Silicon nitride nanoceramics and aluminum nitride nanoceramics are fabricated by pulsed electric current sintering. These nanoceramics could be densified without grain growth, because of high heating rate of the pulsed electric current sintering. A sintering additive is effective for lowering sintering temperature and aluminum nitride nanoceramic could be obtained as a result of 1wt% of Ca_3Al_2O_6 addition.

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SPS processing is extensively applied to the sintering of the powder materials because the characteristics of sintered materials can be improved remarkably. However, it is necessary to consider the deep reasons for the high performance due to SPS processing. In the present study, we introduce two typical results on the synthesis of highly transparent nano-structured alumina and the structural analysis of PSZ(3Y)/SUS410L functionally-graded materials (FGM) and consider the characteristics of SPS processing for the sintering of powder materials from structural standpoints.

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An ultrafine α-alumina powder was consolidated by spark plasma sintering (SPS) and the effect of microstructure on mechanical properies of the sintered compact was examined. In the sintering temperature at 1473K, the sintering was incomplete at the central part, and the periphery was fine microstructure. On the other hand, in the sintering temperature at 1773 K, many fine pores observed in the grains and/or on the grain boundaries. Further, the martens hardness indicated a low value at the central part.

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In order to improve mould filling of aluminium foams into mould cavity, a moulding process of foams is proposed. In the experiment of moulding of Al foams, a precursor made by hot powder extrusion is put into the die for foaming of alulminum and extruded into a rotating mould during foaming at 750 ℃. In case of large inlet diameter of mould, the influence of gravity is significant. When the mould of large diameter is rotated and filled with Al foam, the mould filling ratio is improved.

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Open-cell porous copper (Cu) was fabricated by friction powder compaction (FPC) process, which requires no external heat sources. In this process, a mixture of Cu powder and sodium chloride (NaCI) powder as spacer particle are used as starting materials. The compacting of the powder mixture are conducted only by rotating tool plunged into the mixture. NaCl is removed by placing the sintered mixture in water, and pores are formed. Porous Cu with porosities of 60-80 pct was successfully fabricated. In this study, a relationship between leaching time and removal of NaCl were investigated, and pore structures of obtained porous Cu were nondestructively observed by X-ray CT. In addition the compressive response of obtained porous Cu was investigated.

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Three porous metals, i.e., lotus-type porous copper, aluminum foam, and open-cell type porous nickel, were subjected to multi-pass cold rolling. At the beginning, thickness reduction was mostly converted to volumetric change, while after heavy rolling, elongation in the rolling direction became remarkable. It is found that strain ratio of elongation to thickness, i.e., 'elongation efficiency', increases with decreasing porosity. The trend is sensitive to neither initial porosity nor pore morphology. It can be described with Shima's eq. for sintered metals using modified constants.

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Porous aluminum is a multifunctional material with lightweight and high energy absorption properties. In this study, A1050-ADC12-A6061 functionally graded (FG) porous aluminum of three layer structure was fabricated by friction stir processing (FSP) route. The compression properties and deformation behavior of FG porous aluminum was obtained by compression test. Moreover, pore structures of FG porous aluminum was observed by X ray CT inspection. It was shown that the fabricated FG porous aluminum had three different deformation stages and three plateau regions corresponding to the pore structure and types of aluminum alloy.

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Porous aluminum is a multifunctional material with both lightweight and high energy absorption properties. In this study, functionally graded (FG) porous aluminum was fabricated by spacer method varying pore structures. The obtained FG porous aluminum was observed non-destructively by X-ray CT. Image-based finite element analysis of FG porous aluminum using X-ray CT images was conducted. By comparing the results of finite element analysis and the deformation behavior of actual compressive tests of FG porous aluminum, it was shown that deformation behavior can be controlled by varying pore structures.

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To control porosity of porous metals and/or fabricate solid skin layer at the surface of porous metals, friction stir incremental forming method was applied to form to surface of closed cell type aluminium foam (Shinko Wire Company, Ltd.: ALPORAS). The friction stir incremental forming method was possible to fabricate the solid skin layer with thinner than 0.4 mm on the surface of ALPORAS without causing fracture inside of ALPORAS. The area fraction of metal matrix at the surface was obtained as about 80% in forming conditions of tool rotation rate of higher than 8000 rpm and tool feed rate of 60mm・min^<-1>.

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In this study, porous aluminum core filled in hollow steel pipe composite materials (porous core pipe) was fabricated by applying friction welding. Al plates and blowing agent powder were put into the hollow steel pipe, and the rotating tool was pressed into the Al plates. Friction heat was generated and precursor of porous Al was fabricated by mixing Al plates and blowing agent powder by means of plastic flow. Porous core pipe with metal bonding was successfully fabricated by heating the precursor. The compression properties and deformation behavior of porous core pipe was obtained by the compression test. As a result, energy absorption per unit of volume of porous core pipe increased 1.5 times compare with the hollow pipe. But, the energy absorption per unit mass was slightly decreased.

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Porous aluminum is superior in lightweight, high sound insulation and high energy absorption. In this study, copper powder dispersed porous aluminum core filled in hollow pipe composite materials was fabricated by friction welding. Al hollow disc filled with blowing and reinforcing agent powder was put into hollow pipe and the rotating tool was pressed into Al hollow disc. Frictional heat was softened Al and precursor of porous Al was fabricated because the rotating tool dispersed blowing and reinforcing agent powder into Al by means of plastic flow. It was shown that copper powder dispersed porous aluminum core filled in hollow pipe composite materials with porosity of approximately 60% and formation of CuAl_2 was successfully fabricated at a holding temperature of 1003 K and at a holding time of 6 min 30 sec.

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Porous aluminum is a lightweight material with high energy absorption properties. In this study, impact test of A1050-ADC12 functionally graded porous aluminum fabricated by friction stir processing (FSP) route was carried out. It was shown that deformation began from low strength A1050 layer. This result is consistence with result of static compression test of A1050-ADC12 functionally graded porous aluminum.

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The effects of post-ECAP (equal channel angular pressing) annealing on microstructure and high-cycle fatigue behavior of ultrafine-grained (UFG) copper were examined. Grains with sizes up to a few tens of micrometers surrounded by fine grains were formed after the annealing. The fatigue life of post-ECAP annealed samples in the short-and medium-life fields was found to decrease, while in the long-life field in excess of 10^7 cycles, the fatigue strength was slightly increased. The effect of bimodal microstructure on high-cycle fatigue strength is discussed from the viewpoints of microstructural evolution due to cyclic stresses.

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The braze-pressure-welding was conducted for the SUS316L and SUS304L austenitic steel pipes with various total heating time. The BPW's cleaning step was at 1280℃ with keeping time of 60-360s. The forging process was at 1180℃ with keeping time of 0-60s. For the cross section taken from the parts with distance of 0-20mm from the joint interface, the EPR tests were conducted EPR test was conducted to measure the degree of the sensitization of stainless steel. The cross section on the joint interface, the reactivation value was more than 10% indicating that part was sensitized, on the other parts, the values were lower than 1% and no sign of sensitization was suggested.

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Carbon-carbon composites were brazed to a Ni-based super-alloy (Inconel 600) using a Fe-Cr-Ni filler metal (TB-2720) with a Nb interlayer at 1080℃ for 300s in vacuum 1.33×10^<-2>Pa {1.0×10^<-4>Torr}. The Nb foil with various thicknesses from 0.1 to 0.5 mm was inserted in the brazing interface to relieve residual stress. The metallurgical microstructure of the brazed joint interface was observed through the scanning electron microscope (SEM). By analyzing with the energy dispersive spectroscopy (EDS), the constituents' distribution at the brazed interface was measured. A crack due to residual stress was formed in the C/C composites near the brazed interface of specimens with thinner Nb foil than 0.2mm. The results suggest that in order to release enough residual stress, the Nb foil must be thicker than 0.2mm. When the foil thickness was 0.5mm, the shear strength of the joint was 9.63MPa.

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Currently, plasma gouging machines supplied by domestic equipment manufacturers are classified according to orifice gases used in them; some use mixtures of 30% hydrogen and argon, whereas some use only nitrogen. Stainless steel and aluminum alloy, which were previously used in arc welding, are used with a carbon steel for plasma gouging, thus resulting in high efficiency and high quality gouging. The plasma gouging process using only nitrogen allows carbon steel to be processed with a single gas, which is a potential selling point. However, plasma gouging or cutting using a mixture of gases is more expensive owing to the consumption of the two orifice gases. In order to use hydrogen, which is a combustible gas, special safety control is necessary in the storage of hydrogen gas cylinders. Compressed air can be easily used as an orifice gas; therefore, the author investigated various properties of the plasma gouging method using compressed air. In this lecture, we will report on the results of the investigation on the weldability in a groove formed by the air plasma gouging method.

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This paper describes about the joint properties and its improvement of A5052 autocompleting friction welded joint, that welding method was developed by authors. The fixed specimen had the weld faying surface of 10mm with the overhanging length of 15 or 5mm, and the joint was made with a friction speed of 27.5s^<-1> and a friction pressure of 60 or 80MPa. Then, the effect of the bottom of the grooves (groove bottom thickness) for the insert piece on the joining phenomena and joint properties were investigated. As a conclusion, the joint had 100% joint efficiency with the base metal fracture at the groove bottom thickness of 1.4mm and the fixed specimen overhanging length of 5mm which was made at a friction pressure of 80MPa, although it did not achieve 100% joint efficiency at a friction pressure of 60MPa.

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The friction joining of an alumina-whisker-reinforced aluminum matrix composites bar to a zirconia bar was conducted numerically and experimentally. The numerical analysis was the thermal-elastic-plastic analysis solved using the FEM. The heat input in the numerical analysis was calculated from the results of experiment to make the numerical temperature history agree to the experimental values. The obtained principal strain direction distribution showed the circular band. This band shape was observed by optical microscopy as in agreeing with the whisker distribution in the vicinity of the joint interface.

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