A synchrotron tomographic energy-dispersive diffraction imaging study of the aerospace alloy Ti 6246

摘要

A titanium alloy sample (#6246) containing a linear friction weld has been imaged nondestructively using tomographic energy-dispersive diffraction imaging (TEDDI). The diffraction patterns measured at each point of the TEDDI image permitted identification of the material and phases present (5%). The image also showed the preferred orientation and size-strain distribution present within the sample without the need for any further sample preparation. The preferred orientation was observed in clusters with average dimensions very similar to the experimental spatial resolution (400 m). The length scales and preferred orientation distributions were consistent with orientation imaging microscopy measurements made by Szczepanski, Jha, Larsen & Jones [Metall. Mater. Trans. A (2008), 39, 2841-2851] where the microstructure development was linked to the grain growth of the parent material. The use of a high-energy X-ray distribution (30-80 keV) in the incident beam reduced systematic errors due to the source profile, sample and air absorption. The TEDDI data from each voxel were reduced to an angle-dispersive form and Rietveld refined to a mean χ2 of 1.4. The mean lattice parameter error (d/d) ranged from 10-4 for the highly crystalline regions to 10-3 for regions of very strong preferred orientation and internal strain. The March-Dollase preferred orientation errors refined to an average value of 2%. A 100% correlation between observed fluorescence and diffraction peak broadening was observed, providing further evidence for vicinal strain broadening.