Microstructures of Cr2B- and Fe2B-type borides, which were formed in the surface of SUS-304 by immersing into molten salt, were examined by means of electron diffraction and dark-field imaging techniques as well as high resolution electron microscopy. The orientation relationship between the Cr2B- and Fe2B-type structures was determined to be Cr2B (100)\varparallelFe2B (1\bar10) and Cr2B \varparallelFe2B . The Fe2B-type structure was found to have a twin with the  twin axis. The boundary of the twin lies macroscopically on the (1\bar10) plane, while micro-intergrowth of the two structures was observed near the boundary. Interpretation of the high resolution image of the intergrowth region indicated the existence of the following two kinds of defects; a twin of the Cr2B-type structure with the  twin axis and a (1\bar10) planar defect of the Fe2B-type structure. Geometrical consideration of the Cr2B- and the Fe2B-type structures indicates that both structures can be regarded as a layer-structure: they have almost the same component layers but have different stacking scheme. Atomic arrangements near the observed defects were interpreted from the geometrical similarity of the two structures.
A Cu-14Al-4Ni ternary alloy and three Cu-12Al-5Ni-2Mn-1Ti(mass%) alloys, were quenched from temperatures between 973 K and 1173 K, in order to investigate the effect of quenching temperature on the martensitic transformation temperature of the alloys. Dependence of the martensitic transformation temperature on quenching temperature was observed to exist in the alloys containing Ti, and hence containing a second phase called “x-phase” enriched with Ti and Ni. The martensitic transformation temperatures were lowered by 10-15 K, when the quenching temperatures were increased by 100 K. The phenomenon was explained by the solution of the x-phase particles, especially by partial dissolution of the smallest particles of xS-phase having an average radius of 50 nm. The concentration factor C. F.i(=Cix/Cim) of an alloying element i, where Cix and Cim represent the concentration of element i in xS-phase and in the matrix, respectively, was measured and compared to each other. It was found that the value of C. F.i was almost equal to unity in the case of Al and Mn, whereas it was 7.5 and 239 in the case of Ni and Ti. Transmission electron microscopy revealed that the size of the small xS-particles was reduced, when the specimens were heated at a high temperature such as 1173 K. It is concluded that the observed lowering of the martensitic transformation temperatures is due to redistribution of Ni and Ti atoms from the xS-phase particles to the matrix.
The effect of Ni on the internal magnetic field and the isomer shift of 57Fe in Fe-Cr alloys containing 3 to 14 at%Cr and 70 to 90 at%Cr were examined at room temperature by Mössbauer spectroscopy. A model Fe-28%Cr-5%Ni alloy was aged up to 5000 h at 723 K to investigate the phase decomposition of ferrite in a commercial duplex stainless steel. The alloy finally decomposed into a Cr-rich phase (α′) and an Fe-rich phase (α) after aging. A paramagnetic absorption peak due to the α′ phase has an isomer shift of −0.110 mm/s at room temperature. The value corresponds to a Cr content of 85(±1)at%Cr. The composition of the α phase was estimated to be 11(±1)at%Cr from the average internal magnetic field and the internal field distribution curve. The result of α phase was consistent with a result obtained by atom probe microanalysis. The latter underestimated the Cr content of the α′ phase in comparison with the Mössbauer effect.
In the relation to the smelting reduction of chromite ore, the kinetics of reduction of Mg(Cr0.6Al0.4)2O4 in silicate fluxes with graphite has been investigated at temperatures from 1773 to 1973 K. The reduction rate was strongly dependent on the wetting of the flux to the graphite. The contact area of the flux with the graphite decreased with increasing the basicity B of flux. The reduction rate was described with a 1st-order-type rate equation: log(1−R)=−k·t. The rate constant k reduced abruptly, when the value of B exceeded 1. The activation energy for the viscous flux was larger than that for the fluid slag. The addition of SiC to flux increased the reduction rate, because of the excellent wettability of the flux to the graphite. It is considered that the reduction rate is controlled by the mass transfer of chromium oxide in flux or the chemical reaction at the flux-graphite interface.
The standard Gibbs energies of formation of CoMoO4 and Co2Mo3O8 have been determined in the temperature range from 1123 K to 1273 K by measuring the electromotive forces of galvanic cells having a solid oxide electrolyte. The results are as follows: (1) ΔfG\ominus(CoMoO4)=−917300+271.2T±400 J/mol ΔfG°(CoMoO4)=−917300+271.0T±400 J/mol (2) ΔfG\ominus(Co2Mo3O8)=−2003000+599.6T±1000 J/mol ΔfG°(Co2Mo3O8)=−2003000+599.2T±1000 J/mol \
oindentwhere the superscript \ominus denotes that the standard pressure is 1 bar (100000 Pa) whereas ° denotes 1 atm (101325 Pa).
The activity of the liquid Te-Bi alloys has been determined by the emf measurement of the following galvanic cell: (This article is not displayable. Please see full text pdf.) The activities of bismuth and tellurium in the liquid Te-Bi alloys at 880, 930 and 980 K deviate to negative from Raoult’s law over the whole concentration ranges and do not agree with the result by Predel et al. The γBi° and γTe° values are estimated to be 0.19 and 0.15 at 880 K, 0.25 and 0.18 at 930 K, 0.32 and 0.22 at 980 K, respectively. The α function of bismuth against NBi does not show any constant value, suggesting no regular solution behavior in the system. The free energy of mixing at 980 K shows negative values than ΔGid, and the peak value of ΔG is −8.31 kJ/mol at about NBi=0.51. The heat of mixing also shows negative values. The peak value of ΔH is −9.87 kJ/mol at about NBi=0.45. It is observed that the anomalous peak values in ΔH and ΔS around the composition of Bi2Te3 are affected by the stable compound in the liquid state.
The interfacial tension between a liquid Cu-Bi or Cu-Pb alloy and solid Cu was measured by using multiphase equilibria. The results are summarized as follows: (1) The surface tension of solid Cu coexisting with the liquid Cu-Bi or Cu-Pb alloy is significantly lower than that of pure solid Cu, becase Bi or Pb vapor atoms are adsorbed on the surface. (2) The measured interfacial tension, γSL, between the liquid Cu-Bi or Cu-Pb alloy and solid Cu is in fairly good agreement with that calculted by the Good and Girifalco’s equation (γSL=γSV+γLV−2ΦG(γSVγLV)1⁄2), in which the parameter, ΦG, is assumed to be 0.947.
The chemical stability and adhesiveness of Al diffusion coatings to the substrate have been evaluated under heat cycle conditions by AC impedance techniques. The heat cycle test was conducted by exposure to alternate condition of immersion in Na2SO4-Li2SO4 melt at 973 K and water quenching. The corrosion rate of Al diffusion coatings was monitored when the samples were immersed in the melt. The corrosion rate of Al coating on Ni was greatly accelerated by heat cycles, while Al coating on Inconel 600 showed a very good corrosion resistance and adhesiveness to the substrate even in such severe conditions, probably due to the existence of Cr in the coating layer. The results of monitoring of corrosion rate were well correlated with that of SEM observation of corroded surface. The AC impedance method is considered to be very useful for the rapid evaluation of hot corrosion resistance of coatings under the heat cycle conditions.
Cyclic hot corrosion behaviours of Al diffusion coated Ni3Al and Ni3Si were examined by using fused Na2SO4-NaCl mixtures. Specimens were immersed in fused salts at 1173 K for 10.8 ks and then surface scales were removed. This process was repeated 5 cycles. Ni3Al showed high corrosion loss under first cycle hot corrosion. X-ray diffraction analysis showed that Al2O3 was not detected in the scales. High quantity of Al and high pH value were detected in the dissolved solution of mixtures after corrosion test. It is thought that Al2O3 dissolves in the mixtures as the sodium aluminate and so this alloy dose not indicate the hot corrosion resistance. Hot corrosion resistance of NiAl which was formed as the outside layer of Ni3Al during Al diffusion coating was improved about 3 orders of magnitude for comparison with Ni3Al under first cycle hot corrosion. But corrosion loss of this alloy under the cyclic hot corrosion was increased with increasing the number of cycles. On the other hand, Al diffusion coated Ni3Si and NiAl+0.6 mass%Si alloys indicated excellent corrosion resistance under the cyclic corrosion. Al2O3 layer was observed on the surface after the cyclic corrosion. It is clear that the addition of slight amount of Si to NiAl accelerates the formation of Al2O3 layer and improves the cyclic corrosion resistance in fused Na2SO4-NaCl mixtures.
Nickel-Al particle composites of 5∼23 mol%Al were electrodeposited and heated at 1073 K to get Ni-Al alloy films dispersed with Al2O3 particles. Then, the Ni-Al alloy films were isothermally oxidized in air at 1173∼1373 K, or subjected to a cyclic oxidation test between room temperature and 1273 K. This study was performed to elucidate the Al content which will provide a good oxidation resistance to the alloy film. The structure of the alloy films before and after the oxidation was traced by X-ray diffraction, scanning electron microscopy and X-ray microanalysis. It was found that a less mass gain and a good adhesion of the surface oxide phases are obtained when the Al contents of the Ni-Al alloy films are equal to or greater than 16 mol%. Although the surface oxide of the Ni-16 mol%Al alloy film was NiO and rather thick, it did not spall off the substrate during the cyclic oxidation for 259 ks. In this case, we found a network structure of Al2O3 in the substrate, and which was linked with the bottom of the surface NiO layer. When the Al content of the alloy film was 23 mol%, we found an Al2O3 scale of about 1 μm-thickness, which did not spall off the substrate even after the cyclic oxidation for 259 ks.
The vertical type Ohno Continuous Casting (OCC) equipment has been constructed in an attempt to cast small welding rods of stellite alloy. Rods as small as 2 mm in diameter, which are not possible to obtain by the conventional semi-continuous method, have been successfully cast. The metallographic structures and the presence of internal casting defects have been examined. It was found that the cast products contain unidirectional, uniformly solidified structures and no cavities.
Mullite is one of the most outstanding ceramic materials used at a high temperature in these days. We have made a fundamental research to produce ceramics/ceramics composites by dispersing mullite fibers into the silicate glass matrix using a solidification processing. The influence of parents materials, namely SiO2/mullite systems or SiO2/Al2O3 systems, and melting conditions on the morphology of crystallized mullite were mainly examined. (1) In both systems the mullite nucleated as primary phase during isothermal treatment in the solid/liquid co-existence range grew into fibrous single crystals by cooling. The shape of the mullite changed from fibrous to granular with increasing Al2O3 content in the melt. (2) Mullite nucleated and grew during isothermal treatment at 1973 or 1923 K when the melt contained more than 14.7 mass%Al2O3 in the SiO2/Al2O3 systems and more than 10.7 mass%Al2O3 (15 mass% mullite) in the SiO2/mullite systems. (3) As the mullite grew, the SiO2 content in the melt increases. This induced the increase in viscosity of the melt and then the decrease in diffusion coefficient. As the result, the residual melt solidified to glass. (4) Dendritic mullite fibers could be formed only in the case of 14.7 mass%Al2O3 melt for both systems.
Mechanical alloying (MA) in NH3 has been applied to prepare Fe16N2 powder where two different kinds of iron powders, i.e., elctrolytic Fe powder and carbonyl Fe powder were used as the starting materials. Nitriding has proceeded better in the electrolytic Fe powder than in the carbonyl Fe powder. On the other hand, oxidation has proceeded further in the latter than in the former. For example, after mechanical alloying in NH3 for 160 h 12 at%N and 2.0 at%O were contained in the specimen of the electrolytic Fe iron powder, and 11.5 at%N and 2.7 at%O in the specimen of the carbonyl Fe powder. The MA process under higher pressure of NH3 has an effect on preventing oxidation. The specimen obtained by the MA process showed a super-saturated bcc structure below 14-15 at%N, and Fe3N structure above 18-19 at%N. Fe16N2 could not be obtained by the MG process for the 11.1 at%N and Fe-13.3 at%N specimens prepared by the MA process.
The concept of fractal dimension has been applied to the description of the morphologies of deformed and recrystallized structures of commercial pure iron. The fractal dimensions of the image surfaces were experimentally determined, based on the Box-counting theorem. The results obtained are as follows: (1) The fractal dimension increased with the amount of plastic deformation and grain-size number. (2) The fractal dimension of the deformed structures reached a peak near the approximate recrystallization temperature and decreased gradually with the grain growth.
The influence of boron(B)-doping on microstructures and tensile mechanical properties of heat-refined Ni-34 mol%Al alloys were investigated. The heat refining treatment was composed of oil quenching from 1573 K and tempering at 1073 K. Ultra-fine lamellae structures having an equal volume fraction of γ′ and β phases were produced by this heat-refining process in spite of with and without B addition. The precipitation of γ′ phase at the prior β-grain boundaries, however, became more pronounced with increasing B content. Especially, the filmy γ′ phase which covering grains was formed in 0.1 mol%B doped alloy, though this was not observed for the base alloy without B. The results of tensile tests at 1073 K and the initial strain rate of 7.4×10−5 s−1 showed that base alloy without B fractured in a brittle manner at about 50% strain, while 0.1 mol%B doped alloy elongated to 204% strain. Further at 1123 K, the B doped alloy resulted in the elongation of 260% strain and the strain rate sensitivity exponent of flow stress, m, of 0.44. This indicates the development of superplastic deformation. The apparent activation energy of 337 kJ/mol was estimated for the high temperature deformation. This value is nearly equal to that for the lattice diffusion in each γ′ and β phase. During tensile deformation, the microstructures changed from lamellare to equiaxed grain structure. This seems to crrespond to the change of mechanisms controlling the superplastic deformation of the (β+γ′) two-phase alloy.
The defect strengthening due to the deviation from stoichiometry and the solution hardening by the addition of boron have been investigated in NiAl alloys and the results are compared with the available data for other B2 type intermetallic compounds. It is found that the defect strengthening in NiAl alloys cannot be interpreted solely by the conventional solid solution hardening theory in dilute alloys. By comparison with the results for other B2 type compounds, it is deduced that the degree of defect strengthening is larger in a compound having less compositional range in the binary equilibrium phase diagram within which the B2 structure is stable. These observations imply that in NiAl alloys the defects introduced by the deviation from stoichiometry would heterogeneously be distributed resulting in the formation of some kind of atomistic region in which the solutes are in a short or long range ordereded state. This might be the reason for the excess strengthening over the case for a dilute solution with homogeneous distribution of solutes. The effect of 0.05 mass% boron is found to increase both the lattice parameter and the hardness of NiAl in its Ni-rich compositions, while there is no such effect for the Al-rich deviation from stoichiometry. In the Ni-rich alloys, boron atoms dissolves interstitially and the excess atoms forms borides, while in the Al-rich alloys they all segregate to the grain boundary and do not exist nearby or in the structural vacancies.
Single-beam overwrite performance of the 5.25 inch diam. In3SbTe2 phase-change optical disk was examined at a constant angular velocity of 1800 rpm (v=5-10 m/s). The carrier-to-noise ratio of more than 55 dB and the overwrite modulation of −40 dB were obtained for overwrite frequencies of 2 and 3.7 MHz using a low power laser diode of 30 mW at the wavelength 830 nm. This good erasability was found to be supported by a new erase mode called the “winking erase mode”. This disk presents a highly linear recording density and a long reading data retention time.
Mo-based alloys are promising the candidate materials for structural applications in the advanced nuclear power system. In order to obtain some indication for the alloy design, the high-temperature tensile strength, high-temperature creep strength, corrosion resistance to liquid metal and alloy density were investigated system atically in this study. The high-temperature micro-hardness was measured with binary, ternary and some multi-components alloys, and found to be predictable using the differences in atomic radius and in Young’s modulus between the Mo atom and the alloying element. The high temperature tensile strength was also predictable from the calculated micro-hardness of alloys. The melting temperature which was associated with the high temperature creep strength, was shown to be predicted by the d-electron parameters calculated by the DV-Xα cluster method. The corrosion resistance in liquid sodium was found to be significantly higher for the Mo-based alloys than for Nb-based alloys. In addition, the alloy densities could be estimated readily by taking the compositional average of each densities for constituent metals in alloys. Based on these results, a Mo-Re-W-Zr system was selected as the most promising system, and its properties were estimated with varying alloy compositions. It was concluded that the present predicting method of alloy properties indeed provided a good indication for the efficient alloy design of Mo-based alloys.