Mechanical properties of single and polycrystalline α-Al2O3 coatings grown by chemical vapor deposition

Due to the highly anisotropic mechanical properties of corundum, the lifetime of α-Al2O3 coated cutting tools is strongly influenced by its texture. However, limited literature is available on orientation dependent mechanical properties of α-Al2O3 coatings. Thus, in the present study, (0001), (11-20), (1-102) oriented single crystalline α-Al2O3 coatings and a state of the art (0001) textured polycrystalline α-Al2O3 coating were synthesized using chemical vapor deposition (CVD) on sapphire and cemented carbide substrates and the mechanical properties were investigated. The morphology of the coatings was studied by scanning electron microscopy and the respective orientation verified by electron backscatter diffraction. The (0001) oriented α-Al2O3 single crystalline coating yielded a slightly higher hardness of 34.4 ± 2.0 GPa compared to the other oriented coatings. Also, the maximum Young's modulus was observed for the (0001) oriented α-Al2O3 single crystalline coating, with a value of 451 ± 25 GPa. Furthermore, micromechanical tests were carried out to determine the fracture stress and fracture toughness, where the (11-20) oriented single crystalline coating exhibited the highest values of 11.2 ± 0.4 GPa and 4.1 ± 0.2 MPa m1/2, respectively. Compared to the (0001) oriented single crystalline coating, the state of the art (0001) textured polycrystalline coating exhibits lower hardness, Young's modulus, fracture stress and fracture toughness values.