QUANTITATIVE DEFORMATION STUDIES USING ELECTRON BACK SCATTER PATTERNS

The diffuseness of electron back scatter patterns (EBSPs) is observed to increase with plastic strain. The application of this technique to deformation studies has been limited by the lack of a general method of measuring the pattern quality. The degradation of EBSPs by cold work was thus thoroughly investigated using the A1 6061 alloy for the purpose. Methods for enhancing the Kikuchi band contrast by removal of the background intensity variation from digital images of <112> zone axes present in the EBSP have been developed. The constrast of the Kikuchi bands was quantified using the root mean square intensity of averaged band profiles, while the sharpness of the patterns was assessed by the attenuation of high frequency components of Fourier transforms of the enhanced images and of the averaged band profiles. Tilt was found to effect contrast but not sharpness, while cold work reduced both. However, surface contamination produced effects that were very similar to those of specimen deformation. A method is presented for quantitative determination of EBSP quality, which is independent of grain orientation and is based on the first moment of power spectra (the square of the Fourier transform) of features common to all patterns to be compared.