Joining techniques of aluminide-based intermetallic compounds have been reviewed. Especially, reactive joining techniques based on the combustion synthesis or the Self-propagating High-temperature Synthesis (SHS) method including the reactive sintering and reactive casting are emphasized. Coating and three-dimensional freeform fabrication techniques based on exothermic reactions between metal powder and aluminum droplets and between metal wires associated with micro-arc welding technique are also described.
Although the discussion on the mechanism determining the strength of metals has a long history, it has not come to a satisfactory conclusion on its many aspects. Recent works on this subject is reviewed on the basis of the dislocation theory. Subjects discussed in this article contain such items as (1) strength due to the Peierls stress, (2) solution hardening, (3) precipitation hardening, (4) work hardening, and (5) strength related to the crystalline grain size. Various unsolved problems on these subjects are pointed out. Concerning the Peierls stress, available atomic calculations are still unsuccessful for explaining the general relationship between the stress and the lattice parameters. On the solution hardening, theories presented so far fail to give a quantitative explanation on the temperature dependence of the yield stress. It is suggested that a satisfactory theory should take into account the interaction between a dislocation and plural solute atoms at a thermal activation event. Regarding the work hardening, the necessity of the further discussion on the saturation stress are stressed. Concerning the grain-size effect, the dependence of coefficients in the Hall-Petch relation on the material species should be clarified more precisely.
In the field of municipal solid waste disposal, the direct melting process of the coke-bed type shaft furnace is effective in prolonging the useful life of the final disposal sites and reducing harmful matter such as dioxins. However, recently, it has become necessary to reduce coke consumption for the direct melting process in order to prevent global warming and reduce maintenance costs. Accordingly, the authors have developed technology for injecting various combustibles through the tuyeres of the direct melting furnace. In particular, combustible dust in the pyrolysis gas dischanged from the furnace top was focused to reduce coke consumption. In this study, some experiments on combustible dust injection through the tuyeres were carried out by using an experimental plant and a commercial facility. The main results obtained are as follows: (1) Combustible dust injected through the lower tuyeres is consumed by combustion and melting in the furnace. This technology is effective in reducing coke consumption and fly ash. (2) Combustible dust injection through the tuyeres maintains low Pb concentration in the slag even under the condition of low coke ratio. Moreover, combustibility in the combustion chamber is improved, and the generation of dioxins is suppressed.
In the steelmaking processes the wall material is chosen to be poorly wetted by molten steel to prevent contamination of the molten steel. Information on gas-liquid two-phase flows in a poorly wetted pipe however is very limited. In this water model study the flow pattern, the rising velocities of slugs and bubbles, and liquid flow near the outlet of the pipe were experimentally investigated. The shape and size of bubbles and slugs were affected by the wettability, but the boundary between the slug flow and bubbly flow regimes was not sensitive to the wettability. The rising velocities of bubbles and slugs became higher in the poorly wetted pipe than in the wetted pipe for a low water flow rate. At the outlet of the poorly wetted pipe, periodic generation of small bubbles was observed. The liquid flow near the outlet was measured with particle image velocimetry (PIV). The poorly wetted pipe promoted the horizontal spread of the liquid flow issuing from it.
An Okamoto-cavity microwave-induced plasma (MIP) with a nitrogen-oxygen gas mixture was employed as an atomization and excitation source for emission analysis when organic solvent samples were directly aspirated The mixed gas plasmas could be maintained with a high robustness against the loading of organic solvents such as ethanol and 4-methyl-2-pentanone (MIBK). Also, the introduction of the organic solvents exerted little influence on the emission characteristics of the plasma; the atomic-to-atomic and the ionic-to-atomic intensity ratios of various emission lines were a little varied by introducing organic solutions containing different concentrations of ethanol. This is probably because the organic solvent can be easily removed due to reactions with active oxygen species in the MIP. After test solutions containing Al, Co, Cr(III), Cu, Fe(III), Mo(VI), Ni, and Pb were extracted with MIBK, both the aqueous phase and the organic phase were aspirated into the plasma, giving calibration curves having good linearity, either from the aqueous phase for Al, Co, Cr, Ni, and Pb or from the organic phase for Fe and Mo. This effect can be explained from the partition coefficients of these elements between in MIBK and in water.
Hydrogen absorption into high strength steel bolts and its effects on delayed fracture susceptibility have been investigated, by means of thermal hydrogen analysis on exposed bolts and hydrogen permeation tests under atmospheric exposure. Thermal hydrogen analysis on small parts of exposed bolts showed hydrogen localization near the surface of the bolts. Hydrogen permeation tests under atmospheric exposure showed intermittent hydrogen entry, and maximum instantaneous hydrogen content was bigger than the measured value by the thermal hydrogen analysis. Delayed fracture susceptibility of high strength bolts with tensile strength of 1521 N/mm2 depended upon the safety index defined as the ratio of the threshold hydrogen permeation coefficient (JLth) and the maximum hydrogen permeation coefficient under atmospheric exposure (JLenv). The results suggest that hydrogen at the surface of the bolts plays an important role on delayed fracture.
The striker edge radii of instrumented Charpy impact testing machine standardized in ISO and ASTM are different. Both edge radii are standardized in JIS. However, the effects of striker edge radii on load-deflection curve and absorbed energy are still unclear. In the present study, the effects of striker edge radii, which are standardized in ISO and ASTM, that is, striker edge radii of 2 mm and 8 mm, on load-deflection curve and absorbed energy in instrumented Charpy impact tests were investigated. There is no difference in values of absorbed energy per unit ligament area between the two different striker edge radii when the values are less than 0.75 J/mm2. However, striker edge radius according to ASTM, that is, a striker edge radius of 8 mm, is not appropriate for Charpy impact test method because the four, instead of three, point bending condition occurs during fracture process of specimen with high absorbed energy. The effect of brinell deformation on absorbed energy measured in both striker edge radii is very small.
It is very significant to clarify the fracture toughness properties of candidate canister materials to ensure the structural integrity against the accidents during handling in the storage facility. Fracture toughness tests on the CT specimens cut from base metal, heat affected zone (HAZ) and weld metal in the 2 types of weld joints made by candidate canister materials (SUS329J4L duplex stainless steel and YUS270 super stainless steel) were conducted under various test temperature between 233K and 473K. Stable ductile crack extensions were observed in all of the specimens. The fracture toughness JQ of the base metal and the HAZ of SUS329L4L showed the smallest value at 233K, and increased with temperature, then reached to the largest value at 298K. At the higher temperature, the value of JQ decreased slightly with temperature. While, the value of JQ in the weld metal increased with temperature. The value of JQ of YUS270 increased with temperature. The values of JQ for weld metal in both of the materials were not greater than those in base metal and HAZ at each test temperature. The values of JQ in weld metal of both materials at 213K and 473K were greater than applied J derived from postulated semi-elliptical surface flaw and maximum allowable stress in JSME design coed. This result suggested that these materials have enough toughness for use as the canister material.
In an r.f. glow-discharge plasma, a d.c. bias current can be introduced by connecting an electric circuit comprising a low-pass filter and a variable resistor. The bias current promotes the emission excitations in the plasma, leading to an improvement of the detection power in the optical emission spectrometry. By conducting a bias current of 27 mA, the emission intensities of atomic resonance lines were several times larger than those obtained with conventional r.f.-powered plasmas. The detection limits for determination of alloyed elements in Fe-based low alloyed standard samples were estimated to be 3 ppm Cu for Cu I 324.75 nm, 10 ppm Ni for Ni I 352.45 nm, 6 ppm Ti for Ti I 364.267 nm, and 7 ppm B for B I 208.96 nm.
A trace amount of silver was determined by an electrically heated quartz tube atomization (QTA) atomic absorption spectrometry (AAS) with continuous-flow gas-phase sample introduction technique by use of both tartaric and hydrochloric acids as reaction media, and potassium tetrahydroborate (III) as a reductant. Under the optimized experimental conditions, the best attainable detection limit for silver at 328.07 nm was 0.4 ng mL-1. The instrumental precision expressed as the relative standard deviation (RSD) from ten replicate measurements of 50 ng mL 1 for silver by QTA-AAS was 4.0%. After the effects of diverse elements on the determination of silver were examined, this method was applied to the determination of low concentrations of silver in steels. The results obtained by the present method were in good agreement with the certified values.