We develop a method for high-speed and high-accuracy first-principles calculations to derive the ground-state electronic structure by directly minimizing the energy functional. Making efficient use of the advantages of the real-space finite-difference method, we apply arbitrary boundary conditions and employ spatially localized orbitals. These advantages enable us to calculate the ground-state electronic structure of a nanostructure sandwiched between crystalline electrodes. The framework of this method and numerical examples for metallic nanowires are presented.
Effect of heat treatment on mechanical properties and microstructures of Fe-8Cr-2W-0.1C-0.2V-0.04Ta martensitic steel F82H doped with about 60 mass ppm B or both of 60 mass ppm B and 200 mass ppm N has been examined. The normalization was heated at temperatures from 950 to 1250°C for 1.8 ks, followed by air cooling or water quenching. After tempering treatment at 780°C or 750°C, the distributions of boron, boron nitride and oxygen were measured by a secondary ion mass spectrometry (SIMS). Optical microstructural observation and tensile and Charpy impact tests were performed also. In the boron doped F82H the tensile properties were similar to the non-doped F82H, but the ductile-brittle transition temperature (DBTT) shifted from -43°C to 15°C. SIMS images with high intensity of boron were observed in localized regions of the boron doped F82H. Water quenching reduced the DBTT shift, about 30°C, and the localized boron intensity was slightly decreased. In the boron and nitrogen doped tempered-F82H heat-treated by the water quenching from the normalizing temperature, the properties of tensile and Charpy impact were similar to the non doped F82H, and no pronounced localized boron image was observed in the SIMS image and no intensities of oxides and boron nitride were observed either.
The authors found that liquid Cu droplet wetted and spread very widely on a solid substrate of Fe in a reduction atmosphere after the surface oxidation of the substrate. The mechanism of the unusual wetting behavior was investigated by using surface-oxidized Fe substrate with liquid Cu, Ag, Sn and In. It was found that under reduction atmosphere, fine pores were formed at the surface of the substrate which had been oxidized, and that the pores were connected each other continuously over the whole surface. The liquid metals penetrate into those pores by capillary force to cause the unusual wetting behavior.
Stress corrosion cracking (SCC) occurs in shrouds and piping of low carbon austenitic stainless steels at nuclear power plants. A work-hardened layer, where the transgranular SCC initiates, is considered to be one of the probable cause for this occurrence. In order to clarify the microstructural characteristics of work-hardened layer at the surface of shrouds or piping, the strengthen analysis of low carbon austenitic stainless steel, 316SS, rolled at the reduction in area, RA, of 10, 20, 30, 40 and 50% at room temperature were conducted on a nanoscopic scale, using an ultra-microhardness tester, TEM and SEM. TEM and SEM observation showed that the microstructural parameters are the dislocation cell size, dcel, coarse slip spacing, lcsl, and austenitic grain size, dγ. Referring 10dcel and 10lcsl, Vickers hardness, HV, corresponding to macro strength was expressed as Hv=Hvbas*+Hvsol*+Hvdis*+Hvcel*+Hvcsl*. Hvbas* (= 100) is the base hardness, Hvsol* is the solid solution strengthening hardness, Hvdis* is the dislocation strengthening hardness in the dislocation cell, and Hvcel* and Hvcsl* are the fine grain strengthening hardness due to the dislocation cell and coarse slip. Hvsol* was about 50, independently of RA. Hvdis* was zero at RA<30% and increased at RA>30%. Hvcel* and Hvcsl* increased with increasing in RA and were kept constant at about 50 and 120 at RA=20 and 30%, respectively. It was suggested from these results that all dislocations introduced by rolling might be dissipated for the creation of dislocation cells and coarse slips at RA<30% and that the microstructure contributing to the fine grain strengthening due to the dislocation cell and coarse slip might be accomplished at RA=30%. The dislocation strengthening in the dislocation cell might begin to operate at RA>30%.
Fretting fatigue properties were studied in air and in a simulated body fluid, PBS(−), using a commercial Zr-based amorphous alloy (7.6Ni-12.3Cu-3.5Al-76.6Zr in mass%). Fretting fatigue tests were carried out under load control using a sinusoidal wave with a stress ratio of 0.1, a frequency of 20 Hz in air and 2 Hz in PBS(−) and a contact pressure of 30 MPa for fretting. There was no difference between the stress-number of cycles to failure (S-N) curves of the plain fatigue test in air and in PBS(−), and the 107-cycle fatigue strength was approximately 150 MPa for both environments. The 107-cycle fretting fatigue strength in air was one-third as high as the plain fatigue strength, while the 2×106-cycle fretting fatigue strength in PBS(−) was approximately twice as high as that in air. Although the friction coefficient between the specimen surface and the fretting pad, which affects the fretting fatigue strength, was hardly different between air and PBS(−), SEM observations showed that the actual contact area of the fretting pad on the specimen surface tested in air was smaller than that tested in PBS(−). Thus, we considered that the decrease of the fretting fatigue strength in air was caused by the higher contact pressure of the pad in air than that in PBS(−). XPS analyses also showed that the specimens tested in air and in PBS(−) had the different compositions of the oxide films on their surfaces, suggesting that the difference in the composition of the oxide films affect the fretting damage and thus the fretting fatigue strength.
The microstructures of an A2O3/YAG/ZrO2 eutectic Melt-Growth-Composite(MGC)solidified unidirectionally by the modified-pulling-down method were studied by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and electron backscattered pattern (EBSP) method. The anisotropy of strength was investigated by hardness tests and compression tests at various directions of the composite at elevated temperatures. The eutectic MGC has strong preferred growing orientation and the constituent phases hold the orientation relationship. The eutectic MGC shows excellent high-temperature strength and can deform plastically above about 1500 K. High-temperature strength above 1500 K depends on strain rate, temperature and orientation.
Molybdenum, in many cases, is chosen as a substrate of cesium telluride thin film photocathode for a radio frequency electron gun (RF-Gun), which shows high performance. Therefore, in this study, we chose molybdenum as a substrate for cesium telluride thin film. The dependence of quantum efficiency on the kinds of metals for substrate has not been measured entirely and not been well understood. In this report, showing the result of measurements, we report on the dependence of the quantum efficiency on substrate for the cesium telluride thin film photocathode. In addition to molybdenum, we use tungsten and copper for substrate. We also report on the dependence of the quantum efficiency on the average surface roughness of substrate for cesium telluride thin film when using tungsten and copper as well as molybdenum for the substrate. The rate in the measurement of the dependence of quantum efficiency on the kinds of metals for substrate to incident light wavelength 250 nm was 20% on molybdenum, on tungsten 8.6% and on copper 4.8%, when the tellurium thickness is 10 nm. In the measurement of the dependence of quantum efficiency on the average surface roughness Ra of the substrates, the rate a sample on a substrate of which Ra is less than 0.1 μm shows was 20%, on a substrate of which Ra is 50 μm was 15%. Thus, the quantum efficiency of cesium telluride thin film photocathode depends on the kind of metals for the substrate, and also on the roughness of the surface of substrates.