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 (2.14 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.
First-principles study of fracture toughness enhancement in transition metal nitrides
