Enhanced performance of -Al2O3 coatings by control of crystal orientation

Al2O3 coatings with (101̄2), (101̄4), (0001) and (101̄0) textures were obtained using chemical vapour deposition. The textured coatings were compared with -Al2O3 obtained through the kappa- > 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 and Cu K radiation, respectively. Microtexture was investigated using electron back-scatter diffraction. Wear properties of the -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 -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 -Al2O3 coatings could be controlled by process data during deposition.