Microstructure and mechanical property of TiN/AlN multilayered coatings: The impact of AlN thickness

We have conducted a comprehensive first-principles study of the tensile and fracture process of the TiN(111)/AlN(111) multilayered coatings with different thicknesses of AlN. We find that the ideal tensile strength of TiN/AlN systems is weakened with the increase of the thickness of AlN. A strikingly different fracture mode is identified for the coatings with differing thicknesses of AlN, that is, the fracture occurs in TiN for the coatings with one layer of AlN, while in the AlN for those with three or five layers of AlN. By applying several analytic methods, we attribute such difference to the variation in charge density and atomic hybridization, and demonstrate that charge transfer plays a key role in affecting mechanical properties of the coatings during a tensile process. The theoretical calculations presented here provide insight to atomic-scale effects of the thickness of AlN in complex TiN/AlN multilayered coatings that can be difficult to obtain by experiments alone but which are of practical significance for further understanding and improvement of such functional multilayered coatings.