Mechanical properties and microstructures of polycrystalline ceramic/metal superlattices: TiN/Ni and TiN/Ni 0.9Cr 0.1

Abstract

Polycrystalline superlattice coatings of TiN/Ni and TiN/Ni 0.9 Cr 0.1 of thickness 2–3 μm were deposited onto tool steel substrates using an opposed-cathode reactive unbalanced magnetron sputtering system. The TiN/Ni superlattices have repeated periods (Λ) from 1.8 to 62 nm with various Ni layer thickness (l Ni) to Λ ratios, l Ni/Λ. TiN/Ni 0.9Cr 0.1 superlattices have Λ=1.2–7.4 nm with l NiCr / Λ=0.3. The structures were analyzed by X-ray diffraction, as well as plan-view and cross-sectional transmission electron microscopy. The hardnesses and elastic moduli of the superlattices were measured using nanoindentation techniques. An increase in hardness with decreasing Λ and grain size was observed. A maximum hardness of 3500 kgf mm −2 for TiN/Ni, about 1.5 times of the rule-of-mixtures values, was found at l Ni / Λ=0.16 and Λ=2.2 nm. For TiN/Ni 0.9Cr 0.1, a maximum hardness of 3200 kgf mm −2 was found at l Ni / gL=0.3 and Λ=1.2 nm. No significant variations in TiN/Ni 0.9Cr 0.1 film modulus were found as a function of Λ.