Rotation of Mo-fibers in directionally solidified Ni-Al-Mo eutectic alloys

The interface structure of α-Mo fibers in directionally solidified Ni-Al-Mo eutectic alloys has been investigated by transmission electron microscopy and computer-aided graphical techniques. The Mo fibers have square or rectangular cross sections with well defined flat facets and fundamentally have the Bain orientation relationship with respect to the γ matrix lattice. The crystal lattices of the Mo fibers, however, are often rotated with respect to the matrix lattice about their longitudinal axes. Correspondingly, the facet planes deviate from the exact rational (110)_γ′//(100)_α relationship. A computer aided graphical plotting of the atom arrangement at the interfaces suggests that good atomic matching is kept even after the rotation of fibers. High resolution electron microscopy revealed the incorporation of single atomic structural ledges to keep the coherency of the lattices of the matrix and rotated fibers. The relation between the lattice rotation and the facet plane rotation is well explained by the moire and O-lattice models.