Metastable transition metal aluminum nitride based hard coatings like AlTiN and AlCrN grown by plasma-assisted physical vapor deposition are nowadays widely used to protect high-performance tools against wear and oxidation. The excellent properties of these coatings arise from their ability to form protective Al₂O₃-based oxide scales and from the decomposition of their metastable face-centered cubic (fcc) lattice, resulting in age hardening.

The aim of this presentation is to give a survey of attempts to alloy AlTiN and AlCrN coatings, with the goals to improve hardness and wear resistance, oxidation resistance, toughness, and to reduce friction. Coatings were synthesized by reactive cathodic arc evaporation, and powder-metallurgically produced TiAl and CrAl targets with the alloying elements V, Si, B, Ta, and Ru have been used. Low Si, B and Ta contents are incorporated in the single-phase fcc solid solutions, enhancing both mechanical properties and oxidation resistance. In particular, for AlTiTaN coatings the onset temperature for oxidation is shifted to significantly higher values compared to AlTiN, which is related to a reduction of intrinsic stresses in the rutile layer formed underneath the top Al₂O₃ scale. B alloying of AlCrN results in the formation of a nanocomposite structure, with nanosized fcc grains surrounded by a BN-rich grain boundary layer, giving rise to extremely high hardness values and wear resistance. On the other hand, V alloying can be used to form self-lubricious V₂O₅ oxide layers, where their low friction coefficients in the temperature range between 550 and 700°C arise from liquid lubrication, due the low melting temperature of this phase. Furthermore, low contents of Ru have been shown to increase the toughness of AlTiN coatings, which is assumed to formation of a metallic Ru phase within these coatings.

In summary, alloying of metastable transition metal aluminum nitride based hard coatings enables to design advanced quaternary and multiternary hard coatings with property combinations meeting the requirements of severe machining processes.

Thin films consisting of Al-Si-N were prepared by reactive magnetron sputtering from elemental targets in an Ar/N₂ reactive atmosphere at 200°C. The system shows a solubility limit for silicon at around 6 atomic %. Correspondingly the Al-Si-N system forms, as a function of the silicon content, either a solid solution or a two phase nanocomposite structure,. To understand the the properties and formation of the nanocomposite nanoscaled multilayers were used as a simplified model system. Coatings with a total thickness of about 1 micron and consisting of alternating layers of h-AlN or h-Al_1-xSi_xN (5 nm) and a-Si₃N₄ (from 0.25 nm to 2.0 nm) were prepared. The hardness as well as the residual stress state are strongly influenced by the thickness of the Si₃N₄ layer and the silicon content of the crystallineAl-Si-N layer. Maximum hardness values of 33 GPa are reached for a Si₃N₄ layer thickness of 0.35 nm, whereas the stress state can be tuned between – 1.5 and + 1.5 GPa. Both High Resolution TEM and XRD showed that, for Si₃N₄ layer thicknesses below 1 nm, the Si₃N₄ layers grow heteroepitaxially on AlN. The implication for the hardness of isotropically deposited solid solution and nanocomposite thin films of Al-Si-N will be discussed.

TaN–Cu nanocomposite films were deposited by reactive co-sputtering on Si and tool steel substrates. The films were then annealed using RTA (Rapid Thermal Annealing) at 400 °C for 2, 4, 8 minutes respectively to induce the nucleation and growth of Cu particles in TaN matrix and on film surface. Cu nano-particles emerged on the surface of TaN-Cu thin films were then removed after the samples were tested for their anti-wear and anti-bacterial behaviors. The samples were then re-annealed (rejuvenated), and re-tested for their anti-wear and anti-bacterial behaviors. The results reveal that the rejuvenated samples could have similar anti-wear and anti-bacterial behaviors so long as the annealing conditions were well adjusted. However, the hardness of the samples would decrease to a certain extent.