Restricting dislocation movement in transition metal carbides by phase stability tuning

A mechanism to enhance hardness in multilayer coatings is proposed. Using t he technologically important hard transition metal carbides as prototypes, although the principle is transferable also to other systems, we demonstrat e, from first-principles calculations, that by suitable alloying the energy difference between several competing structures in the transition meta[ ca rbides is small or tunable. This creates multiphase/polytypic compounds wit h a random or controllable layer stacking sequence, systems in which the pr opagation of dislocations can be strongly suppressed by a large number of i nterfaces between structures with different glide systems, accordingly allo wing the possibility of a greatly enhanced hardness. With modern thin-film technologies, it should therefore be possible to deposit such materials tha t will express multilayer characteristics with only minor changes in the ch emical constitution of the material, which is in contrast to conventional s uperlattices.