Conditions of attaining a superhard state at a critical thickness of nanolayers in multiperiodic vacuum-arc plasma deposited nitride coatings

Possible mechanisms of the interfacial interaction in multiperiodic (bilayer) compositions at critical thicknesses (as small as below 10 nm) of conjugated phases have been studied for the first time using structure analysis, numerical simulations, and measurements of mechanical characteristics. For attaining a state of superhigh hardness (above 40 GPa), it is proposed to form coatings with variable layer thicknesses in the bilayer period $\Lambda$. Using this approach, 10-$\mu$m-thick coatings of the TiN/ZrN system with hardness above 44 GPa were obtained for a bilayer period of $\Lambda\approx$ 10 nm with a layer thickness ratio of 1.5/1.