Densification behavior of mechanically milled Cu–8 at% Cr alloy and its mechanical and electrical properties

Synthesis and consolidation behavior of Cu–8 at%Cr alloy powders made by mechanical alloying with elemental Cu and Cr powders,and subsequently,compressive and electrical properties of the consolidated alloys were studied.Solid solubility of Cr in Cu during milling,and subsequent phase transformations during sintering and heat treatment of sintered components were analyzed using X-ray diffraction,scanning electron microscopy and transmission electron microscopy.The milled powders were compacted applying three different pressures(200 MPa,400 MPa and 600 MPa)and sintered in H2atmosphere at 900 1C for 30 min and at 1000 1C for 1 h and 2 h.The maximum densification(92.8%)was achieved for the sample compacted at 600 MPa and sintered for 1000 1C for 2 h.Hardness and densification behavior further increased for the compacts sintered at 900 1C for 30 min after rolling and annealing process.TEM investigation of the sintered compacts revealed the bimodal distribution of Cu grains with nano-sized Cr and Cr2O3precipitation along the grain boundary as well as in grain interior.Pinning of grain boundaries by the precipitates stabilized the fine grain structure in bimodal distribution.     

Microstructure heterogeneity and creep damage of DZ125 nickel-based superalloy

The creep behavior of the DZ125 superalloy at high temperatures has been investigated based on the creep properties measurement and microstructure observations. The experimental results show that, after full heat treatment, the fine and coarser cuboidal γ0precipitates distributed in the dendrite arm and inter-dendrite regions, respectively, the boundaries with various configurations located in the inter-dendrite regions. In the primary creep stage, the cuboidal γ0phase in the alloy transformed into the rafted structure along the direction vertical to the stress axis.The dislocations slipping and climbing over the rafted γ0phase are attributed the deformation mechanism of the alloy during steady-state creep.The(1/2)?1 1 0? dislocations slipping in the γ matrix and ?1 1 0? super-dislocations shearing into the γ0phase are the deformation mechanisms of the alloy in the latter stage of creep. And then the alternate slipping of dislocations results in the initiation and propagation of the micro-cracks along the boundaries until the occurrence of the creep fracture. Since the grain boundaries with various angles relative to the stress axis distribute in the different regions, the initiation and propagation of micro-cracks along the boundaries display the various features.& 2014 Chinese Materials Research Society. Production and hosting by Elsevier B.V. All rights reserved.     

Grain size-dependent electrical resistivity of bulk nanocrystalline Gd metals

The electrical resistivity of the as-consolidated and coarse-grained bulk gadolinium(Gd) metals was studied in the temperature range of 3-315K.The experimental results showed that with decrease in the grain size of Gd grains from micrometer to nanometer range,the room temperature electrical resistivity increased from 209.7 to 333.0 μΩcm,while the electrical resistivity at the low temperature of 3K was found to increase surprisingly from 16.5 to 126.3 μΩcm.The room temperature coefficient resistivity(TCR) values were obtained as 39.2×10-3,5.51×10-3 and 33.7×10-3K-1.The ratios of room temperature to residual resistivity [RRR=ρ(300K)/ρ(3K)] are 2.64,11.0,respectively,for the as-consolidated samples at 280℃ and 700℃ with respect to that of the coarse-grained sample.All results indicate the remarkable influence of the nanostructure on the electrical resistivity of Gd due to the finite size effect and large fraction of grain boundaries.     

Porous SiC ceramics fabricated by quick freeze casting and solid state sintering

Porous SiC ceramics with uniform microstructure were fabricated by quick freezing in liquid nitrogen and solid state sintering.Poly(vinyl alcohol)(PVA) was added as binder and pore morphology controller in this work.The microstructure and mechanical properties of porous SiC ceramics could be controlled by the composition of the aqueous slurries.Both solid content of the slurries and PVA content impacted on the pore structures and mechanical properties of the porous SiC ceramics.The solid content of slurries and PVA content varied from 60 to 67.5 wt%and 2-6 wt%,respectively.Besides,the grain morphology of ceramics was also tailored by changing the sintering temperature from 2050 to 2150 ℃.Porous SiC ceramics with an average porosity of 42.72%,flexural strength of 59.28 MPa were obtained at 2150 ℃ from 67.5 wt% slurries with 2 wt% PVA.     

High temperature oxidation behavior of aluminide on a Ni-based single crystal superalloy in different surface orientations

An investigation on oxidation behavior of coated Ni-based single crystal superalloy in different surface orientations has been carried out at1100 ℃. It has been found that the {100} surface shows a better oxidation resistance than the {110} one, which is attributed that the {110}surface had a slightly higher oxidation rate when compared to the {100} surface. The experimental results also indicated that the anisotropic oxidation behavior took place even with a very small difference in the oxidation rates that was found between the two surfaces. The differences of the topologically close packed phase amount and its penetration depth between the two surfaces, including the ratio of α-Al2O3 after 500 h oxidation, were responsible for the oxidation anisotropy.     

Fabrication of fine spongy nanoporous Ag-Au alloys with improved catalysis properties

Fine NP-AgAu(nanoporous AgAu) alloys with spongy structure was fabricated by chemical dealloying from rapidly solidified amorphous precursors Ag_(38.75-x)Cu_(38.75)Si_(22.5)Au_x(x=0, 0.5, 1 and 5). The results indicate that the addition of small content Au in precursor can refine both the ligaments and pores obviously. Among the present components of the precursors, NP-AgAu alloys dealloying from Ag_(37.75)Cu_(38.75)Si_(22.5)Au_1 had the finest spongy structure. The size of pores was 5–10 nm and the grain size of ligaments was 10–20 nm. It also had the highest surface area of 106.83 m~2g~(-1) and the best catalytic activity towards electro-oxidation of formaldehyde with the peak current of 665 mA mg~(-1).     

Electroch emical properties and interfacial reactions of LiNi0.5Mn1.5O4-δ nanorods

LiNi0.5Mn1.5O4-δ which possesses a high voltage of 4.7 V vs.Li+/Li and stable structure has been considered as a promising cathode material for high energy Li-ion batteries.In this study,well-crystalli...     

Mechanical and thermal properties of NpO2 using LSDAt U approach

The elastic constants,bulk modulus,shear modulus,Young’s modulus,Debye temperature,isobaric heat capacity and minimum thermal conductivity are estimated for NpO2 using plane-wave pseudopotential method within the local spin density approximation plus Hubbard U(LSDAtU) theory.The computed lattice constants are in good agreement with the available experimental results and then three independent elastic constants were computed by means of the stress–strain method.From the knowledge of the elastic constants,the values of Young’s modulus,Poisson,Debye temperature and minimum thermal conductivity are obtained and they are 218 GPa,0.288,453.5 K and0.99 Wm-1K-1,respectively.The obtained mechanical and thermal properties of NpO2 are in agreement with the previous experimental and theoretical data.Our investigations which are unobtainable from previous report can provide valuable reference in the future.     

A first-principles study of displacive β to ω transition in Ti-V alloys

The ground state properties of β and ω phases in Ti-(0–30 at%)V alloys were calculated, and subsequently thermodynamics and energy barriers of the displacive β to ω transition were investigated by first-principles. The results show that the lattice parameters of β and ω phases decreases with increasing V content in Ti-V alloys. The principal lattice strains for the β to ω transition are highly compositional dependent, and the volume variation decreases with increasing V content. The mechanical stability of the ω phase increases initially at the V content around 10 at% and then decreases with increasing V content. Based on the quasiharmonic Debye model, a metastable diffusionless phase diagram has been established, showing that the ω phase is thermodynamically more stable than the β phase at room temperature, anticipating a spontaneous transition from β to ω phases in Ti-V alloys. The calculations of energy pathways indicate that there is an energy barrier during the displacive βto ω transition in Ti-V alloys at temperatures from 100 to 500 K, but not at 0 K.     

Activated carbon derived from rice husk by NaOH activation and its application in supercapacitor

Four activated carbon(AC) samples prepared from rice husk under different activation temperatures have been characterized by N2adsorption–desorption isotherms, thermogravimetric analysis(TGA–DTA), Fourier transform infrared spectroscopy(FTIR) and scanning electron microscopy(SEM). The specific surface area of AC sample reached 2681 m2 g 1under activation temperature of 800 1C. The AC samples were then tested as electrode material; the specific capacitance of the as-prepared activated carbon electrode was found to be 172.3 F g 1using cyclic voltammetry at a scan rate of 5 mV s 1and 198.4 F g 1at current density 1000 mA g 1in the charge/discharge mode.& 2014 Chinese Materials Research Society. Production and hosting by Elsevier B.V. All rights reserved.     

Structural and dielectric study of nano-crystalline single phase Sn1−xNixS (xNi=0–10%) showing room temperature ferromagnetism

SnS is a promising Ⅳ-Ⅵ semiconductor,which is very less explored for diluted magnetic semiconducting and dielectric applications.In this study,the Ni doping(x_(Ni)=0-10mol%) effects on SnS host lattice were investigated.A simple and low cost co-precipitation technique was employed to grow Ni doped SnS powders.The X-ray diffraction confirmed single phase orthorhombic structure with a nano-crystalline nature that was further verified through the surface structure observed by scanning electron microscopy.Near edge x-ray absorption fine structure spectroscopy revealed a shift in the Ni absorption edge towards higher energy,depicting the formation of Ni~(+3) oxidation state.The impedance measurements,in the frequency range 1 kHz to 20 MHz,depict that owing to the excellent sensitivity to the electromagnetic radiations at the low energy,the Ni doped SnS finds potential applications in various energy related devices.Vibrating sample magnetometer measurements have elucidated room temperature ferromagnetism,which depicts potential memory device applications.     

Epoxy/α-alumina nanocomposite with high electrical insulation performance

An experimental study was conducted to improve the electrical insulation of epoxy resin. The effects of boehmite, γ-alumina and α-alumina nanoparticles on the volume resistivity, dielectric strength and glass transition temperature of epoxy nanocomposites were investigated. The results showed that α-alumina nanoparticles displayed obvious advantages in enhancing electrical insulation performance of epoxy nanocomposites, compared to boehmite and γ-alumina nanoparticles. The direct current volume resistivity and breakdown strength of epoxy nanocomposite with 2.0 wt% α-alumina nanoparticles was improved to 2.2 × 10~(18)Ω cm and76.1 kV mm~(-1) respectively. And these improved values of electrical insulation properties are much higher than these of epoxy nanocomposites reported in previous studies. The main reason of these improvements may be that the epoxy/α-alumina interaction zone was enhanced by crosslink.     

Effect of La0.8Sr0.2Co0.2Fe0.8O3-δ morphology on the performance of composite cathodes

In the present work,one dimensional La0.8Sr0.2Co0.2Fe0.8O3 δ(LSCF) nanofibers with the mean diameter of about 100 nm prepared by electrospinning were deposited on Gd0.2Ce0.8O1.9(GDC) electrolyte followed by sintering to form one dimensional LSCF nanofiber cathode. And LSCF/GDC composite cathodes were formed by introducing GDC phases into LSCF nanofiber scaffold using infiltration method. The polarization resistances for the composite cathode with an optimal LSCF/GDC mass ratio of 1/0.56 are 0.27,0.14 and 0.07 Ω cm2at 650,700 and750 1C,respectively,which are obviously smaller than 2.26,0.78 and 0.29 Ω cm2of pure LSCF nanofiber cathode. And the activation energy is1.194 eV,which is much lower than that of pure LSCF nanofiber cathode(1.684 eV). These results demonstrate that the infiltration of GDC into LSCF nanofiber scaffold is an effective approach to achieve high performance cathode for solid oxide fuel cells(SOFCs). In addition,the performance of composite cathode in this work was also compared with that of our previous nanorod structured LSCF/GDC composite cathode.     

Phase stability and thermal conductivity of ytterbia and yttria co-doped zirconia

Rare earth oxides doping has been extensively investigated as one of the effective methods to lower thermal conductivity of 4.55 mol% Y2O3stabilized ZrO2(YSZ) thermal barrier coatings(TBCs).In the present work,5–6 mol% Yb2O3and Y2O3co-doped ZrO2ceramics were synthesized by solid reaction sintering at 1600 1C.The phase stability of the samples after heat treatment at 1500 1C was investigated.Yb2O3and Y2O3co-doped zirconia,especially when Yb2O3/Y2O3≥1,contained less monoclinic phase than single Yb2O3or Y2O3phase doped zirconia,indicating that co-doped zirconia was more stable at high temperature than YSZ.The thermal conductivity of the 3 mol% Yb2O3+3 mol% Y2O3co-doped ZrO2was 1.8 W m 1K 1at 1000 1C,which was more than 20% lower than that of YSZ.     

Properties of garnet-type Li6La3ZrTaO12 solid electrolyte films fabricated by aerosol deposition method

The garnet-type Li_6La_3ZrTaO_(12)(LLZT) solid electrolyte films were fabricated by aerosol deposition(AD)method.Ball-milled LLZT powder with a cubic garnet structure and a particle size of 1-2 urn was used as raw material and deposited directly on a SUS316L or a glass substrate via impact consolidation.As-deposited LLZT film has a cubic garnet structure but contains Li_2CO_3 and La_2Zr_2O_7 phases.SEM observation revealed that the film consists of LLZT particles fractured into submicron size.The impurity phase formation during AD process was caused by the local heating by the collision between LLZT particles and deposition surface and reaction with CO_2.The Li~+ ion conductivity of LLZT film was estimated to be 0.24 × 10~(-5)S cm~(-1) at room temperature.Electronic conductivity of LLZT film was confirmed to be around 10~(-12) S cm~(-1),indicating the dominant Li~+ ion conduction of LLZT film.     

Effect of CuO addition on the sintering temperature and microwave dielectric properties of CaSiO3– Al2O3 ceramics

CuO-doped CaSiO3–1 wt% Al2O3 ceramics were synthesized via a traditional solid-state reaction method, and their sintering behavior,microstructure and microwave dielectric properties were investigated. The results showed that appropriate CuO addition could accelerate the sintering process and assist the densification of CaSiO3–1 wt% Al2O3 ceramics, which could effectively lower the densification temperature from1250 1C to 1050 1C. However, the addition of CuO undermined the microwave dielectric properties. The optimal amount of CuO addition was found to be 0.8 wt%, and the derived CaSiO3–Al2O3ceramic sintered at 1100 1C presented good microwave dielectric properties of εr?7.27,Q f?16,850 GHz and τf? 39.53 ppm/1C, which is much better than those of pure CaSiO3 ceramic sintered at 1340oC(Q f?13,109 GHz).The chemical compatibility of the above ceramic with 30 Pd/70 Ag during the cofiring process has also been investigated, and the result showed that there was no chemical reaction between palladium–silver alloys and ceramics.& 2014 Chinese Materials Research Society. Production and hosting by Elsevier B.V. All rights reserved.     

Infield superconducting properties of nano-sized Ag added Cu_(0.5)Tl_(0.5)Ba_2Ca_2Cu_3O_(10-δ)

Infield superconducting properties of {(Ag)_x/CUTl-1223};(x = 0, 0.5,1.0.2.0 and 4.0 wt %) nanoparticlessuperconductor composites were investigated under different applied magnetic field up to H = 8 T. The increase in critical temperature {T_c(0)} and decrease in normal state resistivity(p_o) were observed with increasing contents of Ag nanoparticles in CuTl-1223 superconducting matrix. The value of T_c~(onset)(K) remained almost unaffected by applying external magnetic field, but a decreasing trend in T_c(0) was observed by increasing the value of external applied magnetic field. The transition region below T_c~(onset)(K) showed Arrhenius behavior due to thermally activated flow of magnetic vortices. Enhancement in flux flow activation energy(U_o) and suppression in transition width(ΔT) of CuTl-1223 phase with addition of Ag nanoparticles showed the improvement in flux pinning strength of superconductor.     

Bionic titania coating carbon multi-layer material derived from natural leaf and its superior photocatalytic performance

Bionic titania coating carbon multi-layer material was fabricated by employing canna leaves as substrate and carbon precursor. Titania nanocrystals were assembled and coated on the natural films. The carbonation treatment under pure N_2 atmosphere yielded the ultrathin multi-film hybrid material. The carbon layer was coated with small anatase titania crystallite(8–10 nm) and possessed a highly specific surface area of 248.3 m~2 g~(-1). Examination using UV–visible spectrophotometer(UV–vis) showed that the band gap of the multi-layer material was reduced to 2.75 eV, and the hydrogen production by photocatalytic splitting of water under visible light irradiation was about 302 μmol g~(-1) after six hour.     

Microstructure, mechanical and thermo-physical properties of hot-pressed Al2O3-GdAlO3-ZrO2 ceramics with eutectic composition

A low cost chemical co-precipitation method was employed to fabricate nanoscale Al_2O_3-GdAlO_3-ZrO_2 powder with eutectic composition. A careful control of reaction conditions was required during the preparation. The synthesized nanopowders exhibited a particle size of 20-200 nm, and were highly dispersive and uniform. The results showed that calcination temperature had an important influence on the phase constituents of the nanopowders. With increasing the calcination temperature, a phase transformation from θ-Al_2O_3 to α-Al_2O_3 and a thermal decomposition from Gd_3 Al_5O_(12)(GdAG) to GdAlO_3 and α-Al_2O_3 occurred in sequence. A calcination temperature of 1300 ℃ was needed for the crystallization of α-Al_2 O_3. These nanosized powders were consolidated via hot pressing to produce a fully densified ceramic composite with eutectic composition. The Al_2O_3-GdAlO_3-ZrO_2 ceramic hot-pressed at 1500 ℃ exhibited a relative density of 99.4%, a flexural strength of 485 MPa and a fracture toughness of 6.5 MPa m~(1/2). The ceramic had a thermal conductivity of 1.9 W m K~(-1) at 1200 ℃ and a thermal expansion coefficient of 9.49 ×10~(-6) K~(-1) at 1100 ℃.     

Structure evolution of Y2O3 nanoparticle/Fe composite during mechanical milling and annealing

Fe-25 wt% Y2O3composite powders have been fabricated by mechanical milling(MM) Fe powders of 100 μm in diameter and Y2O3nanoparticles in an argon atmosphere for the milling periods of4,8,12,24,36,and 48 h,respectively.The features of these powders were characterized by using X-ray diffraction(XRD),scanning electron microscopy(SEM),electron probe micro analyzer(EPMA) and transmission electron microscopy(TEM).The experimental results showed that the mean particle size and crystalline size of MM powders decreased with the milling time increasing.All the elements distributed homogenously inside the powders after 48 h of MM.The lattice constant of the matrix α-Fe kept constant with the milling time,and no solid solution took place during MM process.After 8 h of MM,the α-Fe in each powder became nanocrystalline.After 48 h of MM,Y2O3changes from nanostructure into amorphous structure,and the crystalline size of α-Fe further decreased to 10 nm.The Y2O3in the powders mechanically milled for 48 h kept the amorphous structure after being annealed at 400 1C,and starts to crystallize when the powders are annealed at 600 1C.The amorphous Y2O3contains a small amount of Fe,and crystalline FeYO3appears at 800 1C.