Theoretical and experimental study of the gradient properties and the resulting local crystalline structure and orientation in magnetron-sputtered CrAlN coatings with lateral composition and thickness gradient

Cr–Al–N coatings with a lateral composition gradient were deposited from two segmented Cr/Al targets with different segment size, thus covering the Al content range 0.22 ≲ c ≲ 0.87 and a thickness range from several hundred nanometres to several micrometres. The two-dimensional thickness and composition profiles were determined nondestructively from X-ray fluorescence maps. The results were reproduced by simulations of the flux distribution on the sample surface, combining TRIDYN simulations of the reactive sputter process at the target surface and SIMTRA simulations of the subsequent transport through the gas phase. The phase formation was studied by spatially resolved X-ray diffraction and X-ray absorption spectroscopy at the Cr K edge. For c ≲ 0.69, a single-phase solid solution face-centered cubic (f.c.c.) (Cr,Al)N phase was found, and for 0.69 ≲ c ≲ 0.87 coexisting f.c.c. (Cr,Al)N and hexagonal close packed (h.c.p.) (Cr,Al)N phases were observed. The biaxial texture formation in nearly the entire composition range indicates a zone T growth. Four, mainly composition-dependent, texture regions were identified. All observed textures are closely related to textures reported for the h.c.p. AlN and f.c.c. CrN parent phases. For c ≳ 0.69, a strong thickness dependence of the textures was observed. The measurements reveal an orientation relation between different f.c.c. and h.c.p. textures, indicating that local epitaxy might play a role in the structure formation.