Abstract:Low cycle fatigue (LCF) properties of a nickel-based single crystal (SX) superalloy DD10 with different orientation deviation angles from the [001] axis was investigated at 760 °C and with invariable total strain amplitude of 1.4%. Results reveal that the LCF behavior of DD10 exhibited a strong orientation-dependence. The fatigue life decreased apparently with the increment of the orientation deviation angle. For specimens with the same orientation deviation angle from the [001] axis, those on the [001]-[011] boundary exhibited a longer fatigue life than ones on the [001]-[11] boundary. It was found that the orientation-dependence of fatigue life stems from the difference of accumulated plastic deformation per cycle. On the other hand, both of total stress amplitude and plastic strain amplitude showed a reverse orientation-dependence compared with the fatigue life. However, the orientation deviation showed no influence on the model of fatigue crack initiation and subsequently propagation.

Abstract:Thermal stability of fine-crystal Cr-NbCr₂ alloy prepared by mechanical alloying and hot pressing was researched. The results show that the grain size of Cr matrix has a certain degree of growing up after the thermal exposure, while the particles size of Laves phase NbCr₂ has no obvious change due to its high thermal stability. At the same time, the dislocation in the Cr matrix and the stacking faults/twins in the Laves phase NbCr₂ particles appear in the as-thermally exposed microstructure because of the increase of the compressive stress between Cr matrix and NbCr₂ particles. The as-thermally exposed compressive strength is not lower than the as-hot pressed strength. The Cr-NbCr₂ alloy can still keep higher yield strength and plastic strain after thermal exposure from 800℃ to 1200℃ for 50h. However, the yield strength and plastic strain will decline obviously by further extending the thermal exposure time because of the increase of the grain size.

Abstract:An in situ synthesis method was developed to produce a Ni alloy composite coating reinforced by in situ reacted TiN and TiB2 particles using argon arc cladding (AAC) with different molar ratio of BN/Ti on a 35CrMnSi steel substrate. The microstructures of the clad coatings were characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The results showed that the phases of the coating were TiN, TiB2, TiB, Cr23C6 and γ-Ni. As the BN/Ti ratio increased, the needle-like TiB phase almost disappears and the number of rod-like TiB2 particles increased. Their shape became smaller. The computed results shows that the nucleation driving force of the major reinforcing phases from low to high was TiN-TiB2-TiB at different test temperatures. Moreover, the growth mechanism of the phases is discussed in the Ti-BN-Ni system. The BN/Ti molar ratio was 0.67 showed the highest average micro-hardness and excellent wear resistance at the room temperature under normal atmosphere conditions.

Abstract:The wear properties and microstructure of CO₂ laser cladded Ni-based alloy coatings with 1wt.% nano-CeO₂ and 20wt.% WC addition(CeO₂/Ni) was compared with Ni-based coatings with 1wt.% nano-CeO₂ addition(WC-CeO₂/Ni). Both coatings were successfully cladded on 30CrMnSiNi2A steel with good metallurgical bounding to substrate. The influence of ultra-fine carbide WC on the microstructure of WC-CeO₂/Ni alloy composite coatings were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS) and electron probe micro analysis (EPMA). WC addition increased M₂₃C₆ content, the M₇C₃ decreased. The comparison of comprehensive mechanical properties between coatings with and without fine WC particles were conducted on Vickers hardness and wear-resistance test system. Results indicated that the performance of WC-CeO₂/Ni is better than CeO₂/Ni MMC. Few hot cracks appeared in Ni-based WC-CeO₂ metal matrix composition (MMC) production, which were investigated by SEM and EDS. The crack mechanism can be claimed as Fe dilution and coefficient of thermal expansion for WC-CeO₂/Ni MMC differed from that of base material 30CrMnSiNi2A steel.

Abstract:Under variations of bending radii and material properties, the multi-defect constrained formability of thin-walled commercial pure titanium (CP-Ti) tube is identified to explore the forming potential of this advanced lightweight material via explicit/implicit 3D-FE models and the experiments. The major results show that: 1) The variations of hardening exponents, thickness anisotropy exponent and Young’s modulus, have great effects on bending formability; 2) Compared with the wall thinning and cross-section deformation, the wrinkling instability is the dominant defect to restrain the bending formability of the large diameter thin-walled (LDTW) CP-Ti tube. The bending formability of CP-Ti tube, especially the anti-wrinkling capability, can be improved at elevated temperatures.

Abstract:Laser shock peening (LSP) is a novel surface processing technique for improving the fatigue properties of metal parts, surface roughness is a critical parameter when fatigue strength resistance is concerned. In this paper, a three-dimensional (3D) finite element model was developed in order to assess the surface roughness evolution induced by multiple LSP. A modified finite element analysis (FEA) method was utilized to compute the vertical displacements profiles, discrete data obtained from the numerical simulations were subsequently input to the proposed discretized formula to calculate the surface roughness R_a. The results obtained from the numerical simulations were in good agreement with the experiment data from open literatures, which validates the proposed approach. After the validation of the numerical model, a parametric study was conducted in order to predict the effects of overlap rates, number of impacts, and pulse energy on surface roughness R_a.

Abstract:The age hardening and microstructure of ZA84 magnesium alloy with the combined addition of Cr and Bi was studied by SEM and HRTEM. The results show a trace amount of Cr and Bi has a significant enhancement effect on the hardness of aging. When the ZA84-0.2Cr-0.5Bi alloy aged at 160℃, during the early aging period, the matrix has serious lattice distortion and a large number of crystal defects. The microstructure at the peak aging consists of a large number of rod-like or blocky β1’-MgZn2 phases and granular Bi2Mg3 phases, and the peak hardness value is 92.48HV. When ageing proceeded, the precipitate coarsening resulted in the hardness value reduction.

Abstract:Pilger rolling process has a specific influence on the mechanical properties and texture of zirconium alloy cladding tube. Due to its complexity, experimental research on the Pilger rolling process would be very costly. Therefore, a 3D finite element model was built to simulate Pilger rolling with ABAQUS/standard package. Simulation of a full pass of Pilger rolling of Zr-4 alloy tube, including a series of forward strokes and backward strokes, was carried out. The predicted tube sizes agree well with the experimental results. Additionally, the simulated rolling force also matches well with the force calculated by classic empirical formula, which validates the accuracy of the proposed model. The simulation results show that the stress and strain states in groove-side are different from that in groove-bottom. Moreover, large shear deformation happen in the rolled tube. The simulated shear strain displays substantial fluctuations during rolling, which are attributed to the cyclic position change of element (material point) with respect to the groove-side.

Abstract:Single–phased Mg_2(1+x)Si_0.27Ge_0.05Sn_0.65Sb_0.03 (x = 0.05, 0.08) quaternary solid solutions were prepared by B₂O₃ flux method followed by spark plasma sintering (SPS). The electrical conductivity, Seebeck coefficient and thermal conductivity were measured from 300 K to 800 K. The results show that the electrical conductivity increases while the Seebeck coefficient decreases with temperature for these samples. The lattice thermal conductivities of all the samples are higher than the calculated value using the Abele model. A maximum ZT of 1.0 at 800 K was obtained in the sample with x = 0.08.

Abstract:Microstructure, mechanical properties and bio-corrosion properties of Mg–3Zn–0.2Ca alloys were investigated for biomedical application by optical microscopy (OM), scanning electronic microscopy (SEM), mechanical properties testing, electrochemical and immersion measurement, with the as-cast of this alloy as control. The XRD showed that the main second phases in the cast alloy were Mg-Zn intermetallic compounds such as Mg7Zn3, Mg2Zn3, and Mg4Zn7. In comparison with the cast alloy, the average grain size of the extruded Mg–3Zn–0.2Ca alloy was significantly decreased by 47.6 times from 119.1μm to 2.5μm after extrusion ratio 56:1. The yield tensile strength (0.2%YS), ultimate tensile strength and elongation of the extruded alloys were 205MPa, 336MPa and 17.85%, respectively. The electrochemical and the immersion tests showed that the corrosion resistance of the extruded alloy was obviously higher than that of the cast alloy due to the fine grained microstructure. The new designed Mg–3Zn–0.2Ca alloy showed the good combination of mechanical performance and corrosion resistance for biomedical application.

Abstract:The relationships between H, O, P, S, and N impurities and the type of plasticity mechanism displayed in Ni were studied using density functional theory. We found that different impurities have different segregation tendencies with regards to Ni. S, P, O, and H are most likely to occupy sites on the Ni surface, especially when S and P are the impurities. S, P, H and O have little effect on the deformation mechanism of Ni when located in the grains of the Ni metal. Conversely, N prefers to occupy these grains, readily promoting the dissociation of dislocation into segments, and making cleavage fracture less likely to occur, which enhances dislocation nucleation. S, P and N caused a decrease in the plasticity of Ni, but H and O increased the probability of twinning for Ni. However, these impurities do not switch the deformation mechanism of Ni from dislocation-mediated slipping to twinning.

Abstract:In order to study the effect of V element on Ti alloy, the structure and the elastic modulus of Ti-V alloy in hcp phase was calculated by the first principles pseudopotentials and the plane wave energy band method. The results show that the content of V less 5.6 at. %, theTi-V alloy have steady HCP structure, and with the increasing of the content of V, the body elastic modulus, shear modulus and young"s modulus of Ti-V alloy decrease monotonously, while the poisson ratio increase.

Abstract:To determine the damage and life distribution of Tc4 material used in aero-engine blades under different stress ratio, axial tension and compression fatigue test is conducted. Nonlinear damage evolution equation is put forward for Tc4 material based on Chaboche nonlinear damage model and the fourth strength theory. Computation results are compared with W?hler curve and BP neural network model. According to the simulation and calculation results of the flow field of compressor blades in the maximum continuous working condition, the stress-time history for blades is calculated. From the viewpoint of energy dissipation, the residual strength model of Tc4 material is described based on stress strength interference. Combined with Poisson stochastic process, reliability prediction of the aero-engine’s compressor blades at maximum continuous working condition is accomplished.

Abstract:The Mg-13Zn-xCa-0.5Nd(x=3,4,5,6) alloys containing high-calcium have been prepared under the pretension of a mix gas atmosphere of Ar .The alloys composite were characterized by a variety of techniques: x-ray diffraction, optical metallurgical microscope, scanning electron microscope and mechanical property test. The performance of high Ca on microstructure and mechanical properties of alloy were investigated. The alloy was mainly composed of α-Mg matrix、α-Mg+Mg6Zn3Ca2 eutectic phase and a few amounts of secondary phase(Mg2Ca+Mg6Zn3Ca2)in as-cast state. The grain is extremely refined with the increase of Ca addition. After the solution treatment at 390 oC for 8 h and subsequent aging at 240 oC, the alloy exhibits greatly mechanical properties.The optimum mechanical property of the alloy is obtained by 4% Ca addition after T6 heat treatment. The ultimate tensile strength, yield strength and elongation of the alloy at peak-aged state are 108 MPa, 175 MPa and 6.10% at room temperature respectively. The good mechanical properties are mainly attributed to fine grain strengthening and second phase strengthenin.

Abstract:The true stress-strain curves of as-cast AZ31B magnesium under different temperature and strain rate can be obtained from GLEEBLE compression experiment. Critical strain model, saturated stress model and static stress model can be received by analyzing true stress-strain curves. Based on the classical dislocation density theory and the dynamic recrystallization (DRX) kinetics models, a two-stage constitutive model considering the effect of work hardening-dynamic recovery and DRX is developed for the as-cast AZ31B magnesium alloy. And the relation between the percentage of DRX and flow stress is obtained.

Abstract:The diluent NaCl was added into the W-B₂O₃-Mg system to prepare submicro tungsten boride powders via salt-assisted combustion synthesis. The products were analyzed by XRD, SEM and EDS, and the effect of NaCl content on phase composition, morphology and average particle size of the products were studied. Results show that the combustion synthesis products before leaching mainly consisted of W₂B₅ and MgO, and the morphology of particles was similar to ellipsoid when without adding NaCl. After adding NaCl, combustion synthesis products before leaching mainly consisted of W₂B₅, MgO, WB and B, and the morphology of particles were irregular and particles were slightly reunion together. The products after leaching were composed of small size tungsten boride particles, the average grain size decreased with the increasing of NaCl contents, when the content of NaCl k=20, the smallest particle size was 0.85μm. The purity of products after leaching was higher, the content of W and B were up to more than 98%. The biggest content walue of W and B was 98.51% when the content of adding NaCl was 5%.

Abstract:Four kinds of multiphase refractory Nb-16Si-22Ti-2Cr-2Al-2Hf-xFe(x=0,1,2,3)alloys were prepared by vacuum arc melting. XRD analysis reveals that the composites consist of Nb solid solution(Nbss), intermetallics Nb₃Si and Nb₅Si₃ phase. The addition of Fe promotes the eutectic reaction L→Nbss+Nb₅Si₃, which changes the phases of alloy phases from Nbss + Nb₃Si to Nbss + Nb₅Si₃.The volume fraction of ductile phase Nbss increases with increasing of Fe addition, leading to the reduction of compressive strength. Meanwhile, temperature and strain rate also have important influence on compressive strength of the alloys. The addition of Fe element makes Nb-Si based superalloy have better high temperature plastic deformation ability, which is of great significance to improve the hot workability of Nb-Si alloy.

Abstract:(Nd1-xCex)2Fe14B ribbons were prepared by arc melting followed by melt spinning. It is found that the ribbons are mainly composed of the main phase Nd2Fe14B and α-Fe phase. The optimum magnetic properties can be obtained using the wheel velocity of 30 m/s. With increasing the Ce content, the coercivity reduces from 800 kA/m when x=0 to 413 kA/m when x=0.5. However, the coercivity is anomalously high when the 20% Nd is replaced by Ce. It is attributed to the phase segregation induced by mixed valence state of Ce. No reduction in the maximum energy product is demonstrated when x=0.25. It is suggested that Ce has a great potential application in the permanent magnetic materials.

Abstract:The corrosion behavior and corrosion mechanism of TC4 titanium alloy OCTG in severe CO₂ environment were studied with high temperature and high pressure and stress corrosion cracking (SCC) test, as well as electrochemical in-situ measurement techniques. The results show TC4 titanium alloy dominates the excellent resistance to uniform corrosion, local corrosion and SCC in high temperature and high pressure CO₂ corrosion environment, and the uniform corrosion rate is only 0.0012mm/a at the temperature up to 220℃. The anodic polarization curves of TC4 titanium alloy have the obvious passivation zone in CO₂ environment, and the corrosion reaction is controlled by anodic process. With temperature increased, the corrosion potential and polarization resistance of TC4 titanium alloy decrease, which indicate that the thermodynamic driving force increase, while the dynamic resistance decrease of the electrochemical corrosion, thus the corrosion rate of TC4 titanium alloy increase. However, the protective potential and pitting potential of TC4 titanium alloy are higher enough in high temperature CO₂ corrosion environment, and the polarization resistance is up to 2328.2Ω.cm₂ at 180℃, which still give TC4 titanium alloy the good passivation and re-passivation ability and the superior resistance to CO₂ corrosion at high temperature.

Abstract:The electronic structure and dehydrogenation properties of NaMgH3 and metal(Li/K) substitution for parts of Na have been investigated using the density functional theory. Further calculations of reaction enthalpies along four possible dehydrogenation reaction pathways indicate that reaction pathway 5 is the most realistic ones. The Li doping in NaMgH3 decreases the value of reaction enthalpy and improves thermodynamic properties, but the K substitution has little impact on ones. The electronic densities of states and the mulliken population analysis show that Li doping is of benefit to releasing H because of decreasing the contribution of H to the valence band and weakening the interaction between Li and H. The different Li doping contents of reaction enthalpies are investigated indicate that with the increase of Li contents the structure present more excellent thermodynamic properties. But the Li substitution contents is less than 50.00%.

Abstract:The tensile strength and impact properties at low temperature were investigated on Al-6Mg-0.8Zn-0.5Mn-0.2Zr-0.2Er alloy for cold rolled, warm rolled and fully annealed samples. The original microstructures, tensile fracture and impact fracture were observed using electron back-scattered diffraction(EBSD), transmission electron microscope(TEM) and scanning electron microscope(SEM) in order to analyze the effects of microstructure on tensile property and impact properties. The results showed that, with the decreasing of testing temperature, the stresses are drastically increased as well as the impact properties. The tensile strength and impact property of warm rolled alloy with more sub-boundaries has a higher strength and impact property which realized the matching of high strength and toughness.

Abstract:Ti6Al4V and 316L stainless steel impeller body were formed by electron beam selective melting (EBSM). By comparing the microstructure, dimensional accuracy, surface roughness, hardness, density and tensile strength of the impeller body, the feasibility of applying EBSM process in industrial impeller body manufacturing is evaluated. The results showed that: the tensile strength of Ti6Al4V and 316L stainless steel impeller body were 560MPa ~ 700 MPa and 996MPa ~ 1120MPa respectively, which were higher than the standard level of wrought, met the requirements of industrial use. The Ti6Al4V microstructure in the impeller body were basket-weave α+β, except those in leaf fragments were coarse flakes α + β phase because of their smaller cross-sections, and there were columnar crystals along the building direction. While the 316L stainless steel microstructure in the impeller body presented scaly scan path fusion marks, and there were some coarse dendrites.

Abstract:The Ti-Al-Fe-Mn thermodynamic database was optimized by Calphad method. Based on this database the beta transus temperatures of four ternary systems in Ti-Al-Fe-Mn system was calculated and they were good agreement with experimental values. In this way the reliability of Ti-Al-Fe-Mn quaternary systems was verified. Then α+β/β phase transformation temperatures of a series titanium alloys were calculated by Calphad method and compared with values that previous formulas calculated. Also, a more accurate formula was established based on the values calculated. This results may provide a feasible way for the determination of titanium beta transus temperature.

Abstract:_{:Dense niobium coating was successfully prepared by atmospheric pressure chemical vapor deposition(CVD) method at 1150℃ ,which reached 250μm / h deposition rate. Analysis the post-deposition coating thickness by the gas flow direction,the mole percentage of NbF5, H2, HF and Arin different positionsweredetermined. And got agrowthkinetics equation which agrees well with the experimental results . Further analysis of the kinetic equations showed that the byproduct HF has a greater impact on deposition rate and Ar almost no effect.}

Abstract:In order to explore the thermal stability of AlCrFeNiTi high entropy alloy, the as-cast AlCrFeNiTi high entropy alloy was synthesized by the vacuum arc melting under an argon atmosphere, and the hardness change of alloy in different heat treatments, including heating temperature and holding time was evaluated, and then the relationship between the hardness and microstructures of AlCrFeNiTi alloy was further discussed. Finally, the network model between heat treatments and hardness of AlCrFeNiTi alloy was built by the back propagation artificialSneuralSnetwork (BP-ANN) to predict the hardness of AlCrFeNiTi alloy. The results show that the as-cast AlCrFeNiTi high entropy alloy is composed of two body centered cubic structures, and typical dendrite, interdendrite and eutectic structure (α+β) microstructures are observed. Comparing with as-cast alloy, the microstructures and content of dendrite of alloy under different heating temperature (from 400 to 900℃) and holding time (from 0.5 to 10h) have no significantSchanges, and the hardnesses of these heat treated samples are all higher than HV400, which indicates the AlCrFeNiTi high entropy alloy has a good thermal stability. Furthermore, the established BP-ANN between heat treatments and hardness of AlCrFeNiTi alloy shows better precision and applicability and can be used to guide the industrial applications.

Abstract:Muitiferroic ceramics Bi_0.8Ba_0.2Fe_0.9M_0.1O₃(M = Cr、Mn and Ti) were prepared by using conventional solid state reaction method. The pure phase with rhombohedral perovskite structure (space group R3c) was confimd by the X-ray diffraction measurements for all samples. The maximum value of the remnant polarization (2Pr) and the minimum value of the dielectric constant at room temperature and low frequencyare for Bi_0.8Ba_0.2Fe_0.9Ti_0.1O₃samples are 0.64 μC/cm₂ and 140, respectively. The dielelctric constant and dielelctric loss decrease with increasing frequency and then become nearly constant at higher frequency for all samples. The maximum value of the remnant magnetization (2Mr) for Bi_0.8Ba_0.2Fe_0.9Mn_0.1O₃samples at room temperature is 1.46emu/g by the M-H loops measurements. A remarkable change in the P-E loops were observed whether a bias dc magnetic field was applied or not, approving the existence of the magnetoelectric coupling indirectly therein in multiferroic ceramics Bi_0.8Ba_0.2Fe_0.9M_0.1O₃(M = Cr、Mn and Ti). And the maximum value of magnetoleectric coupling for Bi_0.8Ba_0.2Fe_0.9Cr_0.1O₃samples is 5.8 mJ/cm₃.

Abstract:The first nearest neighbor interatomic potentials of Ni0.75AlxV0.25-x alloy’s for L10, L12 and DO22 phases were calculated out according to the formula which were referenced on the relation equation between interatomic potentials and long range order parameters by Khachaturyan. Then we simulated the precipitation process and the final morphology of Ni0.75AlxV0.25-x alloy using the calculated potentials based on the Microscopic Phase-field method. The results show that the interatomic potentials of L10, L12 and DO22 phases will increase while the temperatures or the atom’s concentration rise. And the interatomic potentials, which change with the temperature and the concentration, match well with the earlier values. The simulation results can obtain the pre-precipitation phase L10, the stable phase L12 and the second phase DO22. And the alloy precipitation morphology is found to be in agreement with the experimental result. The inversion of interatomic potentials by phase field method expands the application of the phase field method in the alloy design.

Abstract:Isothermal compression of the Mo-Nb single crystals was conducted on a Gleeble-3800 thermal simulator at the deformation temperature range of 1100-1300℃with strain rates ranging from 0.001 to 10s-1 and height reduction of 50%, true strain is 0.7. The results show that the deformation temperature and strain rates affected the flow stress during the thermal deformation of Mo-Nb single crystals significantly. The true stree-strain curves exhibit a peak flow stress, flow softening and steady flow behavior. The constents of Mo-Nb single crystals, such as the activation energy Q, the stress exponent n, are calculated. The constitutive equation is estabilished based on a hyperbolic-sine equations of Arrhenius type.

Abstract:Fe_72-xNd₇B₂₁Nb_x(x=0~4.0)bulk alloys with diameter of 2 mm were fabricated by copper mold casting. The influence of Nb addition on the glass forming ability, crystallization and magnetic properties have been investigated by X-ray diffraction (XRD), differential scanning calorimetry (DSC), vibrating sample magnetometer (VSM) and physical property measurement system (PPMS). The results show that appropriate addition of Nb can improve the glass forming ability. The fully amorphous ingots are obtained when Nb content is 2.0 at%, 2.2 at% and 2.5 at%. Nb is found to be effective in adjusting the alloy composition and decreasing the volume fraction of paramagnetic Nd_1.1Fe₄B₄ phase . When Nb content is 2.5 at%, the alloy exhibits optimal hard magnetic properties with the remanence (B_r) of 0.63 T, intrinsic coercicity (H_ci) of 448.97 kA/m and maximum energy product ((BH)_max) of 4.54 MGOe. The enhanced magnetic properties can be abscribed to the strong exchange coupling among grains and and high remanence.

Abstract:A porous Ni-based coating was fabricated by plasma spraying and subsequent remelt method. The microstructure, thermal expansion coefficient and mechanical properties during compress process were analyzed by scanning electron microscope (SEM), micro-hardness tester, thermophysical properties instruments and so on. The results show that the closed and spherical pore with 30-100 μm diameter formed in the remelt coating. The elasticity moudulus of the porous coating descend 69.5% and elasticity deforming scope ascend 68.7% with the porocity ascend to 30.6% from 0.53%. The average linear thermal expansion coefficient increased with the decreasing of porosity in the temperature scope between 40 and 220 ℃. The improvment of elasticity deforming scope of Ni-based alloy due to the formation of closed pore resulted in the decline of thermal expansion coefficient, to achieve the purpose of low thermal expansion and high recoverability.

Abstract:Cu/Al-Si alloy clads were cold roll bonded with a mismatch speed ratio of 1.7 at ambient temperature, and uniform intermetallic compounds(IMCs) formed when these Cu/Al-Si alloy laminates with different silicon content were annealed at 400 ℃ for 30 minutes. With the utilizition of OM, SEM, EPMA, XRD, tensile machine and so on, it showed that the width of IMCs reached the maximum at 8.66%(wt.%) silicon content. With increase of silicon in Al-Si alloy, the tensile strength of laminated composites increased while elongation and peeling strength of composites went down, and their comprehensive properties reached the best at 4.84% with tensile strength and elongation of 188.63 MPa、39.1%, respectively. Meanwhile, fracture morphology of Cu/Al-Si alloy laminates in Cu side was ridge-like, and structure of Al-Si alloy in center region was mainly dimples, the more silicon content in Al-Si alloy, the more dimples appealed.

Abstract:The effects of precipitated phase on the microstructure, deformation mechanism and edge crack behavior of AZ91 hot rolled magnesium alloy plate with different reduction per pass and rolling passes were studied by optical microscope, field emission scanning electron microscope equipped with energy spectrum and tensile testing at ambient temperature. The results indicate that multi-pass with small rolling reduction can reduce the edge cracks and improve the rolling forming ability for AZ91 magnesium alloy; Precipitated phase from the slice layer to spherical particles with tinier size during the rolling deformation is beneficial to inhibit the initiation of crack; The tensile fracture surfaces show obvious intergranular fracture features, and the microcrack primarily distributes around the Mg/Mg₁₇Al₁₂ phase interface and coarser second phase. Spherical precipitated phase particles have been proved to be the initiation source of microcrack, and then the microcrack extends and turns to the microcrack.

Abstract:The surface of as-cast columnar crystal DZ125 alloy was blew sand then heat treatment by the standard heat treatment process obtained the recrystallization with different thickness, and the creep life of the alloy was measured. The effect of recrystallization and its thickness on the creep properties of the alloy was analyzed. The microstructure of the alloy was observed by scanning electron microscope. The experimental results show that the thickness of recrystallization on the surface is different from alloys at varied sand blowing intensity after heat treatment, with the sand blowing intensity increase the thickness increase of the columnar crystal DZ125 alloy. The carbide in the as cast DZ125 columnar crystal alloy is slice, strip or grain, and the carbide after the standard heat treated alloy is dissolved, the size of the slice is reduced, and the surface of slice carbide appears holes. Strip carbides turn into grain, the original grain size reduction. A small amount of grain carbides are precipitated around the grain boundaries after recrystallization. The creep life of 2mm and 4mm sample with different recrystallization thickness is roughly equal under the 980℃ and 235MPa conditions. Compared to the non-occurrence the recrystallization of columnar crystal alloy, the life of the DZ125 alloy was decreased by 30%. During the creep, the carbides in the grain are accumulated and grow around the grain boundary, which is beneficial to improve the strength of grain boundary. During creep the crack initiation is mainly along with the recrystallization grain boundary which vertical the stress axis. Crack initiation points are also existed in the internal of the columnar crystal alloy. The γ′ phase rafted in recrystallization grains indicate that the grain boundaries of recrystallization which weakening the creep strength of the alloy also has certain strength.

Abstract:The hexagonal, monoclinic and cubic structures of Lu₂O₃are studied by the plane wave pseudopotential method based on the first-principles density functional theory. The calculated binding energies reveal that the C-type cubic structure of Lu₂O₃is the most stable. The mechanical properties show that the cubic Lu₂O₃exhibits good ductility and elastic anisotropy. Lu₂O₃is thermodynamically stable. The electronic calculations show the cubic Lu₂O₃ has a direct bandgap. The electrons situated in the bottom of the valance band have the small effective mass and the high degree of nonlocalization. And the electrons transitions between the top of the conduction band and the bottom of the valance band primarily derive from Lu-4f and O-2p states. It forms the covalent bonding of Lu–O by the strong orbital hybridization of 5d orbital of Lu atom and 2p orbital of O atom. The maximal optical reflectivity of the cubic Lu₂O₃ is 0.36 and the optical absorption ability of the cubic Lu₂O₃ is strong in the energy from 3 to 10 eV. Lu₂O₃isa fine optical insulator which has the novel optical properties owning to its perfect transparency in the visibleSandSnearSinfraredSwavelength regions.

Abstract:AZ91D magnesium alloys were processed in the base electrolyte composed with sodium hydroxide and sodium silicate, not containing or containing potassium fluoride respectively, by micro arc oxidation (MAO). Influence of potassium fluoride on growth, microstructure and corrosion resistant of the coatings was investigated. The results show that after potassium fluoride was added to the base electrolyte, the breakdown voltage to the specimen decreased but the breakdown process was more vigorous to lead to formation of larger sparks on the specimen surface during micro arc oxidation. As a result, the grow rate of the coating significantly increased and the obtained coating had a remarkable improvement in terms of coating thickness. Meanwhile, the surface porosity of the coating somewhat increased but the amount of the micro-pores on the coating surface decreased. The addition of potassium fluoride into the electrolyte is helpful for the formation of MgF₂and MgAl₂O₄ phases of the coating. Compared with silicate and oxygen elements from the electrolyte, F_- ion is more likely to be adsorbed by magnesium in the substrate and also easily overcomes the obstacle of the generated coating to migrate into the inner of the coating. The corrosion resistance of the coating treated in the electrolyte with potassium fluoride is increased under the influence of significant increasing in coating thickness mainly and the existence of favorable phases such as MgF₂ newly born and more MgAl₂O₄.,

Abstract:The brittle of Ir single crystal in nature has attracted more attention due to the fact that Ir is a FCC metal. In this paper, nanoindentation experiments were performed on the (100) and (110) planes of Ir single crystal. The results show that the dislocation activation volumes of Ir single crystal were calculated to be 1.09 ?3、1.23 ?3 for the (100) and (110) planes based on the first pop-in data from load-displacement curves. These results clearly demonstrate that the formation of dislocation is probably nucleated heterogeneously from point-like defects, while for the homogeneous nucleation, the activation energy should reach 60.57eV, and the activation radius reaches 1.971nm. In the plastic deformation of Ir single crystal, the deformation dislocation density was found to be the order of 1014m-2, which agrees with the previously reported data, implying that the anomalously high dislocation density does not exist in this nanoindentation experiment. The brittle fracture of Ir in nature may be attributed to the extremely small dislocation activation volume, leading to a large number of dislocation sources, and eventually caused by severely dislocation interaction.

Abstract:Distribution of alloying elements of a Ni-based superalloy after long-time aging is studied employing LEAP 4000X Si. Elements like Ni, Cr and Re preferentially partition to the γ phase, while Al and W have a preference for γ" phase. A local accumulation of Ni is found on the matrix side at the γ/γ" interface, leading to a reduction of interfacial free energy. The sum solute elemental concentrations of ~25 at.% and the experimental partial RDFs of Al-R (R=Re, Ru or W) exhibiting negative correlation at first-NN distances in precipitates indicate that refractory elements substitute preferentially to the Al sublattice sites. The solid-solution strengthening effect of refractory elements and the increase in precipitates volume fraction result in an increase in microhardness, compared to the base Ni-Al-Cr alloy.

Abstract:Ti-16.28Si and Ti-15.46Si-5Cu alloys were preparation by high-energy ball milling, cold-pressureless sintering using Ti, Si and Cu powder. The oxidation mechanism of alloys at high temperature oxidation test under 800℃, 900℃, 1000℃ in air were investigated by analyzing the surface and cross-section morphologies and phase composition of sintered and oxidised samples by means of SEM, EDS and XRD. The results show that two kinds of formula samples are mainly containing of Ti, Ti5Si3 and Ti5Si4 phases after sintered, and contain Cu3Si phase of the formula adding Cu; The density increased with Cu added. The main phase of the oxidised samples for 80 h is TiO2, with a small number of SiO2, Ti3O5, TiO, TiN, CuO or Cu2O phases. The oxidation resistance of two alloys reach antioxidant levels at 800℃ and 900℃. For Ti-16.28Si alloy, it possesses the best oxidation resistance at 900℃ with the single rutile TiO2 phase nearly. At 800℃, Cu significantly improves the oxidation resistance of Ti-16.28Si alloy; Compared to Ti-16.28Si alloy, the average oxidation speed is 57.8% of it when the Cu content is 5wt% . However, under 900℃and 1000℃, the oxidation resistance of Ti-16.28Si alloy reduced with Cu added duo to the existing of Cu3Si phase.

Abstract:Gallium nitride (GaN) nanopencils and nanotowers have been synthesized by chemical vapor deposition (CVD) method using the reaction of Ga₂O₃ and ammonia. The observed morphology of GaN nanopencils is divided into two parts: the bottom is a nanowire with large diameter; the top is a nanowire with small diameter. The observed morphology of GaN nanotowers is a layer structure. The formation mechanism of GaN nanopencils and nanotowers is a vapor-liquid-solid (VLS) mechanism. The turn on field of 2.6 V/μm is obtained for GaN nanopencils and the turn on field of 4.1 V/μm is obtained for GaN nanotowers, which are sufficient for ?eld emission ?at panel displays and cold electron sources in display devices. This growth of GaN nanopencils and nanotowers will facilitate flexible design of device architectures for nanoelectronics.

Abstract:Bi_2.1Sr_1.96CaCu_2.0O_8+d (Bi-2212) precursor powders were synthesized with co-precipitation process, and Bi-2212 single filament tapes were fabricated with powder-in-tube (PIT) technique. Based on SEM observation, the primary grain size of Bi-2212 precursor powders was 3~5 mm. However, after sintering, Bi-2212 grains clustered together and the particle size distribution became quite wide, from 10 mm to over 180 mm. By dividing the particles into four groups with different average particle size, the influences of average particle size on the filament density, microstructures and current capacity of final Bi-2212 tapes were systematically investigated. It was observed that with the decrease of particle size, the filament density increased over the entire cold-working process and heat treatment process. Therefore, the intergrain connection was enhanced, which lead to the obvious increase of current capacity

Abstract:High Nb-containing TiAl alloy (Ti-45Al-8.5Nb-(W, B, Y) (at.%), abbreviated as TAN alloy) was successfully brazed at 1100 °C using Ti-28Ni (wt.%) eutectic brazing alloy. The typical interfacial microstructure was TAN/τ3-Al3Ti2Ni + B2/α2-Ti3Al layer/α2-Ti3Al + δ-Ti2Ni/α2-Ti3Al layer/τ3-Al3Ti2Ni + B2/TAN. The effects of holding time on interfacial microstructure and joining properties of TAN brazed joints were investigated in detail. The results demonstrated that the diffusion of Ni from molten brazing alloy to TAN substrate played an important role in the interfacial microstructure evolution, which resulted in an increase of diffusion zone and a reduction of brazed seam with the prolongation of holding time. Shear test indicated that the maximum shear strength at room temperature and high temperature (600 °C) reached 248.6 MPa and 166.4 MPa respectively when holding time was 15 min. Fracture analyses revealed that brittle fracture preferred to initiate and propagate in the continuous intermetallic layers during shear test.

Abstract:Si/C multilayer films deposited by radio frequency magnetron sputtering were post-annealed at 1100°C for 1 h to produce Si nanocrystals (NCs). X-ray diffraction and Raman spectroscopy were used to analyze the phase composition and atomic vibration spectrum of the multilayer structure. High-resolution transmission electron microscopy was employed to verify the existence of Si NCs and to observe their sizes and morphologies. The results reveal that the Si NCs were formed by solid-phase recrystallization of the nanometer-thick layers of amorphous Si confined between C layers. The NC shape and size could be tuned by changing the modulation ratio of the Si layer and the C layer. When the ratio shifted from 0.5 to 2, the NCs became spherical, elliptical, square, and brick-shaped. This growth mode may be conducive to the design of different Si-based photo-electronic materials...

Abstract:Al₂O₃ dielectrics were fabricated on highly ordered pyrolytic graphite (HOPG) by atomic layer deposition (ALD) and the effects of growth temperatures and number of ALD cycles on growth behaviors were studied. It is found that Al₂O₃ preferentially grows along the step edges which promote the formation of Al₂O₃ nanowires at the initial stage. Al₂O₃ nanowires can exist after 100 ALD cycles at 50, 150, and 200 °C, but discontinuous Al₂O₃ thin films rather than nanowires are evidenced at 100 °C. Moreover, the Al₂O₃ layers evolve into continuous thin films with increasing number of ALD cycles. It suggests the growth behavior undergoes a transition from three-dimensional mode to quasi two-dimensional mode with increasing number of ALD cycles. The rates of transition and lateral growth are dependent on growth temperatures. Raman spectra indicate that HOPG maintains undamaged and greatly reserves its original properties after the deposition of Al₂O₃. The results are of great significance to the fabrication of high-quality dielectric layers on graphene as well as the related devices.

Abstract:In this paper, we have grown the InN films with high orientation and varieties typical micrographs on Si (100) substrate by radio-frequency (RF) sputtering, while Indium was used as Indium target, and Nitrogen was used as Nitrogen source. The X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) show that all the diffraction peaks are identified to be associated with the wurtzite phase of InN, with high orientation of (101), (100) and (002). The Scanning Electron Microscope (SEM) and Energy Diffraction Spectrum (EDS) reveal that the high-quality crystal films of InN with various typical microstructures could be deposited, especially the standard of the hexagon at 60 W and 0.4 Pa. We also calculate the stress of InN films in E₂ (High) by Raman spectra with an excitative wave length λ= 633 nm at room temperature, the values of the stress are different due to various microstructures. The A₁ (LO) peaks are lower due to the high mobility. The calculated energies are 1.07 eV, 1.13 eV and 1.32 eV. The XRD, SEM, XPS, Raman spectra, Hall and UV absorption characterizations reveal that we could grow different microstructures of thin films to adapt the various requirements of sensors and other devices.

Abstract:A large area nanopore array with controllable consistency has been successfully fabricated by direct laser writing (DLW) technique with ultralow one-photon absorption (LOPA). In this technique, a doughnut-shape beam generated by 532 nm continuous-wave laser through a vortex phase plate is focused into the thin film of SU8 photoresist by a high numerical aperture objective. The low absorption of the photoresist at the excitation wavelength allows controllable fabricating structures with sub-diffraction-limit feature size and high aspect ratio. With point-by-point scanning fabrication, nanopore array with the pore’s internal diameter, about ten per cent of incident laser wavelength, far smaller than Abbe’s diffraction limit is achieved. The influences of the exposure intensity and exposure time on the fabricated nanopore size and shape are also investigated by scanning electron microscope (SEM).

Abstract:In order to find the influence of α phase on tensile fracture behavior of high strength-toughness Ti-55531 alloy, different heat treatments and analysis methods including SEM, OM and XRD are adopted. Results show that the content of secondary α phase in bimodal microstructures are increased and the scale became finer, with decreasing of content and scale of primary α phase, so that the strength of alloy are increased and ductility are decreased. In lamellar microstructures, with coarsening of secondary alpha phase, both strength and ductility of the alloy are decreased. In full β microstructures, alloys get well in ductility but bad in strength. Both fracture modes of bimodal and lamellar microstructures are mix modes including transgranular cleavage, microvoid accumulations and intergranular crack fracture. As decreasing of content and scale of primary α phase, the content of secondary α phase are increased and the scale are coarsen, the percentage of microvoid accumulations fracture are decreased and percentage of transgranular cleavage and intergranular crack fracture are increased.

Abstract:The wettability and interface bonding mechanism between 55% SiCp/Al composite materials and PbO-ZnO-B2O3 glass during the sealing process were investigated in this article. The results showed that the glass would spread wider with the increase of temperatures. That is to say the wettability angle became smaller and the wettability was improved. The spreading area of glass on Al2O3 and SiC were larger and the wettability angles were smaller than those on the composites. The sealing temperature between glasses and 55% SiCp/6061Al range from 450~490 ℃. When the sealing temperature is higher than 470 ℃, bubbles would appear in the sealing interface and the number of bubbles increased with the increasing of temperatures, at the same time the size of the bubbles would became larger too. When the sealing temperature is 460 ℃, a 12 μm diffusion region appeared between the glass and 55% SiC/Al composites. When the sealing temperature is 490 ℃, there was a clear boundary between the glass and Al2O3 ceramic, and the SiC particles would diffuse into the glass when the glass and SiC ceramic were sealed together.

Abstract:Thermal oxidation (TO) process was conducted to realize surface treatment of TC4 alloy. Scanning electron microscope (SEM), glow discharge optical emission spectrometer (GDOES), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were employed to analysis the characterizations of the obtained TO layer. Electrochemical corrosion behaviors of the TO layer and TC4 alloy substrate in CO2-saturated simulated oilfield medium were investigated. The results showed that the continuous and uniform TO layer was mainly composed of rutile TiO2 phase. TO treatment had significantly improve the anticorrosion property of TC4 alloy.

Abstract:Bronze powder was used as the raw material and calcium chloride as the space holder. The open cell?bronze foams have been fabricated by sintering and dissolution process (SDP). By varying the volume percentage and the size of the space holder, the bronze foams with porosity ranging from 70% to 90%, and cell size from 1 to 3 mm were produced successfully. The relation between the volume percentage of the space holder and the porosity of?bronze foams was investigated, and the effects of porosity and pore size on the mechanic property of bronze foams were also studied. The pore structure, phase composition and micro structure of bronze foams were observed and analyzed. The experimental results show that plateau stress of bronze foams increases with the decrease of porosity, and the plateau stress is in the range from 12.6 to 2.6 MPa with the porosity of ranging between 77% and 89%. The energy absorption per unit volume (W) of bronze foams with the porosity between 77% and 89% is in the range of 33.5~5.1MJ/m3 when strain is 50%. The maximum ideality energy absorption efficiency is about 0.82. All the results indicate that the bronze foam is a kind of energy absorption material.

Abstract:The effect of homogenizing annealing and thermo-mechanical treatment processes on microstructure and property of Cu-15Ni-8Sn-1.0Zn-0.8Al-0.2Si alloy was investigated using mechanical property test, electrical conductivity measurement, optical microscopy, scanning electron microscopy and transmission electron microscopy. The alloy ingot was two-stage homogenizing annealing treated at 830 ℃/2h+850 ℃/2h, hot rolled by 70%, then solution treated at 850 ℃ for 1 h, followed by 60% cold-rolling deformation and aging treatment at 400 ℃ and 450 ℃ respectively. After aged at 450 ℃ for 30 min, the hardness was 378HV, electrical conductivity was 8.0% IACS, tensile strength was 1144MPa, yield strength was 1098MPa, elongation percentage was 3.29%. During aging at 400 ℃ for 1 h, the hardness was 390 HV, electrical conductivity was 7.4% IACS, tensile strength was 1164 MPa, yield strength was 1112 MPa, elongation percentage was 3.05%. The combined effects of spinodal decomposition strengthening, precipitation strengthening and substructure strengthening were the mainly strengthening mechanism in alloy. Meanwhile, since the precipitation of solute atoms, the solid solubility of matrix was reduced, and the electrical conductivity of alloy was improved. After two-stage homogenizing annealing treatment, the microstructure of alloy was homogeneous equiaxed grain. It was found that spinodal decomposition and L12 ordering (β-Ni3Sn) appeared in the alloy during aging at 400 ℃ for 1h. The crystal orientation relationships between copper matrix and β-Ni3Sn precipitates were determined as: ‖ , ‖ ; ‖ , ‖ .

Abstract:Using alternatively stacked Ti and Ni foils, a Ti₂Ni/TiNi micro-laminated composite was fabricated by hot pressed sintering at 900 _oC. The effect of diffusion time on the microstructure and constitutional phases of the composites was investigated. The scanning electron microscope (SEM), electron probe microanalysis (EPMA), X-ray diffraction (XRD) and differential scanning calorimetry (DSC) were employed to analyze the microstructure, constitutional phases, phase structures and phase transition temperatures of the fabricated composites. The results indicate that Ti and Ni foils are gradually consumed with the increase of diffusion time and three intermetallic layers (Ti₂Ni, TiNi, Ni₃Ti) are produced at the interfaces of Ti/Ni. When Ni foils are completely consumed, Ti atoms diffuse into Ni₃Ti layers, tranforming the Ni₃Ti layers into TiNi. After Ti foils are completely consumed, only alternatively arranged Ti₂Ni and TiNi layers exist. Moreover, there are lots of granular and strip-shaped Ti₂Ni phases distributing in the TiNi layers. The A_s, A_f, M_s, M_f and transition hysteresis temperature (ΔT) of the composite fabricated after 8h diffusion are 75.9 _oC,99.2 _oC,63.6 _oC,45.7 _oC and 32.5 _oC, respectively.

Abstract:Electron beam welding, electron beam isolation welding and electron beam isolation welding-brazing for the dissimilar combination of titanium alloy and stainless steel will be studied in this project. The present results show that the brittle intermetallic compound formed in the welding process is the key factor to influence the joint properties. The penetrated crack is formed in electron beam welding and electron beam isolation welding process directly leading to the joint unsuccessful. In electron beam isolation welding-brazing process, the joints has the characters of welding and brazing and the metallurgically bonded joint is achieved without melting the titanium alloy sheet. Ag and Cu as filler material exhibit good isolation layer which helps minimizing the formation of Ti/Fe intermetalics, aslo has an relaxation effect on the residual stress of the weld. The interalloying of dissimilar materials well controlling, a reaction zone is gained on the interface. The maximum tensile strength of titanium alloy/stailess-steel is up to 100MPa. The welded seams are good shape as well as the back of the joints and there is no crack and detected porosity in the joints through X-ray inspection.

Abstract:NiCoFeCuCr high entropy alloy coatings were in-situ synthesis on the cooper surface using mechanical alloying(MA) method. The phase composition and microstructure of the coatings were characterized using X-ray diffraction(XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy(EDS). The microstructure and the formation mechanism of the coatings were studied. It is revealed that increasing of milling time can enhance the thickness and densification of the coating. The most dense and uniform coating, with an average thickness of 40μm, were synthesized after MA for 5h, which metallurgically bonding with the copper substrate. The formation of the coating can be simpli?ed as follows:(1)Particles hammered into substrate. (2)Powder deposited on substrate through cold welding. (3)Diffusion between theScoating andSthe substrate. (4)Work hardening leading to spalling fatigue.

Abstract:The effects of T6 and T6I4 aging treatments on dynamic mechanical properties and microstructure evolution of 7N01 aluminum alloy at high temperatures were investigated by using the split Hopkinson pressure bar(SHPB), Optical Microscopy(OM) and Transmission Electron Microscopy(TEM). The results show that the dynamic yield stresses of T6I4 and T6 aging state 7N01 aluminum alloy increase with the increasing strain rate. The dynamic yield stress and dislocation density descend with the increasing temperature. The dynamic yield stress of 7N01-T6I4 aluminum alloy is higher than that of 7N01-T6 aluminum alloy at 150℃ and 250℃. At 350℃, the precipitates in 7N01-T6I4 aluminum alloy is dissolved, while the precipitates in 7N01-T6 aluminum alloy is coarsened. As a result, the dynamic yield stress of 7N01-T6I4 aluminum alloy is lower than that of 7N01-T6 aluminum alloy.

Abstract:Aiming at the urgent demand for reliability assessment of TiNi based alloy working in space, Ti44Ni47Nb9 alloy is impacted at 1020 m/s using a powder gun. Phase transformation, microstructure and mechanical properties in Ti44Ni47Nb9 alloy induced by impact are investigated. The results show that no intermediate phase is formed along the impact direction, the phase transformation temperature shifts to a lower temperature along 45° and vertical to the impact direction of impacted Ti44Ni47Nb9 alloy. A large number of cracks appear at the bottom of the crater and walls, there are martensite plates in TiNi matrix, and many dislocations exist in the β-Nb particles and TiNi matrix. The microhardness reduces gradually with the increase in distance from the crate, this is attributed to working hardening and uneven energy distribution caused by high-velocity impact.

Abstract:The effect of cooling rate on microstructure and tensile properties of BT25y titanium alloy were studied using OM, SEM, XRD, and TEM methods. The results indicate that the microstructure of the air-cooled specimen consists of α and β transformed phase, while in oil- and water-quenched microstructure, α, α" and α" martensite phase were found. Lattice parameters of α" phase obtained by XRD analysis show that a is shorter, b is longer in water-quenched microstructure than in oil-quenched one. After aging treatment at 550 ℃/6 h followed by air cooling, the phase component is the same with its unaged counterpart in air-cooled condition; martensite phase decomposed into stable α and β phase in oil- and water-quenched conditions. Room temperature tensile properties after aging treatment were tested. Compared with the air-cooled sample, tensile and yield strength of the sample after oil and water quenching were much higher, accompanied with much lower elongation. The phenomenon was thought to be related to the shape and size of secondary α phase.

Abstract:Considering burr and collapse edge processing defects of Ti alloy honeycomb material using in aerospace with low stiffness and thin-walled, fixation and processing method should be improved. The material was treated by ice fixation method. CNC milling machine was used for the cryogenic processing. The honeycomb properties and reasons of machining defects were analyzed. Low-temperature milling mechanism of ice fixation was established. Results show that compared to the traditional processing way, the ice fixation milling surfaces have great improvement, and the processing defects are effectively suppressed. Moreover the cutting depth has greater influence on surface quality than spindle speed. The new method can improve the strength of honeycomb. Influence order of cutting parameters on the milling force can be obtained: cut deep is the largest and 3 times can be improved, followed by the spindle speed, feed speed which has minimal impact. Conclusion: for efficient processing of metal honeycomb material with small in-plane radial equivalent strength and low rigidity thin-wall, the ice fixation provides a new processing method.

Abstract:The antimony nanoparticles with different particle sizes were prepared by mechanical ball milling method while the particles surface was modified by silane coupling agent KH-570. The tribological properties of experimental lubricating oil, which are 900SN and others lubricating oils containing antimony nanoparticles with various particle size，were studied by reciprocating friction experiment in CFT-1 material performance tester. The worn surface morphology and chemical composition of 45 steel were analyzed by SEM and EDS. The results show that antimony nanoparticles play a role in repairing effect for worn surface basing on micro-filling and adhesion mechanism. With decreasing of particle size of antimony nanoparticles and increasing of frication load, the antifriction and antiwear properties of experimental lubricating oils increase. The experimental lubricating oil containing antimony nanoparticles with 40 nm of particle size has good antifriction and antiwear properties under higher friction load.

Abstract:To explore the application of fluorescence elements in the field of corrosion monitoring, Ce doped YAG (Y3Al5O12) powder and coatings are prepared respectively. The effect of immersion duration in nitric acid is studied on the luminescent intensity. The results show that the YAG: Ce powder is mainly YAG phase. While the plasma sprayed coatings are dominated by YAG and YAP (YAlO3). The porosity and diffraction peak intensity of YAG: Ce coatings increase with the immersion duration in nitric acid. Meanwhile, the diffraction peak position moves for the coatings after they are immersed in the acid. The luminescent intensity of coatings increases firstly, and then decreases, and finally increases with the increment of immersion duration. The luminescent intensity of coatings is influenced by the porosity, crystallinity and phase composition of coatings etc.

Abstract:Li, Fe and V were reclaimed together and preparedSto xLiFePO₄-yLi₃V₂(PO₄)₃ materials from spent LiFePO₄ and Li₃V₂(PO₄)₃ LIBs, for the reason that they have similar characteristics and preparation method. The spent battery materials were roasted under 600 _oC for 1 hour in air atmosphere to remove the PVDF binder, then the active materials and aluminum foil collector can be separated effectively. The different proportion of xLiFePO₄-yLi₃V₂(PO₄)₃(x:y=5:1,7:1,9:1) materials were prepared by roasted products through adjusting the mole ratio of Li, Fe, V and P , ball milling and calcining. The morphology, structure and electrochemical of composite material were performed. The results show that the composite material have the electrochemical properties of LiFePO₄ and Li₃V₂(PO₄)₃ simultaneously, which can significantly improve the LiFePO₄ ratio performance. This dissertation explores a new way for the recycling of spent LIBs. The study is of good application foreground. It is very important for environmental protection, and is believed to bring both economic and social benefits to us.

Abstract:Preparation of NiCrBSi-WC coating on Q235 steel was using the oxygen acetylene flame spray welding and use solid borosiliconizing method to modify the surface of the spray welding layer was modified by laser. The microstructure, phase structure and microhardness of the coatings were analyzed by SEM, XRD, EDS and microhardness tester and the wear resistance of the coating before and after treatment by using the friction and wear testing machine. The results show that the surface of the spray welding layer under the laser scanning process become smooth and dense. The main phase Ni2.9Cr0.7Fe0.36 and FeNi3 components of the coating were not changed, but the main phase in the arrangement of crystal plane with the preferred orientation and the crystallinity increased. The WC part is decomposed into W2C, W and C. And C was dissolved into the Ni based and increased Cr3C2 and other carbides, and the wear resistance of the coating was improved. The hardened layer depth is 0.25mm and its microhardness increased to 909HV. On the basis of the laser remelted coating, boronsiliconizing can increase Ni3B, Ni2B, NiSi etc. boride and silicide hard phase, the average coefficient of friction decreased from 0.583 to 0.428, wear resistance than laser treatment increased nearly doubled.

Abstract:In order to solve the problem of difficult processing about magnesium alloy seamless tube, the process prepared by rotary piercing technology for AZ31 magnesium alloy pipe was studied in the paper. According to the constitutive relation of magnesium alloy during hot working, temperature and strain rate range of 300 ℃-450℃, 0.001 s-1 - 1s-1 were confirmed. According to the theory of skew rolling and the existing three-roll skew rolling equipment, the process parameters were preliminary determined. The coupled thermal-mechanical numerical simulation and experiment research of the AZ31B magnesium alloy billet with the size of Φ40mm×300mm were carried, taking samples after rolling for metallographic analysis.The results showed that the rotary piercing way could produce AZ31 magnesium alloy seamless tube; At 400 ℃, choosing appropriate amount of plug advance、feed angle、roll speed, and piercing gorge diameter would be able to pierce Φ40mm×5.5mm×615mm magnesium alloy tube; After piercing microstructure changed into equiaxed distribution and grains were refined to 3 microns, mechanical performance was improved accordingly. This process could be instead of traditional magnesium alloy extrusion process to produce seamless tube, improving production efficiency, reducing costs, which facilitated subsequent product production.

Abstract:High strain rate compression experiments of U-5.7Nb alloy were conducted at temperatures from -100℃ to 400℃ with split Hopkinson pressure bar apparatus. Results show that the compressive stress-strain response depends sensitively on the applied strain rate and test temperature. The yield stress of U-5.7Nb alloy was found to decreased rapidly with the increasing temperature at a rate of about 2MPa/℃, while the work hardening rate was relatively constant. At temperatures higher than 200℃,the shape of the stress~strain curves changed from duplex yield character to elastic-plastic character for both quasi-static and dynamic compression experiments. The hardening modulus caused by detwinning and the yield stress increased obviously with the increasing strain rates. Finally,the divergency of the low- and high-rate deformation curves at temperature of 400℃ was discussed based on the optical micrography.

Abstract:H62 brass joints were brazed successfully using BAg45CuZn brazing filler metals plated tin coatings. SEM and XRD were used to observe the surface microstructure and phase of tin coatings and H62 brass brazed joint. The tensile strength of H62 brass brazed joints were analyzed using tensile test machine. The results show that the crystallization orientation of tin coating displays (110) and (210) crystal faces. The interface brazing seam and H62 brass produce sound brazed joints after tin electroless plated on filler metal. Then Cu-rich phase in the microstructure of brazed joints decrease, but the Cu5Zn8 intermetallic compound generate. The tensile strength of brazed joints initially increase and then decrease with increasing of plating tin content. When the content of tin electroless plated coating is 6.0 %(wt.%), the maximum tensile strength of brass brazed joints is 353 MPa. The fracture morphology of brazed joints using filler metal with tin coatings display ductile fracture which the same with the joints using the BAg45CuZn brazing filler metal.

Abstract:The effects of different sintering temperature on the microstructure, microstructural evolution, surface porosity and mechanical properties of porous surface NiTi biomedical gradient alloy were investigated. The results show that the gradient alloy are consisted of complex Ti, Ni, Ti₂Ni, Ni₃Ti mixed phase and gradually transformed into NiTi phase also little Ti₂Ni、Ni₃Ti phase with increasing of the sintering temperatures. The cracks and defects at the interface between the matrix and the porous layer are gradually reduced and a stable metallurgical bonding is formed. The inner and outer grains are refined continuously, but the higher sintering temperature leads to the porosity fusion of the porous layer, resulting in the damage of the gradient structure. The porosity and the average pore size of surface layer decreases slowly. The compressive elastic modulus of the alloy changes with the sintering temperature is not obvious, while the compressive strength shows a significant increase trend. Compared with bulk NiTi alloy and porous NiTi alloy, the prepared gradient alloy not only has good interface bonding and surface pore characteristics, high compressive strength and low elastic modulus, but also has excellent super-elastic properties.

Abstract:The single crystal 6H-SiC was irradiated by 400 keV He₊ ions with 1×10₁₆ He₊/cm₂ fluence at 400°C and then annealed for 30min at 1200 and 1500°C. The microstructure was observed by using transmission electron microscopy and scanning electron microscopy. Only the damaged layer was observed and no visible helium bubbles were formed in SiC matrix after helium ion irradiation at 400 °C. However, after annealled at 1200 °C for 30 minutes, platelet-like planar bubbles were formed in the irradiated region, which were distributed mainly on the (0001) plane and less on the (1 1 -2 0) crystal plane. There were no visible size defects formed on 6H-SiC surface after helium ion irradiation. But, blisters and craters were formed after annealing at 1200 °C for 30 min and became easier with annealing temperature increase. Some cracks were generated after annealing at 1500 °C. The mechanism of microstructural evolution was also analyzed and discussed.

Abstract:In this paper, size controllable hollow carbon spheres used as catalyst carrier were prepared by hydrothermal synthesis with glucose as the raw material without adding organic template, the self-made flower-like CeO₂ with a pore size in the range of 30nm~40nm and a specific surface area of 126m₂/g was added as auxiliary catalyst, and the catalyst was prepared by microwave-assisted reduction of chloroplatinic acid with ethylene glycol. The prepared catalyst carrier and auxiliary catalyst were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), infrared spectroscopy (IR), X-ray diffraction (XRD) and specific surface area (BET). The electrochemical performance of the prepared catalyst was tested by electrochemical workstation. The results show that the size distribution of the carbon sphere is between 0.4μm and 0.9μm and the surface contains -OH, -C=O, -COOH oxygen-containing functional groups. The results of electrochemical tests show that compared with the traditional Pt/C catalyst, Pt-CeO₂/C catalyst with the addition of flower-like CeO₂ has better catalytic activity, stability and anti-CO poisoning capacity. With the decrease of the size of the carbon sphere carrier, the catalytic performance, stability and anti-CO poisoning ability of the catalyst was enhanced. The catalyst was prepared by the carbon spheres as the carrier which were prepared under the condition of glucose concentration of 0.5mol/L and hydrothermal reaction time of 4h and the floral CeO₂ as the auxiliary catalyst which has the best activity, stability and anti-CO poisoning capacity for the catalytic oxidation of ethanol.

Abstract:Ti-66Ni (wt.%)+B composite brazing alloy was used to braze Ti₂AlNb alloy. The interfacial microstructure and forming mechanism of the brazed joints were studied. The effect of brazing temperature and B content on the interfacial microstructure and mechanical properties were investigated. The results showed that the typical microstructure of the joint was: Ti₂AlNb/B2/B2+Nb₃Al+τ₃+TiB/τ₃+Ti₂Ni/B2+Nb₃Al

Abstract:The particularity of dual-phase material microstructure makes its micro deformation behavior more complex than single phase material, and the complexity is expressed in stress-strain partitioning and coordination behaviors between two component phases with different properties during the deformation. Moreover, the factors affecting the micro deformation behavior are of multi-scale, therefore it is difficult to conduct quantitatively study at present, and the stress-strain behavior of single phase which is the basis to study the micro deformation behavior of two-phase material is also the hotspot at present. The investigation progress in the stress-strain behavior of single phase is summarized in this paper, and the methods for single-phase stress-strain behavior are introduced. Then the research on micro deformation behavior of dual-phase material from three aspects, which are experiment research, theory analysis and numerical simulation based on finite element method are reviewed. Further more, the drawback of each method is analyzed simply. Finally, several unsolved problems regarding the micro deformation behavior of dual-phase material are proposed.

Abstract:Biodegradable magnesium and magnesium alloys have received much attractions due to their light weight, suitable elastic modulus, biodegradability and excellent biocompatibility. However, the magnesium corrodes too fast in vivo, accompanied with hydrogen evolution and increase of PH value in local tissues around during degradation, which plays a detrimental role in the surrounding tissues and leads to hemolysis and bone tissue absorption sometimes. The poor corrosion resistance of Mg and Mg alloys limits in their clinical applications. Addition of proper alloying elements and surface modification of magnesium alloys are expected to be effective methods for retarding the corrosion rate and attaining controllable degradation behavior of Mg alloys. In this paper, investigations on antibacterial properties and hemolysis of biodegradable magnesium alloys are reviewed and research progresses of biocompatibility of biodegradable magnesium alloys in recent five years are systematically discussed. The development directions and challenges of biodegradable magnesium alloys in the future are presented.