Abstract:With the development of industrial technology and the rising of energy issues, aluminum alloys have become one of the preferred lightening materials for low weight, good corrosion resistance, good forming and processing properties. Taking 5A02 aluminum alloy cold-rolled sheet as the research object, the plastic deformation behavior of 5A02 aluminum alloy under different temperatures and strain rates were analyzed through uniaxial tensile test and metallographic test. Combined with experimental data and Zener-Hollomon parameter model, the constitutive model of 5A02 aluminum alloy under high temperature conditions was studied. The results show that the strain rate and deformation temperature have a great influence on the elongation when the 5A02 aluminum alloy is deformed under high temperature conditions. At strain rates of 0.01s-1, 0.001s-1, 0.0005s-1 and 0.0001s-1, the elongation of 5A02 aluminum alloy is greater than 100% when the deformation temperature is above 250°C. The true stress-strain curve of 5A02 aluminum alloy is characterized by dynamic recovery when the deformation temperature is 150°C~250°C, and the flow stress curve has obvious softening phenomenon when the deformation temperature is above 250°C.

Abstract:The effects of pre-deformation on the aging behavior and mechanical properties of Ti-6Al-4V alloy were studied. Results show that the addition of pre-deformation after the solution process at 940 °C and 955 °C is beneficial in promoting the precipitation of the secondary α phase during the aging of Ti-6Al-4V alloy. When solution temperature was 940 °C, the content of the secondary α phase increased with an increase in pre-deformation amount, its size decreased, and the strength and hardness of the alloy increased monotonously after aging. The tensile strength and hardness of Ti-6Al-4V alloy after aging were evidently higher with pre-deformation than without pre-deformation. Simultaneously, excellent plasticity was maintained. In the case with added pre-deformation, a solution temperature of 955 °C slightly improved the strength and hardness of Ti-6Al-4V alloy compared with a solution temperature of 940 °C. Scanning electron microscopy examinations indicate that the fracture modes of all aged alloys with varying pre-deformation degrees are ductile fracture.

Abstract:A high-pressure 1st stage IGT blade made of René N5 served for nearly 26000 hours was studied to figure out the evolution of microstructure and the degradation degree in different locations of the blade. The morphology and volume fraction of γ′ precipitates, the topological inverse degree, and the morphology and composition of carbides were analyzed. It has been confirmed that the volume fraction of γ′ precipitates and topological inverse degree are applicable to be quantitative microstructural characteristic parameters to characterize the microstructural degradation in the served blade. And the morphology of the γ′ precipitates and the precipitation of TCP can be employed as the qualitative microstructural characteristic parameters. In terms of these parameters, the microstructural degradation of the served IGT blade could be classified into 3 degrees: slightly, moderately and seriously degraded. These results are expected to established as solid foundation for the assessment of the degree of the microstructural degradation of single crystal IGT blades and also have practical significance in service safety.

Abstract:The spark plasma sintering behaviors of ZrB2-based ultra-high temperature ceramics were systematically investigated using nanosized ZrB2 powders. Rapid densification occurred at low temperature (1550 oC) for monolithic ZrB2 due to the nanosized powders. ZrB2-SiC ceramic achieved full densification at 1800 oC by SPS resulting in a high flexural strength of 1078±162 MPa. ZrB2-SiC-Cf composite was successfully prepared by SPS at 1700 oC. The composite showed obvious fiber pull-out on the fracture surface, leading to a high fracture toughness (6.04 MPa·m1/2) and a non-brittle fracture mode. Meanwhile, a high critical thermal shock temperature difference of 627 oC was obtained for ZrB2-SiC-Cf implying an excellent thermal shock resistance of such material.

Abstract:Aiming at the wedge shape problem of rolling section that may occur in the hot rolling process of pure titanium medium and thick plate, combined with the asymmetric characteristics of four-high rolling mill equipment and technology., the elastic deformation model of double cantilever beam roll system is established based on the influence function method. The influence of asymmetrical factors such as the centring error, stiffness difference of mill stand, wedge shape of billet, transverse temperature difference of workpiece and other asymmetric deformation parameters on rolling section wedge shape are investigated. The results indicate that the effect of the above influence factors increase with the increase of the plate width and rolling reduction. The influence of the inlet wedge shape on the outlet wedge shape increases with the increase of the plate width and the decrease of the rolling reduction.

Abstract:In this study, the ITO coatings were deposited on PMMA by high-power?pulse?magnetron?sputtering (HPPMS). The effects of HPPMS on the coatings by different parameters were investigated, and the phase, bonding strength,transmittance and resistivity were characterized by XRD, scratch tester, spectrophotometer and holzer test platform respectively. The results show that phase, bonding?strength, transmittance and resistivity are affected by pulsed bias and flowrate ratio of hydrogen and argon. With increasing the pulsed bias, the bonding?strength becomes better, the best bonding?strength is 56.5N when pulsed bias is 240 V. with the pulsed bias increasing from 0 V to 160 V, the grain size gets bigger, the transmittance becomes better( increasing from 82.24% to 89.82% ) and the resistivity also becomes better (decreases from 0.006571 to 0.000543 Ω.cm). With the flowrate ratio of hydrogen and argon increasing from 0 to 0.05,the transmittance becomes worse (decreasing from 89.82% to 56.12% ).With the flowrate ratio of hydrogen and argon increasing from 0 to 0.03 ,the resistivity becomes better( decreasing from 0.000543 to 0.000212 Ω.cm ) .With the flowrate ratio of hydrogen and argon increasing from 0.03 to 0.05,the resistivity becomes worse(increasing from 0.000212 to 0.000373 Ω.cm) .

Abstract:SnSe is a robust candidate for thermoelectric applications due to its excellent ZT performance. We compare single crystal and polycrystalline SnSe in thermal and electrical properties. The single crystal is synthesized with Bridgeman method, while the polycrystalline is synthesized with melting and SPS. The thermoelectric properties of both materials are measured with four-probe method and laser flash method. The results show power factor of single crystal is twice higher than that of polycrystalline, and thermal conductivity of single crystal are also thrice higher at all temperature range, leading to comparable highest ZT of those two materials. The highest ZT single crystal is 0.65 at 823 K, and 0.5 at 923 K for polycrystalline. These findings yield a foundation for the systematic exploration of SnSe thermoelectric application.

Abstract:MCrAlY coatings are playing an important role in protecting the substrate from oxidation and corrosion at high temperature, which can form dense and continuous oxide scales on the surface to retard the diffusion of cations and oxygen. With the depletion of Al for the growth of alumina layer, the concentration of aluminum in the coating near coating/oxide scales interface decreased, which further suppresses the consecutive Al₂O₃-scale growth, causing the formation of mixed oxide compounds and cracks as well as voids. This process can cause premature failure of the coating. Between the coatings and the superalloy, the interdiffusion process after vacuum heat treatment is beneficial, which can improve the adhesion of the coating and the substrate. However, because of its thermally activated nature, the interface diffusion process will make deleterious effects at elevated temperature. The elements of the substrate, like Ti, W, Mo, can diffuse into coating. Furthermore, the interdiffusion process in the coating/substrate will form a secondary reaction zone (SRZ), which mainly consists of high density of topologically close-packed (TCP) phases, such as σ, μ and Laves phases. These TCP phases in the matrix may reduce the high-temperature fatigue life of the superalloy.

Abstract:In this paper, Multi-walled carbon nanotubes (MWCNTs) and TiO2 were mixed by ball milling to obtain composite powders. The composite powders were characterized by XRD, SEM and network vector analyzer. The absorbing properties of composite powders in space were analyzed by theoretical calculation using numerical model. The results show that the dispersibility of MWCNTs in the MWCNTs/TiO2 compositepowders with anhydrous ethanol wet mixing is better. Wet-mixed MWCNTs/ TiO2 composite powders have better impedance matching characteristics and spatial absorbing ability in 2~18GHz band, which provides theoretical reference for the practical application of composite absorbing materials.

Abstract:In this work, we have successfully prepared CF_x-Cu cathode materials for primary lithium battery through a simple and novel in-situ chemical modification method with high-temperature calcination process. The structure, morphology, reaction mechanism and electrochemical performance of cathode materials were characterized by X-ray powder diffraction, high-resolution transmission electron microscopy, scanning electron microscope, energy dispersive X-ray spectroscopic, thermo gravimetric analysis, cyclic voltammetry and galvanostatic discharge. It can be inferred that copper oxide reacts with inert groups on the surface of CF_x to produce nano-copper particles, which increases the electronic conductivity and diffusion performance of lithium-ion in the CF_x-Cu cathode materials. Therefore, the composite exhibits excellent specific capacity, rate performance and power density. Specifically, the CF_x-Cu composites shows a high discharge specific capacity of 546 mAh/g, a maximum power density of 8393 W/kg, with a discharge voltage platform of 2.0 V at 5 C.

Abstract:Effect of substrate material on the microstructure, texture, phase and hardness of a Ti-48Al-2Cr-2Nb alloy processed by laser melting deposition (LMD) was investigated. With the increase of the number of deposited layers, the microstructure of the deposited layers changes from basket structure to equiaxed structure and finally evolves into lamellar structure, and α2 (Ti3Al) phase decreases and γ (TiAl) phase increases gradually. Different TiAl alloy layers show different microhardness. With the increase of the number of deposited layers, the microhardness decreases. The findings would be a valuable reference for fabricating TiAl components with acceptable microstructure, texture, phase compositions and microhardness by LMD.

Abstract:The phase equilibria of the Cu-Co-Zn ternary system at 800°C and 1000°C were investigated by means of electron probe microanalysis and X-ray diffraction. No ternary compound was found. At 800°C, the solubility of Co in the β-CuZn, and Cu in the β1-CoZn at 800°C were 32.36 at.% and 5.28 at.%, respectively. The γ-Co5Zn21 and γ-Cu5Zn8 showed the same crystal structure, an infinite region of mutual solubility was observed in the Cu-Co-Zn ternary system. It was confirmed that as the temperature rises from 800°C to 1000°C, the liquid-phase region was further expanded. The isothermal section of 1000oC was simple. The phase of β-CuZn, β1-CoZn, γ-Co5Zn21 and γ-Cu5Zn8 was disappeared. The region of liquid phase is very large.

Abstract:Owing to good welding properties and low cost, carbon steel is often used to produce capsules to consolidate TiAl based alloy powders via hot isostatic pressing (HIP). Under high temperature and pressure, the density of TiAl pre-alloyed powders is reduced due to the diffusion of atoms and the capsule fails, forming brittle intermetallics. In order to ensure reliability of the carbon steel capsule, Al₂O₃-ZrO₂ (A-Z) layers was added to the inside wall of the 20# carbon steel capsule via thermal spraying. In the HIP experiment, the capsule with A-Z layers was used to consolidate Ti-46Al-2Cr-2Nb-(W, B) pre-alloyed powders at 1523K and 130 MPa for 2.5 hours, and then treated via HIP at 1603K and 130 MPa for 0.5 hours. To compare, the 20# carbon steel without A-Z layers was formed via processing of Ti-46Al-2Cr-2Nb-(W,B) pre-alloyed powders at 1523K and 130 MPa for 3 hours. The as-formed Hipped capsules were observed under SEM and EDS to evaluate the effects of A-Z layers. The test results reveal that the formation of brittle intermetallics was prevented upon addition of A-Z layers. During HIP, iron atoms of 20# carbon steel capsule could not meet titanium and aluminum atoms in the TiAl based alloy powders by diffusion; hence, the reliability of 20# carbon steel capsules was achieved. In addition, the compactly processed capsule of TiAl based alloy with A-Z layers was fully consolidated and exhibited a fine, nearly full lamellar microstructure. The Tensile strength and elongation of the compact at room temperature surpassed 590 MPa and 2.0% respectively.

Abstract:Magnéli-phases titanium suboxides have been successfully prepared by our aluminum reduction-hydrochloric acid leaching route. The resulting sample was characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), UV-visible diffuse reflectance spectroscopy (UV-Vis DRS) and X-ray photoelectron spectroscopy(XPS).The Characterization results show that the mother phase was Ti4O7 of magnéli phase titanium oxide could be prepared at the calcination temperature of 950°C,roasting time for 20 min and the amount of aluminum was 0.2.The as-prepared magnéli-phase titanium suboxides samples with the diameters of 400~600nm, the surface of magnéli-phase titanium suboxides formation of oxygen vacancies, which has strong UV and visible-light absorption property. The degradation efficiency of 37%, 43%, and 62% was achieved for the as-prepared magnéli-phase titanium suboxides samples after visible light irradiation for 130min.

Abstract:The tensile deformation behavior of an extruded Mg-1Y (wt.%) sheet was investigated in the temperature range of 25 (RT) to 300 ℃ and at strain rates from 0.001 to 0.1 s-1. Ultimate tensile strength (UTS) decreased by 49.3% from 247.9 ± 5.8 MPa when temperature increased from RT to 300 ℃ at the strain rate of 0.1 s-1. It is interesting to note that the flow behavior of the studied sheet exhibited pronounced strain rate sensitivity even at RT. The UTS at RT decreased by 11.8% as the strain rate decrease from 0.1 s-1 to 0.001 s-1. The flow behavior of the alloy can be described by the Garofalo hyperbolic sine constitutive equation in the temperature range of RT to 250 ℃. The measured stress exponent n was 27.8 ± 8.9, and the activation energy Q was 124.6 ± 6.1 kJ/mol. The Q value implied that deformation was controlled by dislocation climb. At intermediate temperature range (~ 150 - 250 ℃), the sheet exhibited serrated flow behavior, and this phenomenon was pronounced at lower strain rates. Simultaneously, the elongation to failure (EL) decreased anomalously with increasing temperature. The above two deformation features were believed to be closely related to the strong interaction between Y solute atoms and dislocations which is known as dynamic strain aging (DSA). The value of strain rate sensitivity ( m ) increased with increasing temperature. The m increasing from 0.068 to 0.11 at 300 ℃ indicated that the addition of Y resulted in the activation of more slip systems. The deformation microstructure observation revealed that twinning was depressed with temperature, which was consistent with the remarkably increased m values. Dynamic recrystallization (DRX) was observed at 300 ℃, and it was promoted with lower strain rate.

Abstract:Pyrochlore-based ceramic is recognized as promising nuclear waste matrice. In this study, pyrochlore-based Y_2-xGd_xTi₂O₇/Cu composite waste forms were rapidly prepared within 5 minutes by combustion reaction plus quick pressing (CR/QP) synthesis route, where CuO was utilized as the oxidant and Ti as the reductant. As the surrogate of trivalent actinide nuclides, Gd was introduced to substitute the Y site with nominal formulation of Y_2-xGd_xTi₂O₇. The results demonstrate that Gd can totally replace the Y site and Gd₂Ti₂O₇ pyrochlore can be readily synthesized. There is no impurity phase generated in the products, and phase separation is not detected in the pyrochlore matrix. The selected Gd_1.0 waste form exhibits promising aqueous durability as the 42 days normalized leaching rates of Cu, Y and Gd elements are evaluated as low as 2.4×10^_-2, 1.1×10^_-5 and 5.3×10^_-6 g.m^_-2.d^_-1.

Abstract:The hot deformation behavior of Al-0.04Er-0.08Zr alloy was investigated by hot compression tests in the temperature range from 200°C to 450°C. True stress-true strain curves were analyzed by linear fitting using Arrhenius-type equation, and deformation microstructure was studied by TEM. The results indicate that dynamic recovery is the dominated softening mechanism for both the solutionized and the aged sample during hot compression. Hot deformation especially at high temperature and low strain rate induced rapid precipitation in the solutionized samples. Dynamic precipitation apparently led to the increase of the flow stress of the solutionized samples during hot compression process, but did not effectively enhance the microhardness of the deformed samples. The dynamic precipitation also led to deviations of the Arrhenius-type fitting of the stress-strain curves.

Abstract:In order to analyze the effect of cooling rate on lamellar morphology and mechanical properties during BASCA treatment in Ti5321 alloy, the lamellar morphology and mechanical properties of the titanium Ti5321 alloy under different BASCA treatment are comprehensively studied. The results show that the cooling rates have decisive influence on the alpha lamellar size formed at slow cooling process after β zone solution. The lamellar size of Ti5321 alloy keeps increase with the decrease of cooling rate, and the growth rate of lamellar in the length direction is much faster than that in the thickness direction. With the increase of cooling rate, the strength of the alloy is in-crease，but the fracture toughness decreases. The cooling rate of 0.5℃/min in this experiment is the optimal cool-ing way which the ultimate tensile strength of alloy can exceed 1200MPa with an excellent fracture tough-ness(KIC≥65MPa.m1/2).

Abstract:3%~5% Ni element is added to the Al-Zn-Mg-Cu deformed aluminum alloy, and a large amount of Al3Ni phases are formed by eutectic reaction, the particle strengthening effect of the Al3Ni phases is added besides of MgZn2 aging strengthening. The increase of Ni content not only improves the casting performance and weldability of the Al-Zn-Mg-Cu deformed aluminum alloy, but also increases the tensile strength and yield strength. The preferred composition of Al-Zn-Ni-Mg-Cu aluminum alloy is Al-5.6Zn-3.5Ni-2Mg-1Cu. Its tensile strength, yield strength and elongation are 650MPa, 572MPa and 7.5%, respectively. The tensile strength and elongation of its welded joint were 323 MPa and 2%, respectively. With the increase of Zn content, the Al3Ni phase changes from interfacial tear to self-fracture. Increasing the content of Ni helps to increase the strengthening effect of Al3Ni phases, but the content of Ni cannot beyond the eutectic point.Decreasing the aspect ratio of Al3Ni particles helps to suppress the self-fracture of Al3Ni phases. Uniform distribution of Al3Ni phase helps to prevent the abnormal growing of recrystallized grains.

Abstract:Based on the high temperature and high pressure corrosion tests, the corrosion behavior of titanium alloy OCTG (oil country tubular goods) in high pH value completion fluid was studied by in-situelectrochemical measurement, the stability of titanium alloy passivation film was investigated by molecular dynamic simulation of thermodynamic, and the reaction enthalpy was calculated by using first-principles method. The results show the corrosion of TC4 alloy in high pH value phosphate completion fluid is very serious, and the uniform corrosion rate is as high as 0.4429 mm/a.The corrosion reaction of TC4 alloy in high pH value phosphate completion fluid is controlled by anodic reaction process.With the increase of temperature, the corrosion potential, the film resistance of corrosion product scale and the polarization resistance decrease significantly, the thermodynamic driving force of corrosion reaction increases, while the dynamic resistance decreases, and the corrosion current density of TC4 alloy increases significantly. In TiO₂ passivation film, the titanium-oxygen bonds of TiO₂ is tending to break due to the immersion of alkaline solution. Furthermore, the interfacial bonding energy between TiO₂ and aqueous solution increases gradually with the increasing of temperature and alkalinity, so the thermodynamic stability of passivation film decreases. In alkaline potassium pyrophosphate solution, TiO₂ passivation film can react with K₂HPO₄ and K₃PO₄ to form porous KTiOPO₄ corrosion product scale, but the thermodynamic tendency of the reaction between TiO₂ and K₃PO₄ is more obvious.

Abstract:In order to grasp the regulation law of existing shape control means and to provide reasonable control strategy to solve the problem of double-rib wave, the problem of double-rib wave occurred frequently and was difficult to control when Sendzimir 20-high rolling mill rolled wide industrial pure titanium strip,Based on ABAQUS finite element software and considering the anisotropic mechanical characteristics of commercial pure titanium strip rolling, an integrated roller-strip model of 20-high rolling mill for realizing the dynamic rolling process of work roll and strip was established., and the calculation accuracy of the model is verified by the actual industrial rolling data. The model is used to simulate the single and combined shape control characteristics of wide industrial pure titanium strip rolled by 20-high rolling mill. The results show that the thickness of 75-300 mm from the edge decreases most significantly with the increase of roll channeling when the backup roll 1 # and 7 #, 2 # and 6 #symmetrical position subsection pressing is combined with the middle cone roll channeling roll, which will lead to or aggravate the double-rib wave; the combination of 3 # and 5 #, 4 # symmetrical position subsection pressing and the middle cone roll channeling can alleviate the problem of the two rib waveform, and it is also found that the adjustment of the middle cone roll channeling can not solve the problem of the double-rib wave.Finally, combined with the shape control characteristics of 20-high rolling mill, a piecewise reduction combination scheme is proposed, which can reduce the compressive stress in the double-rib wave zone,Industrial experiments show that the compressive stress in the double-rib wave zone decreases by 60% after the implementation of the piecewise reduction combination scheme, which effectively alleviates the double-rib wave defects when rolling wide titanium strip on 20-high rolling mill.#$NLKeywords: sendzimir 20-high mill; wide commercial pure titanium strip; high-order buckle; finite element; shape control characteristics;

Abstract:Hot working of FeCrAl alloy for nuclear fuel cladding was investigated by thermal simulation compression experiment under deformation temperature of 800~1000 ℃ and strain rate of 0.001~1 s-1. The constitutive equation of the hot deformation behavior of FeCrAl alloy was established through Arrhenius hyperbolic sine function. Based on the dynamic material model, the processing map of FeCrAl alloy was derived for strain of 0.05~0.8. Results show that the flow stress of FeCrAl alloy decreases with the increase of deformation temperature and increases with the increase of strain rate. Both the deformation temperature and strain rate will affect the microstructure evolution. According to the processing map, the instability zone of flow behavior of FeCrAl alloy expands and then stabilizes with the increase of strain, and the optimal hot processing safety areas of the alloy are determined as follows: 1) the strain rate < 0.008 s-1 and the deformation temperature 880~1000 °C (when the strain is approximately 0.1); 2) the strain rate < 0.027 s-1 and the deformation temperature > 950 °C (when the strain is ≥ 0.3).

Abstract:The equiaxed γ grains and α2/γ laminas are the two main deformed microstructure of beta-gamma TiAl alloy. In this paper, mechanical properties and microstructural evolution of hot forged Ti-44Al-4Nb-4V-0.3Mo-Y alloy with equiaxed and lamellar microstructure were studied during high temperature tension. The results show that tensile temperature has a significant effect on the mechanical properties and microstructures of Ti-44Al-4Nb-4V-0.3Mo-Y alloy. At the same temperature, the tensile strength and yield strength of the TiAl alloy with equiaxed microstructure are slightly greater than those with lamellar structure，however the elongation difference is not significant. With the increase of tensile temperature, the tensile strength and yield strength of TiAl alloy decrease gradually, while the elongation increases significantly. For equiaxed microstructure， increasing tensile temperature, the equiaxed γ grains are elongated and complete dynamic recrystallization occurs to refine the microstructure of the TiAl alloy. For lamellar microstructure, the degree of decomposition of α2/γ laminas and recrystallization of γ laths increase with the increase of tensile temperature. The ductile brittle transition temperature of Ti-44Al-4Nb-4V-0.3Mo-Y alloy is between 750 ~ 800°C.

Abstract:Iron-based metalloceramics functionally gradient material (FGM) was prepared by combustion synthesis casting under an ultra-gravity field through using thermite system with Fe₃O₄/Al/Fe-based Cemented Carbide. Multiphase kinematics characteristics and densification mechanism of cemented carbide particles in ultra-gravity field were explored. The research results indicated that based on the Stocks rules, effect of translational speed of particles in high-temperature melts will be determined by density variation between the particles and melt, ultra-gravity coefficient, radius of particles, temperature and so on. Under certain ultra-gravity coefficient condition, material density was related to bubble size, existence time of iron melt. On the top of the material, there are mainly gathered two kinds of particles with ferrovanadium and ferrochrome, whose size will decrease follow the direction of ultra-gravity field. However, ferromolybdenum mainly gathered in the interface between FGM and 45 steel. The mostSofSdiscrepancies of distribution characteristics for different particles were exhibited because of their difference of density and melting point. The aspect leads to the gradient variation of hardness distribution for the FGM.

Abstract:In this work, the effect of boron content (CB) on the diffusion of hydrogen has been investigated in the ordered Ni3Fe alloy by using the methods of the cathodic charging hydrogen and vacuum stretching. It can be found that the diffusion coefficient of hydrogen decreases while the diffusion activation energy increases with the increase of boron content when CB≤0.06 wt%. The diffusion coefficient of hydrogen is subject to negligible changes and the diffusion activation energy decreases slightly when CB > 0.06 wt %. The atom probe chromatography reveals the segregation of boron atoms at grain boundaries in ordered Ni3Fe alloys. Through the comparative study of the effect of boron content on hydrogen diffusion coefficient and hydrogen embrittlement factor, it is confirmed that boron atom could reduce the hydrogen embrittlement sensitivity of ordered Ni3Fe alloy in hydrogen environment with the reason of reducing the intergranular diffusion coefficient of hydrogen by boron atom in the alloy.

Abstract:The reliability of the joint is mainly determined by the morphology of interfacial IMC and microstructure in joint. In the ultrasonic-assisted soldering process, the behavior of the base metal being dissolved by the liquid solder affects the microstructure of the joint. In this paper, the dissolution behavior of Ni in molten Sn solder with and without applied ultrasonic vibration (USV) was investigated through the immersion experiment. In order to reveal the mechanism of accelerated dissolution by USV, the ultrasonic pressure distribution in molten solder were simulated by finite element analysis and the microstructures after dissolution were observed. The results showed the dissolution amount of Ni in Sn after 10 s of USV was equivalent to a holding time of 5 min without USV. Without USV, the interfacial IMC gradually thicken as the holding time increases, which hinders the diffusion of Ni atoms into the Sn solder. With USV, ultrasonic cavitation caused the infinite dissolution of Ni into tin solder. Furthermore, the dissolved Ni atom at the interface was brought rapidly to the molten solder by the ultrasonic streaming, which cause a large number of elongated rod-shaped Ni3Sn4 precipitated during the subsequent cooling process.

Abstract:A new technology of the integral blisk was proposed recently to improve the thrust-to-weight ratio of the aero-engine, but which may result in high-risk failure near the disk-blade connection area. Therefore, here the molecular dynamics is used to simulate the mechanical properties of the single-crystal/polycrystalline nickel (SPSNi) in the joint zone. Firstly, the tensile atomic diagram of different crystalline nickels are compared. It is found that the degree of amorphization at the interface after tension is aggravated due to the presence of the single crystal/polycrystalline interface, which easily germinates void and exacerbates the risk of sudden fracture of SPSNi. Finally, the effects of the strain rate and temperature are especially investigated.When the strain rate is greater than 1í10_⁸s_^-1 and less than 2í10_¹⁰s_^-1, the tensile mechanical of SPSNi is almost insensitive to the loading strain rate, and the yield strength rises slightly.After exceeding 2í10_¹⁰s_^-1, the yield strength decreases rapidly with the increase of strain rate.This is because a large number of FCC atoms in SPSNi rapidly transform into disordered amorphous structure at high strain rate, resulting in the rapid decline of SPSNi carrying capacity. Strain rate 2í10_¹⁰s_^-1 can be used as the threshold of SPSNi tensile deformation. At different temperatures, the yield strength of SPSNi decreases linearly with increasing temperature, because the initial mosaic structure of dislocation network gradually becomes irregular, and the initial mismatch stress decreases with the increase of temperature under the influence of temperature.

Abstract:The powder deformation behavior, microstructure evolution and mechanical properties of the Nb-35Ti-6Al-5Cr-8V-5C alloys after different ball milling time were investigated using powder metallurgy method by the combination of mechanical alloying and hot press sintering. The result show that the massive metal particles of Nb-35Ti-6Al-5Cr-8V-5C mixed powder are translated into flakes morphology firstly and then deformed into flocculent morphology during the action of impact extrusion as the ball milling time increasing, as well as the TiC powders are distributed uniformly on the surface of flake metal powder. The Nb-35Ti-6Al-5Cr-8V-5C alloy is consisted of Nbss phase and (Nb, Ti)C phase, and the volume of carbide for each alloy is about 11%. The element of Ti is mainly distributed in (Nb, Ti)C and the grain boundary of Nbss, however the element of Al, Cr, V is mainly distributed in Nbss grain. The size of Nbss and (Nb, Ti)C phase is decreased with the increasing of ball milling time. The compressive mechanical properties and plastic deformation capacity at room temperature is significantly increased causing by grain refinement of Nbss and reinforced phase dispersion of carbides. After compression deformation Nbss and carbide have good interfacial bonding, however, the obvious crack with a nearly parallel distribution inside carbides is existed. Furthermore, it is evident that the mechanical property of Nb-35Ti-6Al-5Cr-8V-5C alloy prepared by powder metallurgy is better than that prepared by arc melting method.

Abstract:The high-temperature oxidation behavior of NbZrTiTa high-entropy alloy (HEA) were characterized by cyclic oxidation test, XRD and SEM. The results reveal that the oxidation kinetics curve of NbZrTiTa HEA in the temperature range of 1000-1400 °C satisfies the parabolic law. The oxidation rate constant and oxidation activation energy achieve 1.1×10_^-7~1×10_^-6 g_².cm_^-4.s和97 kJ/mol, respectively. The oxidation type is internal oxidation. During high-temperature oxidation, oxygen diffuses along the TiZr-rich region with the severe lattice distortion and a large number of dislocations, then reacts with the metal components to form unsaturated oxides and saturated oxides sequentially. Because of the high activity of constituent elements and the severe lattice distortion, NbZrTiTa HEA displays an extremely high oxidation activity then exhibits strong potential as structure energetic material.

Abstract:The combined technology of inertial friction welding and isothermal deforming was utilized to prepare IMI834/Ti6246 dual titanium alloy scaled disk. The effect of isothermal deforming on the microstructure and property of inertial friction welding IMI834/Ti6246 dual titanium alloy scaled disk was analyzed. The results show that the inertial friction welding forms the fine microstructure in the welding seam of IMI834/Ti6246 dual titanium alloy, meanwhile results the coarse microstructure of heat affect zone on both sides. The ultrasonic nondestructive testing indicateds that there are some defects in local zone of welded dual titanium alloy scaled disk. After isothermal deforming, the residual inertial defects after inertial friction welding are effectively eliminated and the coarse microstructure of heat affected zone both sides is obviously improved which homogenizes the transition zone between welding seam and both sides. The weld steam of inertial firction welded IMI834/Ti6246 dual alloy scaled disk was effectively strengthened during isothermal deforming. The inertial friction welding and isothermal deforming could be combined to prepare high performance dual titanium alloy disk.

Abstract:The fretting wear behaviors of TC4 titanium alloy under different displacement amplitudes in air, pure water and the artificial seawater of 3.5% NaCl were studied by SRV-IV fretting wear test rig. Scanning electron microscopy and laser scanning confocal microscopy were used to characterize the surface morphology, wear volume and wear profile of the wear scar. Fretting wear mechanism of titanium alloy in different environmental media was analyzed. The results showed that the friction coefficient increase first and then decrease with the increase of the displacement amplitude, while the wear volume increase. Under the dry friction condition, the friction coefficient is higher and unstable, and the wear volume is smaller. The wear mechanism is mainly abrasive wear, adhesive wear and oxidative wear. Compared with dry friction, the friction coefficient in the aqueous water is lower, the wear volume is significantly increased, and the friction coefficient in the artificial seawater is lower and more stable, and the wear profile is deeper, indicating that there is a "positive" interaction between corrosion and wear. The fretting wear mechanism of TC4 alloy in pure water is mainly fatigue wear and abrasive wear; while the fretting wear mechanism in artificial seawater is mainly abrasive wear and corrosion wear.

Abstract:Aiming at the problems that the Ti-6Al-4V blade with thinned edge caused by the corrosion of strong airflow and flue gas, the performance degradation of the remanufacture cladding layer and the interface. The same cladding alloy with high matching degree and good formability with Ti-6Al-4V blade substrate was chosen, through the element matching contrast, the analysis of energy dispersion law, the metallographic evaluation, the remanufacture forming experiment and the verification of basic mechanical properties, the research on the performance of remanufacture cladding layer and interface controlling was carried. The experiments results show that, the content of Ti, Al and V are respectively about 80%, 3.9~5.5% and 3.0~3.5%. The contents of the main elements above are basically consistent with the substrate. The interface is composed of initial equiaxed α phase, partially flake β phase and along with a small amount of needle-shaped α" martensite on the β phase grain boundary, all which constitute the initial basket structure. The β phase in the interface is refined and differentiated into granular, dispersing in the basket tissue. Further, the β phase at the interface is of pinning effect to the grain boundary of the staggered baskets, which is beneficial to improve the coating strength. Finally, the micro-hardness of the coating is 315.08~351.76HV0.1, which is lower than the substrate. Through the research above, not only the good forming of Ti-6Al-4V blade with edge thinning was realized, but also the related technology and methods of the cladding layer and the interface performance controlling were validated effectively.

Abstract:High manganese Hadfield steel is the conventional wear-resistant steel. In order to meet the requirements of complex working conditions, Hadfield steel matrix composites (SMCs) with various volume fraction of TiC were designed and fabricated using an in-situ solidification method. The microstructure and abrasive wear properties of these composites were examined. After heat treatment, the composites consist of austenite and TiC phases. TiC particles were uniformly distributed in the matrix, and the interface between the particles and the matrix was clean. It is found that the wear resistance of the composites can be improved by the introduction of TiC particles. However, with increasing TiC volume fraction, the wear resistance decreased slightly. We found the particle size increased and the particle segregations were formed with increasing TiC volume fraction. The increased wear rate with increasing TiC volume fraction was caused by the fracture of large particles.

Abstract:In this paper, the as-cast microstructure of Ti-15Mo alloy with high oxygen content and the microstructure and corresponding properties obtained by solution treatment at different temperatures are studied. Composition analysis shows that 0.8wt% O is dissolved in the alloy, hereinafter referred to as Ti-15Mo-0.8O alloy. The microstructure transformation of Ti-15Mo-0.8O alloy was observed and analyzed by optical microscope (OM), scanning electron microscope (SEM) and X-ray diffraction (XRD). The results show that the as-cast structure of the alloy consists of α and β phases. After solid solution treatment at 900℃, 1000℃, 1100℃/2h, the phase composition transformation process of the alloy is α+β+TOβ+TOβ; The lattice constant of β phase of alloy gradually increases with the increase of solid solution temperature. Hardness and room temperature compression tests were carried out by Vickers hardness tester and universal testing machine. The results show that the highest hardness of the sample after solution treatment at 1100℃/2h is 455HV20；The sample after solution treatment at 1100℃/2h has the best compression performance, with compressive yield strength of 1617Mpa and compressive strength of 2308Mpa respectively, and compression ratio of 22%.

Abstract:Objective The purpose of this study was to investigate the fibronectin adsorptive capacity of pure titanium surfaces and improve their biological properties by regulating their surface charge. Methods The different surfaces of titanium sheet were obtained by sandblasting with large grit and acid- etching (SLA), and then immersing in different solutions. Surface morphology, elemental composition, roughness, and urface charge status were studied, and fibronectin adsorption assay was performed for comparative analysis. Result The surface morphology of each group was similar, but the surface elements of the different groups were different because of immersion in different liquids. There was no significant difference in the surface roughness of each group. Titanium sheets immersed in calcium chloride solution had the highest protein adsorption capacity (P < 0.01), whereas the control group had the lowest adsorption capacity. Conclusions Immersin. Of titanium sheets in calcium chloride solution containing divalent calcium ions can change their surface charge, enhance their protein adsorption capacity, and improve their biological properties.

Abstract:Single-phase Mg₂Sn crystal was successfully directionally solidified from the melt with a high temperature gradient of 180K/cm. The critical velocity of planar interface and solidified distance for the growth of single-phase Mg₂Sn crystal is predicted theoretically and agrees well with the experimental result. The grown Mg₂Sn crystals exhibit better thermoelectric performance without influence of the second phase Sn. At the temperature ranging from 300 to 700K, the maximum Seebeck coefficient S and electrical conductivity σ reached -261μVK^_-1 and 525?^_-1m^_-1, respectively. The top value of power factor is 2.29mWm^_-1K^_-2 after the doped Bi optimization. The minimum thermal conductivity κ was measured as 4.3Wm^_-1K^_-1 at T=500K. The maximum figure of merit is 0.21 at the doping concentration of 1.5at.%Bi. The method developed in this paper can provide a methodological reference for the preparation of ternary Mg₂B^_IV solid solution.

Abstract:Using Cu-Zn mixed powder as spray powder, Cu-Zn composite coating was prepared on 1Cr13 substrate by low-pressure cold spray technique. The composite coating was annealed at different annealing temperatures, and then the mechanical properties of the coating were tested. Observing the micrographs and testing hardness of composite coatings before and after annealing heat treatment by X-ray diffractometer, field emission scanning electron microscope and microhardness tester. The results show that the copper-zinc composite coatings are dense and the coatings are tightly bonded to the substrate; When the copper-zinc composite coatings are annealed between 200 °C and 300 °C, the metal particles interfaces in the coatings are obvious, and intermetallic compounds are formed in the coatings, such as β(CuZn) and γ(Cu5Zn8). When the annealing temperature is 200 °C, the hardness of copper-zinc composite coating reaches the highest (157.8HV), and the bonding strength reaches the lowest (7.5MPa); When the copper-zinc composite coatings are annealed between 350 °C and 450 °C, the metal particles interfaces in the coatings are not obvious; When the annealing temperature is 450 °C, the hardness of copper-zinc composite coating reaches the lowest (102.4HV), and the bonding strength reaches the highest (13.9MPa).

Abstract:In this work, the effect of trace addition of Ca and Y on the microstructure, mechanical properties and corrosion properties of Mg-6Zn-1Al alloy were investigated. The results show that the second phase in the as-cast ZAM610 alloy is consisted of α-Mg, Mg51Zn20 and a small amount of Al8Mn5 phases. The Mg51Zn20 phase in the as-cast alloy is substituted by Mg32(AlZn)49 with Ca addition. α-Mg, Mg51Zn20, Al2Y and a small amount of Al10Mn2Y phases are found in the Y-containing alloys. Y or/and Ca are added to refine markedly the recrystallized grains of the tested magnesium alloys, and the alloy of Y+Ca addition has the minimum grain sizes. In the Ca-containing alloy, MgZn2 phase is dynamically precipitated during extrusion, which has strong effect of Zener retardation, and formes a double-mode microstructure composed of fine recrystallized grain and coarse deformation zone. ZAMX6100 alloy has the highest tensile strength, yield strength and elongation, which are 354 MPa, 313 MPa and 17.3%, respectively. In addition, Al2Y phase in Y-containing alloy promotes recrystallization nucleation during deformation, resulting in a reduction of deformation bands. The improvement of mechanical properties of tested alloys after microalloying can be attributed to the refinement of dynamic recrystallization grains, the formation of Al2Y phase particles and the dynamic precipitation of MgZn2 phase. For corrosion resistance of the Ca-containing alloy, the raise reason is a large amount of dynamically precipitated MgZn2 phase that prevents the continuous corrosion, while Y element increases the corrosion resistance of the alloy matrix.

Abstract:_{: The electrochemical behaviors of Nd(III) on tungsten electrode and its co-deposition with Al(III) in NaCl-KCl salts at 700 °C were investigated by a series of electrochemical techniques such as cyclic voltammetry, square wave voltammetryand open-circuit chronopotentiometry, and thus Nd-Al alloy was prepared via direct co-deposition of Nd and Al on the inert electrode. The results show thatthe reduction of Nd(III) in NaCl-KCl-NdCl3 melts isa one-step process with three electrons exchanged, and the reaction is anirreversible processcontrolled by diffusionat low scan rate (0.1~0.5V/s) with the calculated diffusion coefficient is approximately 7.6×10^-5cm²/s. After AlCl3introduced into the NaCl-KCl-NdCl3 melts, the curves of cyclic voltammetry, square wave voltammetryand open-circuit chronopotentiometry indicate that three kinds of Nd-Al intermetallic compounds (Nd11Al3, NdAl3 and NdAl2) were formed. It can be deduced that the underpotential deposition of Nd occurs on the tungsten electrode covered with the pre-deposited metal Al from the open circuit chronopotentiometriy. Based on the results of open circuit chronopotentiometriy, the thermodynamic properties of Nd-Al intermetallic compounds were determined by electromotive force measurement at 700 °C, such as the activity of Nd in two-phase coexisting state and relative partial molar Gibbs energies, as well as the standard Gibbs energies ofNd-Al intermetallic compound. Finally, potentiostatic electrolysis was carried out at -2.3Vfor 5h to obtain a product alloys. X-ray diffraction (XRD) and scan electron micrograph (SEM)-energy dispersive spectrometry (EDS) analysis indicated that the obtained alloys were mainly composed of Nd11Al3, NdAl3, NdAl2 and Al phases.}

Abstract:The high-quality GH4169 nickel-base superalloy has higher Nb content, and its microstructure is more sensitive to the process parameters,especially after δ phase aging (DP) treatment, thus it is necessary to study its hot deformation behavior. In this paper, the hot deformation behavior of GH4169 alloy, have been studied by isothermal compression tests at the temperatures of 980-1070°C and strain rates of 0.001-1 s-1. The results show that the deformation temperature and the strain rate have obvious effects on the flow characteristic. Constitutive model was established based on sine-hyperbolic Arrhenius kinetic rate equation, the value of average activation energy ( 528.24 kJ/mol) of GH4169 alloy is obtained in present study,increase of Nb content will increase the modified activation energy significantly. Hot workability is interpreted by processing maps. The optimum hot working conditions for GH4169 ally was low temperature with low strain rate and high temperature with high strain rate area.

Abstract:). In this work, tribological properties of CrN/TiN superlattice coatings deposited on IN 718, WC-6%Co and Si(100) by the combined deep oscillation magnetron sputtering was investigated. Results show that the coating growth was independent of the nature of substrate materials. As the hardness of substrate materials was increased, the scratch critical loads increased. Adhesion failure mode changed from buckling failure to cooperative deformation of substrate/coating system with only small cracks in the whole scratch track. Wear mechanism of the coatings deposited on IN 718 and WC-6%Co changed from abrasive wear and oxidative to mild abrasive wear at a normal load of 2 N. Under normal load of 4 N, the coatings on IN 718 suffered serve oxidative wear, while the coatings on WC-6%Co suffered the combined abrasive and oxidative wear. The production, accumulation and mass transfer of oxides resulted in the oscillation of friction coefficient during dry sliding wear tests.

Abstract:The laser butt welding of GH3625 superalloy fabricated by laser additive was conducted. The microstructure evolution and mechanical properties of the welded joints were analyzed. The results show that a great amount of Laves phase was only precipitated at the grain boundary of upper layer in HAZ, resulting in significant coarsening of the grain boundary. Along the upper layer to the lower layer of the weld, the fusion zone and the intermediate zone are gradually transformed from cell crystal, the columnar crystal and the equiaxed fine crystal of the upper layer to columnar crystal of the lower layer. The number of equiaxed fine crystal growing close to the fusion line is gradually increased. And the central zone is dendritic. The particle of fine γ′ phase is precipitated in the weld. A number of Laves phase precipitates in the inter-dendrtic of the intermediate zone, and the morphology gradually changes from the strip of the upper layer to the particle of the lower layer. The tensile strength of the welded joint is 872 MPa, which is up to 98.2% of the base metal. The elongation is up to 90.7% of the base metal, the fracture surface of weld joint is approximately 45° inclined plane, and the fracture mode is the mixed fracture mode of brittle and ductile.

Abstract:FGH97 nickel-base superalloy were processed at different solution cooling rates, then the microstructure and creep behavior of FGH97 nickel-base superalloy were studied by optical microscope, scanning electron microscope, energy disperse spectroscopy and creep testing machine. The results show that the grain size decreases, the size of γ′ precipitates decreases and the carbide precipitates change from continuous to discrete with the increasing solution cooling rate, and GB carbides are composed of (Ti, Nb, Hf)-rich. The creep performance of the alloy with a solution cooling rate of 94 ℃/min was significantly better than that with a cooling rate of 43 ℃/min under 750℃/450MPa.γ′ cutting is the deformation mechanism of FGH97 alloy under 750℃/450MPa, stress concentration at grain boundary leads to initial cracks, then crack propagates along grain boundary and finally leads to fracture. The disperse distribution carbides on grain boundary can inhibit the propagation of microcracks.

Abstract:MeO-doped Ag/SnO2 electrical contact materials were prepared by mechanical alloying combined with cold pressing-sintering-hot pressing process with CuO and Fe2O3 as dopants. Microstructure and physical properities of the electrical contact materials with different dopant contents were characterized by means of X-ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), metal conductivity tester, thermal conductivity meter and Hall Effect tester. The results showed that, the use of hot pressing process could significantly enhance the bonding strength between SnO2 particles and Ag matrix. Meanwhile, the single doping of CuO and Fe2O3 could improve the electrical performance and thermal conductivity of the MeO-doped Ag/SnO2 electrical contact material, respectively. When a co-doping of CuO and Fe2O3 was used, the Ag-11.5SnO2-0.3CuO-0.2Fe2O3 material presented the optimal electrical and thermal conductivity with electrical resistivity of 2.25μΩ·cm, hardness of 74.8 HV0.5, thermal diffusion coefficient of 111.4 mm2/s and thermal conductivity of 338.6 W/(m.K) at room temperature. A smaller wetting angle of 62.7° between Ag droplets and the (CuO,Fe2O3)-doped SnO2 powders was observed, indicating a better wettability, and the interfaces between SnO2 and Ag grains were well-combined with a lattice mismatch of 14.25% between SnO2 (200) and Ag (111).

Abstract:The in-situ Preparation of WC-6Co composite powder was subjected to dry-bag type cold iso-static pressing without any pre-treatment (The pressing pressure was 1000 bar and the holding time was 15 s). Ultra-fine YG6 cemented carbide was prepared by sintering the pressed blank in a low-pressure sintering furnace at a (sintering temperature of 1360 ℃ with 40 min sintering time, and it was kept under 5 MPa pressure holding for 20 min). To analysis the morphology, metallography and physical mechanics properties of the YG6 cemented carbide, The results showed that: abnormal grain growth can be observed from the Ultra-fine YG6 cemented carbide, the average grain size of the WC alloy is 0.8 μm; The hardness HV30 is 2150±10, which is higher than the conventional Ultra-fine YG6X cemented carbide. Then, the composite powder of WC-6Co was produced to ultra-fine size YG6 cemented carbide through processes of wet-milling, pressure type spray drying, binder adding, extrusion forming, low-pressure sintering. Through the analysis of the effects of different grain growth inhibitor ratios, ball-milling time, extrusion pressure and sintering temperature on the properties of the alloy were investigated by testing the mechanical to the physical properties of the carbide, the results showed that: when 0.3 wt % VC and 0.8 wt % Cr3C2 were added, wet milling 48h , extrusion at 24 MPa pressure and sintering temperature of 1340 ℃, the produced Ultra-fine YG6 cemented carbide has homogenous WC grain size, No WC grains with abnormal growth can be observed from the Metallographic diagram of the YG6 cemented carbide. The average grain size of WC alloy is 0.4 μm, and the grains are in polygonal shapes with relatively round outlines. The strength and hardness of YG6 cemented carbide prepared under these conditions are the highest. The TRS of YG6 cemented carbide is 2250±20 MPa, and the HV30 is 2260±10. Intergranular fracture, along the WC and WC grain boundary fracture or WC and Co grain boundary fracture can be observed from the morphology of fractures.

Abstract:In the present work, a series of single phase Fe-/Ni- double doped skutterudite compounds Co3.8-xFexNi0.2Sb12 (x=0.05, 0.1, 0.15, 0.2) were successful synthesized by 5 min microwave heating for the first time. The resulting ingots was pulverized and sintered by spark plasma sintering to fabricate bulk samples, and their phase composition, grain size, element distribution, thermoelectric transport properties have been investigated systematically. The XRD patterns show that all samples are consistent with single phase of CoSb3. The FE-SEM morphologies reveal that the size of Co3.8-xFexNi0.2Sb12 matrix grain are about 1~3 μm, the average size are about 1~2 μm. The EDS elemental maps revealing uniform Co, Fe, Ni, and Sb distributions. The electrical transport properties were further improved by Ni/Fe double doping, resulting a highest power factor of 2.667×103 μWm?1K?2. The influence of Fe doping on lattice thermal conductivity is not so significant, but there is a relationship between lattice thermal conductivity and grain size, and boundary scattering is most likely to be the dominant scattering mechanism. The lattice thermal conductivity of Co3.65Fe0.15Ni0.2Sb12 is 2.8Wm-1K-1. The Co3.7Fe0.1Ni0.2Sb12 has the highest ZT of 0.50 at 773 K, which are obviously larger than those of Ni- /Fe- single or double doped samples produced via traditional techniques.

Abstract:The filling states, microstructures and mechanical properties of ZL104 aluminum alloy connecting rod prepared by traditional liquid squeeze casting (LSC) and semi-solid squeeze casting (SSSC) processes were investigated. Results show that, During the LSC process, the connecting rod is fully filled and its microstructure is a typical dendritic structure. However, its tensile strength and elongation are lower than the connecting rod prepared by SSSC process. During the SSSC process, when the pouring temperature is higher than 565 ℃, the connecting rod is fully filled; the average grain size and shape factor are improved with the increase in the pouring temperature; the tensile strength and elongation is increased first and then decreased. When the squeezing pressure is higher than 25 MPa, the connecting rod is filled full; with increasing the squeezing pressure, the average grain size is gradually decreased, the shape factor is gradually increased, and the mechanical properties are gradually improved. Additionally, with the increase in the mould preheating temperature, the average grain size and shape factor are gradually increased, and mechanical properties are gradually improved. However, when the mould preheating temperature is higher than 300 ℃, the average grain size is further increase and the shape factor is decreased, resulting in the decrease of the mechanical properties of the connecting rod.

Abstract:In this thesis, cetyltrimethylammonium bromide (CTAB) was used as surfactant. C4H6CoO4·6H2O and FeCl3·6H2O were used as raw materials. The crystallization temperature was 180 ℃, the crystallization time would last 8 h and the solution was passed at pH=11. Cobalt ferrite nanoparticles were prepared by hydrothermal method. The doped rare earth elements Gd3+ was used to control the structure and absorbing properties of cobalt ferrite, and at the same time explore the optimal doping amount of rare earth elements. The structure and absorbing properties of cobalt ferrite were characterized by X-ray diffraction (XRD), fourier transform infrared (FTIR), transmission electron microscopy (TEM) and vector network analyzer (VNA). It was found that during cobalt ferrite preparation, the doping of rare earth elements Gd3+ would have a great influence on grain size, morphology and absorbing properties. The results showed that when the doping amount of rare earth elements was x ≤ 0.1, the decrease of the grain size of cobalt ferrite and increases of the lattice constant gradually with the increase of doping amount, indicating that rare earth elements can make the particles smaller. The absorbing reflectivity of cobalt ferrite reached the minimum values of -14.9 dB when the doping amount of rare earth elements Gd3+ was 0.025.

Abstract:5%, 10% and 15%Yb-doped SrCeO₃-base proton conducting ceramic tubes were prepared by solid reaction. The Electromotive forces (EMF) were continuously detected by the hydrogen probes which were fabricated with the tubes in molten aluminum at 750℃. Hydrogen contents were calculated as a result. Synthesis and pressed process parameters of ceramic tubes were discussed. The effect of Yb-doped amount and assembly methods, air chamber length or bottom thickness of the probes on the response time, sensitivity, accuracy, reproducibility and impedance spectrum characteristics for the hydrogen sensors were studied. The results indicated that the mixed powders were formed purer proton conductor after calcining at 1400°C for 4 hours. The relative density of the tubes can be improved at higher pressure (275MPa) or more holding pressure time (3-6min). The response time of the sensor can be reduced to 2-4 min by using probes which had more Yb doped amount, less tube wall thickness or shorter gas compartment length with inverted U-shaped sealing method. The reference gas flow or pressure had a rapid, outstanding and reversible effect on the EMF. It is necessary to measure and control the reference gas flow or pressure for acquiring the accurate hydrogen content.

Abstract:Selective phase dissolution technology is a simple, economical and effective method for preparing micro/nanostructures, especially in the aspect of ultra-long-diameter ratio, ultra-deep-width ratio and single crystal micro/nanostructures. The principle is to extract micro/nanostructures in two-phase or multiphase alloys, and size control is mainly carried out during the formation of prealloys. Based on a clear distinction between selective phase dissolution and dealloying, the research progress of selective phase dissolution in the preparation of nanoparticles, micro/nanowires, micro/nanoporous and micro/nanochannel structures were reviewed in detail for the first time. Combining with the research work of our group, the technological process was improved, the application scope was broadened, and the types of micro/nanostructures were enriched, which laid a foundation for the wide application of selective phase dissolution in the preparation of micro/nanostructures.