A double exposure method (DEM) was proposed as a stress measurement method using hard synchrotron X-rays for coarse-grained materials or welded parts. Up until now in the DEM, methods such as function approximation and finding straight lines from diffraction spots have been tried. However, sufficient accuracy could not be obtained for images containing a mixture of diffraction spots and rings. In this study, a new method to determine the diffraction radius is proposed. We obtain the waves of circumferential integrals for regions of interest in the front and the rear area detectors, and then determine each diffraction radius using a cross-correlation algorithm. When this method was applied to the measurement of the residual stress in the specimen of the butt-welded pipe, the diffraction radius could be determined with good accuracy. Using the cross-correlation algorithm, the diffraction radius can be determined regardless of the patterns of the diffraction spots or diffraction rings, and this method is the robust and efficient angle determination method suitable for the DEM.

In this study, a direct diode laser with a wavelength of 940 nm was uniaxially scanned on a carbon steel S45C surface at an incident angle δ=15 °. The effects of laser scanning conditions on the surface temperature and the hardened layer depth after quenching were investigated. The following conclusions are obtained using experimental results and transient heat conduction theory. At first, both surface temperature during laser scanning and the total hardened layer depth after quenching are found to be proportional to the laser energy density and, however, increase with an increase in the laser power even at constant energy density. These results indicate that the internal temperature of steel cannot be determined by one-dimensional steady-state heat conduction. Next, the internal temperature of steel is estimated by one-dimensional transient heat conduction. A penetration thickness, which is the depth where the laser energy affects the internal temperature of steel, is considered from the heat conduction theory. As a result, an increment of internal temperature of steel is found to be proportional to a new parameter, √vq₀. The surface temperature during laser scanning and total hardened layer depth after quenching are found to be also proportional to the new parameter, √vq₀, and be expressed as a single regression line of √vq₀, even if the laser output is varied. The dominant parameter that determines the hardened layer depth by laser hardening can be identified.

Non-uniform strain on the surface of magnesium alloys has been found out to affect the formation of a hydroxide layer, which shows corrosion resistance. There is possibility to control the hydroxide layer by applying of variable non-uniform strain to the magnesium alloy surface prior to the layer forming processes. To apply non-uniform strain to AZ91D high pressure die casting magnesium alloy, a sodium bicarbonate peening process was carried out under the following conditions; projection pressure 0.6 MPa, distance between nozzle and material 150 mm, duration 10 seconds. After peening specimens were evaluated with the surface properties, surface and depth residual stress distribution, and non-uniform strain distribution. Peening forms processing layer on surface the depth was 10 to 20 micrometers. In addition, many twins were formed inside the material when using the larger grain size of projectile. It was found out that nou-uniform strain, and compressive residual stress around -130 MPa could be formed by regulating the grain size difference of the sodium bicarbonate projectile.

In ultra low-carbon Fe-18%Ni alloy with a lath martensitic structure, the effects of microstructure and dislocation density on the yielding and deformation behavior were investigated. The microstructure of the matrix became finer with decreasing austenite grain size but no difference was found in the yielding behavior up to 2% deformation. Dislocation density was constant independent of the microstructure and was estimated to be about 1.5 × 10¹⁵/m². The dislocations that had been introduced by martensitic transformation formed a tangled dislocation cell structure within a lath and the amount of dislocation strengthening was determined by a critical stress that was required to make the tangled dislocations bow out. As a result, it was confirmed that the 2% proof stress of the steel used can be evaluated by adding the amount of dislocation strengthening to the friction stress.

We investigated martensitic (α') phase distribution in tensile-deformed SUS304 stainless steel by X-ray diffraction examination at the strain rate from 7.1×10^-4 /s to 9×10² /s. The elongation decreased with increasing the strain rate at the strain rate below 7.1×10^-1 /s and it was almost constant beyond the strain rate. On the other hand, the reduction of area was almost constant at the strain rate below 7.1×10^-1 /s and it gradually decreased with increasing the strain rate. The amount of α' phase (V_α') tended to decrease with increasing the strain rate, and it increased with decreasing the distance from a fractured face. The true strain is calculated from the cross-sectional reduction. The relationship between the true strain and V_α' is described using the Angel's equation, and the α' phase distribution is predicted from the true strain distribution. The V_α' of the total specimen (V_α',tot) and the V_α' around the fractured face (V_α',frac) are calculated from the α' phase distribution. The strain rate dependence of elongation correspond with the strain rate dependence of V_α',tot. The reduction of area tend to decrease with increasing strain rate above 7.1×10^-1 /s when the decrease in the V_α',frac was observed.

Mod.9Cr-1Mo steels are widely used for steam pipes in ultra-super critical power plants. The creep strength of Mod.9Cr-1Mo steel welded joint is significantly lower than that of the base metal. It is necessary to clarify influence of long-term operation on creep strength of welded joints. In this study, a long-term used boiler welded joint which contained coarsening microstructure (CM) in weld metal was used. Creep tests were performed using tensile loading type miniature specimens with 1mm diameter and 5mm parallel length of constituent materials, standard and miniature size welded joint specimens taken from the welded joint. Minimum creep strain rate of the weld metal containing CM was 1000 times faster than that of new weld metal indicating significant reduction of creep deformation resistance and, was 10 times faster than a long-term used weld metal with only dendrite microstructure (DM). Creep rupture time of the standard size welded joint specimens, which failed at the CM in weld metal, was 4 times shorter than that failed at the DM. The miniature welded joint specimens failed at either HAZ or weld metal depending on influence of the CM containing in weld metal. A finite element creep analysis of both standard and miniature welded joint specimens with and without the CM in weld metal indicated that creep strain accumulation in the CM was larger than that in the DM causing shorter rupture time of the welded joints with the CM in weld metal.

In this study, we investigated the effect of the hybrid surface modification composed of plasma nitriding and DLC (diamond-like carbon) coating on the friction-wear properties and fatigue strength of alloy tool steel SKD11. Plasma nitriding and DLC coating improved the friction-wear properties, respectively. The hybrid surface modification was more effective to improve the friction-wear properties, because the planarity of the DLC layers was maintained by the formed hardened layer. The increase of hydrogen quantity in the DLC layers reduced the friction coefficient and improved the wear resistance. DLC coating suppressed fatigue crack initiation from the surfaces of the untreated and plasma-nitrided materials; however, its effect was not marked to improve the fatigue strength.

In order to explore the possibility of evaluating mechanical and thermal properties of thermal barrier coatings (TBCs) by Leeb hardness (HL) test, relationship between mechanical properties and HL value was examined on TBC plate-shaped specimen which was exposed to a high temperature atmosphere. A finite element (FE) analysis of the sphere impact process was firstly performed on a double-layered plate model in order to discuss the experimental relations. Obtained results can be summarized as follows: (1) Results of high temperature exposure tests showed a clear correlation between HL value and Young’s modulus and also thermal conductivity. (2) The FE analysis obtained here supported the relationship between the mechanical properties in TC layers and HL value. Consequently, it was confirmed that Leeb hardness test had capability of non-destructive testing method for assessing the Young’s modulus and thermal conductivity of top coat layer in TBCs.

Since grain refinement such as nano twin and nano crystalline in a metallic material is possible to improve the mechanical property, surface modification to generate such nanostructure is demanded. This study aims to develop ultrahigh velocity impact testing using microparticle to vary metallic microstructure due to severe plastic deformation with high strain rate. Regarding an impact test, this study developed Laser Induced Particle Impact Test (LIPIT), in which laser ablation induces supersonic ejection of microparticle. We first proposed a measurement method of particle velocity using mechanoluminescence (ML). It is found that a particle collision with the ML emits light due to mechanical stimulus. The light is detected using the photomultiplier tube (PMT), so that timing of particle arrival is determined, and then the particle impact velocity is estimated. This measurement method was verified using a high-speed video camera. In addition, to investigate the light emission response of ML, mechanical stimulus using pulsed laser irradiation was applied to the ML. It is found that the peak intensity and decay time in the emission response were dependent on the irradiated laser energy. By converting the irradiated laser energy to impact force using elastic plate theory of transverse impact, the relationship between emission response and impact force was discussed. Finally, our developed LIPIT was applied to a pure copper, producing nano crystalline structure on the surface around the impact indentation crater. In contrast, no deformation twinning was observed in the quasi-static indentation crater. Therefore, the developed LIPIT may realize a new surface modification technique, because this induces severe plastic deformation with ultrahigh strain rates, resulting in microstructural changes.

In this study, we investigated the generation process of anomalous growth regions on InN surface grown on GaN/sapphire template by the DERI (droplet elimination by radical beam irradiation) method using RF (radio frequency) – MBE (molecular beam epitaxy). The anomalous InN growth regions were observed in detail using TEM (transmission electron microscope) and classified into three regions. In the center of the anomalous growth region, there was no InN growth, while InN with a large thickness grew on the inner edge, and the thickness of the InN film on the outer edge increased toward the center. In addition, the dislocation type in the GaN template was discriminated between the abnormally grown and flatly grown InN regions, and it was found that the density of screw dislocations in the GaN template was larger in the abnormally grown InN region. The effects of In droplets on InN growth were classified into three regions, and the formation process of anomalous growth regions was discussed.

The cost reduction of polymer electrolyte fuel cells (PEFCs) has been demanded to further their industrial application. Separators in a PEFC account for a large portion of their production cost; therefore， the development of low-cost separators with high conductivity and corrosion resistance is key to reducing these costs. Several reports have been published on inexpensive stainless-steel separator coatings with tin dioxide or titanium dioxide. In this research， we focused on the use of indium tin oxide (ITO) to improve safety and to ease implementation, we employed deionized water as a solvent instead of methanol. The resulting ITO thin film showed a contact resistance of 8.8 mΩcm², which is comparable to films made from methanol solvent. ITO thin films also exhibited high corrosion resistance under sulfuric acid solution, similar to the actual PEFC operating environment.

This study verified the axial compression load-carrying capacity of concrete column members using normal concrete and recycled aggregate concrete to achieve a carbon-neutral and resource-recycling society in concrete structures. In addition, the axial compression load-carrying capacity of adhesive-applied PCM thickness increased column members using metal-grid verified as a reinforcing method for the assumed degraded damage. The proposed reinforcing method was a high-strength non-shrink mortar increasing thickness using 2 kinds of adhesive and metal grid. The experiment evaluated the axial compression load-carrying capacity of the existing RC column and the reinforced column members by an unconfined compression test. The result shows that the proposed reinforcing method increased the axial compression load-carrying capacity of RC columns using normal concrete and recycled aggregate concrete by 2.0 times due to the confined effect of the metal-grid. Therefore, the proposed reinforcing method can extend the service life of column members using normal concrete and recycled aggregate concrete without demolition and removal. Furthermore, the using recycled aggregate concrete is expected to contribute the reduction of CO₂ emissions in a resource-recycling society for concrete structures.