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

Abstract

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 moduls B, shear moduls G, and Young’s moduls 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 behaviour for TiN, ZrN and HfN and more metallic behaviour for CrN and VN. The fracture toughness KIC and interfacial fracture toughness KICInt for bi-layer combinations of these five nitrides is calculated along the [100] and [110] directions. The largest KIC value is obtained for HfN (2.14 MPa·m1/2) in (100) orientation and for TiN (2.16 MPa·m1/2) 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 = 3.24 MPa·m1/2, is recorded for the HfN/TiN interface in the (110) orientation.