Compatibility stresses in bicrystals of polysynthetically twined TiAl

The microstructure of TiAl alloys contains two types of interfaces. First, the interfaces between rotational domains misoriented by the multiples of 60°. They lie on the planes parallel to the close packed lattice planes and form the blocks separated by the interfaces of the second type, the grain boundaries in commonly used sense. The misorientation of the latter interfaces can be arbitrary and also their plane is not fixed to certain crystallographic orientations. The compatibility stresses caused by the strain response of differently oriented grains to the applied stress can arise on both types of interfaces. Such additional stresses may alter the activity of different deformation modes and can influence the macroscopic behaviour of tested samples. In this paper, we discuss only the compatibility stresses at the ordinary grain boundaries and the blocks of parallel layers are approximated as single crystals. In particular, the grain boundaries important for the directionally grown polysynthetically twinned crystals are analysed.