the Ni-B-C powder can improve the comprehensive electrochemical properties of the hydrogen storage alloy.

    • The superconducting properties research for different sheath MgB2 wiresdoped with graphene

      2019, 48(4):1330-1335.

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      Abstract:Single filament MgB2/Fe(Nb)/Cu wires with or without graphene doping, using Fe and Nb as the diffusion layer, were fabricated by the in-situ PIT method. The heat treatment of sample is at 670~800 ℃ for 2 hours under high purity Ar atmosphere. X-ray diffraction pattern shows the main phase for the wires with heat treatment at 670℃ was whole MgB2 phase, except partial Fe2B impurity phase in Fe sheathed MgB2 wires. Microstructure analysis shows the hole between crystal grains in the wire without doping was bigger than that of Fe or Nb sheathed MgB2wire doped with graphene. Stress-strain test result shows the tensile strain value for the wire before heat treatment was lower than that of wires after heat treatment obviously. Hardenability of Fe sheathed wires was more sharpness. The strength was the maximum for Fe sheathed wires with or without heat treatment. Four probe transfer measurement properties show that the critical current density Jc of Nb sheated wire heat trwatment at 670 ℃ was higher than that of Fe sheated wire at 4.2 k with the field of 2 T,4 T and 6 T. Nb and Fe sheated MgB2 wires doped with graphene possess better transfer porformence at 2 T. The Jc value at 2 T was arrived at 4.5×105A/cm2 for Nb sheated wires. When the field is higher than 4 T, the Jc value of Nb and Fe sheated MgB2 wire doped with graphene was lower than that of undoped wire. The transfer property of Fe sheated wires reduce faster than that of other samples. This indicates that the dopants incompletly enter the crystal structure and led to the reduced flux pinning function at high field.

    • Dealloying Behaviors of Sintered Porous Cu-Zn Alloys

      2019, 48(4):1336-1344.

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      Abstract:Microporous Cu-Zn were prepared by powder metallurgy, which were then employed as precursors to prepare micro-/nano-porous coppers by dealloying. Firstly, the effect of sintering temperature on the microstructures of Cu-Zn precursors was investigated. Then, the phase constitution and microstructures of Cu-Zn alloys after dealloying in HCl solutions with different concentration were compared. Finally, the electrochemical behavior of Cu-Zn precursors during dealloying process was analyzed. The results showed that micro-/nano-porous coppers can be prepared by powder metallurgy and dealloying. Different sintering temperature contributed to the variation of phase content and porous structure of Cu-Zn precursors, which then caused significant differences during delloying process. Cu30Zn70 precursors consisted of Cu5Zn8 and CuZn5, and CuZn5 was corroded preferentially during dealloying process. While Cu50Zn50 precursors consisting of single phase CuZn showed a much slower corrosion rate. Both precursors were dealloyed incompletely in 0.1mol/L HCl solution. When the concentration of HCl solution was increased to 0.5mol/L, Zn was completely dealloyed from both precursors and nanoporous structures were formed in micro-scale ligaments. The diameters of micro pores and nano pores were about 3.02~3.68μm and 157~ 183nm, respectively.

    • Mechanism and microstructure properties of Al-Ti-C mother alloy prepared by titanium hydride-graphite

      2019, 48(4):1345-1351.

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      Abstract:The microstructure and properties of Al-Ti-C master alloy prepared by titanium hydride and graphite were studied by X ray diffraction (XRD)、scanning electron microscope (SEM) and energy dispersive spectrometer (EDS).The results show that the mechanism of Al-Ti-C alloy prepared by the reaction of titanium hydride-graphite and aluminum liquid is that (1) Titanium hydride and graphite are respectively used as titanium and carbon sources, and titanium and hydrogen are obtained by thermal decomposition of titanium hydride.(2)Titanium react with aluminum and graphite to form titanium-aluminum、titanium-carbon or carbon-aluminum compounds.(3) Titanium aluminum, carbon aluminum and titanium carbon compounds have refined Al-Ti-C alloy.The phase composition of the alloy includes α(Al), Ti-Al,C-Al, Ti-C compounds and other phases. The microscopic structure is equiaxed or dendrite structure, and the average grain size is 20~40μm.There are needle like or rod like primary crystals in the alloy matrix. There are petal like primary crystals containing titanium, carbon, iron and silicon on the grain boundaries. The titanium and carbon elements distribute evenly along the grain boundaries and the grains. There is obvious titanium and carbon enrichment and segregation near the primary phase.Cryolite is conducive to the wetting and reaction of carbon and aluminum, the second phase generated more fully and uniform diffusion in the grain.

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