Enhanced performance of α-Al2O3 coatings by control of crystal orientation

α-Al2O3 coatings with (101̄2), (101̄4), (0001) and (101̄0) textures were obtained using chemical vapour deposition. The textured coatings were compared with α-Al2O3 obtained through the κ→α phase transformation. The coating microstructures were studied by scanning electron microscopy and transmission electron microscopy and residual stress and texture were determined by X-ray diffraction using Cr Kα and Cu Kα radiation, respectively. Microtexture was investigated using electron back-scatter diffraction. Wear properties of the α-Al2O3 coatings were evaluated in turning of cast iron and steel. All the studied coatings were under a tensile stress of the order of 0.2–0.7 GPa. The cutting tests confirmed substantial texture effects especially in cutting of steel. The best performance was exhibited by the (0001) textured coatings i.e. when the basal planes of α-Al2O3 grains were nearly parallel to the coating surface. As compared with the other textured coatings, the (0001) textured coating showed a clearly enhanced ability to undergo uniform plastic deformation. The present work also established that the texture of α-Al2O3 coatings could be controlled by process data during deposition.