Cross-interface growth mechanism of nanotwins in extremely high stacking-fault energy ceramic layer

Twins have been proven to greatly enhance the hardness, toughness, thermal stability, and wear resistance of materials. However, the formation of twins in transition nitride ceramics is exceptionally difficult due to their prohibitively high stacking-fault energy. Consequently, reports on nanotwinned ceramic films have been limited in scope. In this study, we utilize the template effect of multilayer structures to induce the growth of nanotwins within the high stacking-fault energy TiN and AlN layers. Theoretical analysis reveals that the growth of nanotwins across the interface is facilitated by the template effect and large internal stress. The former fosters the epitaxial growth of nanotwinned two-sided structures into the TiN and AlN layers. Simultaneously, the pronounced internal stress engenders substantial lateral stress in the TiN and AlN layers immediately above the underlying nanotwin region, ultimately leading to the formation of nanotwins. In addition, due to the differences in lattice constants and crystal structures of TiN and AlN, the maximum thickness of TiN layer that can sustaining stable growth of nanotwins is about 10 nm, whereas for AlN layer is just about 1.5 nm. This study proposes a promising approach to introduce twins in ceramic films with exceedingly high stacking-fault energies and enable advancements in the toughening of ceramic films.