Abstract
The present work nondestructively observed the dual-phase microstructure of Ti-6Al-4V using synchrotron radiation micro-CT imaging at Spring-8 to establish a nondestructive inspection method which clarifies microstructural effect on the internal fatigue fracture. An imaging system with a small pixel size of 0.23 μm/pixel and the field of view of 0.47 mm × 0.47 mm was used to finely resolve the grains with an average size of 10 μm. The needle-shape-specimen whose diameter changes along the longitudinal direction was used to determine the maximum diameter which enables to obtain a clear image of grains. The absorption images inside the specimen at the sections with the diameter less than 0.45 mm resolved the internal grains regardless of the diameter; however the contrast between α phase and β phase was not so high. The phase retrieval processing was applied to the data set in order to obtain better contrast. The phase retrieval images provided the significant contrast between two phases. Based on these results, the micro-CT imaging was conducted on the hourglass-shape-specimen with a diameter of 0.45 mm, in which an internal crack had already initiated and propagated due to the cyclic loading of 107. As a result, the internal crack and its surrounding grains were clearly observed; the positional relation between the crack and the grains could be examined on the image. This result indicates that the internal fracture process can be investigated in terms of the microstructure using micro-CT imaging.
