  Detailed microstructure characterisation and in-situ micropillar compression
were coupled with crystal plasticity-based finite element modelling (CP-FEM) to
study the micro-mechanisms of plastic anisotropy in lamellar TiAl alloys. The
consideration of microstructure in both simulation and in-situ experiments
enables in-depth understanding of micro-mechanisms responsible for the highly
anisotropic deformation response of TiAl on the intra-lamella and inter-lamella
scales. This study focuses on two specific configurations of
{\gamma}/{\alpha}_2 lamellar microstructure with the {\gamma}/{\alpha}_2
interfaces being aligned {25}^o and {55}^o to the loading direction.
Microstructure-based CP-FEM shows that longituginal slip of super and ordinary
dislocations are most responsible for the plastic anisotropy in the {25}^o
micropillar while the anisotropy of the {55}^o micropillar is due to
longitudinal superdislocations and longitudinal twins. In addition, transversal
superdislocations were more active, making the deformation in the {25}^o
micropillar less localised than that in the {55}^o micropillar. Moreover, the
CP-FEM model successfully predicted substantial build-up of internal stresses
at {\gamma}/{\alpha}_2 interfaces, which is believed to be detrimental to the
ductility in TiAl. However, as evidenced by the model, the detrimental internal
stresses can be significantly relieved by the activation of transverse
deformation twinning, suggesting that the ductility of TiAl can be improved by
promoting transverse twins.
