In previous report, magnetostrictive susceptibility of Sm-Fe thin film was increased with small addition of carbon and nitrogen. However, excessive addition of carbon and nitrogen amount cause decreasing of megnetostrictive susceptibility and saturated magnetostriction. In this study, Sm-Fe/Sm-Fe-C-N multilayer thin film was prepared by d.c. magnetron sputtering process. The highest saturated magnetostriction of Sm-Fe/Sm-Fe-C-N multilayer thin film was -800 ppm and highest magnetostrictive susceptibility was 26 ppm/kAm-1 shown at Rt=0.5 Sm-Fe-C-N film thickness ratios.
Magnesium based alloys possess light-weight and high hydrogen absorption capacity so that they have been investigated extensively for several decades. Great attention also has recently been paid to graphite as a hydrogen absorber. In this study Mg-C alloys were prepared by ball milling and their hydrogenation properties were investigated. Powders were first mixed with a 1 : 1 molar ratio of Mg to graphite. Milling balls and a pot were made of SUS304. This process was performed with a vibration ball mill at the speed of 11.8 Hz under an Ar gas atmosphere for 60 hours. The prepared powders were handled in a glove box filled with an Ar gas. After ball milling, samples showed a new X-ray diffraction peak, which was either not a peak from Mg and/or graphite. An affinity for the powders with hydrogen was confirmed at 453 K and the 1.8 MPa hydrogen pressure. The total amount of absorbed hydrogen was estimated to be 2.0 wt% from the thermal desorption spectroscopy (TDS) spectrum.
Irradiation hardening and embrittlement due to high-dose neutron irradiation around 573 K are important issues on RAF/M steels. The purpose of this study is to examine a correlation between tensile property and micro-hardness in F82H steel using neutron and ion-irradiation. Neutron irradiation was performed in HFIR up to 8 dpa at 573 K. Ion irradiation experiment at ~573 K was carried out at the TIARA facility of JAEA. Relationship between the micro-hardness (Hm) and Vickers hardness (Hv) in F82H and its heat treatment variants was calculated by Hv≒60×Hm. The yield stress (σy) was evaluated by σy=3.2~3.4×Hv×(0.1)n (n: work hardening exponent) from this study. Following these equations, it can be estimated that the yield stress of irradiated F82H up to ~100 dpa at 573 K is about 1000 MPa.
Since Anodic bonding of silicon to glass is solid state bonding, it is often used as a MEMS manufacturing technology when accuracy of dimensions is required. However, it is necessary to clarify the relation between bonding conditions or glass compositions and the mechanical properties of anodically bonded joints such as tensile strength and fracture mode. The influence of environmental factors such as high temperature and high humidity on the joints is also not well understood. This study was conducted to investigate the influence of bonding conditions on mechanical properties and on growth of the reaction layer at the bond interface. Moreover, since the transfer of electric charge in the bond interface is likely to be closely related to the anodic bonding reaction, the bonding charge density which flowed into the bond interface was measured during the bonding process, and the relation between the bonding charge density and the tensile strength or the reaction layer was examined. At bonding temperatures below 300°C, tensile strength increased with the bonding time and bonding voltage. At bonding temperatures above 350°C, increasing the bonding time and bonding voltage did not influence tensile strength. At bonding conditions of low charge density, the observed fracture mode was interface fracture. As the bonding charge was increased, tensile strength was stabilized and the fracture mode changed to glass fracture. As the bonding charge density was increased, the reaction layer became thicker, and growth of the reaction layer was controlled by the bonding charge density. There was a tendency towards greater tensile strength with thicker reaction layers. Thus, measuring boding charge during the bonding process helped to clarify the effect of bonding conditions on the joints.
Coal fly-ash bulk materials were prepared by spark plasma sintering (SPS). The as-received coal fly ash produced by Misumi Power Station (The Chugoku Electric Power Co. Inc.), had an average particle size of 19 μm and contained about 2% carbon from unburned coal. The sintering temperature was 1273 K for 10 min. The mass density of the sintered compact was 2.4×103 kg/m3. After three-point flexural testing of the compact, the average flexural strength and Young's modulus were 25.6 MPa and 23.0 GPa, respectively. From the flexural strength, the Weibull modulus was found to be m=6.13, indicating that the compact was a typical ceramics. Fractographic examination indicated that in all specimens the fracture origin was located on the bottom surface and was not an intrinsic flaw. Vickers indentation test showed that the fracture toughness was 0.61 MPa•m0.5 and the calculated critical flaw size c0, was 0.18 mm. This c0 value was larger than that of the voids and the unburned carbon at the fracture surface. It is noteworthy that the mechanical strength of the sintered compact was not affected by the voids and unburned carbon.
Resistive materials with resistivity (ρ) of 5.0 to 689.9×10-8 Ωm and temperature coefficient of resistance (TCR) of 1749 to 4948×10-6 K-1 were successfully fabricated by using the stacking and rolling of metallic sheets of Fe and Cu. The Fe/Cu multilayer structure showed changes of electrical characteristics with the direction of accumulating and the number of sheets accumulating. The TCR values of the specimens decreased with increase of the number of accumulating layers at the parallel direction for current flow. The resistivity of the specimens increased with increase of the number of accumulating layer at the series direction for current flow. This process allows the electrical characteristics to be controlled as required, and the resistance material of a precise resistor for current detection to be made.
Recently, lead-free solders have been used in electronic equipments. There are many reports on mechanical properties of lead free solders. It is important to understand the evolution of solidified structure, though, such reports are few. In order to understand the solidification process, the Sn-Cu alloys, which are one of the candidate alloys for lead-free solders, have been used in this study. Three alloys, hypo-eutectic, eutectic, and hyper-eutectic, have been prepared. The specimen was quenched during solidification. Then the solidified structures of interrupted specimens were compared to thermal histories. In the case of hypo-eutectic and hyper-eutectic alloys, it was found that the undercooling of approximately 10 degrees was necessary for nucleation of β-Sn as a primary dendrite or as a halo. On the other hand, the undercooling was not necessary for crystallization of primary Cu6Sn5. The latter indicates that the primary Cu6Sn5 is easy to nucleate and grow even it is a facet. Primary Cu6Sn5 may be a starting site of a halo, but it doesn't facilitate nucleation of β-Sn. In the case of the hypo-eutectic alloy, a small undercooling for nucleation of eutectic structure was observed. Such undercooling was not observed in eutectic and hyper-eutectic alloys. This may be interpreted by the difference in the liquid composition when the eutectic solidification starts.
Global aluminum consumption has exhibited significant growth in recent years, due to its useful properties. As this will result in a large amount of aluminum accumulation as urban mines, the exploitation of these urban stocks will be an important issue in the future. To examine the recycling potential of urban stocks, a dynamic material flow analysis on aluminum was conducted focusing on Japan, the United States, Europe and China. The concentrations of the alloying elements were also investigated, since carryover of alloying elements during recycling results in off-specification secondary metals and alloys. The recycling of aluminum scrap was optimized from the results of dynamic material flow analysis using multi-material pinch analysis. It was estimated that Japan, the United States, Europe and China have the potential to reduce their primary aluminum consumption to 60%, 65%, 30% and 85% of their present levels, respectively. In 2050, it is estimated that 11400 kt of primary aluminum will be required among the four countries, while 12400 kt of obsolete scrap will not be able to be recycled due to high concentrations of alloying elements.
The heat-resistant Ti alloys have been developed to replace Ni-based superalloys conventionally used for discs and blades in the compressor part of jet engines. DAT54 is a newly developed near-alpha Ti alloy in Japan, is serviceable up to 600°C. Titanium has a high solid solubility limit of oxygen and is susceptible to oxygen. Therefore, a systematic study was carried out at different temperatures to examine the degradation of the titanium alloy DAT54 due to oxidation. Test specimens were exposed at 500°C for 100 h or at 600°C for 500 h. Tensile tests were carried out on both as-received and exposed specimens for comparison between ambient and elevated temperatures. To clarify the influence of surface oxidation, we also examined the mechanical properties of oxidation-layer-removed specimens. Tensile properties of the oxidized specimens at and above 200°C were comparable to those of as-received specimens. However, a dramatic loss in elongation at room temperature was observed. The oxidized specimens form cracks on the brittle rutile layer in the elastic region. At room temperature, those surface cracks could propagate easily through the α-case and the oxide layer as well , because deformation of crack tips to a dull state did not occur due to their brittleness. The notched tensile strength was also shown to be sensitive to oxidation. A creep test was performed under the stresses of 100 and 200 MPa at 600°C. Creep strength was improved after the oxidation, probably due to further precipitation of Ti3Al in the alpha phase. We found that the oxidation-resistant coating dramatically decreased the creep rate and increased the creep rupture life.
Recently, aluminum foams with more homogeneous pores are expected from the improvement of compression strength reliability. In this research, for the closed cell Al foams which are fabricated by adding foaming agent to molten aluminum (direct aluminum foaming in melt), the effect of pore control regarding viscosity, cooling rate and foaming agent size on the uniaxial static compression strength was examined. As a result, it is possible to make small and homogeneous pores by increase in viscosity, improvement in cooling rate and using a smaller foaming agent. However, Al foam with smaller a foaming agent became higher density as well as decreasing the pore size. The increment in the density of Al foam depends on the cell structure (thick cell walls and small pores). This is, the density increases with decreasing average pore diameter. Compression strength (plateau stress) of Al foams with small and homogeneous pores was improved. When the compression strength of Al foams is shown in relation to density and plateau stress, plateau stress was about the square of the increase in density.
The effects of hot rolling conditions on the size of TiC precipitates in Ti-added ferrite-martensite hot-rolled steel sheets and precipitated TiC size on fatigue limit were investigated. Steel sheets were hot-rolled at 1153 K or 1073 K and rapidly cooled to 953 K after hot-rolling and air-cooled for several seconds in order to accelerate ferrite transformation and rapid cooled again to coiling temperature. It was found that TiC particles were coarsened with the decline of finish-rolling temperature (FRT) and the increase of air-cooling time after hot rolling. This is presumably because the decrease of FRT raises the ferrite transformation temperature and TiC precipitation temperature; and the increase of air-cooling time from 953 K results in the coarsening of TiC particles due to growth or Ostwald growth of TiC. As for the relationship between TiC particle size and fatigue limit, it was found that fatigue limit was maximized when the average size of TiC particle was about 7 nm. This indicates that the fatigue limit of Ti added ferrite-martensite hot-rolled steel sheets depends upon precipitation strengthening of precipitates which are not cut by dislocations.
As a new type of metallic biomaterial, porous pure titanium filled with a medical polymer has been developed for obtaining a low Young's modulus similar to that of bone. This type of biomaterials will inhibit the deterioration of mechanical properties due to the presence of pores, and provide biofunctionalities that are intrinsically possessed in certain polymers. However, the inhibition of the deterioration of mechanical properties is not satisfactory because of the poor interfacial adhesiveness between the titanium particles and the medical polymer. Therefore, in the present study, silane coupling treatment is employed in order to improve the interfacial adhesiveness, and silane-coupling-treated (Si-treated) porous pure titanium (pTi) filled with polymethylmethacrylate (PMMA) is fabricated. Subsequently, the effect of the silane coupling treatment on the mechanical properties of the pTi filled with PMMA is investigated. The tensile strengths of the Si-treated pTi filled with PMMA are higher than those of pTi and non-Si-treated pTi filled with PMMA. In the fractographs of non-Si-treated pTi filled with PMMA obtained after the tensile test, the detachment of titanium particles from PMMA is observed; this occurs because of poor interfacial adhesiveness between titanium particles and PMMA. However, in the case of the Si-treated pTi filled with PMMA, the interfacial adhesiveness between titanium particles and PMMA is improved by the silane coupling treatment. This leads to the dispersion of the stress concentration at necks between particles, resulting in an improvement in the tensile strength of pTi. On the other hand, PMMA filling hardly affects Young's modulus of pTi because Young's modulus of PMMA is lower than that of pTi.