Evaluation of Fatigue Damage by Diffraction Contrast Tomography Using Synchrotron Radiation

Abstract

The three dimensional grain mapping technique for polycrystalline material, which is called X-ray diffraction contrast tomography (DCT) has proposed. In the present study, the measurement of DCT was conducted in SPring-8, which is the brightest synchrotron radiation facility in Japan, and the condition of measurement and data procedure are discussed. Developed technique was applied to aluminium alloy and stainless steel. The shape and location of grain could be determined by the developed three-dimensional mapping technique using the apparatus in a bending beam line of SPring-8. To evaluate plastic deformation, the grain orientation spreads of individual grains were measured. The grain orientation spread is caused by the mosaicity, which relates to the dislocation structure in a grain. The grain orientation spread was found to increase with increasing plastic strain. Fatigue damage also could be evaluated by the grain orientation spread in the DCT measurement.

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

“…For either diffraction plane, the average total misorientation β ave is almost unchanged in the elastic region, but increases significantly in the plastic deformation region. For commercially pure iron, the change in average total misorientation is reported to be the greatest in the slip plane, [ 21 ] while the change is similar for all diffraction planes in the present material.…”

“…Nakai et al developed a method of evaluating misorientation, defined as the orientation spread of diffraction spots and corresponding to the number of excess dislocations in the diffraction plane, using DCT. [ 20 ] DCT can be used to observe the misorientation of each grain not only on the sample surface but also inside the sample, as reported by Shiozawa et al [ 21,22 ] and Nakai et al [ 20,23,24 ] . It is a nondestructive observation technique that enables the continuous observation of the local plastic deformation of grains not only on the sample surface but also inside the sample.…”