Non-destructive observations on material structures of Ti-6Al-4V alloy by using synchrotron radiation μCT imaging

In Ti-6Al-4V, fatigue fractures originate from the inside of the material in the very high cycle region (number of cycles to failure > 10⁷) at stresses lower than usual. Because of the difficulties in direct and non-destructive observation of internal cracks, the initiation an propagation mechanisms of internal cracks have not yet been clarified. Recently, μCT imaging using high brightness synchrotron radiation have been provided by the third-generation synchrotron radiation facility such as SPring-8. The very high brightness synchrotron radiation allows for a high spatial resolution of several μm or less. Thus, the present work used μCT imaging and conducted non-destructive observations on material structures which are expected to have a dominant effect on the behavior of internal fatigue cracks. As a result, it was confirmed that α phase and β phase of Ti-6Al-4V can be clearly distinguished using μCT imaging by comparing with the grain structure image observed by scanning electron microscope. (author)