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

alpha-Al2O3 coatings with (10 (1) over bar2), (10 (1) over bar4), (0001) and (10 (1) over bar0) textures were obtained using chemical vapour deposition. The textured coatings were compared with alpha-Al2O3 obtained through the kappa ->alpha 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 K-alpha and Cu K-alpha radiation, respectively. Microtexture was investigated using electron back-scatter diffraction. Wear properties of the alpha-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 alpha-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 alpha-Al2O3 coatings could be controlled by process data during deposition. (C) 2008 Elsevier B.V. All rights reserved.