Automobile transportation is one of the predominant sources of air pollution, producing CO2, NOx, and SOx. The weight reduction of automobiles is essential for reducing the environmental burden during their life cycle. High-tension steel, aluminum alloy and resin are candidates for such purpose. However, substituting aluminum for steel is not always beneficial with respect to reducing the burden on the environment, because the energy consumption during aluminum production is considerably greater than that for steel. A generalized equation has been derived to describe the relationship between the driving distance, weight reduction, materials production route, and change in environmental performance. In particular, the effect of the difference of electricity source for aluminum smelting on life cycle CO2, NOx, and SOx, by substituting aluminum for steel in automobile parts, is discussed. The reduction of CO2 emission can be expected for all cases, if 50% of mass reduction is made. On the other hand, aluminum produced by the uncontrolled coal fire power is not capable of reducing NOx emission. It is also suggested that a reduction of SOx emission can only be obtained when using very clean aluminum.
The activities of indium in liquid In-Bi-Cu and In-Sb-Cu alloys have been determined by emf measurement using a zirconia electrolyte at 982∼1259 K and 871∼1267 K for fifteen and sixteen different compositions of the two alloy systems, respectively. Combining the binary data on In-Bi and In-Cu alloys in the In-Bi-Cu system, and In-Sb and In-Cu alloys in the In-Sb-Cu system, the isoactivity curves at 1050 and 1200 K, 1100 and 1200 K were obtained in the whole composition ranges, respectively. There seem to be no comparable published data.
Synthesis of TiC and Ti/TiC composite has been conducted by mechanical alloying and following Spark-Plasma-Sintering starting from elemental Ti powder with graphite or heptane. From graphite, formation of TiC takes place rapidly after a definite period of milling while it proceeds gradually from heptane. The apparent compositional range of Ti1−xCx is extended to a C/Ti ratio as low as 30/70 when graphite is used, while a mixture of Ti and TiC is obtained at a C/Ti ratio of 32/68 with heptane. Sintering can proceed at substantially lower temperatures compared with the conventional process, the sintering temperature decreasing with lower C/Ti ratios. The lattice parameter of TiC and the density of the compacts decrease with lower C/Ti ratios, but are larger than previously reported ones through conventional methods. The mechanism which causes the differences between graphite and heptane is discussed with respect to the reaction process during milling.
In order to clarify the reliability of Au wire bonds to Al pads, void formation and diffusion behavior were investigated using bonds annealed at various temperatures (423-573 K). We investigated the effects of the annealing environments, Al pad thickness, and bonding conditions on void formation. Voids became larger only when Au-Al intermetallics grew non-uniformly, whereas deleterious voids were not observed in the bonds annealed in vacuum. Oxide film on the surface of Al pads acts as a diffusion barrier at the interface. Optimized bonding conditions (applied pressure, ultrasonic energy) broke up the oxide film, resulting in reduction of void formation. Au5Al2 phase grew dominantly in the early stage of diffusion, then it transformed into Au4Al phase because the Al layer was completely consumed. The activation energy Q of transmission velocity at the Au/Au4Al boundary was 0.85 eV (82 kJ/mol). This is similar to the activation energy of the bond failure by annealing. These results indicate that void formation has a great correlation with the Au4Al growth. It is predicted that the non-uniform diffusion behavior causes vacancies to pile-up and these vacancies coalesce to form several types of voids in the interface.
Mechanical properties were investigated in nickel/nickel alminide laminate materials with various volume fractions of NiAl. Laminate materials were made from the stacked Ni and Al sheets by hot pressing. The final volume fraction of NiAl in these materials were 0.70, 0.50 and 0.37 which were started from the initial thickness of Al sheets of 0.1, 0.05 and 0.025 mm, respectively. The maximum fracture resistance was 17.5 MPa\sqrtm in crack divider orientation and 23.5 MPa\sqrtm in crack arrester orientation. Higher fracture resistance in crack arrester direction was obtained because cracks were blunted and stopped at the ductile metal layer. An effective resistance curve in crack propagation was observed in the specimen with the volume fraction NiAl of 0.37. The relationship between fracture resistance and crack propagation behavior was explained by crack bridging model.
High frequency impedance (Z10kHz) at 10 kHz and low frequency impedance (Z10mHz) at 10 mHz for Type 304 stainless steel were monitored in synthesized ash at 873 K, as well as the corrosion potential. The mixture of Al2O3 particles (120 μm in diameter) and molten salt (NaCl+KCl+Na2SO4+K2SO4+ZnSO4) was used as the synthesized ash. The value of (Z10mHz−Z10kHz)−1 was well correlated with the average corrosion rate obtained from the mass loss measurement. The corrosion rate of Type 304 stainless steel showed a maximum at molten salt contents of 20∼30 mol%. The corrosion potential shifted to less noble values as the amount of molten salt increased up to 40 mol%, and it became constant when the molten salt content exceeded 40 mol%. The corrosion mechanism was discussed on the basis of the obtained corrosion rates and corrosion potential data. Also, in the corrosion ashes collected at actually operating incinerators, the corrosion rate of Type 304 stainless steel was monitored by AC impedance technique. The corrosion rate and amount of molten salt were estimated by comparison with impedence data in the synthesized ash.
As an oxidation protection system for carbon/carbon composites beyond 1973 K, authors have proposed a Y2SiO5 oxidation protection coating system, which is composed of a Y2SiO5 outer layer and a SiC inner layer. This work tried to form the Y2SiO5 layer on CVD-SiC layers by atmospheric plasma spraying (APS), and to adhere both layers with chemical bonding. YSix is composed of Y, Si, C and a few O, and is expected to be useful for adhesion between the Y2SiO5 layer and the CVD-SiC layer. As a surface treatment of CVD-SiC layer for APS, YSix/SiC layers composed of YSix and SiC were formed on the surface of CVD-SiC layers. With the YSix/SiC layers, the surface of CVD-SiC layer can be coarsened, and Y2SiO5 layers can be formed on CVD-SiC layers by APS. The Y2SiO5 layer as formed by APS was not composed of crystallized Y2SiO5 phase. Therefore, the Y2SiO5 layer is expected not to have the same oxygen permeability and thermal expansion coefficient as the crystallized Y2SiO5 phase. But, the Y2SiO5 layer crystallizes by some heat treatments in an oxidizing atmosphere. A heat treatment at 1873 K for 1 hour in Ar atmosphere is an effective method to adhere the Y2SiO5 layers to the YSix/SiC layers with chemical bonding.
Constant-compression speed testing was performed using a 99.999 mass% aluminum polycrystal with a grain size of 1.0 mm at temperatures ranging from 413 to 653 K and initial strain rates ranging from 1.67×10−1 s−1 to 1.67×10−5 s−1. The true stress-true strain curves showed a variation from a single peak type to multipeak type with increasing temperature and with decreasing strain rate. The apparent activation energy for the deformation was measured from the temperature and strain rate dependence of the first peak stress. The value was 136 kJ·mol−1 which is nearly the same value as the activation energy for the self-diffusion of aluminum. Recrystallized grains containing subgrains were observed in the specimens showing stress oscillations. The stress oscillations were assessed to be caused by dynamic recrystallization. The dynamic recrystallization takes place around the first peak stress of the stress oscillation at an initial strain rate of 1.67×10−3 s−1 and at 513 K. The dynamically recrystallized grain size at a strain of 1.0 decreases linearly with increasing Zener-Hollomon parameter Z.
The migration of hydrogen isotopes in pure Pd and Pd-Fe dilute alloys were studied by measuring the electrical resistance at low temperatures. The hydrogen isotopes were charged by heating in a high pressure gas atmosphere of the hydrogen isotopes, or by electrolysis in single crystal plates or polycrystalline wires. The disordered hydrogen isotopes produced by the quenching, migrate to order during annealing. The electrical resistance of the specimen increases due to the ordering and decreases due to the disordering of the hydrogen isotopes. From various isothermal annealing curves for the same specimen, each relaxation time for the resistance increase is determined for various temperatures. The migration energies of hydrogen isotopes are obtained from the above relaxation times for various concentrations of hydrogen isotopes. The obtained values in pure Pd are nearly the same for single crystal specimen and polycrystalline specimen. The values also do not depend on the hydrogen charging method and also on the hydrogen concentration. These values for hydrogen and deuterium atoms are smaller than those values at high temperatures, respectively. This is caused by the tunnel effects of migration which become important at low temperatures for light atoms. The ratio of the diffusion coefficients, DH⁄DD, decreases with decreasing temperature. The migration energies of hydrogen isotopes in Pd-Fe dilute alloys are larger than the values for pure Pd. The behavior of the DH⁄DD ratio of the alloys is also the same for that of pure Pd.
Composition, lattice parameter and lattice distortion of six kinds of quaternary L12-type (AlX)3Ti(V) phases with ternary element X(Mn, Cr, Fe, Ni, Cu or Ag) have been examined by electron micro-probe analysis and X-ray diffraction analysis. Quaternary element, V from 1 to 12 mol% was added to the six kinds of L12-type (AlX)3Ti(V) phases. Measured lattice parameters of L12-type (AlX)3Ti(V) phases exhibited good linear correlation with calculated lattice parameter from atomic sizes and occupation sites of constitutional atoms in the L12-type (AlX)3Ti(V) phases except for the (AlNi)3Ti(V) and (AlCu)3Ti(V) systems. A large amount of residual strain induced by milling of the specimen into powder was found in the L12-type (AlMn)3Ti(8 mol%V). A large amount of lattice distortion was found in the powder specimen of the L12-type (AlFe)3Ti(8 mol%V) phase which was well annealed at 1223 K for 40 min. It was suggested that the L12-type (AlX)3Ti(V) phase may have poor ductility at ambient temperature if their powder specimen exhibit a large amount of lattice distortion after well annealing.
In a chemical vapor deposition technique of silicon carbide on graphite using silicon tetrachloride, methane and hydrogen as raw materials, the effects of deposition conditions on condensed phase, rate-determining step of deposition, film thickness distribution and deposition rate were studied. Although the results of chemical equilibrium calculations generally agreed with the experimental results, the boundary between the β-SiC single-phase formation region and the region containing impurities like free silicon or carbon showed a certain shift. The higher the H⁄Si ratio of input gas, the more uniform thickness distribution of the films. β-SiC crystallinity was the highest when the H⁄Si ratio was around 22. The deposition rate was not affected by the pressure and the H⁄Si ratio, but it increased in proportion to the C⁄Si ratio.
Deformation behavior at high temperature has been investigated for fine-grained Al2O3-20%ZrO2 (3 mol%Y2O3 doped ZrO2) ceramics prepared with no additives in order to characterize the superplastic deformation mechanism. Large strains are obtained by compression tests in the temperature range from 1400 to 1600°C. Grain boundary sliding is clearly found to take place during the superplastic deformation. The strain rate dependence of the flow stress and the apparent activation energy are differ between the lower and higher strain rate regions. The deformation mechanisms contributing to the total strain in the lower strain rate region are grain boundary sliding, intragranular strain and grain boundary diffusion creep. The rate controlling mechanism in the lower strain rate region is interface-controlled diffusion creep. The deformation mechanisms in the higher strain rate region are grain boundary sliding, intragranular strain and grain boundary diffusion creep. Among them, the grain boundary diffusion creep is the rate controlling mechanism and has almost no contribution to the total strain.
Intermediate layers of various metals ranging from reactive metals to noble metals have been applied to the 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 TEM observations. When thin foils of reactive metals Al, Ti, Zr, and Nb were applied as the intermediate layer, the bond strength of SiC to Cu was improved remarkably. In contrast, when intermediate layers of Fe, Ni, and Ag were applied, the SiC specimen separated from the Cu specimen immediately after the bonding operation without application of external load, similarly to the case of bonding without an intermediate layer. In the joint bonded with the intermediate layers of the reactive metals, the intermediate layer was mechanically mixed with Cu to form a mixed region as wide as a few 100 μm. TEM observations have revealed that very thin reaction layers between the ceramics and reactive metals formed. When the Ti intermediate layer was applied, a TiC layer 10-30 nm thick formed over the almost whole 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 and Zr intermediate layers were applied, very thin interfacial layers where Nb and Zr were significantly concentrated were 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.
The creep rupture life of nickel-base superalloys has been predicted using a neural network model within a Bayesian framework. The rupture life was modelled as a function of some 42 variables, including temperature, chemical composition: Cr, Co, C, Si, Mn, P, S, Mo, Cu, Ti, Al, B, N, Nb, Ta, Zr, Fe, W, V, Hf, Re, Mg, ThO2, La, four steps of heat treatment (each has its own temperature, duration and cooling rate), sample shape, solidification method, yield strength, ultimate tensile strength and elongation. The Bayesian method puts error bars on the predicted value of the rupture life and allows the significance of each individual factor to be estimated. The scale of the error bars changes with the accuracy of the prediction: it is large when the prediction is uncertain, indicating that the whole prediction system is reliable.
In this paper, we present a phase field model applied to the solidification process of alloys. Some numerical simulations based on the model have been performed also. Our phase field model is a system of equations which describes the variation of the phase parameter and the concentration of alloy to minimize the free energy of the alloy. In previous work, phase field models for alloys are usually determined by giving the free energy phenomenologically. On the other hand, we begin by referring some theories of statistical physics for mixtures, and then deduce the model consistent with the theories. This is a new point of view in modeling. By virtue of such a modeling, the equations include microscopic parameters discussed in statistical physics theories —interaction energies given to pairs of component atoms, for example— and thus we can apprehend the relation between microscopic parameters and macroscopic phenomena. This paper actually deals with a comparatively simple statistical physics theory based on the regular solution approximation and applies the acquired model to some typical types of alloy. Though the model based on the regular solution approximation is an elementary one, numerical simulations based on the model give realistic results, that is, typical structures in real alloys —cored structures and periodic phase separation patterns in solid alloys— are reproduced qualitatively.
Sample temperature and neck growth were investigated on pulse-current pressure sintering of coarse cast-iron powder (diameter: 200 μm) produced by a gas atomizing technique. At 873 K of die temperature, the temperatures of sample inside and its surface were 950 K and 910 K, respectively. Microstructure observation of the sintered cast-iron revealed that there were no melting and remarkable deformation around the grain interface. Neck growth was governed by plastic deformation during the initial stage of the process. A model calculation of neck growth by assuming the plastic deformation of particles is in good agreement with the experimental results. The results indicate that the initial stage on pulse current pressure sintering is similar to conventional hot-press sintering for coarse cast-iron powder.
The optimum Cu content in the improved 5052 alloy with Cu addition by the electron beam welding process was investigated by the measurement of tensile tests to determine the mechanical strength of the improved 5052 alloys and the interface between the substrate and the improved area of the alloys. The X-ray diffraction or EDAX analysis of the precipitates, the observation of scanning electron micrographs of the samples with or without improved treatment and the fracture surface after tensile tests were also performed. The main results obtained are summarized as follows: (1) The grain size of Al(α) phase in the improved 5052 alloys was below 10 μm in diameter. The Al(α)+Al2Cu eutectic structure crystallized around the Al(α) phase, and its surface area ratio of the eutectic structure increased with increasing Cu content in the improved alloys. However, the surface area ratio of the eutectic structure was almost constant at the Cu content higher than 15 mass%. On the contrary, the surface area ratio of the large size of the Al2Cu intermetallic compound increased with increasing Cu addition at the Cu content higher than 15 mass%. (2) The Vickers hardness of the improved 5052 alloys increased with increasing Cu content in the 5052 alloy. The mechanical properties such as U.T.S. of the improved alloys increased with increasing Cu addition at the Cu content below 10 mass%. The values of U.T.S. were almost constant at the Cu content from 10 to 15 mass%. However, the mechanical strength of the improved 5052 alloys was reduced to the Cu content higher than 15 mass%. The mechanical strength of the interface between the substrate and the improved area was also reduced with increasing Cu content in the range higher than 15 mass%. (3) The fracture cracking initiation is observed around the large size of Al2Cu intermetallic compound, and thus the deterioration in mechanical strength for the improved 5052 alloy and interface between the substrate and the improved area of the samples was caused mainly by the increased large size of the Al2Cu intermetallic compound. From the experimental data, the optimum Cu content in the improved 5052 alloy was decided to be 10 mass%.
In order to elucidate the reaction mechanism for the Tetraethoxysilane(TEOS) thermal decomposition at atmospheric pressure, its pertinent elemental reactions involving the SiO(OC2H5)2 reaction intermediate were first proposed. For respective species formed in these elemental reactions, the total energy and the electronic state were calculated using a semi-empirical molecular method. The adsorption process which involves adsorbent species formation and surface reaction mechanism were then analyzed from the standpoint of molecular orbital formation and charge transfer mechanism, and the results are summarized as follows: (1) A reaction intermediate, SiO(OC2H5)2(1A1), is probably formed through the following β-elimination reaction route: (This article is not displayable. Please see full text pdf.) (2) The adsorption of SiO(OC2H5)2(1A1) on SiO2 occurs with charge transfer from the dangling bond of silicon atom at an active site of the SiO2 surface to the π∗-LUMO unoccupied orbital of SiO(OC2H5)2(1A1). (3) The sequence of surface reactions is considered as follows: \ding172 First, a dissociation reaction of C2H5(2A′) takes place, whereby producing a double bond between silicon atom and oxygen atom of the intermediate, since they possess unpaired electrons. \ding173 Si-O bond is successively formed following the mechanism similar to the one operating in the adsorption of SiO(OC2H5)2(1A1) on SiO2. \ding173 Electronic state of the reactant finally formed is in the 1A1 state, which has a σ-orbital to be fully occupied with electrons.
Refining of Ti powder particles and their dissolution into the Al matrix during mechanical alloying (MA) were investigated by using X-ray diffraction (XRD) and transmission electron microscopy (TEM) as functions of alloy composition, milling time and ball to powder ratio (BPR). It is found that Ti particles less than 20 nm are observed in a dark field image of mechanically alloyed Al-10 mass%Ti whose XRD pattern exhibits no Ti peak. The observed change of lattice constant of Al indicates that about 1 mass%Ti can be solved in Al after MA for a long time, independent of alloy composition, milling time and BPR, suggesting that most of Ti particles are retained in the Al matrix. It is concluded that the disappearance of XRD peaks in mechanically alloyed Al-10 mass%Ti is not simply attributable to the dissolution of the Ti into Al, but is associated mainly with extreme refining and/or heavy straining of Ti particles.
The purpose of the present work is to confirm the condition for obtaining gold-yellow TiN films with the reactive sputtering method without bias and to quantitatively evaluate the colorimetric properties of these films. Therefore, TiN films were prepared by D.C. reactive sputtering under a no-bias condition in the Facing Targets Sputtering (FTS) apparatus, in which a discharge is maintained at a low gas pressure of less than 0.3 Pa. The color of the films was evaluated by means of the chromaticity coordinates, x and y, and the stimulus value, Y, which is an index of the brightness or luminance factor based on a CIE standard colorimetric system. Gold-yellow TiN films were obtained, and a study of their colorimetric properties has provided the following conclusions; (i) Even without bias application, a gold-colored TiN film with higher brightness, Y, has been obtained by deposition at an appropriate mixing ratio of N2/Ar and also under lower total gas pressure. (Y=49-53 for the films deposited at 0.14-0.15 Pa) (ii) The colorimetry of the films is affected by both the mixing ratio and total gas pressure. Particularly, the brightness, Y, varied greatly with a change in total gas pressure. (iii) As the total gas pressure was increased, the column size and oxygen content showed a clear increase. Thus, the films deposited under an atmosphere higher than 0.15 Pa had lower brightness.