In this study, we focused on the principal stress value and direction in weld residual stress fields. We used specimens welded under three heat input conditions, and so the weld metal of each specimen had a different solidification structure. We evaluated the principal stress value and direction of the specimens by X-ray stress measurement. In the specimen welded under the smallest heat input condition, the weld metal showed a clear difference between the maximum principal stress and the minimum principal stress. However, in the specimen welded under the largest heat input condition, the maximum principal stress and the minimum principal stress were almost the same value. The principal stress direction changed significantly and shear stress occurred at the weld metal boundary in the specimens welded under the large heat input condition. In all specimens, the principal stress direction in the base metal changed. As conclusions, when the minimum and the maximum principal stress values were almost the same, the principal stress direction changed more noticeably. Additionally, due to the influence of the edge in the base metal, the principal stress direction changed significantly regardless of the welding condition.
The Japanese sword “WAKIZASHI” used in this study was made by sword craftsman. The surface of blade was finished by rough grinding just before final hand polishing process. In this study, the sword was cut using a wire-electrical discharge machine. Using a cut specimen, microstructure, hardness and carbon content of cross section of blade were measured experimentally. Surface residual stress distributions from the front edge “HASAKI” to the ridge “MUNE” of blade were measured by x-ray stress measurement. The diffraction from 211 plane of ferrite or martensite by Cr-Kα radiation was used. As a result, the edge of blade “HA” had martensite structure. The area of “HA” was 10% of the total cross-sectional area. Other part remained pearlite and ferrite structures. The carbon density between two different carbon steels, the surface layer and core materials, changed continuously by diffusion. The hardness distribution coincided with the carbon content distribution. Biaxial principal compressive residual stresses were found to be generated and have constant stress gradients in depth on the ground blade surface because the ψ-splitting was not observed and the measured 2θ vs. sin2ψ relations could be approximated as a parabolic curve. Large compressive residual stresses more than -1.0 GPa were distributed from “HASAKI” to “HAMON” on the edge of blade. On the other hand, compressive residual stresses diminished gradually to -500 MPa from “HAMON” to “MUNE”. The surface compressive residual stress distribution directly depended on the cross sectional microstructure of sword. Additional compressive residual stress field induced by rough grinding was superimposed on the residual stress field after quenching and tempering process.
The specimen material was austenitic stainless steel, SUS316L. The residual stress was induced by water-jet peening. The residual stress was measured using the 311 diffraction with conventional X-rays. The measured residual stress showed the equi-biaxial stress state. To investigate thermal stability of the residual stress, the specimen was aged thermally at 773K in air to 1000h. The residual stress kept the equi-biaxial stress state against the thermal aging. Lattice plane dependency of the residual stress induced by water-jet peening was evaluated using hard synchrotron X-rays. The residual stress measured by the soft lattice plane showed the equi-biaxial stress state, but the residual stress measured by the hard lattice plane did not. In addition, the distributions of the residual stress in the depth direction were measured using a strain scanning method with hard synchrotron X-rays and neutrons.
The ductile damage progress of the FCC single crystal was verified by the profile analysis using the white X-ray obtained in BL28B2 beam-line of SPring-8. In this study, an aluminum single crystal of the purity 6N was used as a specimen prepared in the I-type geometry for tensile test. The notch was introduced into one side of the center of a parallel part of the specimen by wire electric discharge machining. White X-ray, which has 200 microns in height and 100 microns in width, was incident into the specimen on the Bragg angle θ of 3 degrees in the horizontal plane using energy dispersive X-ray diffraction technique. The specimen was deformed by elongation along crystal orientation , and the diffraction profile of the white X-ray which penetrated it was analyzed. In profile analysis, the instrumental function was defined in consideration both of a divergence by a slit and a response function peculiar to an energy dispersive method. The Gauss component of integral breadth related to non-uniform strain and the Cauchy component of integral breadth related to crystallite size were determined by removing the broadening by the instrumental function from the diffraction profile of white X-ray. As a result, in 1.1% of applied strain, increase of the lattice strain was observed in the direction of about 45 degrees of slant from the notch bottom. However, the Gauss component and the Cauchy component of the integral breadth did not indicate the distinct tendency. In 2.2% of applied strain, the lattice strain reduced in the direction of about 45 degrees of slant from the notch bottom. Non-uniform strain and dislocation density decreased similarly. On the other hand, the development of crystallite was estimated in the area due to the increasing of the Cauchy component. The characteristic of the ductile damage progress near the notch of the aluminum single crystal which has crystal orientation  along the tensile direction was confirmed by this method.
Bending strength in hot-deformed Nd-Fe-B magnets which is brittle materials was investigated by 4-point bending test and after that fracture surface was observed with a scanning electron microscope (SEM). Crystal orientation was evaluated using an electron backscatter diffraction (EBSD). Grains were disk-shaped and microstructural anisotropy was observed. Deformation temperature was set to 750°C, 800°C and 850°C in order to control the grain size. Specimens were cut out in four directions from deformed plates to investigate the relationship between bending strength and grain direction. By observing fracture surface, fracture origins can be divided into three groups - a single void, aggregation of voids and contaminant. The contaminant was located in normal grains region with microstructural anisotropy. The others, however, were fine abnormal grains region without microstructural anisotropy. Bending strength increased with increasing deformation temperature. Higher temperature brings about the increase in crystal growth and crack propagation resistance, because crack has to propagate in a zigzag manner along grain boundary. When the defect is large enough, the tip of the defect closes to the microstructural anisotropy region. Namely, the strength is affected by the direction of specimen. On the other hand, when a defect is small, the influence of specimen direction on the bending strength is small. Small defects are buried in a fine abnormal grain region without microstructural anisotropy.
We deposited copper films which have a different grain size on the silicon single crystal wafer with dc magnetron sputtering. The crystal grain size of the copper films was varied by changing the substrate temperature Ts, which is one of the sputtering deposition conditions, between 64°C and 200°C. The obtained copper films were set on an optical microscope equipped with a vacuum heating device. The films surface were observed with the microscope throughout the thermal cycling between room temperature to 800°C. Next, we examined the temperature which hillocks begin to form. As a result, we confirmed the clear relationship between the temperature which the hillocks begin to form and the initial grain size of the copper film. In the case of low substrate temperature of Ts = 64°C, the initial grain size of copper film was very small, and many hillocks were formed at low heating temperature of 300°C. On the other hand, in the case of high substrate temperature of Ts = 200°C, the initial grain size of copper film was large, and hillocks were not formed below heating temperature of 800°C.