Impact of residual stress on the adhesion and tensile fracture of TiN/CrN multi-layered coatings from first principles

Multilayered TiN/CrN coatings find a wide range of technological applications where their internal hetero-interfaces and corresponding residual stress have been long suspected as capable of influencing their intriguing mechanical and chemical performances such as the thermal stability, hardness, and corrosion, tribological and wear resistance. Here, we investigate, by first-principles calculations, atomic and electronic structures of the TiN/CrN interface and how the residual stress influences the adhesion and ideal tensile strength of the multilayered coatings. We find that calculated adhesion energies of the interfaces with (1 1 1) and (0 0 1) orientations are small under no residual stress, yet increase almost linearly when the residual stress is imposed, suggesting that the residual stress plays a dominant role in affecting adhesion. The strengthened adhesion affected by the residual stress is found to be attributable to the stress-induced shrinkage of bonds, which results in enhanced interactions between the bonds in the TiN/CrN coatings. Using several analytic techniques, we have characterized the electronic structure of the interface carefully and determined the interfacial bonding to be primarily ionic with a small degree of covalency. The tensile simulations reveal that the interface with the (1 1 1) texture is more brittle than that with the (0 0 1), although the former presents greater ideal tensile strength. The findings presented here shed light on the impact of residual stress on the adhesion and ideal tensile strength of the TiN/CrN multi-layers, which information could be hard to obtain by means of experiments alone but which is of practical importance for further understanding and improvement of the multi-layered coatings at atomic scale.