Mesoscale strain measurement in deformed crystals: A comparison of X-ray microdiffraction with electron backscatter diffraction

摘要

Mapping of residual stresses at the mesoscale is increasingly practical thanks to technological developments in electron backscatter diffraction (EBSD) and X-ray microdiffraction using high brilliance synchrotron sources. An analysis is presented of a Cu single crystal deformed in compression to about 10% macroscopic strain. Local orientation measurements were made on sectioned and polished specimens using EBSD and X-ray microdiffraction. In broad strokes, the results are similar to each other with orientations being observed that are on the order of 5° misoriented from that of the original crystallite. At the fine scale it is apparent that the X-ray technique can distinguish features in the structure that are much finer in detail than those observed using EBSD even though the spatial resolution of EBSD is superior to that of X-ray diffraction by approximately two orders of magnitude. The results are explained by the sensitivity of the EBSD technique to the specimen surface condition. Dislocation dynamics simulations show that there is a relaxation of the dislocation structure near the free surface of the specimen that extends approximately 650 à into the specimen. The high spatial resolution of the EBSD technique is detrimental in this respect as the information volume extends only 200 à or so into the specimen. The X-rays probe a volume on the order of 2 µm in diameter, thus measuring the structure that is relatively unaffected by the near-surface relaxation.