Abstract:Confocal laser scanning microscope(CLSM) was used to observe the solidification behavior of Nickel-based single crystal superalloy CMSX-4 in real time. SEM and EDS were used to study the micromorphology and element segregation characteristics of the solidified samples. Shrinkage and carbide formation were observed during alloy solidification. There are three types of shrinkages: square shrinkages, pentagonal star shrinkages and angular shrinkages. The formation mechanism of the three shrinkages is disccused, which is mainly related to the shape of the enclosed area surrounded by the secondary dendrite arms growing in different directions. In addition, carbides are found to be composed of two forms, namely flocculent carbide and lath carbide. Hf elements are enriched in flocculent carbides, while Cr elements are enriched in lath carbides.

Abstract:This work investigates the corrosion behavior of GH3625 alloy under acidic atmosphere SO2 at 900 ℃. The surface morphologies of the corroded specimens and the corrosion products were investigated by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD). The cross-sectional morphology was examined by SEM, EDS, and electron probe micro-analyzer (EPMA) to observe the internal corrosion. The results demonstrate that the corrosion rate of the GH3625 alloy only slightly increased with increasing SO2 content in the acidic environment. A dense oxide film (primarily Cr2O3) forms on the alloy surface which can effectively prevent SO2 from diffusing into the interior of the alloy matrix. Additionally, chromium inside the matrix can combine with sulfur (primarily CrS) retarding corrosion. GH3625 alloy exhibits excellent corrosion resistance under an SO2 environment.

Abstract:In order to further understand the Vacuum arc remelting(VAR) process, with the help of OpenFOAM, an open source CFD computing software, a two-dimensional multi-physical finite volume model (FVM) including electromagnetic field, temperature field and flow field was established to study the macroscopic phenomenon of the unsteady solidification process on GH4698 nickel-based super alloy ingots. Results shows that magnetic induction intensity induced by the current flowing from the crucible to the consumable electrode is mainly concentrated on the upper part of the ingot and rotates along the axis of the ingot. The magnetic induction intensity first increases and then decreases from the center to the edge of the ingot, and reaches the maximum value at the edge of the electrode. Thermal buoyancy and lorentz forces are the main driving forces in the molten pool and their effect on the flow of molten pool is opposite to each other.

Abstract:The creep behavior of Ni-based single crystal superalloys small degree deviated from [001] orientation is strongly influenced by temperature, γ? phase size and the level of applied stress. This article presents a review on effects of small orientation deviation on creep behavior of single crystal superalloys. Different creep properties of the alloys with orientation deviation originate from different creep deformation mechanisms. Besides, these mechanisms correspond to different threshold stress which are associated with the occurrence of primary creep and creep rate. At intermediate temperatures, the creep behavior of single crystal alloys is highly sensitive to small misorientation but relatively insensitive above 850 °C. The size of γ? phase is inferred to exert influence on the creep behavior of alloys with orientation deviation at intermediate temperatures. However, at elevated temperatures, the rafting process can be accelerated by higher thermal activation, thus the mechanical properties become less relevant with the size of γ? precipitates coarsening.

Abstract:The high performance blade has been the widely applied to increase the efficiency of the aircraft engine, and its fabrication has been well developed. However, the appearance of misoriented grains always decrease of production yield. Competitive growth of dendrite arrays with different orientation in directional solidification is an important phenomenon for the fabrication of single crystal blade. The question has caught attention for many years. The tip undercooling has been the only criterion for the elimination of unrefereed dendritic grains for a long time and is implanted in commercial software ProCAST to simulate the grain growth. However, the experimental bicrystal growth in directional solidification identified the drawback of the tip undercooling criterion. Quantitative phase field simulations showed more details of the bicrystal competitive growth. The grain boundary evolution has been one of the key indicators for competitive growth. The previous tip undercooling criterion could not predict the grain boundary evolution. The huge phase field simulations reveal the statistic evolution rule of the grain boundary direction. In this paper, we proposed a sheet sample with multiple bycrystals configurations. The microstructures were observed in a stitching picture. The competitive growth and the grain boundary selection of dozens of biocrystals have been summarized within several samples. The statistical results agree with the phase field simulation. However, the CAFE simulation results from the ProCAST can not predict the grain boundary evolution. The method proposed here can be applied to investigate the competitive growth with a high throughput way. The results are helpful to understand the unoriented grains in fabrication of single crystal blade.

Abstract:The tensile mechanical properties of Ni/Ni₃Al are simulated by molecular dynamics. First, the effect of the content of γ′ strengthening phase on the tensile mechanical properties of Ni/Ni₃Al is studied at room temperature and constant strain rate. The microstructure evolution of Ni/Ni₃Al under the content of γ′ strengthening phase with three typical characteristics is especially investigated. Compared with single crystal Ni, it is found that the γ′ strengthening phase can increase the tensile strength of Ni/Ni₃Al. This is because during the plastic deformation process, as the dislocations continue to multiply, the dislocation density gradually increases, resulting in dislocation plugging, which increases the resistance to dislocation movement, thereby increasing the tensile strength. Secondly, temperature effect of the tensile mechanical properties of Ni/Ni₃Al is studied, and it is found that the tensile strength of Ni/Ni₃Al-10 vol%Ni₃Al decreased with increasing temperature. This is because as the temperature increases, the internal kinetic energy of the atom increases, resulting in the more intense thermal motion of the atoms, and the weaker the bonding force between the atoms. The atoms leaving the equilibrium position have no time to return to the equilibrium position, and the FCC structure is transformed into a large number of HCP structures and other atomic arrangements, which cause lattice distortion and reduce tensile strength. Finally, the effect of strain rate on the tensile mechanical properties of Ni/Ni₃Al is studied. The results show that the tensile strength is not sensitive to low strain rate, but sensitive to high strain rate.

Abstract:The low-cycle fatigue tests for the Inconel 625 alloy were performed at 650°C under three strain waveforms including triangular waveform as well as two sawtooth waveforms with slow-tension followed by fast-compression and fast-tension followed by slow-compression. And the low cycle fatigue deformation and fracture behaviors of the alloy under different strain waveforms were investigated. The experimental results show that the Inconel 625 alloy exhibits the cyclic hardening at the different waveforms and applied total strain amplitudes from 0.3% to 0.7%. When two sawtooth waveforms are adopted, the fatigue life of the alloy will shorten due to the introduction of either tensile or compressive creep strain component, In addition, the relation between the plastic or elastic strain amplitudes and fatigue life as well as between the cyclic stress amplitude and plastic strain amplitude exhibits a single slope linear behavior. The observations on the fatigue fracture surfaces reveal that under three strain waveforms used in this investigation, the fatigue cracks initiate and propagate in a transgranular mode.

Abstract:The Ni-xPt-25Al (x = 0, 10, 20 and 30 at.%) alloys were fabricated by cold crucible levitation melting under argon atmosphere on a water-cooled Cu crucible. The effects of Pt contents on crystal structures, oxidation kinetics, morphologies of oxides, and oxidation resistance of the Ni-xPt-25Al alloys were studied using X-ray diffraction, simultaneous thermal analyzer, scanning electron microscopy, and X-ray photoelectron spectroscopy. The experimental results showed that Pt-modified Ni3Al-based alloys still kept γ′ phases with Pt contents increasing. The heating up and isothermal periods yield to the linear and parabolic kinetic laws, respectively. Pt plays a beneficial role in promoting the formation of oxides, meanwhile, the increased addition of Pt also improved the integrality and compactness of the oxide films.

Abstract:In this paper, electron beam welding of laser additive manufacturing GH4169 alloy with different crystal orientation difference (0°, 45°, and 90°) were conducted, and the microstructure and mechanical properties of the weld metal under different crystal orientation of the parent metals on both sides were analyzed. The results show that the dendrites of weld structure have obvious preferential orientation, and the weld structure continuously grows based on the base metal crystal. With the increase of the crystal orientation difference (0°, 45°, and 90°), the content of the large-angle grain boundary in the central area of the weld increases first and then decreases; for the fusion line area of the weld, the content of the large-angle grain boundary increases first and then decreases from 0°, 45° and 90°. The tensile test results show that the tensile strength of the welded joint decreases as the crystal orientation difference increases, which are 721.8Mpa, 720.7Mpa, and 702Mpa respectively, and they are all lower than the base metal which has a tensile strength of 737.2MPa. The hardness values of the weld areas with different orientation difference (0°, 45° and 90°) fluctuated slightly at 265 HV. The plastic deformation of the weld metal is affected by the crystal orientation of each region of the weld. It has the same distribution trend as the large-angle grain boundary content. The more soft-oriented crystal content in the structure, the greater the amount of metal structure deformation. The greater the degree of bending, the stronger the plasticity of the welded joint.

Abstract:The GH3536 alloy was prepared by selective laser melting, and was subjected to solution treatment and hot isostatic pressing, respectively. The effects of different heat treatment methods on the microstructure, grain boundary morphology and room temperature tensile behavior of GH3536 alloy were studied. The results show that the microstructure of the SLM sample consists of ultra-fine columnar sub-grains and pool boundary, with defects such as pores and microcracks. The relative density of the alloy increases after solution treatment and hot isostatic pressing, respectively, and the microstructures of the two alloys consist of alternating equiaxed grains of different sizes. However, the HIP sample precipitated the M₂₃C₆ phase along the grain boundary, forming a serrated grain boundary. The tensile properties of the SLM samples show obvious anisotropy. The solution treatment can eliminate the anisotropy of the tensile properties of the sample, but the ultimate tensile strength and yield strength are reduced, and the elongation is significantly increased. The HIP sample is similar to the solid solution sample, but its ultimate tensile strength, yield strength and elongation are further improved. Tensile fracture mechanisms of all three alloys are microporous aggregate-type ductile fracture.

Abstract:Based on the forming principle of Hastelloy X alloy prepared by laser melting (SLM), the DLUX subroutine is written in Fortran language to load Gaussian light source, and finite element analysis software ABAQUS is used to numerically simulate the transient temperature field and cooling rate of finite element model, and the analysis results are verified by experiments. The heat transfer, melting, liquid metal flow and solidification process of powder particles and Gaussian light source during forming were studied. The results show that the microstructure of Hastelloy X alloy presents equiaxed crystal with fish scales in cross section and feathery columnar crystal in vertical section. SLM forming produces a large temperature gradient, which is a non-equilibrium dynamic process with high cooling rate. The average cooling rate is 3.02× 106℃/s. Under the effects of high cooling rate and fine grain strengthening, the tensile strength of vertical and cross sections reach 97% and 89% of that of forging, respectively. The yield strength is far better than that of forging process. The vertical section shows high-strength plastic matching performance, meeting the requirements of industry standards.

Abstract:_{: Twin boundary as a low energy stable interface and easy to be regulated in low stacking energy metals has become a hot focus in recent years. There are a lot of annealing twin structures in the solid solution GH3625 alloy. In this paper, the annealing twin structure evolution and the fracture behavior of GH3625 were studied by in situ tension at room temperature, which combined with Scanning Electron Microscopy (SEM) observation and Energy Dispersive Spectrometer (EDS) analysis. The results show that the deformation mode in the twin structure of GH3625 alloy is mainly single slip in the process of tensile deformation, and the twin boundary gradually bends with the increase of deformation during the process of tensile and fracture, but the twin boundaries always exists in the alloy structure, which hinders the dislocation and has good mechanical stability at room temperature. There are both ductile fracture and brittle fracture in GH3625 alloy, the carbide segregation is the main cause of grain boundary crack and intragranular holes formation.}

Abstract:The stress-strain curves of GH4742 at deformation temperature of 980-1100 °C and strain rate of 5×10_^-3 s-1 to 5 s_^-1 were acquired through single-pass isothermal compression experiments. The flow stress, critical strain capacity and structure evolution dynamics of GH4742 during dynamic recrystallization were systematically described on basis of experimental data using KM model, Poliak-Jonas criterion, and Avrami model. Then based on the Prasad power dissipation rate model, the structural transformation volume fraction was introduced to determine the energy variation rules during dynamic recrystallization. The mechanism underlying the dynamic recrystallization of GH4742 was revealed with the help of microstructure characterization. It was found the critical strain capacity of GH4742 during dynamic recrystallization decreased and the structural transformation volume fraction increased with the rise of deformation temperature or the decline of strain rate. The power dissipation rate of complete dynamic recrystallization was larger than 0.44, and the forming mechanism was dislocation-induced continuous dynamic recrystallization.

Abstract:The GH4096 alloy aero-engine labyrinth disk forging was produced by a novel casting wrought method which included electroslag remelting continuous directional solidification, multiple integral forging and isothermal forging and other process. Different cooling rate after solid solution treatment was analyzed on the effect of microstructure and properties of forgings. Microstructure of forgings were analyzed by optical microscope (OM) and scanning electron microscope (SEM). Mechanical properties of forgings were tested, multi-zoned ultrasonic focused inspection was uesd to detect the quality of GH4096 alloy forgings. In addition, full-size labyrinth disks were manufactured and tested. Test results show that two kinds of heat treated forgings process the comparable grain size about 5~20μm and firstly γ’ size about 1~2μm. Compare to oil cooling of solution treated forgings, the forced air cooling of solution treated forgings processes coarser secondary and thirdly γ’ phase, less thirdly γ’ phase content, lower yield strength,lower creep property, lower residual stress and machining deformation. There is no single reflected signal higher than that of Φ0.4mm-15dB, and the clutter signals are lower than Φ0.4mm-21dB. The forced air cooled solution + aging treated full-size GH4096 alloy labyrinth disk passed the over-running test and burst speed test.

Abstract:In order to reveal the evolution of composition and microstructure of GH4169 alloy during the homogenization treatment, the alloy microstructure during heat treatment were in-situ observed by high temperature metallographic microscope. The particle size distribution of Laves phase in the alloy after cooling was analyzed by quantitative metallographic analysis. The distribution characteristics of Nb element in alloy before and after heat treatment were analyzed by EPMA. When the heating temperature of GH4169 alloy rises about 1151 ℃, the initial melting happens around the Laves phase. The particle number of Laves phase in GH4169 alloy increased after heat treatment, the particle size of maximum Laves phase decreased significantly, and the proportion of small Laves phase in alloy increased slightly. At 1180 ℃, there was a certain amount of liquid phase existing in GH4169 alloy, but the NbC phase undissolved. After heat treatment, the segregation of Nb element in the black area between the primary dendrites still existed, but the distribution of Nb element in the γ phase dendrite became more uniform.

Abstract:Stress rupture tests at 975℃/240MPa and microhardness measurements at room temperature were conducted in high W cast superalloy K416 with various Al contents. The results showed that the stress rupture life and microhardness decreased gradually with increasing the content of Al, the stress rupture life of specimens with medium and high levels of Al content were lower than the values in standard. Microstructural characterization indicated that little M₆C carbides and α-W phase were oberved when the Al content was 5.60% (mass fraction, the same below). The area fraction of M₆C carbides and α-W phase increased from 0.08% to 2.1% with increasing the Al content to 6.20%. Meanwhile, the area fraction of γ/γ′ eutectics increased from 12.6% to 21.8%. The increase of Al content showed little effect on the sizes and morphologies of grains, dendrites, MC carbides and γ′ phase. The precipitation of brittle M₆C carbides with high amounts and the depletion of solid solution strengthening element (W) were responsible for the diminished stress rupture property. In addition, the stress rupture mechanisms of K416 alloy with various Al contents were also discussed.

Abstract:The directionally solidified column crystal DZ4125 superalloy was prepared by means of Bridgman directional solidification. The microstructure evolution and the competitive growth of oriented crystal at a constant withdrawal rate were studied. The results showed that the temperature gradients of solid-liquid interface gradually decreased and the primary dendrite spacing increased, as the growth height increased. At the same time, the sizes of the γ′ precipitates gradually decreased and their morphologies changed from irregular butterfly shape into regular cube and sphere shapes. The contents of γ+γ′ eutectics and carbides, which were mostly distributed in the interdendritic areas, increased gradually. Moreover, due to the competitive growth proceeding, the number of columnar crystals decreased significantly with the increase of growth height. With the convex solid-liquid interface, the crystals diverged towards the furnace wall.

Abstract:Cast nickel-based superalloys are widely used in high-temperature parts such as gas turbine and Aeroengine blades. During long-term operation, local damages of blades often occur, but the manufacturing cost is very high. If the local damage can be recovered by additive repairing, the cost and manufacturing cycle would be greatly reduced, and save resources, which has great social benefits and market value. In view of the service circumstances and failure modes of nickel-based cast superalloy blades for gas turbines and aeroengines, combined with the compositions, microstructures and performances of nickel-based cast superalloy, the types, characteristics and formation mechanism of cracks in the repair of additive are analyzed systematically, the primary influencing factors of various cracks are described, and the reduction or avoiding of cracks are summarized from the two aspects of additive technology and material. In addition, the advantages and disadvantages of different methods and the possible research hotspots in the future are analyzed.

Abstract:Helium ion irradiation at 200 °C, 350 °C and 550 °C was performed on a reduced activation ferritic/martensitic (RAFM) steel to investigate the evolution of voids during irradiation. Experimental results showed that radiation damage had a bell-shape distribution along the depth. Both void size and density increased as vacancy production rate increased. When irradiation temperature rose, void size increased and void density decreased. Faceted voids were observed at 550 °C. Voids aggregation at grain boundaries (GBs) and void denuded zones (VDZs) were observed at high temperatures. A phase field model was employed to investigate the void evolution mechanism. The simulation results showed that the void shape may be attributed anisotropic void interface energy. During irradiation, as time goes on, void evolution can be divided into three stages: incubation stage, nucleation stage and growth stage.

Abstract:Based on the bulletproof mechanism of ceramic composite armor, structural design and numerical simulation optimization of SiC/UHMWPE fiber composite armor were carried out to satisfy the protection requirements of vehicle. Penetration depth of bullet was taken as the evaluation standard, and the thickness, shape, size, and layout of SiC wood ceramic bullet proof sheet were considered as the research factors. An orthogonal simulation optimization scheme of four factors and three levels were designed, when the surface density of ceramic composite armor was 38 kg/m2. Bulletproof performance was simulated using ANSYS/LS-DYNA finite element software. The optimized size parameters owing to the minimal penetration depth of bullet were selected. Accordingly, a SiC wood ceramic composite armor was prepared, and the bulletproof performance of designed ceramic composite armor was up to the protection standard of NATO AEP-55 STANAG 4569 level II as determined by the real bullet shooting test. The designed structure had 8-mm-thick SiC wood ceramic bulletproof panel and 13.7-mm-thick UHMWPE fiber bulletproof panel. The bulletproof panel was made of 4900mm2 hexagonal SiC wood ceramic bulletproof sheets. The influencing factors of SiC wood ceramic bulletproof sheet on the bulletproof performance was as follows: arrangement position > thickness > size > shape.

Abstract:Thin molybdenum sheet is a promising material for aerospace applications. Quantifying the mechanical behavior of the molybdenum sheet at elevated temperatures is important to understand the formability of the molybdenum component. To this end, tensile tests were carried out at different temperatures (20-500℃) and strain rates(5×10-4-1×10-2s-1). The rheological, normal anisotropic and fracture behaviors during tension were analyzed. The results show that the deformation resistance of thin pure molybdenum sheet is sensitive to temperature while the r-value (Lankford parameter) varies little within the test temperature range. When the temperature is below 300℃, the strain hardening exponent increases with increasing temperature, and it tends to be stable when the temperature is above 300℃. With the increase of temperature, the elongation to fracture of pure molybdenum sheet increases and then decreases slightly. The crack is generated at the grain boundary, and the separation of crystal grains along grain boundaries causes delamination of fractures. A modified Johnson-Cook model was established to characterize the constitutive behavior of the molybdenum sheet, of which the mean error is less than 5%.

Abstract:Joining niobium and stainless steel is important for lowering the cost of Superconducting Radio-Frequency (SRF) cavities and thus attracting great interests in the superconducting accelerator community. In this article, we reported a vacuum brazing technique between reactor grade niobium and 316L stainless steel using oxygen-free copper as filler material. Microstructure and mechanical properties at different temperature of both samples and transition joints were investigated. The microstructure demonstrated that brittle intermetallic layer was formed and the diffusion phenomenon was observed. In spite of the existence of brittle intermetallic, the brazing joints’ application in SRF cavities was not affected. Mechanical tests, including tensile tests, shear tests were conducted both at room temperature (300 K) and liquid nitrogen temperature (77 K). At liquid nitrogen temperature, the tensile strengths are higher than those at the room temperature, while the shear strengths are reduced due to the formation of brittle intermetallic. The transition joints always have higher mechanical strengths than samples when the thickness of the welding seam was strictly controlled. Leak tests were also performed on the transition. The joints’ leak rates are all lower than 1.1×10_^-11 mbar.L/s, indicating the vacuum brazing technology is applicable to high vacuum vessels used in cryogenic temperature, such as stainless steel helium vessel for SRF cavities.

Abstract:The shell mold filling process for high-Nb TiAl alloys exhausts valve castings by centrifugal investment casting is described in the paper. Compositions of the castings and shell mold are Ti-47Al-6Nb (at.%) and Zircon sand, respectively. As a comparison and verification of the simulation results, a series of shell mold filling experiments of centrifugal casting is carried out. Simulation results indicate that the shell mold filling time is about 3.8s; casting defects distribute along the central line of the exhaust valves, especially in the neck position. The comparison shows that the results of the simulation agree with those experiments. The powder/liquid ratio of 1.5:1 and mixing time of 30min is identified as the proper process for the inner layer slurry in the making shell mold process. There are no noticeable interfacial reactions between casting and shell mold using XRD analysis. The metallurgical analysis results reveal that the lamellar structure is the typical structure for the as-cast exhaust valves, with the grain size of 185-305μm.

Abstract:In this study, dense Co- and Ni-bonded Ti(C_0.6N_0.4) matrix cermets with secondary carbides, i.e., WC, Mo₂C, and NbC, were prepared using liquid phase sintering in vacuum for 60 min at temperatures ranging from 1410 to 1490°C. The detailed microstructural and phase analysis was performed using scanning electron microscopy, electron probe microanalysis, and X-ray diffraction analysis. The effect of sintering temperature on the microstructure, mechanical properties, and machining performance of cermets was investigated. The results showed that sintering temperature had a significant impact on the microstructural characteristics of (Ti, W, Mo, Nb)(C, N)-(Co, Ni) cermets. The total carbon content of cermets decreased with increase in temperature and a carbon-deficient phase (M₆C) was observed in the cermet sintered at 1490°C. The cermets sintered at temperatures of up to 1470°C were composed of an fcc solid solution metal binder and two types of core-rim structured grains, i.e., cubic carbide solution and cubic Ti(C, N) solution phases. The best machining performance on continuous / interrupted turning was found in the cermet sintered at 1470°C because of an optimum combination of hardness and transverse rupture strength.

Abstract:The microstructures and mechanical properties of a newly developed Mg-3.6Zn-0.6Y-0.2Ca matrix composite containing SiC particle before and after extrusion were investigated. The grain sizes of the as-extruded composites were significantly decreased as compared to the as-homogenized composite before extrusion. With increasing the extrusion speed or extrusion temperature, the size of recrystallized grains increased while the volume fraction slightly increased. The size of dynamic precipitated phases increased and the volume fraction decreased with increasing the extrusion speed. With an increase in extrusion speed from 0.01 mm/s to 0.1 mm/s at 230 °C or extrusion temperature from 190 °C to 230 °C at 0.1 mm/s, the yield strength and ultimate tensile strength decreased while the elongation increased. The yield strength, ultimate tensile strength and elongation of composite extruded at optimized extrusion parameters (at 190 °C at 0.1 mm/s) were 312.0 MPa, 347.3 MPa and 6.6%, respectively. The contribution of grain refinement strengthening on the strength increment was higher relative to the thermal expansion effect and precipitates strengthening.

Abstract:The hollow porous NiO/SnO₂ composite nanofibers were prepared by electrospinning method, then the carbon nanotubes (CNTs) were decorated on the surface of the composite fibers and this material marked as CNTs/NiO/SnO₂. On this basis, a gas sensor device was prepared. The thermal decomposition temperature of the composites was determined by TGA, and the heat treatment process was obtained. The morphology, structure, size and surface composition of the composites were characterized by SEM, XRD, TEM and XPS. The test results of the gas sensors based on the composites showed that the gas sensor prepared by CNTs NiO/SnO₂ composite nanomaterial reduces the optimum working temperature in detecting acetone gas, which was 160°C, and the composite nanomaterial also improved the detection sensitivity. The gas sensors based CNTs/NiO/SnO₂ had a good response to 50 ppm acetone, reaching at 25.25, responded quickly to the detection of acetone (~8.2 s) and recovery performance (~10.5 s), while also showing good stability in the 30 day long-term stability test. In this research, the potential value of NiO/SnO₂ composites with decorative CNTs in the detection of acetone was proved. At the same time, the mechanism of the improvement of detection performance of CNTs and hollow porous structure NiO/SnO₂ was discussed.

Abstract:One-dimensional Y2O2SO4:Eu3+ sub-micron rods were synthesized by a facial molten-salt method with Na2SO4 and K2SO4 as the eutectic melt. The crystallography, morphology and luminescence properties of as-synthesized products were characterized by X-ray powder diffraction (XRD), scanning electronic microscope (SEM) and photoluminescence(PL) spectra.The influence of the sintering temperature, Eu3+ doping concentration on the crystallography, morphology, and luminescence properties of the samples were carefully investigated. The pure Y2O2SO4:Eu3+ can be prepared by calcining raw material mixture at 1100℃ for 2 h in air. The monoclinic Y2O2SO4:Eu3+ (10 mol%) sub-micron rods have a length of more than 10 μm and a width of 500~800 nm. The photoluminescence spectra of the Y2O2SO4:Eu3+ sub-micro rods confirmed the strongest red emission peak at 616 nm upon the excitation of 270 nm ultraviolet light, which corresponds to the 5D0→7F2 transition of Eu3+. Moreover, the quenching concentration mechanism of Y2O2SO4:Eu3+ samples with Eu3+ above 10 mol% was also discussed.

Abstract:By controlling the milling time and the mass proportion of Al to Ti, the metallic amorphous Al/Ti spherical particles (Al/Ti alloy) with mean size of 3.76um were fabricated by mechanical milling method. The catalysis effects of the as prepared Al/Ti alloy on the thermolysis of five explosives, i.e. Hexanitrostilbene (HNS), 2,6-diamino-3,5-dinitropyrazine-1-oxide (LLM-105), Cyclotrimethyltrinitroamine (RDX), Cyclotetramethylenetetranilamine (HMX), and Hexanitrohexaazaisowurtzitane (CL-20) were probed using thermal analysis. For HNS, the decomposition peak temperature (Tp) of the doped HNS with the alloy decreased by 6.9°C, 7.2°C, 4.8°C and 5.2°C respectively at different heating rates compared with raw HNS. Similarly, for the rest four explosives, the Tp value of the doped explosives with the alloy mainly decreased compared with the respective raw explosive. All thermodynamic parameters of the explosives were calculated. It indicated that the active energy (EK) of the doped explosives with alloy markedly declined by 52.4 kJ.mol^-1 (HNS), 41.6 kJ.mol^-1 (LLM-105), 8.6 kJ.mol^-1(RDX),48.4 kJ.mol^-1(HMX), and 46.7 kJ.mol^-1(CL-20), respectively. It is ascertained that doping spherical amorphous Al/Ti alloy can promote the thermal decomposition of explosives.

Abstract:The application of magnetic materials is of great significance to the development of cryocoolers. At present, the lack of thermal properties of magnetic materials at temperatures below 80 K severely limits the design and optimization of cryocooler regenerators. A low-temperature apparent thermal conductivity measurement apparatus for granular magnetic materials has been developed. The apparent thermal conductivity of Er3Ni under various pressures of helium in the 4-40 K temperature range has been measured, and then its thermal conduction factor has been calculated. The test results in different temperature ranges show that the apparent thermal conductivity of Er3Ni particles is 0.11-0.22 W/m·K under vacuum, corresponding to the thermal conduction factor of 0.31-0.53. When the pressure increases to 1.4-2.2 MPa, the apparent thermal conductivity tends to a definite value of 3 W/m·K, corresponding to the thermal conduction factor of 7. Furthermore, the heat leakage characteristics of the Er3Ni regenerator under different operating conditions have been studied, and a mixed filling scheme of particles with wire mesh has been proposed to reduce the axial heat leakage between the cold and hot ends of the regenerator. The results show that the cooling performance can be improved after the nylon mesh and 316 L stainless steel mesh are filled in the Er3Ni regenerator, and the reduction of heat leakage under the pressure of 1.6 MPa helium is as high as 12% and 8%, respectively.

Abstract:In this paper, based on theoretical and simulation analysis, the 6061 Al / AZ31B Mg / 6061 Al laminated plates were fabricated by hot rolling, and the microstructure and mechanical properties were investigated in detail. The best coverage rate of 6061Al of the laminated plate was obtained by classical laminated plate theory and the optimal reduction rate of the laminated plate was obtained by Finite Element Method (FEM). According to the theoretical and simulation results, the rolling experiments of 6061 Al / AZ31B Mg / 6061 Al laminated plate were carried out with different rolling temperatures, reduction rates and annealing time. And the microstructure experiment, tensile property test and energy spectrum analysis of the laminated plates were carried out. The results showed that refined grains were discovered in the Mg layer at the interface, and the formation of an intermetallic compound layer consisting of Mg17Al12 and Mg2Al3 was identified at the interface. For the mechanical properties, with the increase of rolling reduction rate, the tensile strength, elongation and interface diffusion thickness of the 6061 Al / AZ31B Mg / 6061 Al laminated plate increased significantly; with the increase of rolling temperature, the tensile strength, elongation and interface diffusion thickness of the laminated plate decreased greatly; with the increase of annealing time, the tensile strength decreased and interface diffusion thickness of the laminated plate increased.

Abstract:The flow behavior of Ti2041 alloy was studied through hot compressive experiments. The constitutive model of alloy established by back propagation (BP) neural network has high accuracy, which correlation coefficient reached 0.99613, the average relative error is 4.498%, the predictive value of deviation within 10% data points up to 92.98%. Based on the experimental data, the strain rate sensitivity, the power dissipation and the instability parameter were investigated. Processing maps were established. Through processing map prediction and microstructure observation, the instability zones are mainly flow localization(650~775℃/0.056~1s-1) and mechanical instability (825~900℃/0.056~1s-1), and the deformation mechanism of the stability zone is mainly dynamic recrystallization. It is found that the optimal deformation parameters are that: deformation temperature760~825℃/825~900℃, strain rate 0.001~0.01s-1 /0.0032~ 0.056s-1.

Abstract:Tungsten is widely used as semiconductor and high-temperature materials. In this study, high-purity well-dispersed micro-spherical W particles were synthesized from commercial ammonium paratungstate [(NH₄)₁₀[H₂W₁₂O₄₂].nH₂O] sequential by ion exchange, extraction, re-crystallization, spraying dry and pyrolysis processes. Impurities in the starting ammonium paratungstate were eliminated by the hydrometallurgy treatments. The morphology and size of as-synthesized W particles were controlled by the spraying dry-pyrolysis treatments. The influences of solution concentration in spraying dry on the morphology of (NH₄)₁₀[H₂W₁₂O₄₂] particles were investigated. The pyrolysed mechanism of as-spraying dried (NH₄)₁₀[H₂W₁₂O₄₂] particles transformed to as-synthesized W particles was revealed. The purity of as-fabricated tungsten powder is higher than 99.995 wt%, and the average size is about 1.5 μm. It should be noted that the hydrometallurgy and powder technology in this study can be applied to synthesize other metal particles with high-performance requirements.

Abstract:The microstructure and phase composition of Mg-9.5Li-2.56Al-2.58Zn alloy were studied. At the same time, the UTM5305 electronic universal testing machine was used to carry out the compression experiments with different strain rate and different deformation amount, to obtain the true stress-strain curve, and to construct the room temperature deformation constitutive equation of the alloy. The microstructure and mechanical properties of the alloy before and after compression were studied.The results show that Mg-9.5Li-2.56Al-2.58Zn alloy consists of five phases: α-Mg, β-Li, Al12Mg17, AlLi and MgLiAl2. β-Li is the matrix phase, α-Mg phase is strip or block, fibrous Al12Mg17 phase is in the interior of α-Mg phase, granular MgLiAl2 phase is distributed on the grain boundary, and intragranular AlLi phase is granular. After solution treatment, the number of precipitates in the alloy structure decreased obviously, and the strength of the alloy increased. According to the real stress-strain curve of Mg-9.5Li-2.56Al-2.58Zn alloy, the effect of strain rate on the flow stress is analyzed. There are peak stress and softening phenomenon after peak value in the compression of extruded and solid solution alloy at room temperature, which is conducive to room temperature forming. The constitutive equation constants n and LnA-(Q/RT) in different states are obtained by linear regression, and the constitutive equation based on Arrhenius model is constructed. With the increase of deformation, the microstructure of the alloy is gradually flattened and elongated, and the AlLi phase is increased.

Abstract:according to the microstructure characteristics of titanium alloy, the texture of laser additive manufacturing TC11 alloy was investigated by EBSD and XRD，from micron scale to centimeter scale, and the effect of scanning area of EBSD on the texture was analyzed. The results show that the texture tested by EBSD are consistent with the results of XRD. The β phase of TC11 alloy shows the<001>?ber texture which parallel to the building direction and lightly (001) [0-10] texture, and the α phase exhibit two fiber textures, <16 0 -16 19>∥[001] and <2 -1-10>∥[001].

Abstract:_{:TiO2 thin films were prepared by Atomic layer deposition on K9 glass. The crystal structure, optical properties and photocatalytic properties of the films at different deposition temperatures were characterized by XRD, SEM, AFM, spectrophotometer and ultraviolet-visible spectrometer. TiO2 thin films were amorphous at 25℃ and 120 ℃, anatase structure was obtained at 210 ℃ and 300 ℃. As the deposition temperature increases, the size of the film shrinks, the surface size decreases, the film becomes denser, and the lower the transmittance, the better the photocatalytic performance. The degradation rate of methyl orange solution can reach 47.16% under 12h visible light irradiation of TiO2 film (2mm * 2mm) prepared at 300 ℃. Increasing the sample surface ares in a tiling manner can significantly increase the degradation of methyl orange solution rate.}

Abstract:The magnetic properties could be improved in rare-earth magnets prepared by the dual-alloy method via mixing two different types of powders. The atoms would diffuse in the sintering, and it is necessary to make clear the effect of atomic diffusion on the magnetic properties. In this paper, the sintered magnets were prepared by mixing Nd13Fe81B6 with TbHx powders. The coercivity is 4.5 kOe in Nd13Fe81B6 magnets, and it increases to 20.0 kOe with 3 wt.% TbHx addition in the sintered magnets. The investigation of thermal activation indicates that the magnetization reversal undergoes the nucleation of reversed domain wall at grain outer-layer. Owing to the thermodynamical origin Tb atoms prefer to diffuse into the grain interior of Nd2Fe14B phase rather than aggregate in the intergranular rare-earth-rich phase. Tb atoms could substitute for Nd and form (Nd,Tb)-Fe-B shell layer with higher anisotropy in the main phase, and so the nucleation field of reversed domain is improved at grain outer-layer, leading to the significant increase of coercivity. However, for 5 wt.% TbHx addition the increase amplitude of coercivity decreases in the sintered magnets. The elemental distribution shows that for 7 wt.% TbHx addition the area of Tb-lean regions decreases, indicating that more amount of Tb atoms diffuse into the grain interior of Nd2Fe14B phase. The enhancement effect of improving the nucleation field is weakened at grain outer-layer, resulting in the reduction of the increase amplitude of coercivity. Regulating the atomic diffusion and optimizing the elemental distribution are necessary to further improve the magnetic properties in the sintered magnets prepared by the dual-alloy method.

Abstract:W-Cu composite are widely used as materials for electronic packaging, electrodes, electrical contacts, and shells of artillery shells because of its low expansion coefficient, high strength, high electrical and thermal conductivity. The traditional preparation methods of W-Cu composite are difficult to take into account the densification and the uniformity of the microstructure, resulting in insufficient electrical and thermal conductivity of the material, and it is difficult to meet the requirements of the modern electronics industry. Using W powder and WC@W powder obtained by carbonization of the surface of W powder as raw materials, W-Cu and WC@W-Cu composites were successfully prepared by composite electroplating technology. The results show that the surface of W-Cu composite is rough and there are holes in the microstructure, while the WC@W-Cu composite has refined grains, and the microstructure is uniform and dense. The W content of WC@W-Cu composite is 43.6wt.%, the hardness is 205HV, the relative density is 99.3%, and the electrical conductivity can reach 54.6MS/m. The WC@W-Cu composite not only increases the W content and significantly improves the hardness, but also is better than the W-Cu composite in relative density and conductivity.

Abstract:In this paper, the molecular dynamics method is used to simulate the c-axis compression model of two voids single crystal magnesium with different arrangement positions at 300K. Combined with the stress-strain curve, potential energy curve, radial distribution function and dislocation density curve of the three models, the compression mechanical properties and structural evolution process are analyzed. The results show that the maximum compressive stress, peak potential energy and corresponding strain can be tolerated when the single crystal is parallel to the loading direction, the second is perpendicular to the loading direction, and the smallest is 45 ° arrangement with the loading direction.The results show that the double void model with 90 ° arrangement with c axis has the fastest viods closure rate.

Abstract:The application of Al-Li alloy sheet with high specific strength and low fatigue crack growth rate for large thin-walled structural parts such as skin is an important way to reduce the weight of aeroplane. The mechanical behaviors of 2198 Al-Li alloy sheet along the rolling direction (RD), 45° and transverse direction (TD) were tested using unidirectional tension. The effect of heat treatment on its anisotropy was studied. The crystallographic texture, aging precipitate and fracture morphology were analyzed for the micro mechanism. It was found that the new-quenched and naturally aged 2198 Al-Li alloy sheet has similar anisotropy. RD has the highest strength, the highest hardening rate and the lowest elongation. 45° direction has the lowest strength and the lowest hardening rate and the highest elongation. The main reason is the strong <112> {110} texture in the rolled sheet. However, the anisotropy of the 2198 Al-Li alloy sheet after artificial aging has changed significantly due to the inhomogeneous precipitation of the T₁ phase. The strength in 45° direction has been greatly improved to the level same as TD. And the hardening rate was significantly reduced. TD becomes the direction with the largest hardening rate. The anisotropy of elongation and fracture shape did not change. It can be seen that the T1 phase caused the anisotropic strengthening of the 2198 Al-Li alloy sheet but it has little effect on the anisotropy of fracture behavior. The purpose of this study is to clarify the effect of heat treatment on the anisotropic mechanical behaviors of 2198 Al-Li alloy sheet, to provide a theoretical basis for the development of its plastic forming process and to help to propose new ideas for strengthening and toughening of 2198 Al-Li alloy sheet.

Abstract:Mn-based Heusler alloys were selected as testing materials in this research, and the samples were prepared by arc-melting, subsequent heat treatment, and made in ribbon form by melt-spinning. The effects of Mn concentration on the crystal structures, magnetic and magnetocaloric properties were studied. It was found that Mn2-xSn0.5Ga0.5 crystalized in hexagonal structure at the room temperature. All samples undergo only second order phase transition at their Curie temperature near room temperature with nearly zero hysteresis. The Curie temperature and the saturation magnetization of the Mn2-xSn0.5Ga0.5 are very sensitive to Mn concentration where both Curie temperature and saturation magnetization decrease with the increase of Mn concentration, from 304 K and 64.1 emu/g to 262 K and 46.7 emu/g for Mn1.2Sn0.5Ga0.5 and Mn2Sn0.5Ga0.5, respectively, which indicates the ferrimagnetic order in these materials. Mn-based Heusler alloys will have a large application prospect in the field of magnetic refrigeration because of the absence of hysteresis and thermal hysteresis and with wide operating temperature range near room temperature.

Abstract:An The fundamental power input coupler is a component of the free electron laser device, which transmits microwave power to the superconducting cavity. In order to improve the transmission performance, the coupler needs to be coated with copper film. In this paper, the coupler was plated with copper film by electroless plating and electroplating, respectively. Though the linear scanning, roughness, X-ray diffraction and residual resistivity ratio, the performance changes of the copper films prepared by these two copper plating methods at room temperature (25 ℃) and after vacuum annealing temperatures (200 ℃, 400 ℃, 600 ℃ and 910 ℃) were investigated. Furthermore, the copper plating technology for the inner surface of bellows of the coupler was determined, and this process was applied to the 1.3 GHz fundamental power input coupler. The results show that the bonding force between the copper film and the inner surface of the coupler and the efficiency of microwave energy transmission can meet the requirements of practical application.

Abstract:The gross slip regimes of TC4 alloy against with various counterface materials and temperatures at critical experimental conditions were selected to study the effect of formation of tribo-oxide layers on wear properties and coefficient of friction of TC4 alloy in fretting wear. Results show that irrespective of tribo-pairs, the coefficient of friction of TC4 alloy had undergone periodic evolutions at room temperature, no tribo-oxide layers had been produced on wearing sufaces and the wear rates were higher. When the samples were heated to 260℃, the COF of TC4/GCr15 tribo-pair appeared the earliest transition from a ‘concave-convex’ dynamic to an approximately ‘straight-line’ stable state, the earliest severe-mild wear transition occurred and tribo-oxide layer had generated resulted in the wear rate reduced signigicantly, however, TC4/Si₃N₄ and TC4/Al₂O₃ tribo-pairs had no abviously tribo-oxide layers formed, and the wear rate climbed sharply to the maximum value. Severe-mild wear transitions of TC4 alloy against with various counterface materials had occurred while the samples were heated to 450℃, the tribo-oxide layers differed from the matrix were formed on worn surface and the wear rates were lower reaching a minimum value. The excellent of wear properties of TC4 alloy in fretting at elevated temperature is attributed to the generation of a tribo-oxide layers with uniform distribution, continuous compressed and good adhesion. The wear mechanisms of TC4 alloy was dominated by adhesive and abrasive wear before the severe-mild transition, while controlled by oxidative with slightly abrasive wear after the transition beginning.

Abstract:In this paper, three kinds of low alloyed Mg-Zn-Y (Mg-0.6Zn-0.1Y, Mg-1.3Zn-0.1Y, Mg-2.0Zn-0.1Y, wt.%) were prepared by conventional casting and then subjected to slow extrusion at low temperature (140°C, 0.1 mm/s). The results showed that with the increase of Zn content, the grain size of the alloy before extrusion gradually decreased. After extrusion, the grains were significantly refined and dispersed nano-precipitated phases were form. At the same time, as the increasing the Zn content, the recrystallization degree of the alloy and the number of nano-precipitation increased, while the basal texture intensity exhibited unobvious change. The mechanical properties of the as-extruded alloys have been dramatically improved. The YS,UTS and ELof Mg-2.0Zn-0.1Y alloy were 406.4MPa, 424.5MPa and 12.2%, respectively. With the increase of Zn content, the elongation of Mg-Zn-Y alloy increased significantly, the fracture morphology changed from cleavage surface to tiny dimples, and the fracture pattern varied from cleavage fracture to ductile fracture.

Abstract:The difference between the diffraction peak position of α phase (0002) and β phase (110) of TC16 (Ti-3Al-5Mo-4.5V) titanium alloy is less than 0.1°. Due to the increase of β phase content, the two peaks overlap severely in the traditional X-ray diffraction test optical path. At present, the α+β two-phase TC16 titanium alloy texture cannot be measured. In this paper, overlapping diffraction peaks were separated from the hot rolled annealed TC16 titanium alloy bar diffraction pattern. The microstructure, texture and mechanical properties of TC16 alloy bar were studied by optical microscope, X-ray diffraction and Vickers hardness tester. The shape of the diffraction peak was fitted by the Cauchy square function on the Matlab platform, and the influence of the change of diffraction optical path parameters on the broadening and overlapping of the α phase diffraction peak and the β phase diffraction peak was investigated. The results show that the X-ray diffraction optical path configuration of the polycapillary and parallel long sola slit solves the problem of overlapping diffraction peaks and improves the accuracy of texture measurement; The test found that there are mainly two texture components in hot rolled annealed TC16 bar, which are <0002> and <101(-)0> double wire texture; The texture makes the transverse tensile strength of TC16 less than the longitudinal tensile strength, the effects of texture on the mechanical properties of titanium alloy are discussed. This research has important theoretical and engineering significance for improving the performance and processing technology of titanium alloy fasteners. At the same time, it also provides a solution for the accurate measurement of the texture of two-phase titanium alloys.

Abstract:To investigate the effect of oxide additives on the creep resistance of Ag based electrical contact materials, Ag-SnO2 contact materials with CuO, WO3 and In2O3 were prepared by powder metallurgy. The creep tests were performed on the tensile specimen at room temperature, and the creep characteristic curves and related parameters were obtained. The creep constitutive equation of the Ag-SnO2 contact materials was constructed. The fracture morphology was analyzed using a scanning electron microscope (SEM). The creep behavior was further simulated by ABAQUS finite element software. The results showed that oxide additives can significantly enhanced the creep resistance of the Ag-SnO2 electrical contact materials due to the improvement of interfacial strength, especially CuO additive has the best effect. It is showed that the simulation results were basically consistent with the experimental data and the error was less than 3 percent. The obtained results are of great reference value for predicting the creep behavior of Ag-based contact material and improving the mechanical properties.

Abstract:The MnBi/Sm₂Co₁₇ composite powder was prepared by chemically assisted high-energy ball milling process, and the effect of the content of MnBi alloy on the magnetic properties and microstructure of the composite powder has been studied. As the content of MnBi alloy increases, the coercivity of the composite powder first increases slightly, and then keep stable at about 8.0 kOe, while coercivity of all the composite powder was lower than 10.8 kOe of pure MnBi milled powder; the saturation magnetization and remanent magnetization of the composite powder gradually decreased. No obvious elements interdiffusion was found in the composite magnetic powder. The exchange coupling effect of the composite powder was analyzed by the Henkel curve. The δM of the composite magnetic powder reaches the maximum value when the MnBi addition amount was 15wt.%, indicating that the composite powder has a strong exchange coupling effect. The evolution of the remanence ratio of the composite magnetic powder with the increase of MnBi alloy content has been analyzed depending on the morphology and the exchange coupling effect of the composite magnetic powder.

Abstract:Abstract: The evolution of macro-texture of hafnium bars at different annealing temperatures was investigated by X-ray diffraction (XRD).The morphology and composition of corrosion products of hafnium bars at 360℃/18.6Mpa water was investigated by scanning electron microscope (SEM) and X-ray energy spectrum analysis (EDS) and X-ray photoelectron spectroscopy (XPS). The results shows that four types of textures appear on the RD-TD plane of the hot-rolled hafnium bars,appear as axial complex textures. The texture of the basal﹛0002﹜shows a strong heredity in each stage, and the rest of the textures has changed differently. The corroded layer of the hafnium bars is formed by stacking oxide particles from 10 to 100 nanometers, the corrosion rate of prismatic {10-10} annealed texture is faster than basel{0002}annealed texture. The corroded layer preferentially forms Hf(4-x)+ oxide, Hf(4-x)+ loses electrons and becomes Hf4+,forming HfO2 with oxygen during the growth .

Abstract:The sorbents with hydrophobic-oleophilicity were the key to solve the problem of oil spills/leakages occurring globally, and it had become an urgent problem on improving the efficiency of oil-water separation. In nature, some plants, insects and animals were survived in the natural environment by super-hydrophobic structures. And enlighten from nature, the super-hydrophobic materials have attracted tremendous attention as application of oil-water separation. At present, zero-dimensional hydrophobic powder/one-dimensional fibers, two-dimensional hydrophobic meshs/fabrics and three-dimensional hydrophobic porous materials were most commonly used for oil/water separation. This paper mainly summarizes the recent researches on the preparation of hydrophobic-oleophilic materials. And finally, the prospects for future investigations of hydrophobic-oleophilic materials are proposed.

Abstract:Compared with other non-degradable medical metal materials, magnesium and its alloys have better biodegradability, and no further surgical removal is required, which reduces the cost of treatment and has become a candidate material for human implants. This article addresses the problem of poor corrosion resistance of medical magnesium alloys that are degradable and absorbed, and their clinical application is greatly limited. The changes in the corrosion resistance of three typical medical magnesium alloys and the related degradation in recent years are introduced. The progress of the research on the corrosion of medical magnesium alloys summarizes the experimental methods and results of studying the corrosion resistance of degradable medical magnesium alloys. It is concluded that medical magnesium alloys in the future must give full play to their advantages of degradable absorption, but also must control the degradation rate during human service.

Abstract:Lithium cobalt oxide (LiCoO₂) is one of the most widely used anode materials for energy storage of 3C digital products. The development of high-voltage LiCoO₂ cathode material will further increase its energy density and battery endurance. In a variety of material modification methods, bulk doping and surface modification are the both effective means to improve the performance of high-voltage LiCoO₂, and have extremely high academic and industrial application values. In this paper, we summarize the research progress of high-voltage LiCoO₂ by introducing common materials used for bulk doping and surface modification of LiCoO₂ cathode materials, and their surface modification, preparation methods, modification mechanisms, and synergistic effects. Moreover, existing problems and future development trends are also pointed out.