Ultra-bright Synchrotron Radiation Research Articles

Misorientation of Grains in Fatigue of Harmonic Structured Steel Observed by Diffraction Contrast Tomography Using Ultrabright Synchrotron Radiation

Misorientation of Grains in Fatigue of Harmonic Structured Steel Observed by Diffraction Contrast Tomography Using Ultrabright Synchrotron Radiation

Observation of flaking process in rolling contact fatigue of bearing steel with spheroidal inclusions by laminography using ultrabright synchrotron radiation X‐rays

AbstractRolling contact fatigue tests were performed on specimens containing spheroidal inclusions to clarify the effect of the orientation of inclusions, and the results were compared with those of specimens containing stringer‐shaped inclusions. For all types of inclusion, cracks first formed on the rolling surface and then propagated in the depth direction, and an internal crack parallel to the rolling surface formed from the deepest point of the vertical crack, which led to flaking. The flaking life of the specimens with spheroidal inclusions was longer than that of the specimens with stringer‐shaped inclusions, where the initiation and propagation lives of cracks were affected by the inclusion shape and size. The surface crack initiation life was shorter for specimens with longer surface inclusions, whereas the crack propagation life decreased with the depth of surface inclusion. The greater the scatter of the size of inclusions, the greater the scatter of flaking life.

Evaluation of Dislocation Density of Coarse and Fine Grains in Bimodal Harmonic Structured Steel Observed by Diffraction Contrast Tomography using Ultrabright Synchrotron Radiation

Evaluation of Dislocation Density of Coarse and Fine Grains in Bimodal Harmonic Structured Steel Observed by Diffraction Contrast Tomography using Ultrabright Synchrotron Radiation

Evaluation of Dislocation Density of Coarse and Fine Grains in Bimodal Harmonic Structured Steel Observed by Diffraction Contrast Tomography using Ultrabright Synchrotron Radiation

Austenitic stainless steels with a bimodal harmonic structure, in which the fine grain structure (Shell) exists around the coarse grain structure (Core), are prepared by powder metallurgy to improve both strength and ductility. Herein, X‐ray diffraction contrast tomography, a 3D grain mapping technique for polycrystalline materials using ultrabright synchrotron radiation X‐rays, is used to reconstruct the grain shape and location and to evaluate the average excess dislocation density of the Core and Shell structures. This technique allows one to evaluate the excess dislocation density not only on the surface, but also inside the sample where damage occurs in tensile tests. The results show that the excess dislocation density of the Shell structure is higher than that of the Core structure. The excess dislocation density of homogeneous austenitic stainless steels with grain sizes similar to the Core structure of the harmonic structured stainless steel is higher than that at comparable stresses, indicating that the deformation of the bimodal harmonic structured alloy is localized in the fine grain structure. This is consistent with the results obtained from electron backscatter diffraction analysis, in which the surface grains are evaluated.

Misorientation Measurement in Tensile Test of Bimodal Harmonic Structured Stainless Steel by Diffraction Contrast Tomography Using Ultrabright Synchrotron Radiation X-ray

Austenitic stainless steel (JIS-SUS304L) with a bimodal harmonic structure, which is defined as a coarse-grained structure surrounded by a network of fine grains, was developed by powder metallurgy to improve both strength and ductility. In the present study, three-dimensional grain mapping for polycrystalline materials, called X-ray diffraction contrast tomography (DCT), was conducted at SPring-8, which is the brightest synchrotron radiation facility in Japan, to elucidate the deformation mechanism of harmonic structured JIS-SUS304L in tension. The average total misorientation tended to increase with stress in tensile tests; however, the total misorientation of the harmonic structured JIS-SUS304L was lower than that of JIS-SUS304L with a homogeneous distribution of coarse grains at comparable stress. Furthermore, the change in the crosssectional area of the harmonic structured JIS-SUS304L was also measured by refraction contrast tomography (RCT) imaging using SPring-8 in tensile tests.

Crystal orientation and residual stress in TiN film by synchrotron radiation

Abstract The residual stress in a TiN film, the thickness of which is less than 1 µm, deposited by arc ion plating was measured using the SPring-8 synchrotron radiation facility installed at Japan Synchrotron Radiation Research Institute (JASRI). Films thicker than 300 nm have a {111} texture, whereas those with a thickness of 100 nm have a relatively random orientation. Instead of the conventional laboratory X-ray equipment, ultrabright synchrotron radiation can be used to precisely measure the residual stress in thin films with a thickness of 100 to 800 nm. The residual stress in thicker TiN films is about 7 GPa in compression and it is not affected by the film thickness. The slightly small compressive stress in a film of 100 nm in thickness may be due to the different crystal orientations in the film.

Observations of Twinning and Detwinning in Magnesium Alloy by Synchrotron Radiation DCT and EBSD

Recently, three-dimensional grain mapping techniques for polycrystalline materials called X-ray diffraction contrast tomography (DCT) have received considerable attention. DCT can simultaneously provide information on the three-dimensional grain arrangement of a sample, such as the shapes, locations, and crystallographic orientations of grains, together with the misorientation of grains. In the present study, the twinning and the detwinning in tension and compression loading in a magnesium alloy was observed by the DCT using ultra-bright synchrotron radiation X-ray, and the electron backscatter diffraction (EBSD) analysis. The shape of each grain in a polycrystalline magnesium alloy was successfully reconstructed and misorientation of each crystallographic plane was successfully measured by DCT. With increasing applied compression stress, the average value of the misorientation was decreased, while it is usually increased with plastic strain for materials without twinning. The value of misorientation increased with unloading process, indicating that the twinning was occurred under the compressive applied stress. The shape of diffraction spots of some grains also shows the twinning under the compressive stress and the detwining under the following tensile stress. The EBSD analysis of specimen surface also shows that the twinning was occurred under the compressive applied stress, and the following applied tension stress brought detwinning.

Observation of Flaking Process in Rolling Contact Fatigue by Laminography Using Ultra-bright Synchrotron Radiation

The flaking failure in rolling contact fatigue (RCF) results from crack initiation and propagation has been believed to originate from non-metallic inclusions located beneath the surface. With conventional microscopies, however, damage process in the internal region of materials could not be observed, then RCF crack initiation and propagation behaviours were observed by using synchrotron radiation computed laminography (SRCL) in the brightest synchrotron facility in Japan, and the effect of the inclusion orientation on the RCF property was examined. In our previous studies, crack initiation and propagation behaviours caused by extended MnS inclusions distributed in depth or transverse (width) direction was observed by the SRCL. In the present study, the fracture mechanism under RCF was discussed on specimens with MnS inclusions distributed in the rolling direction. As a result, vertical cracks were initiated on the surface, parallel to the ball-rolling direction in specimens. The crack propagation direction was then changed perpendicular to the rolling direction. Thereafter, similar with our previous studies, vertical cracks caused the horizontal cracks beneath the surface, when the vertical cracks reached to a critical length. The ratio of the vertical crack initiation life to the flaking life was higher than specimens with other inclusion orientation.

4D observations of rolling contact fatigue processes by laminography using ultra-bright synchrotron radiation

Since rolling contact fatigue (RCF) is known to be affected by non-metallic inclusions, the RCF crack initiation and propagation mechanisms in high-strength steels were observed using ultrabright synchrotron radiation laminography. The material of the sample was a high-carbon chromium bearing steel, which intentionally contained a high concentration of sulfur to enable the observation of crack initiation from MnS inclusions. To conduct an RCF test nearby the experimental hatch of a beam line of a synchrotron radiation facility, a special RCF testing machine was developed. Fatigue tests were interrupted to conduct laminography. The fatigue life for flaking depended on the length, width, and orientation of inclusions. For every length and orientation of inclusions, vertical cracks, whose faces were perpendicular to the rolling direction, first appeared, then horizontal cracks, whose faces were parallel to the sample surface, were formed after the vertical cracks reached a critical length. The initiation life of the vertical cracks and horizontal cracks depended on the length, width, and orientation of the MnS inclusions. The depth of horizontal crack initiation site, however, was almost independent of these parameters. The mechanism of the flaking process, which was directly observed by laminography using synchrotron radiation, was completely different from that previously supposed from observations by conventional microscopy.

Change of misorientation of individual grains in fatigue of polycrystalline alloys by diffraction contrast tomography using ultrabright synchrotron radiation

Abstract: A three-dimensional grain mapping technique for polycrystalline materials, called X-ray diffraction contrast tomography (DCT), was developed at SPring-8, which is the brightest synchrotron radiation facility in Japan. The developed technique was applied to an austenitic stainless steel. The shape and location of grains could be determined by DCT using the apparatus in a beam line of SPring-8. To evaluate the dislocation structure in fatigue, the total misorientation of individual grains was measured by DCT. The average value of the total misorientation over one sample was increased with the number of cycles. In a grain, the change of the total misorientation was largest for the primary slip plane. The maximum change of the total misorientation in fatigue was larger for planes with larger Schmid factor, and the first fatigue crack initiation was occurred in a grain, which had the greatest change of the total misorientation.

Misorientation Measurement of Individual Grains in Fatigue of Polycrystalline Alloys by Diffraction Contrast Tomography Using Ultrabright Synchrotron Radiation

A three dimensional grain mapping technique for polycrystalline materials, called X-ray diffraction contrast tomography (DCT), was developed at SPring-8, which is the brightest synchrotron radiation facility in Japan. The developed technique was applied to a commercially pure iron and austenitic stainless steel. The shape and location of grains could be determined by DCT using the apparatus in a beam line of SPring-8. To evaluate the dislocation structure in fatigue, the total misorientation of individual grains was measured by DCT. The average value of the total misorientation over one sample was increased with the number of cycles. In a grain, the change of the total misorientation was largest for primary slip plane. For austenitic stainless steel (fcc), the change of the total misorientation in fatigue was larger for planes with larger Schmid factor, while it was not depended on the Schmid factor for commercially pure iron (bcc). This different behavior must come from planer slip in fcc structure and wavy slip in bcc structure.

高輝度放射光ラミノグラフィを用いた転動疲労き裂発生および進展挙動に及ぼす介在物配向の影響

In rolling contact fatigue (RCF), cracks initiate and propagate from inclusions beneath the surface. In the present study, crack propagation behavior under RCF was observed by laminography using ultra-bright synchrotron radiation, which is suitable for thin plates, at SPring-8 (Super Photon Ring - 8 GeV). The material had intentionally contains a high concentration of sulfur to enable the observation of crack initiation from MnS inclusion. Fatigue tests were interrupted to conduct laminography by a new developed compact RCF test machine. It was found that vertical cracks, whose face was perpendicular to the rolling direction, were first appeared, then horizontal cracks, those faces were parallel to the sample surface were formed after the vertical crack propagated. And then flaking occurred as the result of the propagation of the horizontal crack. The initiation life of the vertical cracks and horizontal cracks depended on the length and width of the MnS inclusions. And it is considered that the vertical crack is an important factor of flaking life. These mechanisms of flaking process, which was directly observed by laminography using synchrotron radiation, were completely different from conventional RCF mechanism supposed from the surface observations by conventional microscopies.

Effects of inclusion size and orientation on rolling contact fatigue crack initiation observed by laminography using ultra-bright synchrotron radiation

The rolling contact fatigue (RCF) tests were performed on a high-strength steel by a newly developed compact rolling contact fatigue test machine, and the formation and propagation of cracks were observed by the synchrotron radiation computed laminography (SRCL). An increase in the sulfur concentration, i.e., increase in inclusion length, resulted in an increase in the variation of flaking life, and materials with horizontal inclusion showed large variation compared to those with vertical inclusion although average flaking lives are almost identical. In the flaking process, cracks, those were perpendicular to the rolling surface and rolling direction, first formed from an inclusion that was adjacent to the rolling surface. Then, the crack propagated in the depth direction. After the vertical crack propagated to a critical depth, a horizontal crack formed, whose face was parallel to the rolling surface. Finally, the horizontal crack propagated to form flaking.

4D evaluation of grain shape and fatigue damage of individual grains in polycrystalline alloys by diffraction contrast tomography using ultrabright synchrotron radiation

A three dimensional grain mapping technique for polycrystalline materials, called X-ray diffraction contrast tomography (DCT), was developed at SPring-8 (Super Photon ring – 8GeV), which is the brightest synchrotron radiation facility in Japan, and the measurement conditions and data acquisition procedure are discussed. The developed technique was applied to a commercially pure aluminum, commercially pure iron, and austenitic stainless steel. The shape and location of grains could be determined by DCT using the apparatus in a bending beam line of SPring-8. To evaluate the dislocation structure in tensile tests and fatigue tests, the rotation angle spread of individual grains was measured. The rotation angle spread is caused by mosaicity, which is related to the dislocation structure in a grain. The rotation angle spread was found to increase with increasing plastic strain. Fatigue damage could also be evaluated from the rotation angle spread obtained by DCT measurement.

GS0205-423 高輝度放射光によるステンレス鋼の疲労におけるミスオリエンテーション評価

GS0205-423 高輝度放射光によるステンレス鋼の疲労におけるミスオリエンテーション評価

310 高輝度放射光の回折コントラストイメージングによる疲労過程中の転位構造変化の観察(GS3 疲労・破壊(2),研究討論セッション)

310 高輝度放射光の回折コントラストイメージングによる疲労過程中の転位構造変化の観察(GS3 疲労・破壊(2),研究討論セッション)

OS8-17 4D Observations of Pit Growth and Crack Initiation under Corrosion Fatigue of High-strength Aluminum Alloy by Micro CT Imaging Using Ultra-bright Synchrotron Radiation(Environmental effect on fatigue,OS8 Fatigue and fracture mechanics,STRENGTH OF MATERIALS)

OS8-17 4D Observations of Pit Growth and Crack Initiation under Corrosion Fatigue of High-strength Aluminum Alloy by Micro CT Imaging Using Ultra-bright Synchrotron Radiation(Environmental effect on fatigue,OS8 Fatigue and fracture mechanics,STRENGTH OF MATERIALS)

Observation of Rolling Contact Fatigue Cracks by Laminography Using Ultra-bright Synchrotron Radiation

Micro computed laminography imaging using ultra-bright synchrotron radiation (SRCL) was applied to the observation of flaking defects under rolling contact fatigue (RCF) of a high strength steel. Specially fabricated inclusion rich steel plate specimens were employed for the experiments. RCF fatigue tests were carried out near the measurement hatch of SRCL for successive observation of crack initiation and growth behaviors. Specimens before and after the initiation of flaking were observed by SRCL, and the flaking defects and cracks under the surface were successfully detected. The shape and location of RCF crack obtained by SRCL imaging were almost coincident with those obtained by SEM, and detail process of crack initiation and flaking in RCF process can be discussed.

Observation of 3D shape and propagation mode transition of fatigue cracks in Ti–6Al–4V under cyclic torsion using CT imaging with ultra-bright synchrotron radiation

In the present study, micro computed tomography (μCT) imaging by using ultra-bright synchrotron radiation X-ray (SR μCT), which is generated at a facility located in Japan and called SPring-8 (Super Photon ring-8GeV), is used to observe torsion fatigue crack propagation behavior in round bars. It is well known that the transition of crack propagation from the shear mode to the tensile mode takes place in the above case. The transition condition, however, was not discussed in detail in the past, since the crack growth behavior under the surface cannot be provided precisely by the conventional techniques, such as optical microscope, scanning electron microscope, and atomic force microscope. A compact torsion fatigue-testing machine has been recently developed to conduct fatigue tests and measurements of SR μCT concurrently at Spring-8. Therefore, the shape of torsion fatigue cracks can be evaluated quantitatively and nondestructively, and the transition of crack propagation from the shear mode to the tensile mode can be observed three-dimensionally. The condition of the transition of crack propagation is discussed by considering the three-dimensional shape of cracks.

Initiation and Growth of Pits and Cracks in Corrosion Fatigue for High Strength Aluminium Alloy Observed by Micro Computed-Tomography Using Ultra-Bright Synchrotron Radiation

Measurement of shape and dimension of pits and cracks formed in corrosion fatigue tests of a high-strength aluminium alloy, 7075-T651 were conducted by computed-tomography using ultra bright synchrotron radiation X-ray. Complex corrosion process could be observed and detail shapes of corrosion pits could be identified. Sometimes, corrosion pit and corroded area were formed under passive film, and those were not observed from the surface.