The role of strain transfer in the activation of deformation twinning at grain boundaries was characterized in commercially pure titanium deformed in bending. Two different orientations of a textured polycrystal were deformed in bending and were analyzed using electron back-scattered diffraction to determine the active slip and twinning systems in the surface tensile region. Prismatic slip and {10¯12}<¯1011> twinning were the most widely observed deformation modes in both orientations. Non-prismatic slip systems were also activated, most likely to accommodate local strain heterogeneities. A slip-stimulated twin nucleation mechanism was identified for soft/hard grain pairs: dislocation slip in a soft-oriented grain could stimulate twin nucleation in the neighboring hard grain when the slip system was well aligned with the twinning system. This alignment was described by a slip-transfer parameter m′. Twins activated by this mechanism always had the highest m′ value among the six available {10¯12}<¯1011> twinning systems, while the Schmid factor, based on the global (uniaxial tensile) stress state, was a less significant indicator of twin activity. Through slip transfer, deformation twins sometimes formed despite having a very low global Schmid factor. The frequency of slip-stimulated twin nucleation depends strongly on the texture and loading direction in the material. For grain pairs having one grain with a large Schmid factor for twinning, nonparametric statistical analysis confirms that those with a larger m′ were more likely to display slip-stimulated twinning.

Twin Nucleation by Slip Transfer across Grain Boundaries in Commercial Purity Titanium. L.Wang, Y.Yang, P.Eisenlohr, T.R.Bieler, M.A.Crimp, D.E.Mason: Metallurgical and Materials Transactions A, 2010, 41[2], 421-30