Characterization of C11b/C40 lamellae in a MoSi2–15mol%TaSi2 alloy

The crystallography of the lamellar structure composed of the tetragonal C11b phase and the hexagonal C40 phase which is similar to the well-known TiAl/Ti3Al lamellae was investigated by means of transmission electron microscopy in a MoSi2–15mol%TaSi2 pseudo-binary alloy after homogenized at 1400 °C for 168 h. It was found that the orientation relationship between C11b and C40 phases obeys the coincidence of the equivalent hexagonal atomic planes for the two phases. Three distinct variants of this orientation relationship were identified by electron diffraction. 13<21̄1̄0 Dislocations prevail in the C11b/C40 interfaces to accommodate the lattice misfit between the two phases. On the other hand, networks of <100] and <110] dislocations dominate the C11b/C11b boundaries. <100] and <110] dislocations are also present within C11b variant plates while 13<21̄1̄0 and 13<21̄1̄3 dislocations are frequently observed in C40 phase. Significance of the 13<21̄1̄3 c-component dislocations for improvement of the plasticity of C40 phase has been discussed.