Superlattice design has been shown to improve Young's modulus, hardness and toughness of many nitride systems beyond the performance of individual building blocks, especially when the bi-layer period is small, in the nm range. We have applied ab initio calculations to answer whether the weakest links in superlattices are always linked to the chemically inhomogeneous regions interfaces. Our extensive results applied to the TiN/AlN system, a prototype of hard protective coatings, showed that this is not always the case. The weakest link sensitively depends on the crystallography, interface orientation, and loading direction.

Our second example will present a multi-method approach, linking molecular dynamics and density functional theory calculations, and applied to TiAl intermetallic light-weight alloys interfaces. Here, the γ/α2 phase boundaries and γ/γ interfaces play a vital role in determining the alloy mechanical properties. We will present detailed predictions of segregation phenomena to phase boundaries corroborated by APT data available in the literature. Finally, we will discuss the influence of solutes on interfacial mechanical properties.