Shallow and deep nanoindentation on W/NbN nanolayers

Abstract

Superlatice W(100)/NbN(100) with bilayer periods (Γ = 5.6 and 10.4 nm) was non-isostructural superlattice material and fabricated by depositing alternating layers of single crystal tungsten (W), a body-centered cubic metal, and niobium nitride (NbN), a face-centered cubic ceramic, on a MgO single crystal substrate. The lattice constants of the ceramic and metal layers are 0.439 nm and 0.315 nm respectively. The superlattice are nanocomposites that exhibit a hardness at small bilayer repeat periods which exceeds the hardness predicted by the rule of mixtures for normal composites by deep nanoindentation, while shallow nanoindentations does not demonstrate the superhardening. The results indicate that the elastic modulus does not influence the hardness of the superlattice materials. The superhardening results at deeper indentation depths is related to the nature of the interface between the layers in the superlattice materials. Normally, superlattice gains hardness by losing deformability, however, the superlattice demonstrated excellent deformability when reaching the superhardening. © 2007 Springer.