High temperature fracture behavior of tungsten fiber reinforced copper matrix composites under dynamic compression

W_f/Cu₈₂Al₁₀Fe₄Ni₄ composite was fabricated by flow casting method. Dynamic compression tests with strain rate of 1600 s⁻¹ at 20 °C, 200 °C, 400 °C and 600 °C were finished by means of Split Hopkinson Pressure Bar (SHPB). The results showed that the composites possessed obvious high temperature softening behaviors. The damages of W_f/Cu₈₂Al₁₀Fe₄Ni₄ composites all occurred within the tungsten fibers when compressed at 20 °C, 200 °C and 400 °C, indicating that the interface strength of the composites was high. While the damages of the composites occurred either in the tungsten fibers or in the matrix at 600 °C, in addition, the melt of matrix alloy also occurred. Microstructure of the composites after dynamic compressing at 600 °C was analyzed by transmission electron microscope (TEM), observation revealed that there were a lot of high-density dislocations, stacking faults and twins existing in the matrix. It was also found that the precipitated phase in the matrix played the role of the second phase strengthening.     

Magnetoelectric and dielectric properties of Ni0.5Cu0.5Fe2O4–Ba0.5Pb0.5Ti0.5Zr0.5O3 ME composites

The (x) Ni_0.5Cu_0.5Fe₂O₄ + (1−x) Ba_0.5Pb_0.5Ti_0.5Zr_0.5O₃ ME composites have been synthesized by a standard ceramic method. The presence of single phase in x = 0 and x = 1 as well as two phases in x = 0.15, 0.30 and 0.45 composites has been confirmed by XRD. The dielectric constant (ε′) and dielectric loss (tan δ) have been studied as a function of temperature and frequency. These composite materials exhibit maximum dielectric constant with a variation of frequency and temperature. The composite 15% Ni_0.5Cu_0.5Fe₂O₄ + 85% Ba_0.5Pb_0.5Ti_0.5Zr_0.5O₃ had the highest magnetoelectric voltage coefficient of 0.248 mV/cm Oe at room temperature among the studied composites.     

Effect of Nd content on microstructure and mechanical properties of Grf/Al composite

M40 graphite fibre reinforced Al-17Mg matrix composites with different neodymium (Nd) content (Al-17Mg, Al-17Mg-0.2Nd, Al-17Mg-0.5Nd and Al-17Mg-2Nd) were fabricated by pressure infiltration method. Microstructure of Gr_f/Al composites was investigated by XRD, SEM, TEM and HRTEM. Effect of Nd on microstructure and mechanical properties of Gr_f/Al composites were deeply discussed. Al₃Mg₂ and Al₁₁Nd₃ phases followed by segregation of Nd and Mg at carbon-aluminum interface were detected in composites containing Nd. The size and amount of Al₄C₃ phase were increased with Nd content. Bending strength of Gr_f/Al composites were decreased sharply from 1463 MPa (Gr_f/Al-17Mg) to 791 MPa (Gr_f/Al-17Mg-2Nd) after the addition of Nd. The increased Nd content decreased the pull-out of single fibre and bundles, which was due to the high interfacial bonding strength with formation of Al₄C₃, Al₃Mg₂, Al₁₁Nd₃ phases and the transition layer.     

Vickers indentation tests in a Zr62.55Cu17.55Ni9.9Al10 bulk amorphous alloy

Vickers indentation tests were conducted on a Zr_62.55Cu_17.55Ni_9.9Al₁₀ bulk amorphous alloy to investigate the evolution of shear bands and its plastic deformation dimension via a bonded interface technique. Under all indentation loads, the plastic deformation is accommodated through semi-circular and radial shear bands. The plastic deformation dimension increases with increasing the indentation loads. A simplified λ = C(P)^0.5 model was put forward to predict and estimate the plastic deformation dimension characterized by shear bands in the subsurface. For the Zr_62.55Cu_17.55Ni_9.9Al₁₀ amorphous alloy, C is about 15.314 µm/N^0.5. The normalized shear band zone is independent to the indentation load.     

Reaction sintering fabrication of (AlN, TiN)-Al2O3 composite

The (AlN, TiN)-Al₂O₃ composites were fabricated by reaction sintering powder mixtures containing 10-30 wt.% (Al, Ti)-Al₂O₃ at 1420-1520°C in nitrogen. It was found that the densification and mechanical properties of the sintered composites depended strongly on the Al, Ti contents of the starting powder and hot pressing parameters. Reaction sintering 20 wt.% (Al, Ti)-Al₂O₃ powder in nitrogen in 1520°C for 30 min yields (AlN, TiN)-Al₂O₃ composites with the best mechanical properties, with a hardness HRA of 94.1, bending strength of 687 MPa, and fracture toughness of 6.5 MPa m^1/2. Microstructure analysis indicated that TiN is present as well dispersed particulates within a matrix of Al₂O₃. The AlN identified by XRD was not directly observed, but probably resides at the Al₂O₃ grain boundary. The fracture mode of these composites was observed to be transgranular.     

Wettability and reactivity between B4C and molten Zr55Cu30Al10Ni5 metallic glass alloy

The isothermal wetting and spreading behaviors of molten Zr₅₅Cu₃₀Al₁₀Ni₅ metallic glass alloy on B₄C substrates were studied using a modified sessile drop method at 1133–1253 K in a high vacuum. A distinct reaction layer consisting of ZrB₂ and ZrC_x was produced at the interface and displayed good wettability with the molten alloy. The entire spreading kinetics could be characterized by four representative stages: (i) an initial rapid spreading presumably driven by adsorption of the active Zr atoms at the solid–liquid interface, (ii) a quasi-linear and (iii) a linear spreading stage controlled by the chemical reaction between Zr and B₄C in both cases, and (iv) an approach-to-equilibrium stage with precipitation of crystals in the liquid. An increase in temperature promotes the wetting and reaction. In view of the reasonable wettability and reactivity, there is a potential for preparing Zr-base bulk metallic glass matrix composites reinforced by in situ ZrC–ZrB₂ hybrid ceramic particulates using B₄C as a reaction agent by way of an infiltration synthesis technique.     

Characterization of nanosized Al2(WO4)3

Nanosized aluminum tungstate Al₂(WO₄)₃ was prepared by co-precipitation reaction between Na₂WO₄ and Al(NO₃)₃ aqueous solutions. The powder size and shape, as well as size distribution are estimated after different conditions of powder preparation. The purity of the final product was investigated by XRD and DTA analyses, using the single crystal powder as reference. Between the specimen and the reference no difference was detected. The crystal structure of Al₂(WO₄)₃ nanosized powder was confirmed by TEM (SAED, HRTEM). In additional, TEM locality allows to detect some W₅O₁₄ impurities, which are not visible by conventional X-ray powder diffraction and thermal analyses.     

Composition dependent phase connectivity, dielectric and magnetoelectric properties of magnetoelectric composites with Pb(Mg1/3Nb2/3)0.67Ti0.33O3 as piezoelectric phase

Ferrite (Ni_0.6Co_0.4Fe₂O₄) phase, ferroelectric (Pb(Mg_1/3Nb_2/3)_0.67Ti_0.33O₃) phase and magnetoelectric composites of (x)Ni_0.6Co_0.4Fe₂O₄ + (1 − x)Pb(Mg_1/3Nb_2/3)_0.67Ti_0.33O₃ with x = 0.15, 0.30 and 0.45 were prepared using solid-state reaction technique. Presence of Ni_0.6Co_0.4Fe₂O₄ and Pb(Mg_1/3Nb_2/3)_0.67Ti_0.33O₃ was confirmed using X-ray diffraction technique. The scanning electron microscopic images were used to study the microstructure of the composites. Connectivity scheme present in the magnetoelectric (ME) composites are discussed from the microscopic images. Variation of dielectric constant and dielectric loss with temperature for all the composites was studied. Here we report the effect of Ni_0.6Co_0.4Fe₂O₄ mole fraction on connectivity schemes between Ni_0.6Co_0.4Fe₂O₄ and Pb(Mg_1/3Nb_2/3)_0.67Ti_0.33O₃ composite. The variation of magnetoelectric voltage coefficient with dc magnetic field shows peak behaviour. The maximum value of magnetoelectric voltage coefficient of 9.47 mV/cm Oe was obtained for 0.15Ni_0.6Co_0.4Fe₂O₄ + 0.85Pb(Mg_1/3Nb_2/3)_0.67Ti_0.33O₃ composites. Finally we have co-related the effect of Ni_0.6Co_0.4Fe₂O₄ content and dielectric properties on magnetoelectric voltage coefficient.     

Magnetic properties and magnetoelectric effect in Ni0.8Co0.1Cu0.1Fe2O4 + PbZr0.2Ti0.8O3 composites

Composites with compositions x (Ni_0.8Co_0.1Cu_0.1Fe₂O₄) + (1−x) PbZr_0.2Ti_0.8O₃ (x-mole fraction varies as 0.15, 0.25, 0.35 and 0.45) were prepared by standard ceramic method. The presence of constituent phases, namely ferrite and the ferroelectric were confirmed by X-ray diffraction. The structural analyses were carried out using the obtained powder pattern X-ray data. The porosity of the samples was calculated and the values obtained lie between 10% to 19%. To date, the variations in the magnetic properties with variation in ferrite phase in composites and thereby its influence on magnetoelectric effect is not yet reported. The saturation magnetization (Ms) and magnetic moment (η_B) in Bohr magneton were calculated for all the composites. The static value of magnetoelectric voltage coefficient (dE/dH) was measured as a function of intensity of magnetic field. The maximum value of ME coefficient was observed for a composite with 35% ferrite + 65% ferroelectric phase.     

The preparation of Zn-ferrite epitaxial thin film from epitaxial Fe3O4:ZnO multilayers by ion beam sputtering deposition

A new method to grow a well-ordered epitaxial ZnFe₂O₄ thin film on Al₂O₃(0001) substrate is described in this work. The samples were made by annealing the ZnO/Fe₃O₄ multilayer which was grown with low energy ion beam sputtering deposition. Both the Fe₃O₄ and ZnO layers were found grown epitaxially at low temperature and an epitaxial ZnFe₂O₄ thin film was formed after annealing at 1000 °C. X-ray diffraction shows the ZnFe₂O₄ film is grown with an orientation of ZnFe₂O₄(111)//Al₂O₃(0001) and ZnFe₂O₄(1-10)//Al₂O₃(11-20). X-ray absorption spectroscopy studies show that Zn²⁺ atoms replace the tetrahedral Fe²⁺ atoms in Fe₃O₄ during the annealing. The magnetic properties measured by vibrating sample magnetometer show that the saturation magnetization of ZnFe₂O₄ grown from ZnO/Fe₃O₄ multilayer reaches the bulk value after the annealing process.     

The synthesis and selected properties of new compounds: Mg3Fe4(VO4)6 and Zn3Fe4(VO4)6

New compounds: Mg₃Fe₄(VO₄)₆ and Zn₃Fe₄(VO₄)₆ were obtained from a solid state reaction. The temperatures of melting of Mg₃Fe₄(VO₄)₆ and Zn₃Fe₄(VO₄)₆ amount to 950±5 and 850±5°C, respectively. The indexing results and the calculated unit cell parameters for both compounds are given and suggest that both phases are isotypic with Mn₃Fe₄(VO₄)₆. The IR spectra of the above-mentioned compounds are presented.     

Amorphous Ti–Cu–Ni–Al alloys prepared by mechanical alloying

Ti _x (CuNi)_90–x Al₁₀ (x = 50, 55, 60) amorphous powder alloys were synthesized by mechanical alloying technique. The evolution of amorphization during milling and subsequent heat treatment was investigated by scanning electron microscopy, X-ray diffraction, differential scanning calorimetry and transmission electron microscopy. The fully amorphous powders were obtained in the Ti₅₀Cu₂₀Ni₂₀Al₁₀, Ti₅₅Cu_17.5Ni_17.5Al₁₀ and Ti₆₀Cu₁₅Ni₁₅Al₁₀ alloys after milling for 30, 20 and 15 h, respectively. Differential scanning calorimetry revealed that thermal stability increased with the increasing (CuNi) content: Ti₆₀Cu₁₅Ni₁₅Al₁₀, Ti₅₅Cu_17.5Ni_17.5Al₁₀ and Ti₅₀Cu₂₀Ni₂₀Al₁₀. Heating of the three amorphous alloys at 800 K for 10 min results in the formation of the NiTi, NiTi₂ and CuTi₂ intermetallic phases.     

Growth and magnetic properties of ultrathin Ni1 + xFe2 − xO4 films for spin filter junctions

We investigated the spin filter effect in tunnel junctions with a Ni_1 + xFe_2 − xO₄ ferrimagnetic tunnel barrier. For higher T_c above room temperature, Ni_1 + xFe_2 − xO₄ film should be thicker than 4.0 nm and grown above 400 °C. The spin filter junctions (SFJs) of Fe₃O₄(001)/Ni_1 + xFe_2 − xO₄(001)/Al₂O₃/Fe/Au grown on MgO(001) substrates exhibited an inverse magnetoresistance effect at room temperature, which is consistent with the band calculation of NiFe₂O₄.     

Nd60Fe30 − xNixAl10 bulk metallic glasses with high hard magnetic properties

Bulk metallic glasses (BMGs) Nd₆₀Fe_30 − xNi_xAl₁₀ were prepared by suction cast method. The glass forming abilities (GFAs) and the hard magnetic properties of the BMGs were examined by differential scanning calorimeter (DSC) and vibrating sample magnetometer (VSM), respectively. The results show that the largest GFA (T_x / T_m = 0.61) of the alloys was obtained when Fe was substituted by 10% Ni and the rods of Nd₆₀Fe₂₀Ni₁₀Al₁₀ have the coercivity up to 323 kA/m and the remanence up to 9.41 Am²/kg as high as Nd-Fe-Co-Al, the Nd-Fe-based BMGs with highest hard magnetic properties up to date. The homogeneous distribution of Fe-rich nano-clusters, Nd(FeNiAl)₂, in amorphous matrix is responsible for the enhancement.     

Ba(Zn1/3Nb2/3)O3/Ni0.8Zn0.2Fe2O4 magneto-dielectric composite with large dielectric constant and high permeability

Ba(Zn_1/3Nb_2/3)O₃/Ni_0.8Zn_0.2Fe₂O₄ (BZN/NZO) composites were synthesized via the conventional solid-state reaction method. The phase composition and surface morphology of the composites were investigated using XRD and SEM, respectively. The dielectric and magnetic properties of the composites were studied. The results show that the BZN/NZO composites have large dielectric constants and very high permeabilities. For the 20%BZN/80%NZO composite, the dielectric constant and permeability in low frequency range are about 8,000 and 18, respectively. The large dielectric behavior of the BZN/NZO composites is mainly attributed to the Maxwell–Wagner polarization.     

Effect of annealing on characteristics of Ni48Fe12Cr40/Ni80Fe20 bilayer films deposited on Si(1 0 0)/SiO2 by electron beam evaporation

Ni₄₈Fe₁₂Cr₄₀(7 nm)/Ni₈₀Fe₂₀(40 nm) bilayer films and Ni₈₀Fe₂₀(40 nm) monolayer films were deposited at ambient temperature on Si(1 0 0)/SiO₂ substrates by electron beam evaporation. The effect of annealing on the structure, composition, magnetization and magnetoresistance of the Ni₄₈Fe₁₂Cr₄₀/Ni₈₀Fe₂₀ bilayer films was investigated. The structure of the Ni₄₈Fe₁₂Cr₄₀/Ni₈₀Fe₂₀ bilayer films remains stable for annealing temperature up to 280 °C. For the as-deposited bilayer film the introducing of the Ni₄₈Fe₁₂Cr₄₀ underlayer promotes both the [1 1 1] texture and grain growth in the Ni₈₀Fe₂₀ layer. The annealing promotes the grain growth of the Ni₄₈Fe₁₂Cr₄₀/Ni₈₀Fe₂₀ bilayer films when the annealing temperature exceeds 280 °C. After annealing at a temperature over 280 °C, Cr atoms inside the Ni₄₈Fe₁₂Cr₄₀ layer diffuse into the Ni₈₀Fe₂₀ layer and segregate on the surface of the Ni₈₀Fe₂₀ layer. The Ni₄₈Fe₁₂Cr₄₀ underlayer as a seed layer can enhance the anisotropic magnetoresistance ratio of the Ni₈₀Fe₂₀ layer at a annealing temperature up to 280 °C compared with Ni₈₀Fe₂₀ monolayer film. After annealing at a temperature over 280 °C, however, the anisotropic magnetoresistance ratio of the Ni₈₀Fe₂₀ monolayer films exceeds that of the Ni₄₈Fe₁₂Cr₄₀/Ni₈₀Fe₂₀ bilayer films. For all annealing temperatures, the coercivities of the Ni₄₈Fe₁₂Cr₄₀/Ni₈₀Fe₂₀ bilayer films are smaller than those of the Ni₈₀Fe₂₀ monolayer films.     

Nanorod alumina-supported Ni-Zr-Fe/Al2O3 catalysts for hydrogen production in auto-thermal reforming of ethanol

Nanorod alumina-supported Ni-Zr-Fe/Al₂O₃ catalysts were prepared by co-impregnation, characterized by TEM, TPR, XRD, XPS, and TPD-pyridine, and tested in auto-thermal reforming of ethanol. The characterization results indicate that, with iron and zirconia promotion, the Ni_xFe_1−xAl₂O₄ mixture spinel forms, the valence of the surface Ni species is modified, and the acidity decreases. As a result, during a 30-h test over the Ni-Zr-Fe/Al₂O₃ catalyst, sintering is restrained, and the selectivity to hydrogen remains around 85.79% without obvious loss, while the un-promoted Ni/Al₂O₃ shows poor stability and selectivity.     

Electrical conductivity of polycrystalline Fe2(MoO4)3

Measurements of the electrical conductivity of polycrystalline Fe₂ (MoO₄)₃ in the temperature range 370 to 900 K and in the oxygen partial pressure region 10^?4 to 1 atm are presented. Fe₂(MoO₄)₃ is found to be a semiconductor. Differing conduction mechanisms operate, depending on the crystallographic form of Fe₂(MoO₄)₃ and the oxygen partial pressure, and their nature is discussed.     

Tetrahedral quaternary chalcogenides of the type Cu2IIIVS4(Se4)

A survey is given on lattice data and structure types of 40 compounds of the type Cu₂IIIVS₄(Se₄) with II = Mn, Fe, Co, Ni, Zn, Cd, Hg and IV = Si, Ge, Sn. Of the 42 possible compounds, 22 had been known. The missing ones have been synthesized and characterized by x-ray powder methods. Three tetrahedral structure types, differing in symmetry and unit cell size exist: 1) The stannite structure (tetragonal superstructure of sphalerite with a_tetr≈a_Sph, c_tetr≈2a_Sph). 2) An orthorhombic superstructure of wurtzite (a_or≈2a_W, b_or≈a_W√3, c_or≈c_W). 3) A hitherto unknown structure type based on slightly distorted, sphalerite-sized cells of tetragonal, orthorhombic or monoclinic symmetry.     

Sol-gel auto-combustion synthesis of Ni0.5Zn0.5Fe2O4/(SiO2)x (x = 10, 20, 30 wt.%) nanocomposites and their characterizations

A nitrate-citrate-silica gel was prepared from metallic nitrates, citric acid and tetraethoxysilane (TEOS) by sol-gel process, and it was further used to synthesize Ni_0.5Zn_0.5Fe₂O₄/SiO₂ nanocomposites by auto-combustion. The obtained Ni_0.5Zn_0.5Fe₂O₄/(SiO₂)_x (x = 10, 20, 30 wt.%) samples were characterized by IR, ²⁹Si CP/MAS NMR, XRD, TEM, EPR and impedance analyzer measurements. Particle size of these composites was calculated from Scherrer's formula, and that decreased with increasing SiO₂ content. The content of TEOS in the starting solution affects the interaction between NiZn ferrite and silica, and then determines the particle size, dielectric properties and the EPR properties (ΔH_PP, g factor, N_S and T₂) of the as-synthesized powder.