Abstract:The Sr-W type planar hexagonal ferrite was synthesized by a sol-gel method, and its morphology and phase structure were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The microwave absorbing properties of the mixtures with different ratios of Ni/ferrite were studied by vector network analyzer (VAZ). The results demonstrate that with the increase of hexagonal ferrite content, the microwave absorbing peaks of the mixtures shift to higher frequencies, and when the mixture consists of 20% Ni and 80% Sr-W-type ferrite, its microwave absorbing performance is the most advantageous. When absorbing coating thickness is 2 mm, the minimum reflectivity and absorbing peak frequency is –20.69 dB at 12.08 GHz and the bandwidth less than –10 dB reaches 4 GHz. The absorbing peak shifts to low-frequency with the increase of absorbing coating thickness, and when the coating thickness reaches a certain value, the two absorbing peaks appear in the mixture in the frequency range of 2~18 GHz, which is of significance to explore the absorbing material with bandwidth effect.

Abstract:YAG:Ce precursors were synthesized via a homogeneous precipitation method with the addition of different molecular mass of PEG (PEG 6000 and PEG 10000) used as dispersant. The FT-IR spectra show that no significant difference is found between the precursors. SEM images indicate that the size of the primary particles with PEG is much smaller than that of the sample without PEG. Confirmed by the DSC traces and X-ray diffraction (XRD), the crystallization of YAG is a one-step process without any intermediate phase. The crystallization of YAG is significantly promoted and the oxidation of Ce3+ is inhibited by addition of PEG, which enhances the luminescent properties of YAG:Ce phosphor.

Abstract:The formability and the forming accuracy of materials will be greatly improved in high-velocity forming process. However, the fracture mechanism of materials in macro-micro scale keeps unknown or unclear yet. Herein, TA3 titanium alloy was adopted to investigate the fracture mechanism by Hopkinson bar test and analysis approaches of OM, SEM and stress-strain response. The results show that adiabatic shear bands (ASBs) induce the formation and the propagation of macroscale fracture, as well as softening in stress response; the fracture mechanism of TA3 titanium alloy during dynamic deformation in microscale is that spindle-shaped voids nucleate separately and then grow up to impenetrate each other, and finally micro cracks occur; the aggregation of the second-phase particles serves as the source for crack generation.

Abstract:A nanocomposite Mo-4wt% La2O3 cathode was prepared by a high-energy ball-milling and hot pressing technique. The sizes of lanthana particles in the nanocomposite Mo-La2O3 cathode are less than 100 nm; in contrast, the sizes of thoria particles are about 1~2 μm in a commercial W-4wt% ThO2 cathode. The average vacuum arc-starting field intensity of the nanocomposite Mo-La2O3 cathode is 2.97×107 V/m, which is 62.7% lower than that of the commercial W-ThO2. The nanocomposite Mo-La2O3 cathode exhibits superior electron emission performances, and its distribution area and thickness of electron emission spots are remarkably larger, as compared to those of the commercial W-ThO2 cathode. The size of oxide particles has a great effect on the electron emission performances and vacuum arc characteristics of cathode. The electron emission performance of Mo-La2O3 cathode will be improved with decreasing of the lanthana particles size. When La2O3 particle size decreases to less than 100 nm, the electron emission area and ability of the Mo-La2O3 cathode significantly increase. The much enhanced electron emission performance of the nanocomposite Mo-La2O3 cathode is attributed to the formation of a higher inter electric field and space-charge regions at the interphase boundaries between Mo and La2O3 phases.

Abstract:The isothermal hot compression tests of as-extruded Al-12Zn-2.4Mg-1.2Cu alloy were performed on a Gleeble-3500 thermo-simulation machine. Based on the Arrhenius-type constitutive model, the experimental stress-strain data over a wide range of temperatures (523~723 K), strains (0.1~0.6) and strain rates (0.001, 0.01, 0.1 and 1 s-1) were employed to develop a suitable constitutive model to predict the elevated temperature flow behavior. The effects of temperature and strain rate on deformation behavior were represented by Zener-Holloman parameter in an exponent-type equation. The influence of strain was incorporated in constitutive analysis by considering the effect of strain on material constants. Suitability of the developed constitutive model was evaluated by comparing experimental and predicted data in terms of correlation coefficient (R) and average absolute relative error (AARE). Results show that the values of R and ARRE are 0.995 82 and 6.66%, respectively, which indicate that the developed model considering the compensation of stain can predict flow stress of experimental alloy and has good correlation and generalization.

Abstract:Nickel-zinc ferrites (Ni-Zn ferrites) nanocomposites were prepared by a solvothermal method and characterized by X-ray diffraction (XRD), scanning electronic microscope (SEM) and vibrating sample magnetometer (VSM). The effects of solvothermal parameters such as ratio of Ni2+ to Zn2+, the temperature and the time of solvothermal reaction on the magnetic properties and the microstructures of Ni-Zn ferrites were investigated. Results demonstrate that with raising of reaction time, the particles become bigger and more homogeneous, and the saturation magnetization of the Ni-Zn ferrites nanocomposites get higher; and the formation temperature of Ni-Zn ferrites spherical particles is 180 °C; raising Ni2+ concentration in the Ni-Zn ferrites could not change their morphologies. The saturation magnetization of the Ni-Zn ferrites increases with the increase of Ni2+ in the product; it will reach the highest when Ni2+ concentration is up to x=0.30 while it will be the lowest when Ni2+ concentration is down to x=0.20.

Abstract:Dependence of microstructure, texture and tensile properties on working conditions (ram speed and initial billet temperature) in indirect extruded Mg-6wt%Sn alloys were investigated by optical microscope (OM), scanning electronic microscope (SEM), X-ray diffraction (XRD) and a standard universal testing machine. Results show that the grain size, the recrystallization fraction and the dynamic precipitate fraction of the alloys are greatly affected by the working conditions. Their texture intensities weaken as the ram speed and the initial billet temperature increase. Tested in the different working conditions, the ultimate tensile strengths of the Mg-6Sn alloys extruded at high working temperature (controlled by initial billet temperature and ram speed) are remarkably better than those at the medium and low temperatures. The tensile properties of the alloys extruded at the high working temperature are similar to those of a commercial AZ31 alloy extruded at the low temperature, showing the possibility of the development of high speed extruded Mg alloys based on Mg-6Sn alloy.

Abstract:Ag/graphene(Ag/GN) nanocomposites with different Ag contents (0 wt%, 30 wt%, 46 wt%, 56 wt%, 63 wt%) were prepared based on graphene oxide (GO) and AgNO3 by a chemical reduction method. The effects of Ag content on the morphology and the microstructure of Ag/GN nanocomposite were studied by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and Raman spectroscopy. The results indicate that GO and silver ions in reaction solution have been reduced to Ag/graphene nanocomposites. The obtained GN nanosheet is piled up by 3~4 carbon atom layers, and Ag nanoparticles are deposited on the surface of GN. The intercalation of Ag nanoparticles prevents the aggregation of graphene effectively, resulting in large specific surface area. The size and the distribution of Ag nanoparticles are related to Ag content. When Ag content is low, Ag nanoparticles with sizes of 25~50 nm are well dispersed and deposited on GN nanosheets uniformly. However, high Ag content (more than 46%) causes the agglomeration of Ag nanoparticles. Additionally, Ag nanoparticles enhance surface-Raman effect of graphene.

Abstract:In order to evaluate the application possibility of the Nb-Si based alloys as cutting tool materials, we investigated the microhardnesses and the macrohardnesses of three alloys (Alloy 1#: Nb-12Ti-16Si-16B, Alloy 2#: Nb-23.5Ti-16Si-10B, Alloy 3#: Nb-20Ti-16Si-1.5B) selected from NbB, Nb3B2 and Nb3Si primary phase regions, respectively, in liquidus projection of the Ni-Ti-Si-B quaternary system. The microhardnesses were measured at a load of 200 g for 15 s using Hx-1000 TM hardness tester. Macrohardness measurement was performed using a Rockwell C scale (HRc). High microhardnesses were obtained for the Nb-based intermetallics: NbB (16.58 GPa in Alloy 1#), Nb3B2 (10.08 GPa in Alloy 2#) and Nb3Si (12.12 GPa in Alloy 3#), which are attributed to strong covalent bonding and appreciable solid solution hardening in these phases. Furthermore, macrohardnesses (HRc) of these three alloys are all above 70, i.e. 77, 75 and 78, respectively, which are primarily provided by certain volume fractions of the hard intermetallic phases in the Nb-Ti-Si-B alloys. The macrohardness (HRc) values of these alloys are higher than those of carbon tool steels (HRc~65) and high speed steel (HSS, HRc~67).

Abstract:Small angle X-ray scattering technique was used to study the particle size of precipitated phase of Cu-0.69Cr-0.13Zr alloy aged at 470 °C, and the aging time was from 1.5 h to 3.5 h. The statistical particle size of precipitated phase is 4.97~5.48 nm, and with the aging time increasing, the precipitated phase particles have no obvious growth. When the aging temperature is 470 °C, and the time is 2.5 h, the particle size of the precipitated phase in the sample is about 5 nm measured by the method of transmission electron microscope. The two methods agree well with each other. It shows that the small angle X-ray scattering technique can be used for measuring the size of aging precipitation of Cu-0.69Cr-0.13Zr alloy and the experimental result is accurate. Compared with the transmission electron microscope measurement, the small angle X-ray scattering technique is of more statistical significance and more valuable.

Abstract:The purpose of the present work is to investigate the deformation failure behavior of tungsten alloy long rob penetrating into armor target by metallographic analysis and numerical simulation. Microstructure evolution of the residual projectile was studied using SEM and OM. The results show that mushroom-like-head of penetrator is formed during penetration due to severe plastic deformation, and W grains in the mushroom are elongated heavily. An adiabatic shear band is observed perpendicular to the penetration direction in the front mushroom about 1 mm, in which W grains seem dissolving due to local temperature rise, and micro-cracks are developed both in W grains and W-W interface. Numerical simulation shows that the mushroom forms and falls off continuously during penetrating, so the long rob becomes shorter for the erosion. Severe plastic deformation in the mushroom is similar to plastic flow, and the deformation localization occurs mainly upon the both sides or the front of the mushroom.

Abstract:The effect of the rare earth Y addition on the microstructure and mechanical properties of ZL205A alloy was studied by OM, SEM and XRD before and after heat treatment. The fluidity of the alloy was also tested. Results show that when the content of Y is 0.2wt% and 0.3wt%, the grains refinement effect is better. With the increase of Y, the θ phase distribution transforms from reticular into dendritic, and the yield strength and tensile strength decrease. Trace Y addition decreases the fluidity of ZL205A alloy. When the Y content is 0.3wt%, the tensile strength and the ductility increase significantly after T6 heat treatment. Heat treatment process can reduce the composition segregation of alloys and improve the microstructure, resulting in a better comprehensive mechanical performance. After adding a small amount of Y, the compound AlCuY, which has high melting point, low strength and is difficult to be melted, can decrease the amount of θ phase, which is an important reason to the declined mechanical properties.

Abstract:Influence of alloying element silicon on the thickness of interface diffusion, the recrystallized structures, the interface bonding strength, the microhardness of the matrix and interface for Cu/Al clod-rolling cladding in a heat treatment condition was investigated by measuring and observing the mechanical properties and microstructures of the composite interface. The results show that silicon is able to discourage the diffusion of Cu and Al atoms, control the growth of metallic compounds between Cu and Al, refine the grains and increase the microhardness of aluminium matrix. But silicon decreases the interface bonding strength at high heat treatment temperature for a long holding time.

Abstract:The damaged K403 superalloy blades were repaired and remanufactured by a powder metallurgy repairing process (china powder metallurgy, CPM), using nickel-based superalloy powder containing a small amount of B alloy and nano-Ni powder separately. X-ray diffraction, scanning electronic microscope (SEM), EDX, and EPMA electro-probe were employed to investigate the phase composition, morphology and microstructure of the repaired areas. Meanwhile, performances of repairing areas and interface bonding were evaluated. Finally, the mechanism on the densification of repairing areas and the bonding of interface were also examined. The results show that the damaged blades could be restored to the original shape and size by CPM process, using appropriate repairing powder. In addition, it shows better properties using B alloy powder addition for K403 repairing. The diffusion of element B plays a key role in the densification of repairing areas and bonding of interface, in which the reaction equation could be expressed as NimBn+(Cr, W)→γ+(Cr2,W)B2. According to calculation, in the CPM process, the concentration of element B in the interface could be decreased to below the eutectic concentration.

Abstract:The transition metal M (Ti, V, Mn, Co) substituting for parts of Li in the LiNH2 hydrogen storage materials have been studied by plane wave pseudopotential methods based on the first principles and the density functional theory. The crystal and electronic structure, binding energy, and H vacancy formation energy for Li(M)NH2/M(=Ti, V, Mn, Co) were calculated. Results show that the stability of the Li(M)NH2 and the bond strength between N and H atoms are reduced when the Li atoms of LiNH2 are partially replaced by the Ti, V, Mn, or Co atoms. The best effect is got by Ti doping. The calculated vacancy formation energy of Li(M)NH2 is 1.365, 0.829, 0.486, and –0.079 eV for M=Ti, V, Mn and Co, respectively. It is found that the decreased dissociation energy of H is obtained by Ti, V, Mn, Co substitution to Li of LiNH2, showing the improvements of the dehydrogenation ability for Li(M)NH2. The effect of Ti is better as a catalyst than that of V, Mn, and Co.

Abstract:The morphology and growth behavior of interfacial intermetallic compound (IMC) layer for the Sn3.0Ag0.5Cu0.05Cr (SACCr)/Cu joints after isothermal aging at 150 °C for 0, 168, 500 and 1000 h were investigated, and they were compared with Sn3.0Ag0.5Cu (SAC). The results show that the trace Cr dispersed or dissolved in SAC solder effectively inhibits the IMC layer growth at the interface of SACCr/Cu joints. The longer the aging time, the more obvious the inhibiting effect of Cr on the overgrowth of IMC layer of solder/Cu joints. The average thickness of IMC layer of SACCr/Cu solder joints is about 5.13 μm after aging for 1000 h, only 45% of that of the SAC/Cu solder joints.

Abstract:Ceramic coatings were prepared by a constant current mode on the surface of 2A12 aluminum alloy, which employed the rare earth cerium dioxide (CeO2) adding to silicate electrolyte. Effects of CeO2 concentration on the morphology, organization, roughness, hardness and corrosion resistance of the micro-arc oxidation ceramic coatings were analyzed using scanning electron microscope, X-ray diffraction, roughness tester, hardness tester and polarization curve, respectively. The results illustrate that surface roughness and pore diameter of the coatings decrease after adding CeO2, while the thickness increases. Most of the CeO2 deposit on coatings in the form of CeO2 compound. A few of CeO2 participate in reaction and generate CeO and CeAl11O8. CeO2 promotes phase transformation from γ-Al2O3 to α-Al2O3; furthermore, the hardness of coatings is improved. When the concentration of CeO2 is in the range of 3 g/L~4 g/L, the corrosion resistance of the coatings is optimal.

Abstract:Powder metallurgical Ti-5Al-2.5Sn ELI (extra low interstitial) alloy was prepared in a container by hot isostatic pressing (HIP). The effects of HIP temperature, particle size of powders and heat treatment temperature on the microstructure have been investigated. Particle morphology would be observed in the powder compact sample, with its relative density of 99.2% at the holding temperature of 800 °C. Within the temperature ranging from 900 to 940 °C, the microstructure has developed into fully dense and fine equiaxed grains. When the sample is compacted in α phase region, significant diffusion of Fe can be hardly observed at the boundary of the container and the compact; in α+β or β phase region, fast diffusion of Fe in β phase may do harm to surface quality of the powder compact. The mean grain size and the residual porosity of PM alloy increase with the increase of powders’ particle size. There is no obvious change in the microstructure of PM alloy after heat treatment in α phase region. Temperature induced porosity doesn’t appear until the heat treatment temperature rises up to 1000 °C.

Abstract:The corrosion inhibition behaviors of sodium phosphate (SP) on AZ31 magnesium alloy in 3.5 wt% sodium chloride solution were investigated by electrochemical impedance spectroscopy (EIS), potentiodynamic polarization curve, static weight-loss test and scanning electron microscope (SEM). The results indicate that SP protects AZ31 magnesium alloy from corrosion in 3.5 wt% sodium chloride solution, and the inhibition efficiency increases with higher SP content. When the SP concentration is 1.0 g/L, the inhibition efficiency is up to 81.5%. Moreover, according to the results of SEM, it is found that the corrosion inhibition of AZ31 magnesium alloy by SP is attributed to the protective film containing Mg(OH)2 and Mg3(PO4)2 formed on the electrode surface. The compact film, which reduces the substrate contact with Cl-, thus inhibits the anodic reaction of the magnesium alloy.

Abstract:A structurally toughened metal matrix composite reinforced by cast tungsten carbide particles (WC/W2CP) was fabricated by vacuum fusion sintering. Microstructure and properties of the particle-reinforced regions (WC/W2CP-NiCrBSi) in the composite reinforced by primary and modified WC/W2CP were investigated by SEM, EDS, microhardness testing and image analyzing. Effects of the surface-modified WC/W2CP on the wear behavior of the composite were estimated on a ring-disc wear tester at room temperature and 600 °C. The results show that the dissolution of surface-modified WC/W2CP is effectively restrained and the content of the residual WC/W2C eutectic in particle is 2.6 times of the primary WC/W2CP. The wear rate of the composite reinforced by modified WC/W2CP decreases significantly compared with the composite reinforced by primary WC/W2CP at room temperature and 600 °C. The laminated structure self-protecting layers are formed on the worn surface of the composite at 600 °C, resulting in a lower wear rate than that at room temperature.

Abstract:Using palladium chloride (PdCl2) as the palladium precursor, ethanol as reducing agent and cetyltrimethylammonium bromide (CTAB) as a stabilizer and guiding agent, Pd nanoplates were synthesized via photothermally assisted solution approach with visible light from a commercial incandescent lamp as light source. The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED) and UV-visible absorption spectroscopy. The effect of CTAB amount on the growth morphology and size of palladium nanomaterials was also investigated. The electrocatalytic properties of the nano-Pd modified glassy carbon electrode for ethanol oxidation were investigated by cyclic voltammetry. The results indicate that the morphology and size of the Pd nanoparticles can be controlled by adjusting the mole ratios of PdCl2 to CTAB. The polygonal Pd nanoplates with a narrowly distributed size of 46 nm are obtained when the mole ratio of PdCl2 to CTAB is 1:80 and the irradiation time is 6 h, which show the excellent electrocatalytic activity and anti-poisoning faculty for the ethanol oxidation.

Abstract:The third-generation hyperbranched polyester (HBPE-3) was synthesized with pentaerythrite as core molecule and 2, 2-dimethylol propionic acid as AB2 monomer using step by step polymerization process at first. Then the Ag-Cu alloy particles were synthesized in HBPE-3 by a reductive technique. The synthesized hyperbranched polyester and Ag-Cu alloy particles were characterized by Fourier transform infrared spectroscopy (FT-IR), UV-visible absorption spectra (UV-vis), X-ray diffraction, laser light scattering, scanning electron microscopy (SEM) and thermogravimetric (TG). The results show that there exists HBPE-3 on the Ag-Cu alloy particles surface. The Ag-Cu alloy particles have strong absorption peaks at around 210 and 450 nm. The XRD patterns of Ag-Cu alloy particles are in agreement with the standard cards. Most of particle sizes of Ag-Cu alloy particles are around 1.2 μm. The Ag-Cu alloy particles have good thermal stability.

Abstract:Dry sliding wear tests of TC11 alloy sliding against GCr15 and M2 steels were performed at 400, 500 and 600 °C using a high-temperature wear tester. The effect of counterface materials on elevated-temperature wear behavior of TC11 alloy was studied. Results show that irrespective of counterface materials, the wear rate of TC11 alloy decreases with the increase of temperature, and TC11 alloy presents excellent elevated-temperature wear resistance. In most cases, with the increase of the load, the wear rate keeps a lower value with a small fluctuation. However, the wear rate of the TC11 alloy noticeably increases under more than 200 N at 400 °C with GCr15 steel as counterface and under more than 200 N at 400, 500 °C with M2 steel as counterface. Compared with GCr15 steel, M2 steel results in slight increase of the wear rate for the TC11 alloy. The high wear resistance of TC11 alloy is attributed to the protective role of tribo-oxide layer. The hard M2 steel (compared with soft GCr15 steel) is liable to damage the protective role of tribo-oxide layer.

Abstract:W-10wt%Ti alloys prepared by solid state sintering were treated at –196 °C. The properties and microstructures of W-10wt%Ti alloys were analyzed comparatively by microhardness measurement, X-ray diffraction, SEM and TEM. The results show that after cryogenic treatment, W-10wt%Ti alloys are still composed of W-rich and Ti-rich solid solution. The content of Ti-rich phase increases and then decreases with prolonging the cryogenic time, but there is no obvious change for the Ti-rich phase in the sample with 24 h cryogenic treatment compared with the untreated sample. The alloy grain size also increases and then decreases, and it is reduced by 24.6% after 24 h cryogenic treatment, reaching the minimum; meanwhile, the grain sizes are uniformly distributed. Cryogenic treatment can significantly improve the microhardness and relative density of WTi10 alloy, and the hardness after 24 h cryogenic treatment is about 2.5 times higher than that of originality; the preferred orientation of the alloy cryogenic treated for 24 h is changed from (110) to (110) and (200).

Abstract:The non-magnetic Cu60Ni40 alloy substrates containing strong cube texture were prepared by rolling assisted biaxially textured technology (RABiTS). The surface textures of the Cu60Ni40 alloy substrates after cold-rolling and the recrystallization treatment were studied. The results show that the key factors that influence grain orientation in Cu60Ni40 alloy substrate are the total amount of rolling deformation and recrystallization annealing process. Through the large deformation of cold-rolling, the strong copper-type rolling texture in the Cu60Ni40 alloy substrates can be obtained. The content of the cube texture (≤10°), the fraction of small angle and Σ3 grain boundaries in the Cu60Ni40 alloy substrates prepared by optimized cold rolling and two-step recrystallization annealing process are 99.7%, 95.1% and 0.1%, respectively.

Abstract:A method for recycling ZM6 magnesium alloy chips and Mg-Ce alloy chips by hot extrusion was studied. Effect of extruding times on microstructure and mechanical properties of the alloy was analyzed and the fracture behavior was discussed. The results indicate that after the first extrusion, tensile strength and elongation to failure of the alloy are very low because Mg-Ce intermediate alloy chips have not been broken. Tensile strength and elongation to failure of the alloy are obviously improved because of well-proportioned distribution of Mg-Ce intermediate alloy chips after the fifth extrusion. Ultimate tensile strength and elongation to failure of the alloy increase with the extrusion times increasing. Increasing range decreases with the extrusion times increasing. After the fifth extrusion, ultimate tensile strength and elongation to failure of the alloy are 300 MPa and 14.8%, respectively. Fracture mode of the specimen is transgranular dimple fracture.

Abstract:Porous one-dimensional nanobelts of vanadium nitride (VN) with homogenous size were prepared by a hydrothermal method combined with subsequent nitriding treatment for anode materials of lithium ion battery. The samples were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) as well as X-ray photoelectron spectroscopy (XPS). Results show that the specific capacitance of the VN nanobelts can reach 374 mAh/g for the first time of charge/discharge under the current density of 40 mA/g. The coulomb efficiency is above 97% after stabilization of four cycles and the capacitance can keep 250 mAh/g after 100 cycles.

Abstract:Fe-based binary mixed metal oxides (MFe2O4, M= Co, Zn, Ni, ……) has attracted prominent interest as advanced anode materials for high-performance lithium-ion batteries (LIBs), thanks to their appealing advantages including low cost, non-toxicity, high theoretical specific capacity, environment friendly properties, and so on. In this review, we mainly introduced synthetic methods, micro-structures and electrochemical Li-storage performance of the MFe2O4 electrodes as striking anodes for next-generation LIBs. Also efficient strategies were proposed to well address lots of issues that the MFe2O4 anodes faced in their commercial application. Furthermore, the future trends and prospects were highlighted herein.