In the present paper, the dc longitudinal field and ac frequency dependence of the magnetoimpedance, magnetoresistance, magnetoreactance and magnetoimpedance-phase of NiFeMo permalloy ribbon are investigated. The value of the magnetoimpedance ratio (Z(0)−Z(5172A·m−1))⁄Z(0) of NiFeMo permalloy ribbon can reach 39.54% at 0.3 MHz. We also found that the change ratios of the magnetoimpedance (Z(0)−Z(5172A·m−1))⁄Z(0), the magnetoresistance ratio (R(0)−R(5172A·m−1))⁄R(0) and the magnetoreactance ratio (X(0)−X(5172A·m−1))⁄X(0) intersect at 0.27 MHz where the change ratio of the magnetoimpedance phase (θ(0)−θ(5172A·m−1))⁄θ(0) is zero.
Corrosion of NiMo2B2-dispersed Ni-based alloy containing Co, Mn, Cr, Fe or Cu was examined by measuring the mass loss and the corrosion potential in 6 mass%HNO3 aqueous solution and by metallography. The corrosion was accelerated by addition of Co or Mn while it was retarded by addition of Cr, Fe or Cu. In particular, the addition of Cu greatly improved the corrosion resistance. The corrosion proceeded by a mechanism in which the Ni-matrix phase worked as anode while the NiMo2B2 phase worked as cathode. The addition of Cu shifted the corrosion potential of the Ni-matrix phase to the noble side by about 15 mV, and consequently the difference in the corrosion potential between the Ni-matrix phase and the NiMo2B2 phase decreased. As a result the preferential corrosion of the Ni-matrix phase was extremely retarded.
Mo-40 mol%TiC and Mo-20 mol%Nb-40 mol%TiC in-situ composites were synthesized by hot-pressing mixed Mo, Nb and TiC powders. Both composites consist of two phases, Mo solid solution (A2) and TiC (B1), after hot-pressing at 2073 K and 70 MPa for 2 h followed by annealing at 2073 K for 24 h. Porosity of hot-pressed compacts decreased by Nb addition to Mo-40 mol%TiC. The composites have different microstructural features. Clusters consisting of fine bcc particles are observed in sizes similar to original Nb powder in Mo-20 mol%Nb-40 mol%TiC, while there are no clusters in Mo-40 mol%TiC. These composites show excellent strength superior to monolithic TiC at high temperatures. The addition of Nb to Mo-40 mol%TiC suppresses effectively intergranular fracture above 1473 K. Furthermore, fracture toughness of these composites is higher than that of monolithic TiC. Fracture toughness of Mo-20 mol%Nb-40 mol%TiC is slightly lower than that of Mo-40 mol%TiC. The obtained results are discussed in relation to microstructural characteristics.
The effects of deviation from stoichiometry and boron addition on the mechanical properties of A15 type Nb3Ir intermetallic compounds were studied. All the alloys, with and without boron, were prepared by arc-melting, followed by homogenization at 2073 K for 86.4 ks in an argon atmosphere. The amounts of boron addition were 0.05 mass% and 0.15 mass%. Mechanical properties were investigated by micro-Vickers hardness measurements at room temperature and compression tests up to 1773 K. It was found that the lattice parameter of Nb3Ir decreases, while the micro-Vickers hardness increases monotonically with increasing Ir concentration, and that there is no singularity at stoichiometry in the Ir concentration dependence of micro-Vickers hardness and lattice parameter at room temperature. The 0.2% flow stress was not observed due to premature failure in all the Nb3Ir alloys with or without boron in the temperature range of room temperature to 1473 K. At 1773 K, the 0.2% flow stress was observed which increases with increasing Ir concentration, and it was higher in the boron-free alloys. Unfortunately, there was no favorable effect of boron addition on ductility improvement in Nb3Ir alloys, because boron is almost insoluble in Nb3Ir intermetallic compound, and the addition of boron leads to the formation of boride mainly at the grain boundaries. The 0.2% flow stress of the A15-type intermetallic compounds dropped rapidly above 0.6Tm, and the temperature is higher than that for other intermetallic compounds such as NiAl, Ni3Al and TiAl.
The short-range atomic order in amorphous and liquid ZnSnAs2 has been studied with electron diffraction and neutron diffraction. It has been shown that the local structure in amorphous ZnSnAs2 maintains the crystalline chalcopyrite structure, in which a central As atom is tetrahedrally surrounded by two Zn and two Sn atoms, while, its crystalline atomic order is markedly broken in the liquid phase, accompanying a change of the bonding nature. The structure in the liquid phase is considered to be similar to that in liquid metals. The structural and bonding differences in solid and liquid phases correspond reasonably to a rapid increase of the electrical conductivity and paramagnetic susceptibility on melting. The short-range structure in amorphous and liquid ZnSnAs2 has been discussed referring to the related crystalline lattices.
For transparent materials such as silicate glasses, an absorber layer of a laser beam and an emitter layer of an infrared ray are essentially required for measuring thermal diffusivity by the laser flash method with an infrared ray detector. Platinum (thickness: 1.0 μm) and molybdenum (thickness: 0.7 μm) thin layers were formed by sputtering on both sides of a transparent specimen with a disk shape. Then such metal coating was tested at elevated temperatures. The platinum thin layer was found to work well to measure thermal diffusivity of silica glass at temperature below 1000 K. The molybdenum coating was also successfully applied to the measurement of thermal diffusivity for silicate glass in the temperature range between 750 and 1569 K with considering radiative heat transfer inside the specimen.
A new electrocatalyst which enables direct methane use in solid oxide fuel cells (SOFCs) was examined. The dispersion of Co0.5Ni0.5O particles into a porous-platinum-based anode increased the cell performance in an SOFC using a stabilized-zirconia electrolyte. Among the catalysts studied, Co0.5Ni0.5O, CoO, and NiO, the increase was the most prominent for Co0.5Ni0.5O. The anodic polarization resistance and the production rates of CO, CO2, and H2 in the outlet gas showed a high Co0.5Ni0.5O catalytic activity for the electrochemical oxidation of methane, indicating the activation of the steam-reforming reaction caused by the formation of surface active sites in relation to the cation vacancy in the CoO–NiO solid solution.
Centrifugal casting of Aluminum melts containing suspended ceramic particles has been studied. One dimensional heat transfer model coupled with equations for force balance on particles is formulated and analysed to predict the particles distribution in the casting region, the temperature distribution in the casting and mold regions, and solidification time of the casting. The model takes into consideration propagation of solid-liquid interface and movement of particles due to centrifugal acceleration. The solution of the model equations has been obtained by pure implicit finite difference technique with modified variable time step approach. The effect of various parameters like particle size, mold rotational speed, relative density difference between melt and particle, etc. on segregation of particles and solidification time have been examined. For a given set of operating conditions, the thickness of the particle rich region decreases with increase in rotational speed of the mold, particle size, relative density difference between the particle and melt, and the melt superheat. Solidification time increases as the heat transfer coefficient at the metal-mold interface decreases.
Intermediate layers of various metals ranging from reactive metals to noble metals have been applied to friction bonding of SiC (pressureless-sintered silicon carbide) to Cu (oxygen-free copper), and their influences on the bond strength and microstructures of the joint have been systematically investigated by means of TEM observations. When a thin foil of reactive metal, Al, Ti, Zr, or Nb, was applied as the intermediate layer, the bond strength of SiC to Cu was improved considerably. In contrast, when an intermediate layer of Fe, Ni, or Ag was applied, the SiC specimen separated from the Cu specimen immediately after the bonding operation without the application of external load, similar to the case of bonding without an intermediate layer. During friction bonding with an intermediate layer of reactive metal, the intermediate layer was mechanically mixed with Cu to form a very complicated microstructure extending over a region as wide as a few 100 μm. TEM observations have revealed that very thin reaction layers between the SiC and reactive metals were formed. When the Ti intermediate layer was applied, a TiC layer 10–30 nm thick was formed over almost the entire area along the interface, and between this layer and the SiC matrix a very thin layer of a Cu solid solution was detected. On the other side of the TiC layer, a Ti5Si3 layer ∼100 nm thick was partially observed. When the Nb or Zr intermediate layer was applied, a very thin interfacial layer, in which Nb or Zr was significantly concentrated, was observed in addition to the reaction layers of Nb5Si3, NbC, and ZrC. These interfacial layers can be characterized by their much smaller thickness and finer grain size than those observed in diffusion-bonded and brazed joints. Apart from the layers mentioned above, amorphous silicon oxide layers were occasionally observed, suggesting that the reactive metal enhanced the removal of the oxide film on the SiC surface.
Electrical conductivity measurements are used here to estimate the Gibbs energy change for formation of ternary oxide from binary oxides. The theoretical background and the advantages of the present method are discussed. As a demonstration, the standard Gibbs energy change of the reaction, (Remark: Graphics omitted.) was estimated by electrical conductivity measurements of two kinds of SrCrO4 oxides, one equilibrated with Sr3Cr2O8 and the other with Cr2O3. The standard Gibbs energy change of the reaction is obtained as ΔG°⁄kJ mol−1=−409+0.252T(±10), 1323∼1373 K. The resulting value is in good agreement with that obtained by measurement of the equilibrium oxygen pressure using a solid oxygen concentration cell.
The usefulness and validity of energy dispersive grazing incidence X-ray reflectometry (ED-GIXR) have been demonstrated for characterizing the liquid/liquid and liquid/solid interfaces. The present method appears to hold promise in reducing difficulty of conventional angular dispersive method due to absorption with an upper half liquid layer by enabling the use of high energy white X-ray radiation and obtaining much higher reflected intensity. An apparatus newly built for the exclusive use of the ED-GIXR is described with some selected examples of X-ray reflectivity profiles of solution/mercury and solution/electrode interfaces.
This study was performed to investigate the influence of fuel/oxygen ratio (F/O = 3.2, 3.0, 2.8) on the characteristics of the HVOF sprayed Cr3C2 (7 mass%NiCr) coatings after heat treatment up to 1000°C. Decomposition and oxidation of the Cr3C2 occurred during spraying. The degree of decomposition from Cr3C2 to Cr7C3 was increased with decreasing the F/O ratio. The micro-structural differences of the as-sprayed coatings with F/O ratio cannot be distinguished. However, large pores were diminished and then the coatings became dense by heat treatment. Micro-hardness of the as-sprayed coating which is sprayed with F/O = 3.2 condition was the highest (Hv300=1140) and the hardness was increased to 1660 after heat treatment at 1000°C for 50 h in air. It was supposed that hardness was increased due to the formation of Cr2O3 within the Cr3C2/Cr7C3 matrix and the densification of the coating layer during heat treatment. Mass loss of the as-sprayed coating by erosion varied from 79 to 80.8 mg depending on F/O ratio and varied from 47.2 to 49 mg after heat treatment at 600°C. Erosion resistance of the coating was improved about 40% after heat treatment at 600°C. It is concluded that improvement of erosion resistance of the coatings was due to production of the coatings with a very dense microstructure, high cohesive strength and a very high hardness value by heat treatment.
The formation of non-metallic inclusions with variations in various oxygen, nitrogen and titanium contents in low carbon steels has been studied. The relationship between the nature of non-metallic inclusions and the formation of acicular ferrite has been also investigated. It is found that the non-metallic inclusions observed in this study are mainly consist of Ti2O3 and TiN together with a small amount of other complex oxides containing Mn and Si. It has been confirmed that Ti2O3 and TiN play an important role in formation of acicular ferrite as a nucleation site and an austenite grain refiner, respectively. But it is not clear yet whether TiN acts as a nucleation site or not. It is also found that the volume fraction of inclusions is more effective than the type or size distribution of the non-metallic inclusions on the formation of acicular ferrite.
In order to identify the dominant mechanism of ionic conduction, the electrical conductivity and ionic mobility of the glasses (AgX)0.4(Ag2O)0.3(GeO2)0.3 (X=I, Br, Cl) were measured separately in the temperature range from 293 to 393 K by coupling the AC technique with the TIC method. Electronic conductivity was also measured at 293 K by the Wagner polarization method. The total electrical conductivity of these glasses was found to be as high as 10−1 Ω−1 m−1, and the mobility about 10−6 m2 V−1 s−1. The variation of total electrical conductivity and mobility at constant temperature and composition with the type of halide occurred in the sequence, Cl<Br<I. For each composition, both conductivity and mobility increased with temperature. The mobile ion concentration was found to be about 1023 m−3 at 293 K, and it was insensitive to the type of halide as well as temperature. The results suggest that the change in ionic conductivity with the temperature and the type of halide present is mainly attributable to the change in ionic mobility rather than carrier concentration. Moreover, the electronic conductivity was found to be about 10−6 Ω−1 m−1 at 293 K. Thus, the electronic contribution to the total conductivity is negligibly small.
The effect of ferromagnetic metal Co on the glass-forming ability and magnetic properties for the Fe75−xCoxGa5P12C4B4 glassy alloys was investigated. The additions of 10 to 15 at%Co were found to be effective for the extension of the supercooled liquid region (ΔTx) defined by the difference between the glass transition temperature (Tg) and crystallization temperature (Tx). The ΔTx value is 37 K for the Fe75Ga5P12C4B4 alloy and increases to 48 K for the 10, 12.5 and 15 at%Co alloys. The liquidus temperature (Tl) of the 10, 12.5 and 15 at%Co alloys decreased by the addition of Co and the reduced glass transition temperature (Tg⁄Tl) increased. The largest Tg⁄Tl is 0.61 for the Fe65Co10Ga5P12C4B4 alloy. These glassy ribbon alloys exhibit good soft magnetic properties of 1.15 to 1.33 T for saturation magnetization and 2.4 to 3.6 A/m for coercive force. Based on the large ΔTx and high Tg⁄Tl values, we tried to prepare bulk glassy Fe75−xCoxGa5P12C4B4 (x=10, 12.5, 15) rods in a cylindrical form with different diameters. The glassy single phase was obtained in the diameter of 1.5 mm in the composition range of 10 to 15 at%Co.
New Fe-based glassy alloys in Fe–Co–Nd–Dy–B system with high boron concentrations were found to exhibit a wide supercooled liquid region exceeding 50 K. The high stability of the supercooled liquid enabled us to produce cylindrical bulk glassy alloys with diameters up to 0.75 mm by copper mold casting. The glass transition temperature (Tg), crystallization temperature (Tx), supercooled liquid region ΔTx (=Tx−Tg) and heat of crystallization of the φ0.75 mm rod of glassy Fe62Co9.5Nd3Dy0.5B25 alloy are 844 K, 899 K, 55 K and 4.46 kJ/mol, respectively. No appreciable difference in the thermal stability is seen between the bulk rods and melt-spun ribbon. The saturation magnetization (Is), coercive force (Hc), saturated magnetostriction (λs) and Curie temperature (Tc) of the melt-spun Fe62Co9.5Nd3Dy0.5B25 ribbon are 1.37 T, 4.58 A/m, 17.9×10−6 and 663 K, respectively, and Is and Tc are nearly the same as those for the bulk glass rods with diameters of 0.5 and 0.75 mm. The success of forming the Fe-based bulk glassy alloys exhibiting good soft magnetic properties is promising for future development as a new type of soft magnetic material.