| Résumé | 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 C 11, C 12, and C 44, 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 C 12 - C 44 indicate brittle behavior for TiN, ZrN, and HfN and more metallic behavior for CrN and VN. The fracture toughness KIC and interfacial fracture toughness K IC Int for bilayer combinations of these five nitrides is calculated along the [100] and [110] directions. The largest K IC value is obtained for HfN (2.14 MPa m 1/2) in (100) orientation and for TiN (2.16 MPa m 1/2) 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 K IC Int=3.24 MPa m 1/2 is recorded for the HfN/TiN interface in the (110) orientation. Copyright © 2011 by ASME. |
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