This work investigates the growth of two different TiAl(Si)N multi-nanolayer systems deposited by HiPMS at 450 °C on Si (100) and WC-Co substrates. A graphical outline showing the composition of the targets used for each layer is presented in Fig. 1. The first system consists of TiAlSiN layers, where the Ti:Al ratio is the only difference between each sublayer. The second system is formed by TiAlN/TiAlSiN multi-nanolayers with same Ti:Al ratio but different bilayer thicknesses. Microstructural characterization and chemical analyses were performed by Field Emission Scanning Electron Microscopy and Energy-dispersive X-ray Spectroscopy, respectively. X-ray diffraction in Grazing incidence and Bragg-Brentano configurations were employed to identify the phases and texture. The nano-multilayers interfaces were analysed by Secondary Ion Mass Spectrometry depth profiling. The mechanical properties were measured by nanoindentation. Tribological performances were assessed by dry ball-on-disc tests at room and high temperatures. Nano scratch tests were also carried out to evaluate film adhesion.

The nano-multilayers are formed by the same phases present in the constituting monolayers: hexagonal + cubic and cubic + cubic (Fig. 1). However, both cubic films showed different textures, changing from (220) to (111) with the addition of 3 at. % of Si in the films. Surprisingly, the texture of the cubic + cubic multilayers was different from both initial monolayers and influenced by the substrate: (002) for multilayers on Si substrate and no clear presence of peaks for multilayers on WC-Co substrate. This is understood considering that the first stages of growth of monolayers would follow a (002) preferred orientation to minimize the surface energy, while developing a major preferred orientation (220 or 111) after a certain thickness threshold. The deposition of each sublayer would act as a seed for TiAl(Si)N re‑nucleation [1,2], leading to the observed (002) orientation. The lack of peaks in the WC-Co substrate is likely due to its higher complexity. Similar observations were made on cubic+hexagonal films. The hardness of the nano multilayers tend to be similar to the average values of their weakest sublayer, indicating that the rule of mixture was not fulfilled in both multilayer systems. In addition, any influence of the bilayer thickness was not noticed on the hardness. Furthermore, Elastic modulus results are discussed considering the less ‘local’ characteristic of this property, which makes its quantitative determination very sensitive, even for penetration depths lower than 10% of the film thickness.

[1] G. Abadias Surface and Coatings Technology, 2008, 202, 2223 – 2235.
[2] G. Abadias et al. Surface and Coatings Technology, 2016, 308, 158 – 167.