Transmission electron microscopy analysis of the interfaces of TiAlN/Mo multilayers

Abstract

This paper focus on the analysis of the interfaces of nanocomposite TiAlN/Mo multilayers by high-resolution transmission electron microscopy (HRTEM). These thin films were deposited by reactive magnetron sputtering, with modulation periods below 7 nm. The structural disorder at the interfaces was probed by the analysis of the X-ray diffraction data, and afterwards correlated with the TEM observations on the cross-sections of the TiAlN/Mo multilayers. For specific deposition conditions, these structures can be prepared with relatively planar interfaces, revealing layer-by-layer growth. For modulation periods below 3 nm the intermixing acts a major role in the degradation of the multilayer chemical modulation. IntroductionIn specific engineering of multilayer coating design there is an important need of modelling in order to find the optimum conditions for the individual components of the bilayer. Nitride/metal multilayered coatings have attracted considerable attention because they combine properties of both hardness and elasticity; it has also been shown that nitride/metal multilayers [1] represent a promising category of coatings for improving surface mechanical properties due to the resulting hardness and elasticity, which is greater than that of the individual layers. The system that is studied in this work is a Ti 0.4 Al 0.6 N/Mo multilayer structure where the metal (bcc -body centered cubic) provides a softer and ductile layer while, the nitride (fcc -face centred cubic) accounts for the high hardness.

Nanostructured Coatings

“…This increased hardness effect has been observed for many other nitride/nitride multilayer systems [6,7], but also for nitride/metal systems, where the materials have different crystal structures [8,9]. Figure 24.3 shows an example of the dependence of the hardness on the modulation period for TiAlN/Mo multilayers.…”

“…It is easy to see why interface effects dominate the structure and properties of nanostructured coatings. The Hardness as a function of the modulation Λ for Ti0.4Al0.6N/Mo multilayers comprising 250 bilayers, fabricated by magnetron sputtering with substrate bias −100 V. For Λc ≥ 4 nm, the continuous curve represents the fitting to a HallPetch law [9]: H = H0 + kΛ −p , where k is a constant reflecting the effect of interface hardening and p is an exponent in the range 0.3-0.7 most important parameter controlling the increase in hardness of the stack in an A/B/A/B. .…”