Anisotropic lattice expansion and shrinkage of hexagonal TiAlN and CrAlN films

Ti1−XAlXN and Cr1−XAlXN films were synthesized by the arc ion plating method differing in the second metal contents X and investigated on their crystal structures, lattice parameters and microstructures. X-ray diffraction patterns showed that crystal structures of both Ti1−XAlXN and Cr1−XAlXN films changed from the NaCl-type (cubic structure; c-) to wurtzite-type (hexagonal structure; h-) at Al contents X=0.6–0.7. Lattice parameters of c-Ti1−XAlXN and c-Cr1−XAlXN with Al contents X⩽0.6 uniformly decreased with respect to all lattice spacings with increasing X values. On the other hand, for h-Ti1−XAlXN and h-Cr1−XAlXN films with X⩾0.7, anisotropic lattice expansion and shrinkage were observed with the a- and c-axes. The lattice spacing expanded in the a-direction and shrank in the c-direction by adding Ti and Cr atoms with larger atomic radius into AlN structure, respectively.