Computational Evaluation of Adhesion and Mechanical Properties of Nanolayered Erosion-Resistant Coatings for Gas Turbines

A computational method to evaluate fracture toughness of prospective erosion-resistant coatings using a combination of first-principles density functional theory (DFT) calculations and fracture mechanics is proposed. Elastic coefficients $C11$⁠, $C12$⁠, and $C44$⁠, the ideal work of adhesion $Wad$⁠, bulk modulus $B$⁠, shear modulus $G$⁠, and Young’s modulus $E$ of transition metal nitrides with a cubic structure such as TiN, CrN, ZrN, VN, and HfN are calculated. Both the $G/B$ ratio and Cauchy pressure $C12−C44$ indicate brittle behavior for TiN, ZrN, and HfN and more metallic behavior for CrN and VN. The fracture toughness $KIC$ and interfacial fracture toughness $KICInt$ for bilayer combinations of these five nitrides is calculated along the [100] and [110] directions. The largest $KIC$ value is obtained for HfN $(2.14MPam1/2)$ in (100) orientation and for TiN $(2.16MPam1/2)$ in (110) orientation. The lowest fracture toughness, in both orientations, is found for CrN. Among ten coherent interfaces of the five investigated nitrides the largest value of interfacial fracture toughness $KICInt=3.24MPam1/2$ is recorded for the HfN/TiN interface in the (110) orientation.