Period dependence of hardness and microstructure on nanometric Cr/CrN multilayers

Polycrystalline Cr/CrN multilayers were deposited on silicon substrates by r.f. magnetron sputtering from a pure Cr target alternating a pure Ar atmosphere and a N2/Ar reactive mixture. Bilayer period values varied from nanometric range (2–20 nm) to higher values. Coatings structural properties were analyzed by X-ray diffraction (SEM) and cross-sectional transmission electron microscopy (TEM). The multilayer period and relative thickness were clearly determined, and a polycrystalline epitaxial cube-on-cube structure was found on Cr/CrN multilayers. This epitaxial relationship between layers inside each columnar crystallite is given by Cr (001)||CrN (001) and Cr [100]||CrN [110]. Nanoindentation measurements showed multilayer hardness reaching almost 30 GPa in the nanometric range, more than two-times higher than the expected from rule-of-mixtures. Changes in microstructure and hardness were also investigated.