Fracture Properties of α- and κ-Al2O3 Hard Coatings Deposited by Chemical Vapor Deposition

Although alpha- and kappa-Al2O3 hard coatings deposited by chemical vapor deposition are well established in the metal-cutting industry for their ability to increase the performance and lifetime of cutting tools, the literature on their fracture properties is scarce. Thus, within this study, the microstructure and mechanical properties of alpha- and kappa-Al2O3 coatings were investigated and compared to each other. X-ray diffraction and scanning electron microscopy combined with electron backscatter diffraction showed that both coatings exhibited a fiber texture, where the alpha-Al2O3 coating displayed a (0001) texture and the kappa-Al2O3 coating a (001) texture with a certain (013) contribution. Higher hardness and Young's modulus values of 31.0 & PLUSMN; 0.9 GPa and 474.6 & PLUSMN; 12.5 GPa, respectively, were obtained for the alpha-Al2O3 coating, compared to 24.2 & PLUSMN; 0.8 GPa and 356.8 & PLUSMN; 7.9 GPa for kappa-Al2O3. While the alpha-Al2O3 coating exhibited a higher fracture stress of 8.1 & PLUSMN; 0.3 GPa (compared to 6.4 & PLUSMN; 0.6 GPa for kappa-Al2O3), the kappa-Al2O3 coating showed a higher fracture toughness of 4.4 & PLUSMN; 0.3 MPa*m(1/2) (compared to 3.2 & PLUSMN; 0.3 MPa*m(1/2) for alpha).