Experimental assessment of the contribution of annealing twins to CSL distributions in FCC materials

The correlation between CSL distributions and annealing twins was assessed for a wide range of fee materials using the electron backscattered diffraction technique. The maximum frequency of twin boundaries determined experimentally (=61%) is consistent with the previously proposed theoretical limit of 2/3. The frequency of special grain boundaries (Σ1-Σ29) was found to lie within limits defined by (1) an upper limit based upon twin energetics leading to the creation of additional special grain boundaries, and (2) a lower limit arising from isolated twinning events. Moreover, the occurrence of Σ3n grain boundaries is attributed to the geometric interaction of twin related variants. Its effect is shown to be minimal at low frequencies of Σ3, but significantly higher at twin densities greater than approximately 40%. These experimental observations are consistent with the previously proposed model of Palumbo et al.[1] which predicts a 'Twin-Limited Microstructure' consisting entirely of special grain boundaries.