Abstract:Rigid restraint thermal self-compressing bonding (TSCB) by localized induction heating, a new diffusion bonding technology was proposed in this paper. Experiments were conducted on Ti6Al4V plates to prove the feasibility of rigid restraint thermal self-compressing bonding by local induction heating. Moreover, finite element analysis was employed to numerically investigate the thermal elastic-plastic stress-strain cycle during thermal self-compressing bonding by localized induction heating. Results show that solid-state joint with homogeneous microstructure and excellent mechanical properties was attained. By localized induction heating, an internal elasto-plastic stress-strain field is developed which makes the bond interface subjected to thermal compressive action. This thermal self-compressing action combined with the high temperature on the bond interface promotes the atom diffusion across the bond interface to produce solid-state joints.

Abstract:This paper details the production of a series of Ti-xV-15Cr (x=20,25,30,35) alloys by directed energy deposition (DED) technology, and pure Ti, pure V, and pure Cr powders were used as raw materials. The effects of V content on grain morphology, microhardness, elastic modulus and the flame-resistant properties of Ti-xV-15Cr alloys were determined. It was found that the microstructures of Ti-20V-15Cr, Ti-25V-15Cr and Ti-30V-15Cr alloys were composed of columnar grains growing epitaxially and fine equiaxed grains at the top region, with the aspect ratio of the columnar grains decreasing gradually with increasing V content. The microstructure of Ti-35V-15Cr alloy was composed of full near equiaxed grains except the very top region, which is very different from those of Ti-20V-15Cr, Ti-25V-15Cr and Ti-30V-15Cr alloys. The formation mechanism of microstructure was explained by combining the columnar to equiaxed transition (CET) model and the relationship between the height of the columnar grains layer and Z axis increment (ΔZ). The average microhardness of Ti-xV-15Cr alloys increases slightly with increasing V content, and the elastic modulus falls between 123.8 GPa to 137.6 GPa. Flame-resistant test showed that Ti-35V-15Cr alloy exhibits the best flame-resistant properties.

Abstract:Deuterium (D) induced cracking (DIC) of Ti was in-situ investigated by the hot stage microscope (HSM) technique combined with the pressure-volume-temperature (PVT) method. Only several cracks were observed on the surface of Ti upon exposure of D2 at 550℃, while more unique circular cracks appeared when Ti was heated from room temperature up to 550℃ in the D2 atmosphere. The morphology changes of Ti induced by deuterium during heating is consistent with the characteristics described by the preferred edge-attack model. X-ray photoelectron spectroscopy (XPS) measurements indicated that the surface passivation layer on Ti, mainly consisting of titanium oxides, carbides and nitrides, played an important role in the formation of circular cracks.

Abstract:In order to analyze the material removal mechanism of single crystal γ-TiAl alloy in grinding, the molecular dynamics model of Ti-Al alloy ground by two abrasive grains was established. The influence of lateral and longitudinal spacing of the diamond abrasive on the material removal mechanism of the single crystal γ-TiAl alloy was revealed. The results showed that the microcutting process of single crystal γ-TiAl alloy is accompanied by the change of temperature, potential energy and dislocation, as well as lattice phase transition. Cutting force, cutting temperature, potential energy and removal efficiency increase with the increase of lateral spacing, but are less affected by longitudinal spacing. The number of lattice phase transition atoms increases with the increase of lateral spacing and decreases with the increase of longitudinal spacing. With the increase of laterial and longitudinal spacing, the number of dislocations, total length of dislocations, and density of dislocations will increase accordingly.

Abstract:In the current study, the effect of sample dimensions and process parameters (beam current, scan speed, offset focus and scan length) of EBM system on microstructure of the EBM built Ti-6Al-4V has been investigated. In general, it can be observed that the microstructures of EBM built Ti-6Al- 4V consist of columnar grains of prior β phase. Inside the columnar grain typical (α+β) structures namely Widmanst?tten α platelets with rod like β phase formed on the interfaces of the fine α grains has been observed. Grain boundary α layer is found to be formed along grain boundary of prior β columnar grain. With increasing thickness of the test slab, beam energy density and scanning length, the diameter of prior β columnar grain increases and they follow the build direction. The columnar grain diameter also decreases with increase in height. With increasing thickness and beam energy density α platelets get coarser.

Abstract:Thermecmaster-Z thermal processing simulation machine was used to conduct isothermal compression tests on Ti60 alloy, and the flow curves of the alloy were obtained under the conditions of deformation temperature 700 ~ 950℃, strain rate 0.001 ~ 10s-1 and true strain 0.51. The flow curves of Ti60 alloy were corrected by considering the effect of friction and heating on flow stress.The results show that the effectof friction and heatinghas significant influence on the flow stress of Ti60 alloy.The influence of friction increases with the increase of strain, while the influence of heating increases with the decrease of deformation temperature and the increase of strain rate. The flow curve presents flow steady typeafter correctingby the effect of friction and heating,which can more accurately reflect the dynamic response of the flow stress of Ti60 alloy to the true strain.

Abstract:Silicon diffusion coating has been prepared on TC4 alloy by pack cementation technique to improve its high temperature oxidation resistance. The microstructure, high temperature oxidation behavior and failure mechanisms of the coating were studied. The results show that the coating has a dense multilayer structure, mainly consisted of a TiSi₂ outer layer, a TiSi middle layer, and a Ti₅Si₄+Ti₅Si₃ inner layer. The high temperature oxidation tests show that a protective scale composed of SiO₂ and TiO₂ formed on the surface of the coating during oxidizing at 850 ℃ in air, imposed to relatively good anti-high temperature oxidation property of the coating. The inter-diffusion of Ti and Si between the coating and the substrate caused the increase of TiO₂ in the scale and lacking of Si source, resulting in the degeneration of the protective scale. The high P-B ratio between the oxides and the coating, together with the mismatch of the thermal expansion coefficients among the oxides and the coating should be the main factors responsible for cracking and spallasion of the scale.

Abstract:The effects of annealing temperature, cooling rate and multiple annealing process on microstructures, tensile properties and corrosion behavior of a new near-α titanium alloy-Ti90 were comparatively investigated.The results show that when specimens were annealed in the two-phase region,as the annealing temperature increased, the deformed structure gradually spheroidized with a decreased fraction of primary α phase (α_p) and an increased fraction of β-transformation structure (β_t), in which the secondary α phase (α_s) precipitated and coarsened gradually. Those changes finally rose up to the reduced strength and improved plasticity. When annealing in single β phase zone, a fine lamellar microstructure was obtained with fairly coarse original β grains, which resulted in a sharp decrease in the plasticity of the alloy. After water cooling, the acicular α′ martensite phase was precipitated inside β grains, which significantly improved the strength while maintaining good plasticity. With multiple annealing, the size of α_p and β_t increased, and α_s coarsened, leading to a simultaneous decrease in the strength and plasticity of the alloy. The polarization curve test results show that Ti90 alloys with four different microstructures all exhibite passivation behavior in 3.5% NaCl solution with low passivation current density, which implicates a good corrosion resistance. The corrosion resistance of different microstructures is in the order of bimodal microstructure > equiaxed microstructure > Lamellar microstructure.

Abstract:The quasi-static and dynamic reload compression tests were conducted to explore the changes in mechanical properties of Ti6321 alloy bimodal structure after preshock. The optical microscopy (OM) and transmission electron microscopy (TEM) were used to observe and analyze the microstructures. The results show that the static and dynamic yield strength and average flow stress of Ti6321 alloy after pre-shock are higher than those of the original sample, but the fracture strain and impact absorption energy are significantly reduced, and the preshock sample is more likely to appear an adiabatic shear failure after SHPB loading. TEM results showed that twins were formed inside the sample after the preshock of the light gas gun, which caused the Ti6321 titanium alloy to exhibit a shock wave strengthening effect.

Abstract:In order to study the influence of hydrogen on the high temperature deformation behavior and microstructure evolution of 45Ti-47Zr-5Al-3V alloy, a dynamic thermal simulation machine was used for the as-cast alloy with and without hydrogen under different deformation conditions. The flow stress and deformation activation energy of TiZrAlV alloy can be significantly reduced by adding proper amount of hydrogen. The activation energy of unhydrogenated and hydrogenated alloy is 339.7 kJ/mol and 286.5 kJ/mol. Meanwhile, the optimum thermal processing parameters are 700-900℃, 0.01-1s-1. The OM and EBSD microstructure observations show that adding hydrogen can refine the as-cast structure, increase the β-phase content and promote dynamic recrystallization, thus significantly reducing the flow resistance of the alloy, expanding the hot processing window and improving the thermal processing performance.

Abstract:Titanium alloy Ti5Al2.5Sn ELI is an important structural material in the field of aerospace and others. In the paper, the influence of casting process on the as-cast structure and tensile properties of titanium alloy Ti5Al2.5Sn ELI at room temperature was studied by pouring three kinds of mold with one furnace alloy. The results show that the surface of casting samples from graphite mold is rough, while that of the ceramic and metal mold is smooth; the macrostructure of samples from graphite mold is composed of numbers of equiaxed crystal and some columnar crystal, that of the metal mold is some equiaxed crystal and numbers of columnar crystal, and that of the ceramic mold is numbers of columnar crystal and little equiaxed crystal; the microstructure of the alloy under different processes is composed of irregular boundary α cluster, and the inner part is sheet α phase, and the width of α sheet of graphite mold is the smallest, that of metal mold is the second, and that of ceramic mold is the largest; the tensile strength of alloy is 715~731 MPa, the elongation is 8~15 %, the elongation of samples from the graphite mold is the highest, that of metal mold is the second, that of ceramic mold is the lowest, and the influence of molds on the elongation is obvious, but that on the strenths is little; the difference of surface morphology and thermal conductivity of mold, and the difference of α cluster size and α sheet thickness of samples are the main reasons for the phenomena.

Abstract:Accelerating and improving the process of osseointegration is a research hotspot of oral implantology, and electrical stimulation of osteogenesis is one of the research directions. In view of the bone"s piezoelectric properties and the defects of exogenous electrical stimulation, the application of piezoelectric materials to generate endogenous electrical stimulation to promote osteogenesis is of great significance. As an environmental-friendly lead-free piezoelectric material, barium titanate has a piezoelectric effect in the tetragonal phase. Especially it has good biocompatibility and can promote bone formation under load conditions. Here we used anodic oxidation technology and hydrothermal reaction to construct a barium titanate piezoelectric coating on the titanium surface. By optimizing the experimental parameters and setting the limit concentration, we explored the synthesis conditions of the tetragonal barium titanate coating.Meanwhile, the piezoelectric potential of coating particles was verified by finite element simulation. By modifying the surface of the dental implant, we hope to provide a new method to promote implant osseointegration.

Abstract:In the present work, low cycle fatigue (LCF) behavior of Ti-35421 titanium alloy with bimodal microstructure consists of lath α (αp) and βtrans were investigated by strain-controlled mode at room temperature. Results indicated that the cyclic stress amplitude of the bimodal microstructure Ti-35421 alloy show cyclic softening at first, then reach to cyclic stability at high strain amplitude (Δεt/2=1.0%, 1.2%, 1.4%, 1.6%). However, the cyclic stress response was characterized by cyclic saturation at low strain amplitudes (Δεt/2=0.6%, 0.8%). One of fatigue crack source was found by fracture morphology observation when Δεt/2=0.6%, while a large number of small secondary cracks occurred on the surface. On the contrary, multiple fatigue crack sources generated when the strain amplitude increased to 1.6%, the number of secondary cracks reduced, but the length and width of the secondary cracks increased significantly. TEM results indicated that a large number of dislocations generate at the αp/βtrans interface at the low strain amplitude (Δεt/2=0.6%), which might lead to micro-crack nucleation due to the stress concentration. Meanwhile, at high strain amplitude ( Δεt/2=1.6%), deformation inhomogeneity phenomena happened in the αp phase, a large number of dislocation tangles and dislocation debris formed in the αp phase, and some dislocation pile-ups formed in the αs phase, which is not founded in the β substrate.

Abstract:The evolution of grain morphology is accompanied with grain boundary (GB) migration, and the grain morphology significantly determines the properties. Therefore, the key problem in engineering research is to obtain expected microstructures by controlling GB migration. The understanding on GB migration in metals was reviewed and the current study on TiAl alloys was given in this paper. First, the phenomenon and physical model of GB migration were introduced. Then the driving force, especially the diffusion and stress, was analyzed. Further, the influence factors of GB migration were discussed, including misorientation, grain boundary triple junctions, curvature and temperature. Finally, some applications of the regulation of GB migration were introduced. Combined with in-situ observation, for the first time, the GB migrations of TiAl alloys in single-phase regions at high temperatures were analyzed.

Abstract:3D printing technology is challenging the dominant position of traditional manufacturing processes, especially in the field of metals represented by titanium alloys. In this paper, the research status of mainstream printing technologies used in manufacturing titanium and titanium alloys is introduced. The basic forming mechanism and existing problems of each technology are analyzed in detail. The challenges of process application and possible measures to solve these problems are pointed out. Meanwhile, the main advantages and disadvantages of these technologies are compared for selecting the optimum 3D printing process according to the practical application requirements. The representative applications and related properties of various types of 3D printing titanium and titanium alloys are summarized, and the development direction of 3D printed high-performance titanium parts is pointed out.

Abstract:This article introduces the current research progress and theoretical basis of designing the TWIP / TRIP (TRIP: transformation induced plasticity; TWIP: twin induced plasticity) metastable β titanium alloys, and summarizes β-grain sizes, yield strength and work hardening capability achieved in the double twined {332} <113> and {112} <111> metastable β titanium alloys. The application and limitation of Bo-Md diagram in the design of multi-component titanium alloys are further discussed, especially the effect of different secondary phases (α-phase and ω-phase) on the stability of the matrix β-phase. The factors that influence the deformation mechanisms of TWIP / TRIP metastable β titanium alloys are emphasized in terms of the matrix β phase stability, precipitated phases, β-grain sizes and crystallographic orientations, in which the current deficiencies of this field are analyzed. Furthermore, the effect of double twinning mechanisms on the mechanical properties of titanium alloys is briefly discussed as well. Finally, by summarizing the research progress and related issues, this article conveys the new insights into the development of high-strength and tough titanium alloys.

Abstract:AZ31 rods have been prepared by the extrusion-shear (ES) process with different shear angles 150°, 135° and 120°. The commercial AZ31 magnesium alloy was prepared by ES process which includes direct extrusion process and subsequent shearing process.Microstructures evolution of AZ31 alloys with bimodal grains have been investigated by using optical microscopy, scanning electron microscopy and electron backscattered diffraction. The research results showed that proportion of the large grain area increases with rising of strains. From the OM images it can be seen bimodal grained structures, and the narrow coarse grains are surrounded by the fine grains.the texture changes with different shear angles of the ES process from the pole figures.Both the yield strengthes and the peak strengthes increase with decrease of the shear angles gradually.As the shear strains increases, the proportion of large grains increases while the size of small grains increases because both the deformation and the dynamic recrystallization fraction increase with the decreases of shear angles.

Abstract:Layered FeSe has become one important superconducting material, but the major challenge in the growth of large crystal makes it difficult to further clarify the underlying superconducting mechanism. In this research, large crystals with a typical size of 7×2×2 mm3 are obtained simply by using KCl flux with a controlled temperature gradient inside the flux. Superconducting tetragonal β-FeSe phase with the basal plane of (101) face is identified by X-ray diffraction analysis. The super large crystals show outstanding superconducting performance with transition happened at 9 K according to the DC magnetization measurements and broad resistive transition to zero resistance at 10 K with an onset temperature of 15 K. Our work has provided a convenient method to synthesis large FeSe single crystals which is promising in investigations of FeSe-based superconductors.

Abstract:To improve the interface bonding characteristics between copper and ceramic in Cu-(Ti3SiC2)p composites preparation, electroless copper plating on Ti3SiC2 powder surface and its electrochemical characteristics was investigated in this paper, using environmental friendly ascorbic acid as reducing agent and D-glucose sodium as complexing agent. The modified effects of lauryl sodium sulfate (SDS) combined Polysorbate 80 (Tween-80) surfactants on electroless copper plating was analyzed as well. Electrochemical mechanism and parameters optimization of this system was predetermined using linear sweep voltammetry and open circuit potential-time method. The results showed that the polarization current density could be improved by raising reaction temperature and the concentration of Cu (II) and ascorbic acid, which may certainly contribute to accelerate the process of electroless plating. New nuclei were developed from the Ag catalytic activated center implanted on the surface of the copper-coating (Ti3SiC2)p particle, and microspheres with more Ag catalytic active centers promote the formation of copper coatings. Modifying effect of combined modifiers with SDS ( 6-22 g/L) and Tween-80 (8-12 ml/L) were superior to single one. The total mole ratio of Cu to Ti3SiC2 of the best coating sample was 1:0.54, modified by SM4 (SDS and Tween-80 complex) modifier. Electrostatic effect together with steric hindrance effect play a crucial synergistic role for nuclei and growth controlling of copper on (Ti3SiC2)p surface.

Abstract:Bulk alloys Nd1Ni5-xCx(x=0.0,0.1,0.3,0.5) are prepared by arc smelting and planetary grinding. X-ray diffractometer(XRD), Scanning electron microscopy (SEM), vibrating sample magnetometer (VSM), vector network analyzer(VNA) and other instruments were used to detect its structure, morphology and electromagnetic characteristics. The results show that, with the increase of C content, Ms and Hc of the sample tend to decrease, the absorption peak of electromagnetic wave moves to high-frequency, and two effective bandwidth (RL≤-10) appeared when the additive amount of C is x=0.5, respectively are 8.28~9.82 GHz and 11.17~12.03 GHz, which increases the applicable frequency band of the powder. In addition, With the change of the thickness, the frequency band with great impedance matching changes greatly, so that the reflection loss can be adjusted in the larger frequency band. Those change makes the powder has the possibility of wide application.

Abstract:The regulation of structure and composition is very important for obtaining stainless steel with good comprehensive properties. In present paper, Fe2O3 powers with different excess ratios were added in reaction powders to make aluminothermic reaction completely and reduce the content of Al in the 316L ASSs. The effects of excess Fe2O3 in reactions on microstructure and tensile properties of micro-nano structure of 316L austenitic stainless steels were analyzed in detail. The results showed that, with the increase of Fe2O3 excess percentage, the volume fraction of ferrite phase reduced significantly while the volume fraction of nanocrystalline increased from 87.4 % to 93.4 % and the average grain size decreased from 32 nm to 22 nm. The comparative analysis showed that the Fe2O3 excess percentage of 5.0 % was the best process parameter for the 316L ASSs preparation by the aluminothermic method. For the single phase austenitic steel prepared under this condition, the tensile strength was 573.92 MPa, the yield strength was 340.12 MPa, and the elongation was about 4.68 %.

Abstract:To improve optical property and coloration effect, La, Nd and Bi co-doped TiO₂ films were synthesized via a Sol-Gel method, by using butyl titanate as precursor on the surface of ITO glass substrate. Structural surface morphologies and electrochromic properties of the as-prepared films were examined with TG-DTA、XRD、UV-vis and Electrochemical workstation. The results showed that anatase TiO₂ formed from TiO₂ dry gels after heat treatment at 400℃, 500℃, 600℃, and showing tendency of the higher the temperature heat treatment, the more complete the crystal development. La, Nd and Bi doped TiO₂ increased the disorder of the TiO₂ octahedron, resulting in increase of the amorphized degree. TiO₂ films prepared with acurate 12% tetrabutyl titanate exhibited the best electrochemic properties. TiO₂ films heat-treated at 500℃ showed excellent electrochemical properties. TiO₂ films separately doped with molar amount fraction of 8%La, 18%Nd, 6%Bi, possess excellent electrochemic properties,and single doping effect is in the order of 6% Bi < 8 %La<18% Nd. La-Nd-Bi co-doped TiO₂ is anatase with a very high amorphized degree, with the best cyclic valtammentry and highest amorphized degree when the molar amount ratio of La:Nd:Bi=4^:10^:2.

Abstract:In the present study, the very high cycle fatigue properties of two high strength martensitic steels containing two different types of (Ti,Mo)C precipitates with and without electrochemical hydrogen charging were investigated. Results revealed that spherical undissolved (Ti,Mo) particles and non-metallic inclusion with a hydrogen desorption activation energy of 142.6 and 70.9 kJ/mol, respectively could not trap hydrogen through electrochemical charging; diffusible hydrogen trapped by dislocations and grain boundaries with a desorption activation energy of 16.9 kJ/mol could rapidly diffuse to crack tip or stress concentration field then reduced the threshold value of stress intensity factor (SIF) of crack growth remarkably, resulting in a decrease of fatigue strength, this portion of hydrogen could diffuse out of sample after atmosphere exposure for 96 h and would have no deleterious effect on fatigue strength; hydrogen trapped by fine, temper-induced (Ti,Mo) precipitates with a desorption activation energy of 17.0 kJ/mol could not diffuse out of sample even atmosphere exposure for 336 h, however could desorb from the trap site under cyclic loading then diffuses to the crack tip or stress concentration field, resulting in a decrease in fatigue strength. Considering the hydrogen content in each hydrogen trapping site the deleterious effect of hydrogen trapped by fine, temper-induced (Ti,Mo) precipitates was relatively small compared to the diffusible hydrogen trapped by dislocations and grain boundaries.

Abstract:When an aircraft, spacecraft, automobile, ship, or other engineering facility is impacted by other objects during service, the damage caused by the component may cause a failure of the component or even a catastrophic accident. How to take effective measures to monitor and assess such active impact damage is essential. To locate impact damage precisely in real-time in an engineering structure, a non-contact impact damage location method based on scanning laser Doppler vibrometer (SLDV) was proposed in this paper. The Hilbert-Huang Transform (HHT) was applied to the signal processing to obtain the best response frequency spectrum. The separated IMF1 was used in the circular trajectory positioning imaging of amplitude total addition and amplitude multiplication. The experimental results indicate that HHT can be used to achieve non-contact impact damage localization of composite materials.

Abstract:A series of plate-type V₂O₅-MoO₃-Nd₂O₃/TiO₂ catalysts with different amounts of neodymium were prepared to investigate the impact of neodymium addition on selective catalytic reduction (SCR) of NO with NH₃. XRD, N₂-adsorption, XPS, H₂-TPR, Raman and NH₃-TPD were carried out to characterize the catalysts. It was found that with the suitable addition of Nd (0.25% and 0.5%) to V₂O₅-MoO₃/TiO₂ catalyst not only brought to the improvement of the reduction property, but also increased the O_α/(O_α+O_β) ratio of the catalyst, which leaded to the enhanced catalytic efficiency. However, when the content of Nd was excessive (0.75% and 1%), the acid sites of the catalysts decreased evidently. Accordingly, the catalytic performance of these catalysts was relatively low. What is more, the mechanical property of the catalyst declined when the content of Nd was excessive. Among the catalysts investigated, VMoNd(0.5%)/Ti catalyst had the best catalytic performance.

Abstract:Using first-principles calculations based on density functional theory, we probe the band structures, half-metallicity and magnetic properties in Cr₂VZ (Z = P and As) full-Heusler alloys. The results reveal that Cr₂VZ (Z = P and As) is stable in ferri-magnetic configuration. The total magnetic moment of Cr₂VAs is -2 μ_B per formula unit at the equilibrium state, obeying the Slater–Pauling rule . Cr₂VP is a common magnet. Based on the hybridization between the Cr?3d and V?3d electrons, we analyzed the origin of energy gap in the minority channel.

Abstract:In this work，the microstructure evolution and mechanical properties of Mg-12Gd-1Zn-0.5Zr-0.5Ag (in wt.%) alloys with different contents of Al and Li elements by T6 heat treatment were investigated. The results indicate that new Mg3Gd particles are precipitated in Mg-12Gd-1Zn-0.5Zr-0.5Ag alloy and most Al2Li3 phases in Mg-12Gd-4Al-3Li-1Zn-0.5Zr-0.5Ag and Mg-12Gd-6Al-5Li-1Zn-0.5Zr-0.5Ag alloys become smaller and more evenly distributed after T6 heat treatment. The grain size and c/a ratio values of the as-aged Mg-12Gd-4Al-3Li-1Zn-0.5Zr-0.5Ag alloy and Mg-12Gd-6Al-5Li-1Zn-0.5Zr-0.5Ag alloy are decreased significantly than that of as-aged Mg-12Gd-1Zn-0.5Zr-0.5Ag alloy, which results in improved tensile strength and plasticity. The best combination of tensile strength, elastic modulus and plasticity is as-aged Mg-12Gd-6Al-5Li-1Zn-0.5Zr-0.5Ag alloy, the ultimate tensile strength, modulus and ductility are 210 MPa, 50.7 GPa and 24.8%, respectively.

Abstract:Lotus-type porous Mg-Zn alloys were fabricated successfully by Bridgman-type directional solidification method. The pore structure and porosity of Mg alloys at different Zn content and hydrogen pressure were studied. The porosity of Mg-1wt.% Zn was predicted through the theoretical calculation. The results show that pore structure can be influenced by the addition of Zn element. As the content of Zn increases from 0 to 2 wt.%, average pore diameter increases. The porosity of Mg-1wt.%Zn alloy clearly decreases with the increasing of the hydrogen pressure from 0.1MPa to 0.6MPa. Based on a model for estimating the solubility of hydrogen in multi-component molten metals, the calculated results of porosity at the solidification stage (20mm height) with a changed hydrogen pressure in Mg-1wt.%Zn alloy, are in good agreement with the experimental results. Through observations on the microstructures, the column grains of Mg-Zn alloy are changed into equiaxed grains as the content of Zn increases. Also, the formation of pore at different solidification stages was studied, which can supply theoretical basis for the fabrication of Gasar Mg-Zn alloy in the biological applications.

Abstract:An ultrafine-grained (UFG) pure zirconium(Zr) refined by compounding with a size of Φ4 × 6 mm was subjected to a unidirectional compression test using a Gleeble-3800 thermal simulation tester at the temperature of 300 °C–450 °C and a strain rate range of 0.001–0.05 s_-1. Experimental results show that the process parameters influence the flow stress of the UFG pure zirconium. Experimental data and microstructure analysis, reveal that DRX is more likely to occur at higher deformation temperature and lower strain rate. The critical strain and critical stress of UFG pure zirconium were determined. In addition, a critical strain model of UFG pure zirconium was established by introducing Zener–Hollomon paramete Z. The constitutive model of UFG pure zirconium was confirmed based on DRX volume fraction and proven to occur at a strain of 0.1 to 0.45.

Abstract:Due to the limited available piece length of Y_0.5Gd_0.5Ba₂Cu₃O_7-z (YGdBCO) coated conductors (CCs), joints are inevitable for manufacturing high temperature superconducting (HTS) devices. The stable operation of HTS devices is largely determined by the quality of joints, because the electromechanical performance of joints is usually lower than that of original tapes. In this work, lead-free Sn42Bi58 solder was applied to make the lap joints for YGdBCO CCs. Compared with conventional Sn60Pb40 solder, lead-free Sn42Bi58 solder is environmentally friendly and soldering operation at lower temperatures below 150℃ because of about 40℃ lower melting point further reduces the CCs deterioration in joining process. The influence of loading pressure, pressurization speed and lapped length on the critical current, resistance and n values of the YGdBCO joints were investigated by measurement of voltage-current curve at self-field and liquid nitrogen temperature. By optimizing soldering technique, the 25 cm-long joints with quite low resistance of 4.35~5.58 nΩ and comparable critical current with virgin CCs were repeatedly achieved with pressure of 12.5 MPa and pressurization speed of 50 N/s. The mechanical behaviors of the joints under axial tension were studied and the critical axial tension force of single CCs and joint portion is 213 N and 212 N, respectively. The above results show that compared with traditional soldering techniques, the robustness and reproducibility have been significantly improved for the soldering joints with low resistance and high tension performance by the joining technique based on this lead-free Sn42Bi58 solder, which offers another promising choice for joints manufacturing in the large scale applications of YGdBCO CCs.

Abstract:In order to improve the heat transfer characteristics of plane flow casting cooling roll and improve the transverse thickness uniformity of Fe-Si-Be amorphous strip, a numerical model of axial heat transfer channel is established. Based on the analysis of the current axial flow and heat transfer characteristics of cooling roller, a design method of spherical heat transfer channel is proposed. Based on the field synergy theory, the spherical channel is optimized and verified by experiments. The results show that the heat transfer efficiency of the cooling water in the channel decreases gradually along the water flow direction, and the heat transfer mainly occurs near the inner wall of the cooling roller. The temperature in the middle of the existing cooling roller outer wall is much higher than that at both ends, and the axial temperature difference is obvious. The spherical channel can strengthen the heat transfer in the middle of the cooling roller, reduce the temperature, thermal deformation and axial deformation difference of the outer wall, and significantly improve the transverse thickness of the amorphous thin strip with the decrease of the radius of the sphere. The heat transfer in the middle of the channel increases obviously, but the flow resistance also increases sharply. There is an optimal channel optimization radius based on the comprehensive flow resistance and heat transfer characteristics conditions.

Abstract:The isothermal constant strain rate compression experiment was carried out on Zr-4 alloy samples by using a Gleeble-3500 thermal simulator. The thermal deformation behavior was analyzed, and the physical constitutive model based on strain compensation Zr-4 alloy was established by combining the influence of deformation temperature on Young"s modulus and self-diffusion coefficient. The results show that the peak stress of the alloy is sensitive to the deformation temperature and strain rate, and the peak stress will increase with the increase of the strain rate or the decrease of the deformation temperature. The constructed physical constitutive model can better predict the flow stress of the alloy in the thermal deformation process, and its correlation coefficient R is 0.986. The data points with the predicted value deviation less than 10% account for 93.2%, and the average relative error is 6.3%.

Abstract:Creep life prediction is an important issue for components used for nuclear breeders at high temperature. Through analysis on creep data of 316H stainless steel served in reactor vessels, the steady creep rate equation was obtained by rate temperature parameter model. Reasonable statistical test results supported the reliability function of creep property. σ-RTP-R curves and T-[σ]-R curves were proposed for 316H stainless steel based on the distribution of Z’-parameter in this paper. The allowable stresses in service temperatures from 550℃ to 700℃ were also obtained according to the standard methods specified in ASME BPVC. The results demonstrate that RMB" model has not only good precision in comparison of other existent creep models, but also high prediction. The experimental creep data completely drop into 99.7% confidence interval of predicted results by reliability function. The steady state creep behavior and allowable stress of 316H stainless steel in experimental conditions can be well evaluated by the present models.

Abstract:The Fe73.5Si13.5B9Cu1Nb3 alloy ribbons fabricated at circumference speed of 14.65 and 43.96 m/s (labeled as C1 and C2) have investigated by XRD, VSM, electrochemical workstation and SEM. The XRD results show that the low cooling rate sample (C1) has a nanocrystalline/amorphous dual-phase structure and the high cooling rate sample (C2) has an amorphous structure. VSM results show that both C1 and C2 alloy have excellent soft magnetic properties, and C1 alloy shows a strong magnetic anisotropy, which induced by both the ordered atomic bonds of nanocrystalline phase and strong interaction between the nanocrystalline phase and amorphous matrix. The electrochemical polarization test results show that the corrosion resistance property of C2 alloy is better than that of C1 alloy，which is attribute to the heterogeneity structure and internal stress in the ribbon surface formed on the spinning process.

Abstract:Fe-Cr-Mn-based stainless steel alloy powder was prepared by mechanical alloying method, which is induced by high energy milling. The milled powders were respectively annealed and sintered via hot pressing sintering method, and the phases evolution, microstructure and corrosion resistance were respectively analysed. It is found that the Fe-Cr-Mn-based stainless steel alloy prepared by mechanical alloying is mainly composed of metastable nanocrystalline ferrite phase. After annealing or hot pressing sintering, ferrite phase will transform into austenite phase, and the transformation temperature range from 650 °C to 700 °C. The powder milled for 16 h is hot pressed at 900 °C and 200 MPa for 1 h for bulk alloy. The average grain size of pressed bulk alloy is submicron, which displays high hardness and good corrosion resistance. The hardness, polarization voltage and polarization current are respectively 535 HV, -0.28 V and 1.43×10_^-9 A.cm_^-2.

Abstract:Mg-1.5Y alloy sheet was prepared by cross-rolling technology. The effect of recrystallization annealing (475 ℃×15 min) on microstructure, macro-texture, mechanical properties and stretch formability of Mg-1.5Y alloy sheet was primarily studied. The results show that the uniform equiaxed grains were formed through strong static recrystallization after recrystallization annealing. The texture of as-rolled alloy sheet exhibited a subrotund-bimodal orientation distribution, and the basal-pole intensity peak tilts about ±20° from normal (ND) to rolling direction 2 (RD2). The texture orientation distribution was more dispersed and randomized after recrystallization annealing. The basal-pole intensity peak split along the intersection angle of rolling direction and a weakened butterfly-shaped multi-peaks texture orientation distribution was finally forming. Besides, the maximum intensity of basal plane decreased from 5.0 to 2.8. The fracture elongation and index of Erichsen test of as-annealed alloy sheet are 30.5% and 4.4mm respectively, which are improved about 63% and 42% compared with as-rolled alloy sheet.

Abstract:In recent years, the research of doped modified TiO₂ nanotubes as photocatalytic materials has received widespread attention. In this paper, anodic oxidation method is used to prepare regular and ordered TiO₂ nanotubes on the surface of Ti plate, and the chemical reagents containing Fe and N elements are directly added to the electrolyte to modify them. Sem, X-ray diffractometer and X-ray photoelectron spectroscopy were used to characterize TiO₂ nanotubes, and the optimal preparation conditions of TiO₂ nanotubes were determined. Finally, the transient photocurrent curve, open-circuit potential curve, and linear voltammetric scanning curve were used to compare their photoelectrochemical performance. The study found that 1% Fe element doped material has better photoelectric response, and the open circuit potential can reach 0.34V under light; 9% N element doped material has the best photoelectric activity, and open circuit potential can reach 0.317V.

Abstract:In this paper, fusible alloy with rated temperature of 142℃ were designed by add Cu and Sb element into Sn-Bi eutectic alloy. Besides, the melting temperature, phase composition, quasi-static tensile properties and mechanical properties of solder joints were studied. The results show that the addition of Cu and Sb increases the melting point of the alloy, but the subcooling and latent heat of melting of the alloy decrease. After adding Cu and Sb elements, a bulk SnSb phase and long Cu₆Sn₅ and Cu₃Sn phases were formed in the alloy matrix. These second phases strengthened the tensile strength of the alloy, but reduced the plasticity of the alloy. The strength of (Sn58Bi)3Cu3Sb fusible alloy is 85.4 MPa, the plasticity is 15.5%, and the melting point is 141.8 ℃. The shear strength of the welded joint with copper clad plate is significantly higher than that of Sn-Bi eutectic alloy, which can reach 55.7 MPa

Abstract:In order to obtain both high mechanical properties and released energy density, multilayered Al/Ni energetic structural materials were prepared by electrodeposition and hot pressing method in this paper. The effect of hot pressing temperature on the exothermic properties of Al/Ni energetic structural materials was studied. The damage effect of the energetic fragment on double target boards at various impact velocities was obtained through shooting experiments. The results showed that with the increase of the hot pressing temperature, the diffusion reaction at Al/Ni interfaces increased, leading to a decrease of exothermic heat from 898 J/g to 782 J/g. Under high-speed impact, the Al/Ni energetic fragment experienced a violent deflagration reaction, which had a significant damage effect on the double target boards. When the impact velocity of the energetic fragment increased from 1241 m/s to 1478 m/s, the perforation size of the main target plate was almost unchanged, however the damage area of the after-effect target plate increased significantly.

Abstract:V-Al alloy membrane has good resistance to hydrogen embrittlement and high hydrogen permeability, which is expected to become a substitute material for replacing Pd alloy membrane in the future. The microstructure of V-Al alloy not only affects the hydrogen separation performance, but also affects the strength and plastic forming properties. A series of binary alloys of V-xAl(x=5, 10, 20, 30)were prepared by vacuum non-consumable arc melting. The effect of Al content on microstructure evolution and mechanical properties of as-cast V-xAl alloy was investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), Vickers hardness tester and tensile testing machine. The results show that the solidification microstructure of these V-xAl alloys is composed of V-based solid solution and Al₂O₃ particles. The addition of Al element results in grain refinement, and cause the reduction of grain size with the increase of the Al content. When the content of Al element is 5at.%, the elongation of the alloy is slightly reduced, but the tensile strength reaches a maximum of 236Mpa, which is 12% higher than pure V. This is attributed to the combined effect of both solid-solution hardening and precipitation strengthening. When the content of Al element reaches 10at.% or more, the Al₂O₃ particles coarsen, the tensile strength of the alloy decreases, the plasticity decreases sharply, and the alloy loses plasticity.

Abstract:The microstructure of AZ80 magnesium alloy under different conditions was observed and studied using electron backscatter diffraction (EBSD) technology, the microstructure evolution of AZ80 magnesium alloy under different conditions was analyzed. The results show that in accordance with the order of as-cast, homogenized and deformed states, the average grain size gradually decreases, the average grain shape aspect ratio showed a trend of increasing first and then decreasing, the network β-Mg17Al12 phase gradually disappeared, improved plasticity and strength of the material. The coordination of grain boundaries is mainly affected by grain boundary migration and geometrically necessary dislocations density, with the migration of grain boundaries, the low-angle grain boundaries gradually increase, which hinders the progress of recrystallization, and the recrystallization area has a tendency of increasing first and then decreasing, the substructure region gradually decreases, and the disappearance of the substructure region provided energy for the formation of twins and promoted the formation of twins. The geometrically necessary dislocations density has a trend of reducing first and then increasing, the decrease of geometrically necessary dislocations density promotes the growth of twins and the rotational movement between grains, the increase of geometrically necessary dislocations density hinders the growth of twins and the rotational movement between grains. The deformed magnesium alloy has a typical basal texture.

Abstract:As a novel additive manufacturing technique, laser powder bed fusion (LPBF) provides a new forming method for the fabrication of divertor mono-block for the future nuclear fusion reactor. In this study, pure tungsten samples were built by the LPBF technique horizontally and vertically. It is found that under the heat load of 15 MW/m2, there were severe melting and sputtering in the vertically built samples, while only a little cracking and sputtering occured in the horizontally built samples. It is believed that the anisotropy of the thermal conductivity in LPBFed tungsten samples is caused by the microstructure difference in different directions. For the horizontally built sample, the direction of the heat flow is parallel to the building direction, and the coarse columnar grains grown along this direction is favorable for heat conduction. For the vertically built sample, the heat flow direction is perpendicular to the building direction, grain boundariesand the crack network would hinder the heat conduction. Therefore, the heat accumulated on the surface of vertically built sample could cause melting. This study shows that the building direction has an unavoidable impact on the fabrication of divertor mono-block using the LPBF technique.

Abstract:FeSe has a unique ground state in which superconductivity coexists with a nematic order without long-range magnetic ordering, providing a significant opportunity to investigate the correlation between the nematic phase and the unconventional superconductivity in iron-based superconductors (IBSs). Previous studies have shown that the nematic phase was gradually suppressed by isovalent S substitution in FeSe1-xSx, meanwhile, the superconducting gap structure abruptly changed once the nematic phase vanished at the quantum critical point x ~ 0.17, indicating that the nematic phase plays a key role on the pairing mechanism. Unfortunately, the crystals with S doping level x > 0.21 have not yet synthesized via the conventional crystal growth method until now, which limited the research on the high doping levels.This work have successfully prepared FeSe0.36S0.64 crystals with superconducting transition temperature Tc ~ 5 K using hydrothermal method for the first time. In order to get more insight into the normal state properties, the article presented the magnetoresistance and Hall effect measurements by six-probe method. It is found that the Kohler"s rule is strongly violated, and the negative Hall coefficient shows strong but nonmonotonic T-dependence below about 120 K, which may be intimately related with the multiband electronic structure in this system. The hydrothermal method is of great significance for the crystals grown of FeSe1-xSx with different S doping level and the investigation of the unconventional superconductivity in 11-type IBSs.

Abstract:In order to study the precipitation process and crystal structure evolution of copper precipitate in ferritic stainless steel, the growth process of copper precipitate was observed by atomic probe chromatography (APT) and high resolution transmission electron microscopy (HRTEM).As a result, the size of copper precipitate increases and the quantity density decreases with the prolonging of annealing time. And the shape of the precipitated phase changes from the initial spheroid to ellipsoid, and finally to rod. The growth curve can be fitted into a formula , which is consistent with Ostwald ripening rule. The orientation relationship between 9R structure and matrix is . The precipitation sequence of copper precipitate in the ultrapure ferritic stainless steel is bcc→9R→3R→ fcc.

Abstract:High temperature & high pressure were used for the preparation of WTi10 alloy. The density and microstructure of alloys were analyzed by Electron Probe Microanalysis, Scanning Electron Microscope and X ray diffraction, especially the evolution of phase. In addition, effect of phase differences on sputter target and the optimal processing parameters were researched. The various effects on preparation of WTi10 alloy were studied. The results indicate that temperature was most important one. The density of alloy increases with temperature. When the temperature was above 1250℃, the microstructure was mainly consisted of β phase with body-centered cubic. In which were the W particle, β phase of W-rich solid solution and β1 phase of Ti-rich solid solution in microstructures. Sputter target have demand that the less of β1 phase and β phase, the better. As a result, the optimum processing temperature was between 1400℃ and 1500℃. The time of high temperature & high pressure processing was inversely proportional to its temperature. And then, pressure exceeds 15 MPa was required.

Abstract:During the operation of nuclear plants, the reaction of Zr and water produces ZrO2 and hydrogen atoms, some of which enter the zirconium alloys. Hydrogen in zirconium alloys affects not only mechanical properties, but also corrosion resistance. The degree of influence is closely related to alloy composition and corrosion conditions. The corrosion mechanism Zr-4 (Zr-1.3Sn-0.2Fe-0.1Cr, mass fraction, %) alloy in LiOH aqueous solution affecting by hydrogen is still controversial. Therefore, the effect of pre-charging hydrogen on the corrosion resistance of Zr-4 in 0.01 M LiOH aqueous solution was investigated.Two batches of Zircaloy-4 specimens were pre-hydrided using gaseous or electrolytic hydrogen charging methods to obtain the predetermined hydrogen level: less than 120 μg/g H and more than 120 μg/g H. Then all the as-received specimens and hydrogen-charged specimens were corroded in lithiated water with 0.01 M LiOH at 360 ℃ and 18.6 MPa in a static autoclave. The mechanism about the effect of hydrogen on the corrosion behavior of zirconium alloys was discussed based on weight gain, microstructure of oxide films, compressive stress and Li+ depth profile in the oxide film. Results showed that Zircaloy-4 specimens with 20~250 μg/g hydrogen exhibited better corrosion resistance compared with the as-received ones. The corrosion resistance of Zircaloy-4 became better with increasing the hydrogen content. The integrity of the oxide film on the hydrogen-charged specimens was better than that on the as-received specimens, which indicates a slower microstructural evolution of the oxide film on the hydrogen-charged specimens. The hydrogen-charged specimens had a less undulate oxide/metal interface. Compared with the as-received specimens, the compressive stress in the oxide film on the hydrogen-charged specimens was lower and showed a less gradual gradient with the increase of oxide thickness. The concentration of Li+ in the oxide film on the hydrogen-charged specimens was lower, and it dropped down quickly along the depth of oxide film. In this way, the microstructural evolution of the oxide film was retarded and the corrosion resistance of Zircaloy-4 was improved by pre-charging hydrogen.

Abstract:A series of Cu-W alloys added with Boron powder were prepared by means of powder metallurgy-infiltration process. The effects of Boron addition on the microstructure and properties of CuW alloys were investigated.The static properties, the vacuum breakdown property and the wear resistance were studied respectively. The results show that boron element and W were in-situ reacted and formed tungsten boride pahse in the sintering process of W skeletons. The hardness of the CuW alloy increases to 215HB owing to the strengthens of W skeletons. Meanwhile,the breakdown strength is increased by 63.2%, the chopping current is decreased 21%, and the coefficents of friction is decreased 32.7%, respectively. The wear resistance of the CuW alloys is enhanced significantlly. The metallographic analysis of CuW alloys after vacuum breakdown showed that the splash of liquid copper is decreased, the breakdown areas increase but the erosion pits become shallower and smaller.

Abstract:The pressure of tritium gas vs. time curves of LaNi3.70Al0.75Mn0.55 alloy absorbing tritium in the constant volume condition at room temperature were studied. Mechanism of tritium absorption and their effect on the tritium absorption rate were analyzed. The results indicated that the pressure decreases rapidly in the initial stage of absorbing tritium, and the T/M can reach to 1.5 std.cc/g in 15 s, the highest tritium absorption rate reaches to 0.28 std.cc·g-1·s-1 maxed out at the α+β phase. The dissociation and chemical adsorption of tritium on the surface of the alloy are the speed control steps at the initial stage of tritium absorption. When the T/M > 15 std.cc/g, the reaction results in phase transition to form tritium compounds, the control steps of tritium absorption is nuclear growth.

Abstract:Powder metallurgy (P/M) Inconel 718 superalloy was processed through hot isostatic pressing (HIP) route by SS-PREP powder. Effect of heat treatment on the microstructure and mechanical properties of superalloy was research. The results indicated that the distribution of size of Inconel 718 superalloy SS-PREP powder uniformity, with the fine degree of sphericity. HIP at 1210℃/120MPa for 4h, average size of grain was 50μm, tensile strength at room temperature was 1260MPa. Tensile strength at room temperature achieve to 1404MPa through solution treatment at different temperatures and two-step ageing treatment, and Tensile strength at 650℃ achieve to 1150MPa. Optimum properties of Inconel 718 superalloy appears when solution treatment at 980℃.

Abstract:With the increasing demand for long period and high fuel consumption in commercial reactors, fuel pellets would face to more severe service conditions. Further improve the properties of uranium dioxide fuel is the key problem in the development of new nuclear fuel elements. Based on the progress in doped fuel pellets in recent years, this paper systematically discusses the types of doped elements and their influence on the performance of uranium dioxide fuel pellets, expounds the relationship between the microstructure and performance of doped fuel, and points out the existing problems and development trend for doped uranium dioxide fuel. The results would provide valuable references for promoting development of the safety performance of fuel pellets.