Computational evaluation of interfacial fracture toughness of thin coatings

A computational method to evaluate fracture toughness of single- and multilayered coatings using first-principles density functional theory (DFT) calculations was proposed. This method was first applied to calculate elastic properties and fracture toughness K-IC of single crystalline TiC and several transition metal nitrides with cubic structure, such as TiN, CrN, ZrN, VN and HfN. After comparison with known experimental data and other DFT results, the reliability of present calculations was favourably confirmed. Next, DFT was applied to calculate the ideal work of adhesion W-ad, Young's modulus E and interfacial fracture toughness K-IC(Int) for bi-layer combinations of five transition metal nitrides in (100) and (110) surface orientations. For the analyzed coatings, the following trends were observed: E(100) > E(110), W-ad(100) < W-ad(110) and K-IC(Int)(100) < K-IC(Int)(110), demonstrating that it is the W-ad that plays a decisive role in determining interfacial fracture toughness of these materials. All interfaces formed with TiN in the (110) orientation showed the best combination of adhesion and Interfacial fracture toughness.