Investigation of crack growth in deposited and perfect Ti/TiN structure by molecular dynamic simulation

The existence of defects and residual stresses in the multilayer coatings could reduce their crack resistance. By using the method of molecular dynamics (MD) simulation, the crack propagation behavior in deposited Ti/TiN bilayer is compared with its perfect structure. For this purpose, TiN was deposited on Ti substrate, then crack growth was investigated in the two structures. The growth of TiN film on Ti was island growth, and the structure has defects and residual stress. The results showed that both the biaxial and normal residual stresses in the substrate and film are tensile and compression, respectively. The cohesive energy of the interface was calculated by energy difference along the atomic layers. In the following, a crack was considered perpendicular to the Ti/TiN interface in both models, with an initial length of 15 Å. Due to the brittle behavior of the ceramic layer, crack propagates rapidly until interface. The plastic deformation of the Ti layer and the structure of the interface blunt the tip of the crack and prevents to fail. Also, the critical stress for crack growth in a regular structure is found to 2.5 times of its value in the layered structure because of defects and tension in the layered structure