Abstract:The age hardening behavior and the relevant strengthening mechanisms of Ti-10Mo-8V-1Fe-3.5Al (TB3) alloy have been investigated. A transmission electron microscope (TEM) was used to investigate the microstructures of aged and deformed TB3 specimens. It can be observed that dislocations can bypass the small α platelets in early aged samples. However, in late aged samples. the precipitated α platelets are large with high volume fraction, so that the β grains are divided into isolated β cells. In other words, the β grains are heavily refined. During plastic deformation, the dislocations generated in these β cells can not bypass the large α platelets by Orowan mechanism, but are confined within them. The strength model of the early aged TB3 alloy (aging time less than 2 h) is established by combining the law of mixtures with Orowan strengthening theory. For late aged TB3 alloy (aging time longer than 2 h), the strength model is established by combining the law of mixtures with fine grain strengthening theory. The predicated yield strength according to the modified strength models above can meet well with the measured values

Abstract:Thin TiO2 films in-situ grown on titanium alloy substrate were prepared in 0.05 mol/L H2SO4 electrolyte using the micro plasma oxidation method. The photocatalytic properties of the prepared thin TiO2 films were investigated using Rhodamine B solution as a target pollutant. In order to improve the photocatalytic properties of the obtained TiO2 films, different contents of Nb(NO3)3 were added into the H2SO4 electrolyte and the Nb-doped TiO2 films in situ growth were obtained. The influences of the doping ions on the surface morphologies, the crystal phase compositions and microstructures of the TiO2 films were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The results show that doping of Nb ions can refine the mesoporous TiO2 grain and increase the specific surface area. But doping of Nb ions has little influence on the crystal phase composition and the lattice parameters. Otherwise, doping of Nb ions can improve the photocatalytic activity of TiO2 thin films, when the Nb(NO3)3 is 1.2 g/L, the degradation rate of Rhodamine B solution in 90 min reaches 85%, showing the strongest light degradation ability

Abstract:Amorphous Fe78Si9B13 and nanocrystalline Fe73.5Cu1Nb3Si13.5B9 alloys with low coercivity, high saturation magnetic flux density and high permeability have attracted extensive attention. In this paper the influence of corrosion on their soft magnetic properties of Fe78Si9B13 and Fe73.5Cu1Nb3Si13.5B9 alloys tested in the NaOH solution (pH=9~10) was investigated. Changes of soft magnetic properties including effective permeability, coercivity and saturated magnetic flux density were analyzed. The samples were characterized by X-ray diffraction and 3D high depth of field microscope. The results show that some orange precipitates corresponding to an iron oxide are produced in the solution after corrosion, and the structures of Fe78Si9B13 and Fe73.5Cu1Nb3Si13.5B9 alloys remain unchanged. The soft magnetic properties of these alloys decrease after corrosion. The decrease of effective permeability μe and saturated magnetic flux density Bs, after corrosion, observed in the amorphous Fe78Si9B13 sample, was larger than that observed in the nanocrystalline Fe73.5Cu1Nb3Si13.5B9 sample.

Abstract:Cu46Zr46Al8 bulk metallic glass (BMG) was prepared by low purity sponge zirconium instead of high purity crystal bar zirconium, and via the microalloying of adding a small amount of yttrium. The results show that the glass forming ability (GFA) and the thermal stability of the Cu46Zr46Al8 alloy are improved by yttrium addition. When the addition amount of Y is 2at% and 3at%, the enhancement of GFA is most significant. The compressive fracture strength of Y microalloyed BMG is more than 2 GPa, which is much higher than that of BMG alloy produced with high purity raw materials, but its plasticity deteriorates obviously.

Abstract:This study is aimed to adopt the powder metallurgy method to prepare copper alloy series (Cu/AlN) nanocomposites with high strength and high conductivity. Optical microscopy, transmission electron microscopy, and scanning electron microscopy were used to examine the effect of different process conditions (temperature, pressure, repressing pressure, and resintering temperature) on the structure and mechanical properties of the composites. The results show that the density of the sample increases with the increase of pressure and sintering temperature. The Brinell hardness of the sample increases with the increase of repressing pressure, sintering temperature and AlN nanoparticle content. However, when AlN nanoparticle content is >0.5 wt%, the Brinell hardness of the composites decreases. The bending strength of the sample increases with the increase of repressing pressure and sintering temperature.

Abstract:SMAT-MAO composite coating, consisting of a bottom nanocrystalline layer and a top ceramic coating, was designed and fabricated on the surface of 2024 Al alloy. The microstructure and the phase composition of SMAT-MAO coating were examined using X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The fatigue life of the treated alloy was evaluated. The results indicate that the SMAT-MAO coated samples with 5 and 10 μm thick ceramic coatings exhibit improved fatigue lifetime, increasing by 21.9% and 23.2%, respectively. The improved fatigue property is attributed to the combined effect of nanocrystalline structure and the residual compressive stress induced in the substrate near the ceramic coating. With ceramic coating thickness increasing to 15 μm, the fatigue lifetime of the SMAT-MAO coated sample is lightly reduced due to the protrudent degrading effect caused by the much bigger pores and pre-existing micro cracks on the coating surface

Abstract:GdVO4:Eu3+ nanophosphors were prepared via molten salt synthesis. Equal moles of NaNO3 and KNO3 were used as reaction medium, rare earth nitrates and NH4VO3 as precursors, and NaOH as alkalizer. X-ray diffraction (XRD), Fourier transform infrared (FT-IR), transmission electron microscopy (TEM), photoluminescence (PL) spectrum and lifetime were used to characterize the nanophosphors. XRD demonstrates that NaOH concentration and the sintering temperature play important roles in the crystallinity and the phase purity of the products. The optimum NaOH concentration and sintering temperature are 2:40 and 400 °C, respectively. TEM micrographs show that the GdVO4:Eu3+ nanocrystals exhibit a cubic morphology and have a mean size of about 20 nm, which is in good agreement with that calculated by Scherrer’s formula. Both the cell parameters and the volume of GdVO4:Eu3+ nanocrystals decrease due to the existence of big quantity of dangling bonds on the particle surface. Upon excitation at 315 nm, the GdVO4:Eu3+ nanocrystals show the strong characteristic emission of Eu3+, which indicates the efficient energy transfer from VO43- groups to Eu3+. The best doping concentration of Eu3+ in GdVO4 is determined to be 5 mol%.

Abstract:A semi-solid metal ingot of ZK60-2Ca alloy was prepared by near-liquidus casting, and its microstructure evolution was studied. It is found that due to the special refining effect of Zr, ZK60-2Ca alloy directly achieves a spherical or nearly spherical structure, without the process of dendrite spheroidization. The effect of cooling rates on the casting microstructure was also investigated through adopting different moulds with various cooling rates. The effects of holding time on the microstructure of the alloy were also studied. The results indicate that with the casting temperature decreasing and holding time extending to 60 min, the grains are refined and homogenized gradually, the grain size is 21 mm as well as the roundness is 1.29. With a bigger cooling rate, the grains become smaller and spherical. In addition, the evolution mechanism of casting microstructure for near-liquidus casting was discussed

Abstract:To study the behavior of hydrogen corrosion on U-2.5%Nb alloy (mass fraction), a gas-solid reaction system with an in-situ microscope was designed. The nucleation and growth of hydride of U-2.5%Nb alloy were observed continuously and recorded by the system. The results show that the growth velocity of hydride can be well characterized by the in-situ microscope. The growth kinetics result indicates that the relation between growth velocity of hydride and time is linear. Hydride front velocity increases with the increasing temperature, which follows the Arrhenius law at about 125 oC. The reaction activation energy is 24.34 kJ/mol. But at high temperature (>125 oC), the growth velocity decreases sharply with the increasing temperature

Abstract:In order to investigate the effect of homogenization annealing on the second phases of Mg-3Al-1Zn-2.2/5Sr magnesium alloys, the type and formation theory of second phases in the as-annealed Mg-3Al-1Zn-2.2/5Sr alloys were investigated by scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and X-ray diffractometer (XRD) combined with Pandat thermodynamic calculation software. The results indicate that after homogenization annealing at 400 oC for 15 h and cooling in furnace, the fraction volume of Al in (Mg, Al)17Sr2 phase preliminarily formed in the as-cast structure of Mg-3Al-1Zn-2.2/5Sr alloys decreases slightly. In addition, a huge number of granular Al4Sr phases are formed along the edge of the (Mg, Al)17Sr2 phase in Mg-3Al-1Zn-2.2Sr alloy, while the change of (Mg, Al)17Sr2 is hardly to be observed in the microstructure of the alloy with 5% Sr addition.

Abstract:Mg-Zn-Zr-Y alloys containing quasicrystal phase were prepared by an as-cast method with water-cooling. On this base, the effects of different Zn and Y content (the same Zn/Y ratio) on microstructure and micro-hardness were also discussed. The results show that the increase of cooling rate by water-cooling can increase the volume fraction of quasicrystal phase (I-phase, Mg3YZn6) of Mg-Zn-Zr-Y alloy. The decreasing of grain sizes of the as-cast alloy is due to the increase of constitutional supercooling by Y addition. The solid solubility of Zn in α-Mg matrix mainly affects the hardness of the matrix, and the hardness of I-phase is much higher than that of the matrix. The liquidus temperature decreases substantially while the solid temperature does not change with Y addition, which weakens the hot cracking tendency of the ingot due to the decrease of freezing range.

Abstract:The effects of casting parameters on casting process of AA7050 alloy were investigated by coupling thermal, fluid flow and stress fields based on the parameters provided by an aluminum corporation. The results show that the casting speed has a prominent effect on stress field while the influences of casting temperature and water flow rate are not obvious. The optimization of casting parameters was performed through numerical simulation in order to solve hot tearing problem in 800 mm round billets

Abstract:Rare earth oxides Re2O3 (Re=Pr, Nd) doped SrTiO3 ceramics with the formula of [Re0.02Sr0.97(VSr)0.01]TiO3 (Re0.02Sr0.97TiO3: Re-STO) were prepared by a solid state reaction method. The X-ray diffraction (XRD) results indicate that Re-STO ceramics have a single cubic perovskite structure which is similar to that of pure SrTiO3. Scanning electron microscopy (SEM) analysis shows inhomogeneous grain size distribution in Re-STO ceramics with big grains of about 10 μm and small ones of about 1 μm, and the small grains normally exist in grain boundaries and/or triangle grain boundaries among big grains. The dielectric properties of Re-STO ceramics were measured by HP4294 precision impedance analyzer, JJC9906-A breakdown strength testing instrument and FMRL bias voltage testing system, and the energy storage characteristics was evaluated. The results show that the relative dielectric constants of Re-STO ceramics (Pr-STO: εr=1860; Nd-STO: εr=1670), prepared at the optimized sintering temperature of 1350 oC, increase by more than 5 times than that of pure STO ceramics (εr=300 kHz), while the dielectric loss of Re-STO ceramics still remains lower than 0.03 (1 kHz). The breakdown strength Eb of Re-STO ceramics is higher than 15 kV/mm. Under the bias voltage testing conditions used in this study, the εr of Re-STO ceramics changes within ±12%, and the relationship between energy storage density and bias voltage is in good line with quadratic parabola function. Therefore, Re-STO ceramics can be treated as linear dielectrics, which should be very promising for medium/high voltage solid state energy storage applications. Meanwhile, the relationship between the phase structure, microstructure, possible defect structure and the dielectric properties, energy storage characteristics of Re-STO ceramics were also discussed.

Abstract:The electronic structure and magnetic properties of Co-doped ZnS (zinc blende) were studied with the first-principle method using PW91 within the generalized gradient approximation (GGA) for exchange-correlation. Geometric parameters, formation energies, magnetic moments, density of states, and electron charge densities were investigated. It is found that the formation energy is less than 0 as one Co atom is doped into the middle of the super cell (2×2×2), which indicates that this structure is stable for Co-doping. And the density of states (DOS) near to the Fermi leVel (EF) indicates the presence of a half-metallic character which is caused by p-d hybridization between the Co 3d and S 3p. When two Co atoms are doped into the ZnS (zinc blende), antiferromagnetic (AFM) state is the most stable configuration in the system of Co-S-Co. But in the case of Co-S-Zn-S-Co, the most stable configuration is ferromagnetic (FM) state

Abstract:Microstructure and tensile properties of laser deposited Ti60A high temperature titanium alloy was investigated after 600 oC, 100 h isothermal exposure and cyclic thermal exposure. Results indicate that the volume fraction of α phase increases slightly after isothermal exposure. While the broken β and coarsened α platelets occur in the alloy after cyclic thermal exposure and the volume fraction of α phase even increases about 12%. The precipitation of fine ordered coherent Ti3Al and 100~150 nm hexagonal quaxi-S2 type ellipsoidal silicide (TiZr0.3)6Si3 is nearly the same in the alloy after isothermal or cyclic thermal exposure. The tensile properties of the alloy are significantly decreased after thermal exposure. In particular, the ductility of the alloy after cyclic thermal exposure is almost lost, which is closely related to the obvious microstructural changes produced by cyclic thermal stress

Abstract:The interrupted oxidation behavior of Hf and Y micro-alloyed TiAl-based alloys with high Nb content at 900 oC in static air was investigated. The results show that the addition of 0.5%Hf (mol%, similarly hereinafter) has few effects on the oxidation resistance of the high-Nb alloy, the addition of 0.1%Y improves the oxidation resistance, while the combined addition of 0.1%Y and 0.5% Hf enhances the adherence of oxide scale but reduces the oxidation resistance. Oxidized samples were examined by scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and X-ray diffraction analysis (XRD). It is found that the addition of 0.1%Y and the combined addition of 0.5%Hf and 0.1%Y promote the formation of continuous and compact Al2O3 oxide scale. The combined addition of 0.5%Hf and 0.1%Y into the high-Nb alloy results in the partial internal oxidation of the alloy, impairing the oxidation resistance of TiAl

Abstract:Porous Ti-Si materials were prepared by a combustion synthesis method. The atomic ratios of Ti:Si were 1:1, 5:4, 5:3 and 3:1. The combustion characteristics, phase composition, pore structure and microstructure of the products were investigated. It is found that, with the increase of Ti content, the rate of the combustion wave and the combustion temperature first increase and then decrease, and the highest combustion temperature is 2075 K. The main products are TiSi, Ti5Si4, Ti5Si3 and Ti5Si3 at the Ti:Si atomic ratios of 1:1, 5:4, 5:3 and 3:1, respectively. The open porosities of the products are within the range of 42.43%~49.42%. The median pore diameters are within the range of 64.10~18.11 μm and decrease with the increase of Ti content. The highest compressive strength is 23.15 MPa. The main pore formation mechanism includes the residual pores among the particles of the powder compacts, and the in situ pores owing to the molten silicon particles flowing during the combustion synthesis reaction. The large pores are formed by the interstitial hole combining with the in situ pores, and the small pores are formed by the decrease of the molar volume during the solution-precipitation process

Abstract:Based on TZM molybdenum alloy, powder metallurgy methods were using to prepare La-TZM alloy plates with solid-liquid doped rare earth lanthanum and substitution of organic carbon stearic for traditional graphite by mixing, pressing and sintering, hot-rolling, warm-rolling, and cold rolling. La-TZM alloy plates were heated at 300, 450, 600, 800 and 1000 oC in the furnace to calculate the mass loss of the samples. The oxidation behavior was analyzed by the differential thermal analysis. The results show that the tensile strength and elongation of La-TZM plate are 1361.74 MPa and 8.81%, respectively, higher than those of traditional TZM plate. The fiber of La-TZM alloy plate is slim and homogeneous. The second phase of La-TZM alloy plate is smaller and disperses homogeneously. The La-TZM alloy has a more compact structure due to the lanthanum doping. The minute lanthanum oxide particles are pinned at the grain boundaries and refine the grains. Oxide layer generated on the matrix surface can form a compact coating, which effectively blocks the surface from being corroded by oxidation. The oxidation resistance of La-TZM alloys is enhanced, expanding its application range

Abstract:NiO/Ni multilayers were deposited alternately by reactive magnetron sputtering and conventional magnetron sputtering. Phase structure, microstructure and photoelectric properties in different annealing environments were studied. XRD and TEM results indicate that NiO and Ni layers appear alternately in as-grown multilayers. Only NiO(111) preferred orientation is found in the films after atmosphere annealing, but multilayer structure still exist in the films after vacuum annealing, whose crystallization increases obviously. Both the as-grown and vacuum annealed films show a low visible light transmittance and a resistivity as low as 10-5 Ω·cm, while the films annealed in the air exhibit a high resistivity as well as a low transmittance of 49.3%.

Abstract:Cu-Ag alloys were prepared by the integrated technique of continuous casting and cold-drawing and finally aged. Mechanical and electrical properties of the alloys with different true strain η were measured. The change rules of their microstructure and mechanical and electrical properties were investigated and their strengthening mechanism and conductive mechanism were also discussed. The results show that with the increase of the true strain, the ultimate tensile strength and hardness of Cu-Ag alloys firstly increase significantly and then slowly and finally remarkably but the change rules of electrical conductivity with the increase of the applied strain is opposite completely. This preparation method of Cu-Ag alloys is simple and can improve their comprehensive performance

Abstract:The effects of FSP (friction stirring processing) on microstructure and properties of the Al3Zr/6063Al composite were investigated, which was obtained in 6063-5wt%(K2ZrF6) system. OM, XRD and SEM were used to observe the morphology, distribution and dimensions of in-situ Al3Zr particles, and then the properties were analyzed. It is found that reinforcement particles of the composite are finer and more uniform after FSP; matrix grains crush and grain shape changes; tensile strength and elongation become larger; the composite shows superplastic deformation, especially when the deformation temperature is 500 oC and strain rate 1.67×10-2 s-1, it achieves 348.16% elongation rate.

Abstract:A dark gray, uniform and better corrosion resistant Zn-Mn based conversion coating on the Mg-Li alloy was prepared using the phosphate baths. The temperature of phosphate solution was discussed in this experiment. The surface morphology of the conversion coatings was observed by scanning electron microscopy (SEM), and the chemical composition and crystal structure were analyzed by X-ray photoelectron spectroscopy (XPS), energy dispersive spectrometer (EDS) and X-ray diffraction (XRD). The corrosion resistance of Mg-Li alloy and phosphate conversion coatings were investigated by means of potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and a mass loss method. The results show that the Zn-Mn phosphate conversion coating is composed of Zn, Zn3(PO4)2, MnHPO4 and Mn3(PO4)2. The corrosion resistance of permanganate conversion coatings is improved greatly compared with that of Mg-Li alloy. When the temperature of phosphate solution is 45 oC, the phosphate conversion coating exhibits the smallest corrosion current density, the highest capacitance arc and minimum corrosion rate, so the conversion coating presents the best corrosion resistance behavior