Superhardness effects of heterostructure NbN/TaN nanostructured multilayers

Although superhardness effects have been extensively investigated for epitaxial ceramic nanomultilayer films with the same crystal structures in the last decade, those for multilayers with different crystal structures have been seldom studied. In this article, NbN/TaN nanomultilayers have been designed and deposited by reactive magnetron sputtering. The results showed that the crystal structures of NbN and TaN are face-centered cubic and hexagonal in superlattice films, respectively, and the lattice plane (111) of NbN is coherent with the (110) of TaN, i.e., ${111}fcc-NbN∥{110}h-TaN.$ The results of microhardness measurement showed that the superhardness effects of NbN/TaN multilayers exist in a wide range of modulation period from 2.3 to 17.0 nm. This phenomenon is different from that of epitaxial ceramic multilayers where the maximum hardness usually takes place at a modulation period of 5.0–10.0 nm. It is proposed that the coherent stresses and the structural barriers (fcc/hexagonal) to dislocation motion between NbN and TaN layers are the main reasons for the high-hardness value in a wide range of modulation periods.