Surveillance data for pressure vessel steels of the 51 LWR plants in Japan were analyzed to make clear the effect of neutron irradiation on the brittle transition temperature of the steels. The clear difference observed in the rise of the ductile to brittle transition temperature between the normal and accelerated irradiation samples is considered to be due to the effect of neutron flux. The present analysis is discussed in comparison with the result of computer simulation based on the rate equations of the radiation damage process and the recent experiments of APFIM and positron annihilation.
Results of three test methods were compared among different laboratories to determine a standard measurement method of critical current (Ic) as a function of bending strain for Ag alloy-sheathed Bi-2223 superconductor tapes. The die-press, the weight-wind, and the bending-rig methods were used. Specimens were bent at room temperature and the Ic values were measured at 77 K and in the self-field. After Ic measurement of an unbent specimen, bending of the specimen and subsequent Ic measurements were done from 0.2% to 1.0% in 0.2% steps of strain on single specimens. Both Ic and Ic/Ic0 values start to decrease from 0.4% strain and continue to decrease up to 1.0% strain. Moreover, data scattering starts to increase stepwise at 0.4% strain, being a function of the magnitude of Ic and Ic/Ic0 values with strain for all the test methods. Regarding the statistical analysis on the data, results showed that the data obtained using the die-press method were reasonable and no serious defects were associated with this method. On the other hand, results of the bending-rig method showed a lower Ic/Ic0 degradation rate with bending strain than those of other two methods, which exhibited nearly the same degradation rate. The use of solder for the current contact induced extra thermal strain in the specimens. Consequently, the data for the irreversible strain scatter. Examining the difference in the resistance of the current contact part between the method using solder and the way a specimen is mechanically clamped, the mechanical method is useful and does not affect the test results. Results show that the mechanical method for the current contact increases the test method's effectiveness and reliability.
We studied effects of heating rate, holding temperature and holding time on porosity and pore morphology of aluminum foams fabricated by powder metallurgy process. When the temperature of the specimen exceeds the melting point, the specimen starts foaming. The porosity of the molten specimen increases with increasing furnace temperature, and the porosity of the aluminum foam reaches about 80%. Pore morphology of aluminum foam becomes inhomogeneous because the cell face of the aluminum foam collapses during the passage of time. The heating rate hardly affects the maximum porosity. The furnace temperature as holding temperature are closely related with the porosity of aluminum foam. The porosity map of heating rate and elapsed time was obtained, and the aluminum foam with arbitrary porosity can be made using the porosity map.
Self-interstitial atoms (SIAs) in bcc iron display unusual migration behaviors; strong anisotropy toward a <111> direction with occasional rotation to an equivalent direction as well as retracing the same way as it has come, and also ultra-high mobility when they are clustered. These singularities cannot be explained by simple interstitial or interstitialcy diffusion mechanisms. However, some of them will be well accounted if the SIA could behave as a soliton, which makes three-dimensional movements in appearance, but essentially a serial combination of one-dimensional migration. Indeed, a crowdion, one of the isomeric configurations of the SIA, has an atomic arrangement very similar to the one-dimensional dislocation core structure, whose migration kinetics has been well modelled by a one-dimensional soliton equation. Here we report a decisive observation that both a single and colliding two crowdions really behave as solitons in iron crystals using molecular dynamics simulations. In addition, we ascertain that the present results are attributed to the intrinsic nature of the crowdion where an overall potential felt by atoms therein is very shallow and periodical along the migration direction.
We observed a reconstructed Si(110) surface using an ultrahigh-vacuum (UHV) non-contact atomic force microscope (NC-AFM). The Si(110) surface has several characteristic structures, such as the 16×2, (17, 15, 1) 2×1, 1×1, zigzag structures. We demonstrated the AFM observation of the surface formed upon annealing the samples in direct current heating so as to clean the surface. We obtained the same structures in the AFM observation as the proposed 16×2 model of a Si(110) reconstruction in a STM observation. The UHV NC-AFM results substantiated that the Si(110) surface has a characteristic 16×2 structure.
The AlN/Al base composite has been made through a solid-liquid reaction between molten Al and BN powder under either the atmosphere of N2 or Ar. However, the volume fraction of AlN in the composite is larger in the former case than in the latter case, when both compared under the same forming condition besides the difference in the atmosphere. This fact suggests that extra AlN may be formed under the N2 atmospheric condition through the direct reaction between Al and N, and brings forth the idea that the reactant B in molten Al may play some promoting role on the formation of AlN. To verify this hypothesis, such experiments as B containing Al base alloy is heated under various pressures of N2 have been performed. These experiments have shown some interesting results concerning the morphology of AlN particles formed, and have suggested a “promoting effect of B for the AlN formation”.
In the development of the adsorption refrigerator, one of the most serious concern is to protect the corrosion from aluminum heat exchanger in deoxidized water. Two kinds of corrosion protection methods were discussed. One was to form an SiO2 Sol/Gel film of which thickness is about 2 μm on the aluminum surface and the other was to add small amount of SiO32- in the deoxidized water. When an aluminum sheet of A1N99 coated with the SiO2 Sol/Gel film on the surface was immersed in deoxidized water, corrosion did not occur during 10000 h. In the case of actual aluminum heat exchanger with the same film on the surface, although corrosion did not happen during the first 1800 h, it came out suddenly after 1800 h. From the result of this corrosion performance, the aluminum heat exchanger with the SiO2 Sol/Gel film is not considered to be proper for the application to the refrigerator. The effect of SiO32- in water to protect the corrosion was investigated and it was confirmed that corrosion from the aluminum heat exchanger with the SiO2 Sol/Gel film did not occur for at least 5000 h in the deoxidized water with 5 ppm SiO32-.
Relationship between fracture toughness and shear band length (SBL), crack tip opening displacement (CTOD) on the specimen surface and stretched zone width (SZW) on the fracture surface in Zr-, Cu- and Ti-based bulk metallic glasses (BMGs) was investigated in order to examine the mechanisms that the BMGs show a high fracture toughness. Zr50Cu40Al10 and Zr50Cu30Ni10Al10 BMGs fabricated by an ark tilt casting method, and Cu60Zr30Ti10, Ti41.5Zr2.5Hf5Cu42.5Ni7.5Si1 BMGs fabricated by a high-frequency induction casting method were used. The fracture toughness test was conducted based on ASTM E399. Compact type specimen was used (1.0 mm, 2.0 mm and 2.3 mm in thickness, thickness:width=1:4). Fatigue pre-crack was induced under ΔK less than 6 MPa•m1/2. The crack length and SZW were measured on the fractographs by scanning electron microscope (SEM), and the SBL and CTOD were measured on the photographs of specimen surfaces by the SEM. Observed SBL and CTOD in each BMG showed the near values of the plastic zone size and CTOD calculated by the fracture mechanics under the plane stress condition, respectively. By the stereo-matching observation on the fracture surfaces, the crack tip inside the specimen clearly opened and a stretched zone area was shown. Average SZW in front of the fatigue crack in the Zr- and Cu-based BMGs was roughly proportional to the fracture toughness value.