High-throughput first-principles search for ceramic superlattices with improved ductility and fracture resistance

Superlattices—alternating coherently grown materials of nm thicknesses—proved their potential for enhancing typically antagonistic properties of ceramics: ductility, hardness, and fracture toughness. Material selection, however, is far from trivial, as superlattice films do not simply combine mechanical properties of their layer components. Here we employ high-throughput density functional theory calculations to develop design guidelines for nanolaminates combining cubic transition metal nitride and/or carbide ceramics. Out of 153 MX/M*X* superlattices (M, M* = Al, Ti, Zr, Hf, Nb, V, Ta, Mo, W, and X, X* = C, N) 145 are chemically and mechanically stable and most often contain vacancies on the non-metallic sublattice. Superior ductility together with moderate-to-high fracture toughness and interface strength (above that of the cubic TiN) narrow the set of perspective candidates. Key ingredients promoting the interface-induced enhancement of hardness and/or fracture toughness are lattices parameter and shear modulus mismatch of the layer components. Adding the requirement of phonon stability yields MoN/M*N, M* = Nb, Ta, Ti; TiN/WN (nitrides); HfC/M*N, M* = Mo, W; NbC/M*N, M* = Mo, W; TaC/M*N, M* = Mo, W; VC/M*N, M* = Hf, Ta, Zr (carbonitrides); as the top candidates for novel superlattice films.