Superhardness effects of heterostructure NbN/TaN nanostructured multilayers

Although superhardness effects have been extensively investigated for epita xial ceramic nanomultilayer films with the same crystal structures in the l ast decade, those for multilayers with different crystal structures have be en seldom studied. In this article, NbN/TaN nanomultilayers have been desig ned and deposited by reactive magnetron sputtering. The results showed that the crystal structures of NbN and TaN are face-centered cubic and hexagona l in superlattice films, respectively, and the lattice plane (111) of NbN i s coherent with the (110) of TaN, i.e., {111}(fcc-NbN)parallel to {110}(h-T aN). 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 ce ramic multilayers where the maximum hardness usually takes place at a modul ation 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 a nd TaN layers are the main reasons for the high-hardness value in a wide ra nge of modulation periods. (C) 2001 American Institute of Physics.