Misorientation Measurement 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 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.

Evaluation of Fatigue Properties under Four-point Bending and Fatigue Crack Propagation in Austenitic Stainless Steel with a Bimodal Harmonic Structure

“…Consequently, the harmonic-structured SUS304L exhibits a lower resistance to fatigue crack growth owing to grain refinement, and the formation of pores is suppressed by MM. In the future, the three-dimensional fatigue crack shape [41][42][43][44][45][46] and the misorientations near the crack initiation site [47][48][49] will be measured for SUS304L with fatigue damage using synchrotron radiation to describe the mechanism of fatigue crack initiation and propagation in greater detail.…”

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

“…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.…”